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Archive for the ‘Myocardial Metabolism’ Category


Hypertriglyceridemia: Evaluation and Treatment Guideline

Reporter and Curator: Dr. Sudipta Saha, Ph.D.

 

Severe and very severe hypertriglyceridemia increase the risk for pancreatitis, whereas mild or moderate hypertriglyceridemia may be a risk factor for cardiovascular disease. Individuals found to have any elevation of fasting triglycerides should be evaluated for secondary causes of hyperlipidemia including endocrine conditions and medications. Patients with primary hypertriglyceridemia must be assessed for other cardiovascular risk factors, such as central obesity, hypertension, abnormalities of glucose metabolism, and liver dysfunction. The aim of this study was to develop clinical practice guidelines on hypertriglyceridemia.

The diagnosis of hypertriglyceridemia should be based on fasting levels, that mild and moderate hypertriglyceridemia (triglycerides of 150–999 mg/dl) be diagnosed to aid in the evaluation of cardiovascular risk, and that severe and very severe hypertriglyceridemia (triglycerides of >1000 mg/dl) be considered a risk for pancreatitis. The patients with hypertriglyceridemia must be evaluated for secondary causes of hyperlipidemia and that subjects with primary hypertriglyceridemia be evaluated for family history of dyslipidemia and cardiovascular disease.

The treatment goal in patients with moderate hypertriglyceridemia should be a non-high-density lipoprotein cholesterol level in agreement with National Cholesterol Education Program Adult Treatment Panel guidelines. The initial treatment should be lifestyle therapy; a combination of diet modification, physical activity and drug therapy may also be considered. In patients with severe or very severe hypertriglyceridemia, a fibrate can be used as a first-line agent for reduction of triglycerides in patients at risk for triglyceride-induced pancreatitis.

Three drug classes (fibrates, niacin, n-3 fatty acids) alone or in combination with statins may be considered as treatment options in patients with moderate to severe triglyceride levels. Statins are not be used as monotherapy for severe or very severe hypertriglyceridemia. However, statins may be useful for the treatment of moderate hypertriglyceridemia when indicated to modify cardiovascular risk.

 

References:

 

https://www.medpagetoday.com/clinical-connection/cardio-endo/77242?xid=NL_CardioEndoConnection_2019-01-21

https://www.ncbi.nlm.nih.gov/pubmed/19307519

https://www.ncbi.nlm.nih.gov/pubmed/23009776

https://www.ncbi.nlm.nih.gov/pubmed/6827992

https://www.ncbi.nlm.nih.gov/pubmed/22463676

https://www.ncbi.nlm.nih.gov/pubmed/17635890

 

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https://www.youtube.com/v/AfO51ELsECg?fs=1&hl=fr_FR

Effects of Heterogeneous Diffuse Fibrosis on Arrhythmia Dynamics and Mechanism. Ivan V. Kazbanov et al (2016), Scientific Reports http://dx.doi.org/10.1038/s...

Sourced through Scoop.it from: www.youtube.com

See on Scoop.itCardiovascular Disease: PHARMACO-THERAPY

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https://www.youtube.com/v/n1VgTSondUE?fs=1&hl=fr_FR

Nanoparticle-Mediated Targeting of Cyclosporine A Enhances Cardioprotection Against Ischemia-Reperfusion Injury Through Inhibition of Mitochondrial Permeabil…

Sourced through Scoop.it from: www.youtube.com

See on Scoop.itCardiovascular and vascular imaging

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Functional Human Cardiac Progenitor Cells

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Generation of Functional Human Cardiac Progenitor Cells by High-Efficiency Protein Transduction

 

The reprogramming of fibroblasts to induced pluripotent stem cells raises the possibility that somatic cells could be directly reprogrammed to cardiac progenitor cells (CPCs). The present study aimed to assess highly efficient protein-based approaches to reduce or eliminate the genetic manipulations to generate CPCs for cardiac regeneration therapy. A combination of QQ-reagent-modified Gata4, Hand2, Mef2c, and Tbx5 and three cytokines rapidly and efficiently reprogrammed human dermal fibroblasts (HDFs) into CPCs. This reprogramming process enriched trimethylated histone H3 lysine 4, monoacetylated histone H3 lysine 9, and Baf60c at the Nkx2.5 cardiac enhancer region by the chromatin immunoprecipitation quantitative polymerase chain reaction assay. Protein-induced CPCs transplanted into rat hearts after myocardial infarction improved cardiac function, and this was related to differentiation into cardiomyocyte-like cells. These findings demonstrate that the highly efficient protein-transduction method can directly reprogram HDFs into CPCs. This protein reprogramming strategy lays the foundation for future refinements both in vitro and in vivo and might provide a source of CPCs for regenerative approaches.

Significance

The findings from the present study have demonstrated an efficient protein-transduction method of directly reprogramming fibroblasts into cardiac progenitor cells. These results have great potential in cell-based therapy for cardiovascular diseases.

 

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Empagliflozin

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Empagliflozin Benefits in EMPA-REG Explored in Diabetics Initially With or Without Heart Failure

Marlene Busko

http://www.medscape.com/viewarticle/854542

 

ORLANDO, FL — Patients with type 2 diabetes and established CVD who received the antidiabetic sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin (Jardiance, Lilly/Boehringer Ingelheim), as opposed to placebo, had a reduced risk of being hospitalized for heart failure or dying from CVD during a median follow-up of 3.1 years. The finding was strongest in patients without heart failure at baseline[1]. The finding is noteworthy in part because associated heart failure has been a concern, justified or not, with some other diabetes medications.

In these high-risk patients, empagliflozin resulted in a “consistent benefit” in these outcomes, Dr Silvio E Inzucchi (Yale University School of Medicine, New Haven, CT) said, presenting these findings from a prespecified secondary analysis of the EMPA-REG OUTCOME trial at theAmerican Heart Association (AHA) 2015 Scientific Sessions.

Unlike the gasps and applause that greeted him when he presented the trial’s primary outcome results at the European Association for the Study of Diabetes (EASD) 2015 Meeting in Stockholm in mid-September, the audience reaction this time was more measured. The trial had also been published at about the time of its EASD presentation [2].

The principal findings showed that compared with patients who took placebo, those who were randomized to empagliflozin had a 38% (P<0.001) reduced risk of CV death and a 35% P=0.002) reduced risk of hospitalization for HF, at a median follow-up of 3.1 years.

In the current secondary analysis, the 90% of patients who were free of heart failure at study entry showed a steep and significant drop in HF hospitalizations during the trial. There was also a drop in HF hospitalizations with active therapy in the minority who had HF at baseline, but it failed to reach significance.

“I think metformin is likely to remain our first-line oral therapy for patients with type 2 diabetes,” Dr Donald M Lloyd-Jones (Northwestern University Feinberg School of Medicine, Chicago, IL), cochair at an AHA press briefing, told heartwire from Medscape. “There is an alphabet soup of diabetes medications,” with multiple agents that effectively lower blood glucose and reduce patients’ risk of retinopathy, nephropathy, and neuropathy.

However, “it was . . . unexpected that [empagliflozin], as reported recently [at the EASD meeting and] in the New England Journal of Medicine [has an] effect on CV death and other CV events.” This is still an early stage of research, he cautioned, and it is not known how the drug exerts its CV effects and whether there is a class effect. “But [this] could be a game changer, because we would love to have [antidiabetic] medications that not only control blood sugar but also reduce death and [other] hard events,” he said.

 

First CV Outcomes Trial in this Drug Class

Until now, none of the antiglycemic medications has also been shown to improve HF outcomes, Inzucchi explained. “We’ve actually been searching decades for a diabetes medicine that will not only lower blood glucose but also reduce cardiovascular complications,” he said in a press briefing. “And I would remind you that based on the 2008 FDA guidance to industry, all new diabetes medications need to be tested for cardiovascular safety before being allowed on the market,” he added.

EMPA-REG OUTCOME is the first published, large CV-outcome trial of an SGLT-2 inhibitor.

As previously described, the trial randomized 7028 adult patients who had type 2 diabetes and established CVD to receive 10 mg/day or 25 mg/day empagliflozin or placebo. The CVD included prior MI (46.6%), CABG (24.8%), stroke (23.3%), and peripheral artery disease (PAD) (20.8%).

The patients were also required to have an HbA1c level between 7% and 10%, body-mass index (BMI) <45, and, because the drug exerts its effects via the kidney, estimated glomerular filtration rate (eGFR) >30 mL/min/1.73 m2.

“Importantly, study medication was given upon a backdrop of standard care—antihyperglycemia therapy, as well as other evidence-based cardiovascular therapies such as statins, ACE inhibitors, and aspirin,” Inzucchi stressed.

 

Spotlight on HF Outcomes

The current analysis dove deeper into the heart-failure outcomes in the trial.

The risk of hospitalization for HF or CV death was consistently significantly lower in patients who received empagliflozin vs placebo, in subgroup analyses related to age, kidney function, and medication use (ACE inhibitors/angiotensin receptor blockers [ARBs], diuretics, beta-blockers, or mineralocorticoid-receptor antagonists).

Overall, the patients who received empagliflozin had a 34% reduced risk of being hospitalized for HF or dying from CV causes and a 39% reduced risk of being hospitalized for or dying from HF.

Risk of Hospitalization or Death, Empagliflozin vs Placebo

Outcome HR (95% CI) P
Hospitalization for HF or CV death 0.66 (0.55–0.79) <0.00001
Hospitalization for or death from HF 0.61 (0.47–0.79) <0.00001

Most patients (90%) did not have HF at baseline.

In the patients without HF at baseline, “as you might expect, [HF] hospitalizations were relatively small in number” (1.8% of patients on the study drug and 3.1% of patients on placebo), said Inzucchi. There was a statistically significant 41% reduced risk of HF hospitalization in patients without HF at baseline on the study drug vs placebo (HR 0.59, 95% CI 0.43–0.82).

In the smaller number of patients who did have HF at baseline, the rate of hospitalizations for HF was much higher (10.4% of patients on the study drug and 12.3% of patients on placebo). But in this case, the difference between patients on the study drug vs placebo was not statistically significant (HR 0.75, 95% CI 0.48–1.19).

The results were similar when the analysis was repeated for the combined outcome of hospitalization for HF or CV death.

“Not surprisingly,” adverse events were more common in sicker patients with baseline HF; genital infections, a well-known adverse event in drugs that increase glucose in the urine, were three times more common in those patients, said Inzucchi.

“I think these are very compelling data, but early days,” said Lloyd-Jones.

Inzucchi receives research grants from Genzyme and honoraria from Boehringer Ingelheim, Merck Sharp & Dome, Sanofi, Amgen, and Genzyme, and he is a consultant on advisory boards for Boehringer Ingelheim, Sanofi, and Amgen. Disclosures for the coauthors are listed in the abstract. Lloyd-Jones has no relevant financial relationships.

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A new way of moving – Michael Sheetz, James Spudich, Ronald Vale

Larry H Bernstein, MD, FCAP, Curator

Leaders in Pharmaceutical Intelligence

Series E. 2; 5.5

 

J Clin Invest. 2012 Oct 1; 122(10): 3374–3377.

http://dx.doi.org:/10.1172/JCI66361

The MBI community congratulates Michael Sheetz upon winning the prestigious Albert Lasker Basic Medical Research Award. Michael Sheetz, Director of the Mechanobiology Institute, Singapore, Distinguished Professor of the Department of Biological Sciences, NUS and William R Kenan, Junior Professor at Columbia University, shares this award with two of his collaborators, James Spudich (Stanford University) and Ronald Vale (University of California, San Francisco). The Award was presented at a ceremony on Friday, September 21, 2012, in New York City.

 

The Albert Lasker Basic Medical Research Award was given to Prof Sheetz, Prof Spudich and Prof Vale in honor of seminal contributions made in establishing methods to study cytoskeletal motor proteins. These developments paved the way to study molecular motors and enabled the discovery of the motor protein, kinesin. The landmark achievements in deciphering new components of cellular motors, which helped explain how these motors worked, were pivotal in understanding the basic fundamental process of energy conversion within the cell. These have led to explorations of these physiologically relevant molecules, as potential drug targets in a variety of disease conditions.

 

Many basic cellular functions depend on the directed movement of cytoplasmic organelles, macromolecules, membranes or chromosomes from one place to another within the cell. The transport of this intracellular cargo is achieved by molecular motor proteins, such as myosin and kinesin, which provide force and movement through the conversion of chemical energy (ATP) into mechanical energy. Molecular motor proteins move along scaffolds made of specific protein polymers, with kinesins moving along microtubules and myosins along actin filaments, in order to carry their cargo to the appropriate destination within the cell.
Subsequently, Sheetz and Spudich worked out an in-vitro method for visualizing actin filaments creeping along myosin coated surfaces, and this system still remains the gold-standard assay for studying myosin movement. With a read-out in hand, many details of the mechanism of action of the motor molecules within the cell were worked out. Michael Sheetz and colleagues, Ronald Vale and Thomas Reese, carried out pivotal experiments that ultimately led to the discovery of kinesins, a novel and hitherto unknown family of motor proteins. These experiments involved the development of an in vitromotility assay, whereby proteins from the cytoplasm of neuronal cells were shown to power the movement of microtubules across the surface of glass coverslips. This technique was found to be a sensitive and rapid assay for testing the activity of kinesin and was adopted by numerous labs following these crucial initial experiments.

For more details of the award winning contribution towards understanding the basics of cellular machinery, please go to http://www.laskerfoundation.org/media/index.htm and also http://www.laskerfoundation.org/media/pdf/2012citation_basic.pdf

 

Michael Sheetz, along with James Spudich and Ronald Vale strongly believe in an open culture of scientific exchange. ‘The most interesting scientific insights result from collaborative, interdisciplinary adventures’, has been the one common theme of Michael Sheetz career. A firm believer of an open laboratory concept where students from different labs and backgrounds, share bench space and often ideas, he emulated the Open Lab model (learn more about MBI’s open labs) at the Mechanobiology Institute, Singapore. This new model of open laboratory environment in interdisciplinary institutes provides an excellent way to encourage fast paced discovery process.

My greatest excitement comes from considering the puzzle provided by an unexpected result when new technology is applied to an old problem, says Professor Sheetz.

In his acceptance essay, which can be read here (PDF), Michael Sheetz refers to the importance of collaborations, where the parties are learning from each other and also ‘encourages young scientists to perform speculative experiments whenever they have such an idea, even if most of them fail; since an experiment, even a flawed on, can reveal the solution to an important problem’.

 

The Mechanobiology Institute is delighted to announce that Michael Sheetz has been selected as a Massry Prize Laureate for 2013.

michaelSheetz_WB_9079Shared with James Spudich (Stanford University) and Ronald Vale (University of California, San Francisco), the award to the trio is a recognition of their work defining molecular mechanisms of ‘intracellular motility.’

This process involves the deployment of molecular machines to move cargo on molecular tracks which are a part of the cellular skeleton.

The discovery of a novel family of motor proteins, the kinesins, by Michael Sheetz, Ronald Vale and Thomas Reese and the methodology developed for the same, proved to be pivotal and the technique developed led to many further discoveries by different laboratories.

Subsequently, Sheetz and Spudich worked out an in-vitro method for visualizing actin filaments creeping along myosin coated surfaces, and this system still remains the gold-standard assay for studying myosin movement. With a read-out in hand, many details of the mechanism of action of the motor molecules within the cell were worked out.

 

 

 

 

 

 

The Lasker Awards: motors take centre stage

Nature Cell Biology | Editorial
Nature Cell Biology 14,1113(2012)  http://dx.doi.org:/10.1038/ncb2618

Michael Sheetz, James Spudich and Ronald Vale have now joined the list of Lasker laureates, having jointly received the 2012 Albert Lasker Basic Medical Research Award for their “discoveries concerning cytoskeletal motor proteins, machines that move cargoes within cells, contract muscles, and enable cell movements”1.

Although the mechanism of action and the cellular functions performed by force-generating cytoskeletal motors, including their roles in intracellular trafficking, cell migration, cell division and muscle contraction, are now a fundamental part of cell biology, in the 1970s and 1980s they were still mostly a mystery. Following a postdoctoral fellowship under the guidance of Hugh Huxley, a pioneer of muscle contraction studies, James Spudich established his independent work at the University of California San Francisco (UCSF) and later at Stanford University on what was, at the time, the largely unchartered territory of myosin activity and function. A fortuitous crossing of paths occurred in 1982, when Michael Sheetz joined the Spudich laboratory on sabbatical from his own independent research at the University of Connecticut Health Center. Working together, Spudich and Sheetz demonstrated myosin movement on actin filaments using the Nitella axillaris alga as a model, and later established an in vitro reconstitution system that demonstrated the ability of purified myosin to move on purified actin filaments in the presence of adenosine triphosphate at rates consistent with those of muscle contraction. This seminal work was published in Nature in 19832 and 19853.

Spurred by the exciting work on myosin-based movement, Ronald Vale, then a graduate student at Stanford University, decided with Michael Sheetz to define the particle movement observed in squid axons. Their experiments at the Marine Biology Laboratory in Woods Hole led to a series of groundbreaking Cell publications in 19854, 5, 6, 7, 8, which determined that axonal movement was not driven by myosin on actin filaments as they had anticipated, but was instead occurring on microtubules and was powered by a then-uncharacterized factor that they purified and named kinesin.

These initial efforts investigating myosin- and kinesin-powered motility, and the in vitro assays developed to characterize cytoskeletal motor activities, opened up new and fascinating avenues of research and have become a corner-stone of cell biology today. Following these key discoveries, Spudich went on to define many other aspects of myosin activity and function. Vale continued his work on molecular motors and their cellular roles in his independent research at UCSF, and Sheetz followed a varied research career ranging from motility studies to work on cell adhesion and mechanosensing at Columbia University and the Mechanobiology Institute in Singapore.

In honouring the early work of Sheetz, Spudich and Vale, the Lasker Foundation recognizes the significance of the cytoskeletal motor field in biology, and also the importance of understanding the principles underlying cellular motor function in human diseases in which such activities are deregulated. Indeed, the characterization of normal myosin and kinesin activity and function has served as the spring-board for studies on their impaired or aberrant action in disease, with the goal of developing therapies for heart conditions in the case of myosins, and neurological disorders and malignancy in the case of kinesins.

It should also be noted that the discoveries acknowledged by the Lasker Award and the subsequent scientific careers of the three awardees were the outcome of an inspired mix of cell and molecular biology, biochemistry and physics, among other disciplines, and are thus a testament to the importance of fostering multidisciplinary science. Moreover, as the three award recipients eloquently noted in their Lasker Award acceptance remarks, the motivating force during the exciting times of their initial research on motors was not only a thirst for discovery and a passion for science, but also a strong collaborative spirit. As a fundamentally creative and adventurous endeavour, science is often seen by outsiders as a solitary pursuit of inquiry and testing one’s own ideas. However, the reality of a bustling laboratory reveals that teamwork, discussion and brainstorming, and a successful combination of different personalities, are just as important as individual intellect and drive. In that respect, the dedication, creativity and collaborative efforts of Sheetz, Spudich and Vale should be an inspiration to scientists everywhere.

References

  1. www.laskerfoundation.org/awards/2012_b_description.htm
  2. Sheetz, M. P. & Spudich, J. A. Nature 303, 3135 (1983).
  3. Spudish, J. A., Kron, S. J. & Sheetz, M. P. Nature 315, 584586 (1985).
  4. Vale, R. D., Schnapp, B. J., Reese, T. S. & Sheetz, M. P. Cell 40, 449454 (1985).

One path to understanding energy transduction in biological systems

James A Spudich

http://www.laskerfoundation.org/awards/pdf/2012_b_spudich.pdf

Who is not fascinated by the myriad biological movements that define life? From cell migration, cell division and a network of translocation activities within cells to highly specialized muscle contraction, molecular motors operate by burning ATP as fuel. Three types of molecular motors—myosin, kinesin and dynein— and nearly 100 different subtypes transduce that chemical energy into mechanical movements to carry out a wide variety of cellular tasks. Understanding the molecular basis of energy transduction by these motors has taken decades. Our understanding of molecular motors could be viewed as beginning with the two 1954 papers in Nature by Hugh Huxley and Jean Hanson and Andrew Huxley and Rolf Niedergerke, respectively, where the authors proposed the sliding-filament theory of muscle contraction. But a good place to start my story is 1969, when Hugh Huxley, on the basis of his remarkable X-ray diffraction experiments on live muscle coupled with electron microscopy, postulated the swinging crossbridge hypothesis of muscle contraction1. Thus, more than 40 years ago, he proposed the basic concepts of how the myosin molecule produces the sliding of actin filaments to produce contraction. Hugh Huxley laid the foundation for the molecular motor field, and we are all indebted to him. My beginnings in myosin research began as a postdoctoral fellow in Hugh’s laboratory at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, coincidentally in 1969. But my fascination with science began much earlier.

Neither of my parents was college educated, but they both had keen intellects, positive and enthusiastic outlooks and profound work ethics. My father was intrigued by how things work and shared that interest with my brother John and me. After the coal mines closed, my father taught himself electrical engineering, founded the Spudich Electric Company and patented one of his inventions. He often told John and me, “do whatever excites you, but do it well and be respectful of people you interact with.”

I was captivated with chemistry from a young age. Beginning at the age of six, I mastered every chemistry set I could get. The myriad chemical reactions that could be created using everyday materials, sometimes with marvelously explosive results, fed my excitement for chemistry. It was a world unfamiliar to my parents, but they respected my preoccupations and cleared the pantry of our modest home for me to set up a lab with discarded equipment given to me by my high school chemistry teacher Robert Brandsmark. My brother John has also followed the allure of science into an exciting and distinguished career in basic research. His work has established the molecular basis of signaling in an important class of rhodopsins that he discovered in 1982 (ref. 2). John was my first collaborator.

A chance encounter with Woody Hastings at the University of Illinois launched my experimental-science career. Throughout my undergraduate years, I worked with Woody on bioluminescence in Vibrio fischeri3. I was inspired by his high-spirited fascination with biology and was fortunate to be invited to help him teach in the physiology course at the Marine Biological Laboratory (MBL) in Woods Hole (Fig. 1). At the MBL, I was introduced to the breadth and potential of many biological systems, including muscle contraction.

In 1963 I joined the PhD program in the new Department of Biochemistry at Stanford University, founded by Arthur Kornberg. One of the many remarkable aspects of the biochemistry department was that, although Arthur was my thesis advisor, all the faculty members were my mentors. This unique environment shaped the way I do research and taught me how to be a responsible colleague and a mentor to others (Fig. 2). I learned how important it is to reduce complex biological systems to their essential components and create quantitative in vitro assays for the function of interest. Those years also made it clear to me that interdisciplinary approaches would be key to understanding complex biological processes. So I decided to do postdoctoral work in both genetics and structural biology. I spent one year at Stanford with another influential role model, Charley Yanofsky, working on the genetics of the Escherichia coli tryptophan operon. I then joined Hugh Huxley’s laboratory in Cambridge.

I chose to study the  unanswered questions in cell biology at the time when I established my own laboratory – how the chemical energy of ATP hydrolysis brings about mechanical movement and what roles a myosin-like motor might have in nonmuscle cells.

The essential first steps were to develop a quantitative in vitro motility assay for myosin movement on actin, which is crucial for understanding the molecular mechanism of energy transduction by this system, and to develop a model organism to unravel the molecular basis of the myriad nonmuscle-cell movements that are apparent by light microscopy. We explored Neurospora crassa, Saccharomyces cerevisiae, Physarum polycephalum, Dictyostelium discoideum, Nitella axillaris and other organisms, all unfamiliar to me at the time. The giant cells of the alga Nitella were particularly intriguing because of their striking intracellular cytoplasmic streaming that was visible under a simple light microscope. Although not suitable for biochemistry or genetics, Nitella would assume an important role in my lab a decade later, after Yolande Kersey in Norm Wessells’s laboratory in the Department of Biological Sciences at Stanford showed oriented actin cables lying along chloroplast rows in these cells 5. The slime mold Dictyostelium proved best for our initial biochemical approach 6. Margaret Clarke, my postdoctoral fellow, identified a myosin in Dictyostelium. We also showed that actin is associated with the cell membrane in this organism, and we isolated membranecoated polystyrene beads with actin filaments emanating from them. We were tremendously excited about the possibilities these results presented as a small step along the way to an in vitro motility assay where these actin-coated particles could move along a myosin-coated surface (Fig. 3).

Figure 3 Dictyostelium has a muscle-like myosin and membrane-associated actin. (a) A possible scheme for pulling two membranes together (redrawn from ref. 6). (b) Margaret Clarke discovered myosin II in Dictyostelium and showed that it forms bipolar thick filaments, similar to muscle myosin. (c) Phagocytized polystyrene beads offered an opportunity to explore one version of an in vitro motility assay where the beads may be pulled along by myosin. Taken from my laboratory notebook, 21 January 1973.

Figure 4 One approach to an in vitro motility assay from a totally defined system. (a) The concept was to observe myosin-coated beads moving along fixed actin filaments oriented by buffer flow. The actin filaments had biotinylated severin bound to their barbed ends; the barbed ends were attached to an avidin-coated surface by way of the tight avidin-biotin link. The filaments were oriented by buffer flow. B, biotin; S, severin. (b) Myosin-coated beads were observed by light microscopy to move upstream toward the barbed end of the surface-attached actin filaments. The position of each of the three bead aggregates is shown as a function of time. This was the first demonstration of quantitative, directed movement of myosin along actin with a totally defined system (taken from ref. 11). ATP binding releases the myosin Myosin binds to actin ATP ADP Pi ADP .

In 1977 I joined the Department of Structural Biology at Stanford. In the next years we extensively characterized the actin-myosin system in Dictyostelium. My student Arturo De Lozanne made the chance discovery that genes in Dictyostelium can be knocked out by homologous recombination and provided the first genetic proof that myosin II is essential for time that myosin II drove the forward movement of cells. Dietmar Manstein, Meg Titus and Arturo then extended these experiments to create a myosin-null cell8, which was crucial to our later work using mutational analysis to define the structure-function relationships of the myosin molecule and for important experiments in support of the swinging cross-bridge hypothesis9. Interestingly, reports from a number of laboratories between 1969 and 1980 did not support the swinging cross-bridge model, and it was more imperative than ever to develop a quantitative in vitro motility system to test the various models under consideration. In 1981 we identified and purified Dictyostelium severin, a protein that tightly binds the ‘barbed ends’ of actin filaments. This provided an opportunity to try another version of an in vitro motility assay. Using biotinylated severin, we attached the actin filament barbed ends to an avidin-coated slide and flowed aqueous solution over them. Long filaments attached to the surface at one end would be expected to orient in the direction of the flowing solution (Fig. 4a). We placed myosin-coated beads on these actin-coated slides and added ATP but saw only sporadic movements. In retrospect, we probably did not have sufficient alignment of filaments; we were not monitoring filament alignment at that time by electron microscopy, as we did later.

A key breakthrough occurred in 1982 when Mike Sheetz came to my laboratory on sabbatical. Not certain what component of our system might be limiting our approach, we took advantage of the known orientation of actin filaments in Nitella5 to overcome the actin filament alignment problem. Peter Sargent, a neurobiologist in the Structural Biology Department at that time, helped us cut open a Nitella cell, and we attached it to a surface to expose the actin fibers. We added myosin-coated beads and eureka! We saw robust ATP-dependent unidirectional movement along chloroplast rows, which mark the actin fibers 10.

Armed with the Nitella results, Mike left my lab and went to the MBL to explore whether myosin-coated vesicles may account for the particle movements observed in squid axons. Ron Vale, then a graduate student at Stanford with Eric Shooter, was fascinated by the movement of organelles in nerve axons and joined Mike at the MBL. To their great surprise, they found that movement in axons is not myosin driven. Instead, they discovered the new molecular motor kinesin, a discovery that completely energized the field and opened up years of exciting work from their laboratories and many others. ..

 

The combination of the in vitro motility assay and the Dictyostelium myosin-null cell provided powerful tools for Kathy Ruppel, Taro Uyeda, Dietmar Manstein, William Shih, Coleen Murphy, Meg Titus, Tom Egelhoff and others in my lab to use mutations along myosin to define the biochemical, biophysical and assembly properties of the molecule. Our results were consistent with the proposed actin-activated myosin chemomechanical cycle derived largely from the elegant biochemical kinetic studies from Edward Taylor’s laboratory in the early 1970’s (ref. 15) (Fig. 5). Then, in 1993, Ivan Rayment and his colleagues16 obtained a high-resolution crystal structure of myosin S1. Ivan’s pivotal work allowed us to place our mutational analyses in a myosin structure-function context.

Figure 5 The actin-activated myosin chemomechanical cycle. This cycle, extensively studied by many researchers over several decades, was derived from kinetic studies of Lymn and Taylor 15. A mechanical stroke only occurs when the myosin is strongly bound to actin. Our mutational analyses of Dictyostelium myosin II probed each of the steps shown and provided structure-function analyses that helped define how the myosin motor works. ADP-Pi , ADP and inorganic phosphate, the products of ATP hydrolysis, remain bound to the active site until actin binds to the myosin.

Figure 6 In vitro motility taken to the single-molecule level using the physics of laser trapping. (a) The Kron in vitro motility assay observing fluorescent actin filaments (yellow) moving on a myosin-coated (red) surface. (b) Two polystyrene beads attached to the ends of a single actin filament are trapped in space by laser beams. The filament is lowered onto a single myosin molecule on a bump on the surface (gray sphere). (c) Jeff Finer building the dual-beam laser trap in around 1990.

Fundamental issues still remained— primarily to establish the step size that the myosin takes for each ATP hydrolysis, which was under considerable debate.

more…

One of my great satisfactions is that the more detailed understanding of energy transduction by myosin has led to potential clinical therapies. A small molecule that binds and activates b-cardiac myosin is now in clinical trials for the treatment of heart failure, and another small molecule currently in clinical trials activates skeletal muscle contraction and may aid patients with amyotropic lateral sclerosis and other diseases.

 

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Metabolic Genomics and Pharmaceutics, Vol. 1 of BioMed Series D available on Amazon Kindle


Metabolic Genomics and Pharmaceutics, Vol. 1 of BioMed Series D available on Amazon Kindle

Reporter: Stephen S Williams, PhD

 

Leaders in Pharmaceutical Business Intelligence would like to announce the First volume of their BioMedical E-Book Series D:

Metabolic Genomics & Pharmaceutics, Vol. I

SACHS FLYER 2014 Metabolomics SeriesDindividualred-page2

which is now available on Amazon Kindle at

http://www.amazon.com/dp/B012BB0ZF0.

This e-Book is a comprehensive review of recent Original Research on  METABOLOMICS and related opportunities for Targeted Therapy written by Experts, Authors, Writers. This is the first volume of the Series D: e-Books on BioMedicine – Metabolomics, Immunology, Infectious Diseases.  It is written for comprehension at the third year medical student level, or as a reference for licensing board exams, but it is also written for the education of a first time baccalaureate degree reader in the biological sciences.  Hopefully, it can be read with great interest by the undergraduate student who is undecided in the choice of a career. The results of Original Research are gaining value added for the e-Reader by the Methodology of Curation. The e-Book’s articles have been published on the Open Access Online Scientific Journal, since April 2012.  All new articles on this subject, will continue to be incorporated, as published with periodical updates.

We invite e-Readers to write an Article Reviews on Amazon for this e-Book on Amazon.

All forthcoming BioMed e-Book Titles can be viewed at:

https://pharmaceuticalintelligence.com/biomed-e-books/

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Table of Contents for Metabolic Genomics & Pharmaceutics, Vol. I

Chapter 1: Metabolic Pathways

Chapter 2: Lipid Metabolism

Chapter 3: Cell Signaling

Chapter 4: Protein Synthesis and Degradation

Chapter 5: Sub-cellular Structure

Chapter 6: Proteomics

Chapter 7: Metabolomics

Chapter 8:  Impairments in Pathological States: Endocrine Disorders; Stress

                   Hypermetabolism and Cancer

Chapter 9: Genomic Expression in Health and Disease 

 

Summary 

Epilogue

 

 

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Neutraceuticals

Author and Curator: Larry H Bernstein, MD, FCAP 

 

Introduction

This article is concerned with a very fast growing part of the food industry. Unfortunately, there have been such products that were sold that did not contain what was purported to provide the benefit. This segment of the medicinal industry is regulated as FOOD (food product), unlike pharmaceuticals. This means that the basic safety requirement is compliance with a labeling standard.  There are no clinical trials.  The incentive for the development in this sector is from 2,500 years of history in the use of plants for health benefits.  The new science that can improve the potency and the safety is the technology that has grown up to extract, refine and produce the active substance in pure form.  The methods used called Flow Chemistry has been covered recently by Anthony Melvin Crasso at his outstanding pharmaceutical site.  I shall list important articles that have been in the Pharmaceutical Intelligence site at the end of this discussion.

Antidiarrheal and antioxidant activities of chamomile (Matricaria recutita L.) decoction extract in rats

Hichem Sebai, Mohamed-Amine Jabri, Abdelaziz Souli, Kais Rtibi, et al.
J Ethnopharmacol 152(2014)327–332
http://dx.doi.org/10.1016/j.jep.2014.01.015

Ethnopharmacological relevance: Matricaria recutita L. (Chamomile) has been widely used in the Tunisian traditional medicine for the treatment of digestive system disorders. The present work aims to investigate the protective effects of chamomile decoction extract (CDE) against castor oil-induced diarrhea and oxidative stress in rats. Methods:The antidiarrheal activity was evaluated using castor oil-induced diarrhea method. In this respect, rats were divided into six groups: Control, Castor oil, Castor oil + Loperamide (LOP) and Castor oil + various doses of CDE. Animals were perorally (p.o.) pre-treated with CDE during 1 hand intoxicated for 2 or 4h by acute oral administration of castor oil.  Results: Our results showed that CDE produced a significant dose-dependent protection against castor oil-induced diarrhea and intestinal fluid accumulation. On the other hand, we showed that diarrhea was accompagnied by an oxidative stress status assessed by an increase of malondialdehyde (MDA) level and depletion of antioxidant enzyme activities as superoxide dismutase(SOD), catalase (CAT) and glutathione peroxidase (GPx). Castor oil also increased gastric and intestinal mucosa hydrogen peroxide (H2O2) and free iron levels. Importantly, we showed that chamomile pre-treatment abrogated all these biochemical alterations. Conclusion: These findings suggested that chamomile extract had a potent antidiarrheal and antioxidant properties in rats confirming their use in traditional medicine.

Anti-diarrheal activity of methanol extract of Santalum album L. in mice and gastrointestinal effect on the contraction of isolated jejunum in rats

Huimin Guo, Jingze Zhang, Wenyuan Gao, Zhuo Qu, Changxiao Liu
J Ethnopharmacol 54(2014)704–710
http://dx.doi.org/10.1016/j.jep.2014.04.043

Ethnopharmacological relevance: Santalum album L., namely Sandalwood, honoredas “Green Gold”, is a traditional Chinese herb which has the effects of antidiarrheal and antibacterial activity. But there is limited scientific study on its activity and mechanism in gastrointestinal disorders.
Materials and methods: in vivo, after intragastric administration, the methanol extract of Sandalwood (SE) (200, 400 and 800 mg/kg) were studied in castor oil-induced diarrhea mice. By the test of small intestinal hyperfunction induced by neostigmine, SE was studied on gastrointestinal transit including gastric emptying and small intestinal motility. Meanwhile, in vitro, the effects of SE (0.02, 0.05, 0.1, 0.2, 0.3, 0.4 mg/mL) on the isolated tissue preparations of rat jejunum were also investigated. The rat jejunum strips were precontacted with acetylcholine (Ach; 10-6M), 5-hydroxytryptamine (5-HT, 200 μM) or potassium chloride (KCl; 60mM) and tested in the presence of SE. In addition, the possible myogenic effect was analyzed in the pretreatment of the jejunum preparations with SE or verapamilin Ca 2+-free high-K+ (60mM) solution containing EDTA. Results: At doses of 200, 400 and 800 mg/kg, SE showed significant anti-diarrheal activity against castor oil-induced diarrhea as compared with the control. At the same doses, it also inhibited the gastric emptying and small intestinal motility in the mice of which small intestinal hyperfunction induced by neostigmine. It caused inhibitory effects on the spontaneous contraction of rat-isolated jejunum in dose-dependent manner ranging from 0.02 to 0.4 mg/mL, and it also relaxed the Ach-induced, 5-HT-induced andK+-induced contractions. SE shifted the Ca 2+concentration–response curves to right, similar to that caused by verapamil (0.025mM).
Conclusions: These findings indicated that SE played a spasmolytic role in gastrointestinal motility which was probably mediated through inhibition of muscarinic receptors, 5-HT receptors and calcium influx. All these results provide pharmacological basis for its clinical use in gastrointestinal tract.

Apocynin attenuates isoproterenol-induced myocardial injury and fibrogenesis

Li Liu, Jingang Cui, Qinbo Yang, Chenglin Jia, Minqi Xiong, et al.
Biochem Biophys Res Commun 449(2014)55–61
http://dx.doi.org/10.1016/j.bbrc.2014.04.157

Oxidative stress is mechanistically implicated in the pathogenesis of myocardial injury and the subsequent fibrogenic tissue remodeling. Therapies targeting oxidative stresss in the process of myocardial fibrogenesis are still lacking and thus remain as an active research area in myocardial injury management. The current study evaluated the effects of a NADPH oxidase inhibitor, apocynin, on the production of reactive oxygen species and  the development of myocardial fibrogenesis in isoproterenol (ISO)-induced myocardial injury mouse model. The results revealed a remarkable effect of apocynin on attenuating the development of myocardial necrotic lesions, inflammation and fibrogenesis. Additionally, the protective effects of apocynin against myocardial injuries were associated with suppressed expression of an array of genes implicated in inflammatory and fibrogenic responses. Our study thus provided for the first time the histopathological and molecular evidence supporting the therapeutic value of apocynin against the development of myocardial injuries, in particular, myocardial fibrogenesis, which will benefit the mechanism-based drug development targeting oxidative stress in preventing and/or treating related myocardial disorders.

Anti-tumor effect of Shu-gan-Liang-Xue decoction in breast cancer is related to the inhibition of aromatase and steroid sulfatase expression

Ning Zhou, Shu-Yan Han, Fei Zhou, Ping-ping Li
J Ethnopharmacol 154 (2014) 687–695
http://dx.doi.org/10.1016/j.jep.2014.04.045

Ethnopharmacological relevance: Shu-Gan-Liang-Xue Decoction (SGLXD), a traditional Chinese herbal formula used to ameliorate the hot flushes in breast cancer patients, was reported to have anti-tumor effect on breast cancer. Estrogen plays a critical role in the genesis and evolution of breast cancer. Aromatase and steroid sulfatase (STS) are key estrogen synthesis enzymes that predominantly contribute to the high local hormone concentrations. The present study was to evaluate the anti-tumor effect of SGLXD on estrogen receptor (ER) positive breast cancer celllineZR-75-1, and to investigate its underlying mechanisms both in vitro and in vivo.
Materials and methods: The anti-tumor activity of SGLXD in vitro was investigated using the MTT assay. The in vivo anti-tumor effect of SGLXD was evaluated in non-ovariectomized and ovariectomized athymic nude mice. The effect of SGLXD on enzymatic activity of aromatase and STS was examined using the dual-luciferase  reporter (DLR) based on bioluminescent measurements. Aromatase and STS protein level were assessed using Western blot assay. Results: SGLXD showed dose-dependent inhibitory effect on the proliferation of ZR-75-1 cells with IC50 value of 3.40 mg/mL. It also suppressed the stimulating effect on cell proliferation of testosterone and estrogen sulfates (E1S). Oral administration of 6 g/kg of SGLXD for 25 days resulted in a reduction in tumor volume in non-ovariectomized and ovariectomized nude mice. The bioluminescent measurements confirmed that SGLXD has a dual-inhibitory effect on the activity of aromatase and STS. Western blot assay demonstrated that the treatment of SGLXD resulted in a decrease in aromatase and STS protein levels both in vitro and in vivo. Conclusion: Our results suggested that SGLXD showed anti-tumor effect on breast cancer cells both in vitro and in vivo. The anti-tumor activity of SGLXD is related to inhibition of aromatase and STS via decreasing their expression. SGLXD may be considered as a novel treatment for ER positive breast cancer.

Cardioprotective effect of embelin on isoproterenol-induced myocardial injury in rats: Possible involvement of mitochondrial dysfunction and apoptosis

Bidya Dhar Sahu, Harika Anubolu, Meghana Koneru, et al.
Life Sciences 107 (2014) 59–67
http://dx.doi.org/10.1016/j.lfs.2014.04.035

Aims: Preventive and/or therapeutic interventions using natural products for ischemic heart disease have gained considerable attention world wide. This study investigated the cardioprotective effect and possible mechanism of embelin, a major constituent of EmbeliaribesBurm, using isoproterenol (ISO)-induced myocardial infarction model in rats.
Materials and methods: Rats were pretreated for three days with embelin (50mg/kg,p.o) before inducing myocardial injury by administration of ISO (85mg/kg) subcutaneously at aninterval of 24h for 2 consecutive days. Serum was analyzed for cardiac specific injury biomarkers, lipids and lipoprotein content. Heart tissues were isolated and were used for histopathology, antioxidant and mitochondrial respiratory enzyme activity assays and western blot analysis. Key findings: Results showed that pretreatment with embelin significantly decreased the elevated levels of serum specific cardiac injury biomarkers (CK-MB, LDH and AST), serum levels of lipids and lipoproteins and histopathological changes when compared to ISO-induced controls. Exploration of the underlying mechanisms of embelin action revealed that embelin pretreatment restored the myocardial mitochondrial respiratory enzyme activities (NADH dehydrogenase, succinate dehydrogenase, cytochrome c oxidase and mitochondrial redox activity), strengthened antioxidant status and attenuated ISO-induced myocardial lipid peroxidation. Immunoblot analysis revealed that embelin interrupted mitochondria dependent apoptotic damage by increasing the myocardial expression of Bcl-2 and downregulating the expression of Bax, cytochrome c, cleaved-caspase-3&9 and PARP. Histopathology findings further strengthened the cardioprotective findings of embelin. Significance: Result suggested that embelin may have a potential benefit in preventing ischemic heart diseasel like myocardial infarction.

Effect of Matricaria chamomilla L. flower essential oil on the growth and ultrastructure of Aspergillus niger vanTieghem

Marziyeh Tolouee, Soheil Alinezhad, Reza Saberi, Ali Eslamifar, et al.
Intl J Food Microbiol 139 (2010) 127–133
http://dx.doi.org:/10.1016/j.ijfoodmicro.2010.03.032

The antifungal activity of Matricaria chamomilla L. flower essential oil was evaluated against Aspergillus niger with the emphasis on the plant’s mode of action at the electron microscopy level. A total of 21 compounds were identified in the plant oil using gaschromatography/massspectrometry(GC/MS) accounting for 92.86% of the oil composition. The main compounds identified were α-bisabolol (56.86%), trans-trans-farnesol (15.64%), cis-β-farnesene (7.12%), guaiazulene (4.24%), α-cubebene (2.69%), α-bisabololoxideA (2.19%) and chamazulene (2.18%). In the bioassay, A.niger was cultured on Potato Dextrose Broth medium in 6-well microplates in the presence of serial two fold concentrations of plant oil (15.62 to 1000 µg/mL) for 96h at 28°C. Based on the results obtained, A. niger growth was inhibited dose dependently with a maximum of ∼92.50% at the highest oil concentration. A marked retardation in conidial production by the fungus was noticed in relation to the inhibition of hyphal growth. The main changes of hyphae observed by transmission electron microscopy were disruption of cytoplasmic membranes and intracellular organelles, detachment of plasma membrane from the cell wall, cytoplasm depletion, and completed is organization of hyphal compartments. In scanning electron microscopy, swelling and deformation of hyphal tips, formation of short branches, and collapse of entire hyphae were the major changes observed. Morphological alterations might be due to the effect on cell permeability through direct interaction of M. chamomilla essential oil with the fungal plasma membrane. These findings indicate the potential of M. chamomilla L. essential oil in preventing fungal contamination and subsequent deterioration of stored food and other susceptible materials.

Related articles in Pharmaceutical Intelligence.

Plant-based Nutrition, Neutraceuticals and Alternative Medicine: Article Compilation the Journal PharmaceuticalIntelligence.com

https://pharmaceuticalintelligence.com/2014/09/01/compilation-of-lpi-articles-on-plant-based-nutrition-and-neutraceuticals-alternative-medicine/

What do you know about Plants and Neutraceuticals?

https://pharmaceuticalintelligence.com/2014/07/30/what-do-you-know-about-plants-and-neutraceuticals/

The Discovery and Properties of Avemar – Fermented Wheat Germ Extract: Carcinogenesis Suppressor

https://pharmaceuticalintelligence.com/2014/06/07/the-discovery-and-properties-of-avemar-fermented-wheat-germ-extract-carcinogenesis-suppressor/

Introduction to Metabolomics

https://pharmaceuticalintelligence.com/2014/10/21/introduction-to-metabolomics/

Summary of Genomics and Medicine: Role in Cardiovascular Diseases

https://pharmaceuticalintelligence.com/2014/01/06/summary-of-genomics-and-medicine-role-in-cardiovascular-diseases/

Natural Products Chemistry

https://pharmaceuticalintelligence.com/2015/01/27/natural-products-chemistry/

Diet and Diabetes

https://pharmaceuticalintelligence.com/2015/03/02/diet-and-diabetes/

An Overview of Clinical Microbiology, Classification, and Antimicrobial Resistance

https://pharmaceuticalintelligence.com/2015/01/17/an-overview-of-clinical-microbiology-classification-and-antimicrobial-resistance/

Diabetes Mellitus

https://pharmaceuticalintelligence.com/2014/10/24/diabetes-mellitus/

Mechanisms of Drug Resistance

https://pharmaceuticalintelligence.com/2014/10/09/mechanisms-of-drug-resistance/

Antioxidant Potential of “Maltese Mushroom” (Cynomorium coccineum)

https://pharmaceuticalintelligence.com/2013/01/27/antioxidant-potential-of-maltese-mushroom-cynomorium-coccineum/

Advances in Separations Technology for the “OMICs” and Clarification of Therapeutic Targets

https://pharmaceuticalintelligence.com/2012/10/22/advances-in-separations-technology-for-the-omics-and-clarification-of-therapeutic-targets/

Acute Lung Injury

https://pharmaceuticalintelligence.com/2015/02/26/acute-lung-injury/

The Vibrant Philly Biotech Scene: Focus on KannaLife Sciences and the Discipline and Potential of Pharmacognosy

Curator and Interviewer: Stephen J. Williams, Ph.D.

https://pharmaceuticalintelligence.com/2015/02/19/the-vibrant-philly-biotech-scene-focus-on-kannalife-sciences-and-the-discipline-and-potential-of-pharmacognosy/

Complex Models of Signaling: Therapeutic Implications

https://pharmaceuticalintelligence.com/2014/10/31/complex-models-of-signaling-therapeutic-implications/

Parasitic Plant Strangleweed Injects Host With Over 9,000 RNA Transcripts

Reporter: Aviva Lev-Ari, PhD, RN

https://pharmaceuticalintelligence.com/2014/09/02/parasitic-plant-strangleweed-injects-host-with-over-9000-rna-transcripts/

Health benefit of anthocyanins from apples and berries noted for men

https://pharmaceuticalintelligence.com/2014/07/06/health-benefit-of-anthocyanins-from-apples-and-berries-noted-for-men/

Requiem for Palliative Cardiology: The Voice of Dr. Esselstyn on Plant-Based Nutrition

Reporter: Aviva Lev-Ari, PhD, RN

https://pharmaceuticalintelligence.com/2014/02/02/requiem-for-palliative-cardiology-the-voice-of-dr-esselstyn-on-plant-based-nutrition/

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Depth Underwater and Underground

Writer and Curator: Larry H. Bernstein, MD, FCAP 

 

Introduction

Deep diving for mammals is dangerous for humans and land based animals for too long, and it has dangerous consequences, most notable in nitrogen emboli  with very deep underwater diving. Other mammals live in water and have adapted to a water habitat.  This is another topic that needs further exploration.

Deep diving has different meanings depending on the context. Even in recreational diving the meaning may vary:

In recreational diving, a depth below about 30 metres (98 ft), where nitrogen narcosis becomes a significant hazard for most divers, may be considered a “deep dive”

In technical diving, a depth below about 60 metres (200 ft) where hypoxic breathing gas becomes necessary to avoid oxygen toxicity may be considered a “deep dive”.

Early experiments carried out by Comex S.A. (Compagnie maritime d’expertises) using hydrox and trimix attained far greater depths than any recreational technical diving. One example being the Comex Janus IV open-sea dive to 501 metres (1,644 ft) in 1977. The open-sea diving depth record was achieved in 1988 by a team of Comex divers who performed pipe line connection exercises at a depth of 534 metres (1,752 ft) in the Mediterranean Sea as part of the Hydra 8 program. These divers needed to breathe special gas mixtures because they were exposed to very high ambient pressure (more than 50 times atmospheric pressure).

Then there is the adaptation to the water habitat as a living environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.

http://en.wikipedia.org/wiki/Deep_diving

Marine ecosystems are part of the earth’s aquatic ecosystem. The habitats that make up this vast system range from the productive nearshore regions to the barren ocean floor. The marine waters may be fully saline, brackish or nearly fresh. The saline waters have a salinity of 35-50 ppt (= parts per thousand). The freshwater has a salinity of less than 0.5 ppt. The brackish water lies in between these 2. Marine habitats are situated from the coasts, over the continental shelf to the open ocean and deep sea. The ecosystems are sometimes linked with each other and are sometimes replacing each other in other geographical regions. The reason why habitats differ from another is because of the physical factors that influence the functioning and diversity of the habitats. These factors are temperature, salinity, tides, currents, wind, wave action, light and substrate.

Marine ecosystems are home to a host of different species ranging from planktonic organisms that form the base of the marine food web to large marine mammals. Many species rely on marine ecosystems for both food and shelter from predators. They are very important to the overall health of both marine and terrestrial environments. Coastal habitats are those above the spring high tide limit or above the mean water level in non-tidal waters.  They are close to the sea and include habitats such as coastal dunes and sandy shores, beaches , cliffs and supralittoral habitats. Coastal habitats alone account for approximately 30% of all marine biological productivity.

http://www.marbef.org/wiki/marine_habitats_and_ecosystems

All plant and animal life forms are included from the microscopic picoplankton all the way to the majestic blue whale, the largest creature in the sea—and for that matter in the world. It wasn’t until the writings of Aristotle from 384-322 BC that specific references to marine life were recorded. Aristotle identified a variety of species including crustaceans, echinoderms, mollusks, and fish.
Today’s classification system was developed by Carl Linnaeus external link as an important tool for use in the study of biology and for use in the protection of biodiversity. Without very specific classification information and a naming system to identify species’ relationships, scientists would be limited in attempts to accurately describe the relationships among species. Understanding these relationships helps predict how ecosystems can be altered by human or natural factors.

Preserving biodiversity is facilitated by taxonomy. Species data can be better analyzed to determine the number of different species in a community and to determine how they might be affected by environmental stresses. Family, or phylogenetic, trees for species help predict environmental impacts on individual species and their relatives.

http://marinebio.org/oceans/marine-taxonomy/

For generations, whales and other marine mammals have intrigued humans. 2,400 years ago, Aristotle, a Greek scientist and philosopher, recognized that whales are mammals, not fish, because they nurse their young and breathe air like other mammals. There are numerous myths and legends surrounding marine mammals. The Greeks believed that killing a dolphin was as bad as murdering a human. An Amazon legend said that river dolphins came to shore dressed as men to woo pretty girls during fiestas. During the Middle Ages, there were numerous legends surrounding the narwhals’ amazing tusk, which was thought to have come from the unicorn.

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Marine mammals evolved from their land dwelling ancestors over time by developing adaptations to life in the water. To aid swimming, the body has become streamlined and the number of body projections has been reduced. The ears have shrunk to small holes in size and shape. Mammary glands and sex organs are not part of the external physiology, and posterior (hind) limbs are no longer present.

Mechanisms to prevent heat loss have also been developed. The cylindrical body shape with small appendages reduces the surface area to volume ratio of the body, which reduces heat loss. Marine mammals also have a counter current heat exchange mechanism created by convergent evolution external link where the heat from the arteries is transferred to the veins as they pass each other before getting to extremities, thus reducing heat loss. Some marine mammals also have a thick layer of fur with a water repellent undercoat and/or a thick layer of blubber that can’t be compressed. The blubber provides insulation, a food reserve, and aids with buoyancy. These heat loss adaptations can also lead to overheating for animals that spend time out of the water. To prevent overheating, seals or sea lions will swim close to the surface with their front flippers waving in the air. They also flick sand onto themselves to keep the sun from directly hitting their skin. Blood vessels can also be expanded to act as a sort of radiator.

One of the major behavioral adaptations of marine mammals is their ability to swim and dive. Pinnipeds swim by paddling their flippers while sirenians and cetaceans move their tails or flukes up and down.

Some marine mammals can swim at relatively high speeds. Sea lions swim up to 35 kph and orcas can reach 50 kph. The fastest marine mammal, however, is the common dolphin, which reaches speeds up to 64 kph. While swimming, these animals take very quick breaths. For example, fin whales can empty and refill their huge lungs in less than 2 seconds. Marine mammals’ larynx and esophagus close automatically when they open their mouths to catch prey during dives. Oxygen is stored in hemoglobin in the blood and in myoglobin in the muscles. The lungs are also collapsible so that air is pushed into the windpipe preventing excess nitrogen from being absorbed into the tissues. Decreasing pressure can cause excess nitrogen to expand in the tissues as animals ascend to shallower depths, which can lead to decompression sickness,  aka “the bends.” Bradycardia, the reduction of heart rate by 10 to 20%, also takes place to aid with slowing respiration during dives and the blood flow to non-essential body parts. These adaptations allow sea otters to stay submerged for 4 to 5 minutes and dive to depths up to 55 m. Pinnipeds can often stay down for 30 minutes and reach average depths of 150-250 m. One marine mammal with exceptional diving skills is the Weddell seal, which can stay submerged for at least 73 minutes at a time at depths up to 600 m. The length and depth of whale dives depends on the species. Baleen whales feed on plankton near the surface of the water and have no need to dive deeply so they are rarely seen diving deeper than 100 m external link. Toothed whales seek larger prey at deeper depths and some can stay down for hours at depths of up to 2,250 m external link.

http://marinebio.org/oceans/marine-mammals/

Human Experience

Albert Behnke: Nitrogen Narcosis

Casey A. Grover and David H. Grover
The Journal of Emergency Medicine, 2014; 46(2):225–227
http://dx.doi.org/10.1016/j.jemermed.2013.08.080

As early as 1826, divers diving to great depths noted that descent often resulted in a phenomenon of intoxication and euphoria. In 1935, Albert Behnke discovered nitrogen as the cause of this clinical syndrome, a condition now known as nitrogen narcosis. Nitrogen narcosis consists of the development of euphoria, a false sense of security, and impaired judgment upon underwater descent using compressed air below 34 atmospheres (99 to 132 feet). At greater depths, symptoms can progress to loss of consciousness. The syndrome remains relatively unchanged in modern diving when compressed air is used. Behnke’s use of non-nitrogencontaining gas mixtures subsequent to his discovery during the 1939 rescue of the wrecked submarine USS Squalus pioneered the use of non-nitrogencontaining gas mixtures, which are used by modern divers when working at great depth to avoid the effects of nitrogen narcosis.

Behnke’s first duty station as a licensed physician was as assistant medical officer for Submarine Division 20 in San Diego, which was then commanded by one of the Navy’s rising stars, Captain Chester W. Nimitz of World War II fame.
In this setting, Dr. Behnke spent his free time constructively by learning to dive, using the traditional ‘‘hard-hat’’ gear aboard the USS Ortalon, a submarine rescue vessel to which he also rotated. Diving was not a notable specialty of the Navy at the time, and the service was slow in developing the infrastructure for it. Dr. Behnke devoted his efforts to research on the topic of diving medicine, as well as developing a more sound understanding of the biophysics of diving. In 1932, he wrote a letter to the Surgeon General describing some of his observations on arterial gas embolism, which earned him some accolades from the Navy and resulted in his transfer to Harvard’s School of Public Health as a graduate fellow. After 2 years at Harvard, the Navy assigned duty to Dr. Behnke at the Navy’s submarine escape training tower at Pearl Harbor. He worked extensively here on developing techniques for rescuing personnel from disabled submarines on the sea floor. In 1937, he was one of three Navy physicians assigned to the Navy’s Experimental Diving Unit. This team worked on improving the rescue system, plus updating the diving recompression tables originally developed by the British in 1908.

The intoxicating effects of diving were first described by a French physician named Colladon in 1826, who reported that descent in a diving bell resulted in his feeling a ‘‘state of excitement as though I had drunk some alcoholic liquor’’.
The etiology of this phenomenon remained largely unknown until the 1930s, when the British military researcher Damant again highlighted the issue, and reported very unpredictable behavior in his divers during descents as deep as 320 feet during the British Admiralty Deep Sea diving trials. Two initial theories arose as to the etiology for this effect, the first being from psychological causes by Hill and Phillip in 1932, and the second being from oxygen toxicity by Haldane in 1935.

Dr. Behnke and his colleagues at the Harvard School of Public Health had another idea as to the etiology of this phenomenon. In 1935, based on observation of individuals in experiments with a pressure chamber, Dr. Behnke published an article in the American Journal of Physiology in which he posited that nitrogen was the etiology of the intoxicating effects of diving.

Nitrogen narcosis, described as ‘‘rapture of the deep’’ by Jacques Cousteau, still remains a relatively common occurrence in modern diving, despite major advances in diving technology since Behnke’s initial description of the pathophysiologic cause of the condition in 1935. The development of symptoms of this condition varies from diver to diver, but usually begins when a depth of 4 atmospheres (132 feet) is reached in divers using compressed air. More sensitive divers can develop symptoms at only 3 atmospheres (99 feet), and other divers may not be affected up to depths as high as 6 atmospheres (198 feet). Interestingly, tolerance to nitrogen narcosis can be developed by frequent diving and exposure to the effects of compressed air at depth.

  1. Acott C. A brief history of diving and decompression illness. SPUMS J 1999;29:98–109.
    2. Bornmann R. Dr. Behnke, founder of UHMS, dies. Pressure 1992; 21:14.
    3. Behnke AR, Thomson RM, Motley P. The psychologic effects from breathing air at 4 atmospheric pressures. Am J Physiol 1935; 112:554–8.
    4. Behnke AR, Johnson FS, Poppen JR, Motley P. The effect of oxygen on man at pressures from 1 to 4 atmospheres. AmJ Physiol 1934; 110:565–72.

Exhaled nitric oxide concentration and decompression-induced bubble formation: An index of decompression severity in humans?

J.-M. Pontier, Buzzacott, J. Nastorg, A.T. Dinh-Xuan, K. Lambrechts
Nitric Oxide 39 (2014) 29–34
http://dx.doi.org/10.1016/j.niox.2014.04.005

Introduction: Previous studies have highlighted a decreased exhaled nitric oxide concentration (FE NO) in divers after hyperbaric exposure in a dry chamber or following a wet dive. The underlying mechanisms of this decrease remain however unknown. The aim of this study was to quantify the separate effects of submersion, hyperbaric hyperoxia exposure and decompression-induced bubble formation on FE NO after a wet dive.
Methods: Healthy experienced divers (n = 31) were assigned to either

  • a group making a scuba-air dive (Air dive),
  • a group with a shallow oxygen dive protocol (Oxygen dive) or

a group making a deep dive breathing a trimix gas mixture (deep-dive).
Bubble signals were graded with the KISS score. Before and after each dive FE NO values were measured using a hand-held electrochemical analyzer.
Results: There was no change in post-dive values of FE NO values (expressed in ppb = parts per billion) in the Air dive group (15.1 ± 3.6 ppb vs. 14.3 ± 4.7 ppb, n = 9, p = 0.32). There was a significant decrease in post-dive values of FE NO in the Oxygen dive group (15.6 ± 6 ppb vs. 11.7 ± 4.7 ppb, n = 9, p = 0.009). There was an even more pronounced decrease in the deep dive group (16.4 ± 6.6 ppb vs. 9.4 ± 3.5 ppb, n = 13, p < 0.001) and a significant correlation between KISS bubble score >0 (n = 13) and percentage decrease in post-dive FE NO values (r = -0.53, p = 0.03). Discussion: Submersion and hyperbaric hyperoxia exposure cannot account entirely for these results suggesting the possibility that, in combination, one effect magnifies the other. A main finding of the present study is a significant relationship between reduction in exhaled NO concentration and dive-induced bubble formation. We postulate that exhaled NO concentration could be a useful index of decompression severity in healthy human divers.

Brain Damage in Commercial Breath-Hold Divers

Kiyotaka Kohshi, H Tamaki, F Lemaıtre, T Okudera, T Ishitake, PJ Denoble
PLoS ONE 9(8): e105006 http://dx.doi.org:/10.1371/journal.pone.0105006

Background: Acute decompression illness (DCI) involving the brain (Cerebral DCI) is one of the most serious forms of diving related injuries which may leave residual brain damage. Cerebral DCI occurs in compressed air and in breath-hold divers, likewise. We conducted this study to investigate whether long-term breath-hold divers who may be exposed to repeated symptomatic and asymptomatic brain injuries, show brain damage on magnetic resonance imaging (MRI).
Subjects and Methods: Our study subjects were 12 commercial breath-hold divers (Ama) with long histories of diving work in a district of Japan. We obtained information on their diving practices and the presence or absence of medical problems, especially DCI events. All participants were examined with MRI to determine the prevalence of brain lesions.
Results: Out of 12 Ama divers (mean age: 54.965.1 years), four had histories of cerebral DCI events, and 11 divers demonstrated ischemic lesions of the brain on MRI studies. The lesions were situated in the cortical and/or subcortical area (9 cases), white matters (4 cases), the basal ganglia (4 cases), and the thalamus (1 case). Subdural fluid collections were seen in 2 cases. Conclusion: These results suggest that commercial breath-hold divers are at a risk of clinical or subclinical brain injury which may affect the long-term neuropsychological health of divers.

Decompression illness

Richard D Vann, Frank K Butler, Simon J Mitchell, Richard E Moon
Lancet 2010; 377: 153–64

Decompression illness is caused by intravascular or extravascular bubbles that are formed as a result of reduction in environmental pressure (decompression). The term covers both arterial gas embolism, in which alveolar gas or venous gas emboli (via cardiac shunts or via pulmonary vessels) are introduced into the arterial circulation, and decompression sickness, which is caused by in-situ bubble formation from dissolved inert gas. Both syndromes can occur in divers, compressed air workers, aviators, and astronauts, but arterial gas embolism also arises from iatrogenic causes unrelated to decompression. Risk of decompression illness is
affected by immersion, exercise, and heat or cold. Manifestations range from itching and minor pain to neurological symptoms, cardiac collapse, and death. First aid treatment is 100% oxygen and definitive treatment is recompression to increased pressure, breathing 100% oxygen. Adjunctive treatment, including fluid administration and prophylaxis against venous thromboembolism in paralyzed patients, is also recommended. Treatment is, in most cases, effective although residual deficits can remain in serious cases, even after several recompressions.

Bubbles can have mechanical, embolic, and biochemical effects with manifestations ranging from trivial to fatal. Clinical manifestations can be caused by direct effects from extravascular (autochthonous) bubbles such as mechanical distortion of tissues causing pain, or vascular obstruction causing stroke-like signs and symptoms. Secondary effects can cause delayed symptom onset up to 24 h after surfacing. Endothelial damage by intravascular bubbles can cause capillary leak, extravasation of plasma, and haemoconcentration. Impaired endothelial function, as measured by decreased effects of vasoactive compounds, has been reported in animals and might occur in man. Hypotension can occur in severe cases. Other effects include platelet activation and deposition, leucocyte-endothelial adhesion, and possibly consequences of vascular occlusion believed to occur in thromboembolic stroke such as ischaemia-reperfusion injury, and apoptosis.

Classification of initial and of all eventual manifestations of decompression illness in 2346 recreational diving accidents reported to the Divers Alert Network from 1998 to 2004 For all instances of pain, 58% consisted of joint pain, 35% muscle pain, and 7% girdle pain. Girdle pain often portends spinal cord involvement. Constitutional symptoms included headache, lightheadedness, inappropriate fatigue, malaise, nausea or vomiting, and anorexia. Muscular discomfort included stiffness, pressure, cramps, and spasm but excluded pain. Pulmonary manifestations included dyspnoea and cough.

Other than depth and time, risk of decompression sickness is affected by other factors that affect inert gas exchange and bubble formation, such as immersion (vs dry hyperbaric chamber exposure), exercise, and temperature. Immersion decreases venous pooling and increases venous return and cardiac output. Warm environments improve peripheral perfusion by promoting vasodilation, whereas cool temperatures decrease perfusion through vasoconstriction. Exercise increases both peripheral perfusion and temperature. The effect of environmental conditions on risk of decompression sickness is dependent on the phase of the pressure exposure. Pressure, exercise, immersion, or a hot environment increase inert gas uptake and risk of decompression sickness. During decom-pression these factors increase inert gas elimination and therefore decrease the risk of decompression sickness. Conversely, uptake is reduced during rest or in a cold environment, hence a diver resting in a cold environment on the bottom has decreased risk of decompression sickness. Rest or low temperatures during decompression increase the risk. If exercise occurs after decompression when super-saturation is present, bubble formation increases and risk of decompression sickness rises.

Exercise at specific times before a dive can decrease the risk of serious decompression sickness in animals and incidence of venous gas emboli in both animals and man. The mechanisms of these effects are unknown but might involve modulation of nitric oxide production and effects on endothelium. Venous gas emboli and risk of decompression sickness increase slightly with age and body-mass index.

Arterial gas embolism should be suspected if a diver has a new onset of altered consciousness, confusion, focal cortical signs, or seizure during ascent or within a few minutes after surfacing from a compressed gas dive.

If the diver spends much time at depth and might have absorbed substantial inert gas before surfacing, arterial gas embolism and serious decompression sickness can coexist, and in such cases, spinal cord manifestations can predominate. Other organ systems, such as the heart, can also be affected, but the clinical diagnosis of gas embolism is not reliable without CNS manifestations. Arterial gas embolism is rare in altitude exposure; if cerebral symptoms occur after altitude exposure, the cause is usually decompression sickness.

Nondermatomal hypoaesthesia and truncal ataxia are common in neurological decompression sickness and can be missed by cursory examination. Pertinent information includes level of consciousness and mental status, cranial nerve function, and motor strength. Coordination can be affected disproportionately, and abnormalities can be detected by assessment of finger-nose movement, and, with eyes open and closed, ability to stand and walk and do heel-toe walking backwards and forwards. Many of these simple tests can be done on the scene by untrained companions.

Panel: Differential diagnosis of decompression illness
Inner-ear barotrauma
Middle-ear or maxillary sinus overinfl ation
Contaminated diving gas and oxygen toxic effects
Musculoskeletal strains or trauma sustained before, during, or after diving
Seafood toxin ingestion (ciguatera, pufferfish, paralytic shellfish poisoning)
Immersion pulmonary edema
Water aspiration
Decompression chamber

Decompression chamber

Decompression chamber. fluidic or pneumatic ventilator is shown at the left. The infusion pump is contained within a plastic cover, in which 100% nitrogen is used to decrease the fi re risk in the event of an electrical problem. The monitor screen is outside the chamber and can be seen through the viewing port. Photo from Duke University Medical Center, with permission.

Long-term outcomes of 69 divers with spinal cord decompressionsickness, by manifestation
n %
No residual symptoms 34 49·3
Any residual symptom 35 50·7
Mild paraesthesias, weakness, or pain 14 20·3
Some impairment of daily activities 21 30·4
Difficulty walking 11 15·9
Impaired micturition 13 18·8
Impaired defecation 15 21·7
Impaired sexual function 15 21·7

Decompression illness occurs in a small population but is an international problem that few physicians are trained to recognise or manage. Although its manifestations are often mild, the potential for permanent injury exists in severe cases, especially if unrecognised or inadequately treated. Emergency medical personnel should be aware of manifestations of decompression illness in the setting of a patient with a history of recent diving or other exposure to substantial pressure change, and should contact an appropriate consultation service for advice.

Diving Medicine: Contemporary Topics and Their Controversies

Michael B. Strauss and Robert C. Borer, Jr
Am J Emerg Med 2001; 19:232-238
http://dx.doi.org:/10.1053/ajem.2001.22654

SCUBA diving is a popular recreational sport. Although serious injuries occur infrequently, when they do knowledge of diving medicine and/or where to obtain appropriate consultation is essential. The emergency physician is likely to be the first physician contact the injured diver has. We discuss 8 subjects
in diving medicine which are contemporary, yet may have controversies associated with them. From this information the physician dealing primarily with the injured diver will have a basis for understanding and managing, as
well as where to find additional help, for his/her patients’ diving injuries.

Over the past 10 years, new knowledge and equipment improvements have made diving safer and more enjoyable. Estimates of actively participating sports divers show a striking increase over this time interval while the number of SCUBA diving deaths annually has remained nearly level at approximately 100. A further indicator of recreational diving safety is that reflected in the nearly constant number of diving injuries (1000 per annum) over the most recent 5 reported years, or approximately 0.53 to 3.4 incidents/10,000 dives.

Divers Alert Network.
The Divers Alert Network (DAN) is a nonprofit organization directed and staffed by experts in the specialty of diving medicine.6 DAN provides immediate consultation for both divers and physicians in the diagnosis and initial management of diving injuries. This 24-hour service is available free world-wide through a dedicated emergency telephone line: 1-919-684-4326. The DAN staff will also identify the nearest appropriate recompression treatment facility and knowledgeable physicians for an expedient referral. General diving medical inquiries can be answered during normal weekday hours either through an information telephone line: 1-919-684-2948 or through an interactive web site http://www.diversalertnetwork.org.

Use of 100% Oxygen for Initial, on the Scene, Management of Diving Accidents
The breathing of pure oxygen is crucial for the initial management of the diving related problems of arterial gas embolism (AGE), decompression sickness (DCS), pulmonary barotrauma (thoracic squeeze), aspiration pneumonitis, and hypoxic encephalopathy associated with near drowning. In 1985, Dick reported that in many cases the neurologic symptoms of AGE and DCS were resolved with the immediate breathing of pure oxygen on the surface. The breathing of pure oxygen reduces bubble size by increasing the differential pressure for the inert gas to diffuse out of the bubble and it also speeds the washout of inert gas from body tissues. The early elimination of the bubble prevents hypoxia and the interaction of the bubble with the blood vessel lining. This interaction leads to secondary problems of capillary leak, bleeding, inflammation, ischemia, and cell death. These secondary problems are the reasons not all DCS symptoms resolve with recompression chamber treatment. The immediate use of pure oxygen for the medical management of these diving problems is analogous to the use of cardiopulmonary resuscitation for the witnessed cardiac arrest; the sooner initiated the better the results.

Diving Education

Medical Fitness for Diving

Asthma has the potential risk for AGE. Neuman reviewed the subject of asthma and diving. He and his coauthors recommend that asthmatics who are asymptomatic, not on medications and have no exercised induced abnormality on pulmonary function studies be allowed to dive.

Conditions leading to loss of consciousness, such as insulin dependent diabetes and epilepsy, can result in drowning. Carefully controlled diving studies in diabetics, who are free from complications, are now defining the safe requirements for diving. Epilepsy remains as a disqualification except in individuals with a history of febrile seizures ending prior to 5 years of age.

Availability of Hyperbaric Oxygen Treatment Facilities

The availability of these chambers makes it possible for divers who become symptomatic after SCUBA diving to readily receive recompression treatment. This is important because the closer the initiation of recompression treatment to the onset of DCS (and AGE) signs and symptoms, the greater the likelihood of full recovery.

Improved Diving Equipment

Mixed and Rebreather Gas Diving
Mixed gas diving involves changing the breathing gas from air which has 20% oxygen to higher oxygen percentages (nitrox). As the amount of oxygen is increased in the gas mixture, the amount of the inert gas (nitrogen) is reduced. With oxygen enriched air there is less tissue deposition of inert gas per unit of time under water for any given depth. However, because of increased oxygen partial pressures, the seizure threshold for oxygen toxicity is lowered. For normal sports diving activities, oxygen toxicity with mixed gas diving is only a theoretical concern.

Decompression Illness is More Than Bubbles

When AGE occurs, DCS symptoms may be concurrent or appear during or after recompression treatment even though the decompression tables were not violated on the dive. When DCS occurs in this situation it appears resistant to recompression treatment (Neuman) perhaps because of the inflammatory reaction generated by the bubble-blood vessel interaction from the AGE. In cases of DCI where components of both DCS and AGE are suspected, the diver should be observed for a minimum of 24 hours after the recompression treatment is completed for the delayed onset of DCS.

No theory of DCS discounts the primary role of bubbles in this condition. However, new information suggests that there are precursors to bubble formation and post-bubbling events that occur as a consequence of the bubbles. As mentioned earlier, venous gas emboli are a common occurrence diving ascent and ordinarily are filtered out harmlessly by the lungs. Precursors to DCS include stasis, dehydration and too rapid of ascents. These conditions allow the ubiquitous VGE to enlarge, coalesce and occlude the venous side of the circulation. Massive venous bubbling to the lungs can cause pulmonary vessel obstruction described as the chokes. If right to left shunts occur in the heart, VGE can become AGE to the brain. If the arterial flow is slow enough and/or the gradients large enough, autochthonus (ie, spontaneous) bubbles can form in the arterial circulation and lead to any of the consequences of AGE. In such situations it could be difficult to determine whether the DCI event was from AGE or DCS even after careful analysis of the dive profile. Hollenbeck’s model for diving paraplegia includes the setting of venous stasis (Batson’s plexus of veins) in the spinal canal, bubble formation, bubble enlargement possibly from off gassing of the spinal cord, blood vessel occlusion, and venous side infarctions of the spinal cord.
Contemporary Management of DCS

Problem Intervention Effect
Bubble Recompression
with HBO
Reduce bubble size
1. Washout inert gas.
2. Change bubble composition by diffusion.
Stasis and dehydration Hydration: oral fluids if alert, IV fluids otherwise. Improve blood flow.
InflammationCell Ischemia ? Anti-inflammatory medicationsHBO Reduce interaction between bubble and blood vessel endothelium.
Improve oxygen availability to hypoxic tissues, reduce edema and also reduces the interaction between bubble and blood vessel endothelium.

.

Conclusions

We anticipate that in the future there will be further improvements for the safety and enjoyment of the recreational SCUBA diver. For example, the dive computer of the future will be able to individualize dive profiles for different personal medical parameters such as age, body composition and fitness level. Diver locators could quickly target a missing diver and save time and gas consumption as well as prevent serious diving mishaps. Drugs may be developed that would minimize the effect of bubbles interacting with body tissues and prevent DCS and AGE.

Extracorporeal membrane oxygenation therapy for pulmonary decompression illness

Yutaka Kondo, Masataka Fukami and Ichiro Kukita
Kondo et al. Critical Care 2014; 18:438 http://ccforum.com/content/18/3/438/10.1186/cc13935

Pulmonary decompression illness is rarely observed in clinical settings, and most patients die prior to hospitalization. We administered ECMO therapy to rescue a patient, even though this therapy has rarely been reported with good outcome in patients with decompression illness. In addition, we had to select venovenous ECMO even with the patient showing right ventricular failure. A lot of physicians may select venoarterial ECMO if the patient shows right ventricular failure, but the important physiological mechanism of pulmonary decompression illness is massive air embolism in the pulmonary arteries, and the bubbles diminish within the first 24 hours. The management of decompression illness therefore differs substantially from the usual right-sided heart failure.

Extremes of barometric pressure

Jane E Risdall, David P Gradwell
Anaesthesia and Intensive Care Medicine 16:2
Ascent to elevated altitude, commonly achieved through flight, by climbing or by residence in highland regions, exposes the individual to reduced ambient pressure. Although there are physical manifestations of this exposure as a consequence of Boyle’s law, the primary physiological challenge is of hypobaric hypoxia. The acute physiological and longer-term adaptive responses of the cardiovascular, respiratory, hematological and neurological systems to altitude are described, together with an outline of the presentation and management of acute mountain sickness, high-altitude pulmonary edema and high-altitude cerebral edema. While many millions experience modest exposure to altitude as a result of flight in pressurized aircraft, fewer individuals are exposed to increased ambient pressure. The pressure changes during diving and hyperbaric exposures result in greater changes in gas load and gas toxicity. Physiological effects include the consequences of increased work of breathing and redistribution of circulating volume. Neurological manifestations may be the direct result of pressure or a consequence of gas toxicity at depth. Increased tissue gas loads may result in decompression illness on return to surface or subsequent ascent in flight.

  • understand the physical effects of changes in ambient pressure and the physiological consequences on the cardiovascular respiratory and neurological systems
  • gain an awareness that exposure to reduced ambient pressure produces both acute and more chronic effects, with differing signs, symptoms and time to onset at various altitudes
  • develop an awareness of the toxic effects of ‘inert’ gases at increased ambient pressures and the pathogenesis and management of decompression illness

Decompression illness According to Henry’s law, at a constant temperature the amount of gas which dissolves in a liquid is proportional to the pressure of that gas or its partial pressure, if it is part of a mixture of gases. Breathing gases at increased ambient pressure will increase the amount of each gas dissolved in the fluid phases of body tissues. On ascent this excess gas has to be given up. If the ascent is controlled at a sufficiently slow rate, elimination will be via the respiratory system. If the ascent is too fast, excess gas may come out of solution and form free bubbles in the tissues or circulation. Bubbles may contain any of the gases in the breathing mixture, but it is the presence of inert gas bubbles (nitrogen or helium) that are thought most likely to give rise to problems, since the elimination of excess oxygen is achieved by metabolism as well as ventilation. These bubbles may act as venous emboli or may trigger inflammatory tissue responses giving rise to symptoms of decompression illness (DCI). Signs and symptoms of DCI may appear up to 48 hours after exposure to increased ambient pressure and include joint pains, motor and sensory deficits, dyspnoea, cough and skin rashes.

Neurological effects of deep diving

Marit Grønning, Johan A. Aarli
Journal of the Neurological Sciences 304 (2011) 17–21
http://dx.doi.org:/10.1016/j.jns.2011.01.021

Deep diving is defined as diving to depths more than 50 m of seawater (msw), and is mainly used for occupational and military purposes. A deep dive is characterized by the compression phase, the bottom time and the decompression phase. Neurological and neurophysiologic effects are demonstrated in divers during the compression phase and the bottom time. Immediate and transient neurological effects after deep dives have been shown in some divers. However, the results from the epidemiological studies regarding long term neurological effects from deep diving are conflicting and still not conclusive.

Possible immediate neurological effects of deep diving
Syndrome Pressure
Hyperoxia/oxygen seizures >152 kPa (5 msw)
HypoxiaHypercapnia
Nitrogen narcosis >354 kPa (25 msw)
High pressure nervous syndrome >1.6 MPa (150 msw)
Neurological decompression sickness

Neurological effects have been demonstrated, both clinically and neurophysiologically in divers during the compression phase and the bottom time. Studies of divers before and after deep dives have shown immediate and transient neurological effects in some divers. However, the results from the epidemiological and clinical studies regarding long term neurological effects from deep diving are conflicting and still not conclusive. Prospective clinical studies with sufficient power and sensitivity are needed to solve this important issue.

Today deep diving to more than 100 msw is routinely performed globally in the oil- and gas industry. In the North Sea remote underwater intervention and maintenance is performed by the use of remotely operated vehicles (ROV), both in conjunction to and as an alternative to manned underwater operations. There will, however, always be a need for human divers in the technically more advanced underwater operations and for contingency repair operations.

P300 latency indexes nitrogen narcosis

Barry Fowler, Janice Pogue and Gerry Porlier
Electroencephalography, and clinical Neurophysiology, 1990, 75:221-229

This experiment investigated the effects of nitrogen narcosis on reaction time (RT) and P300 latency and amplitude, Ten subjects breathed either air or a non-narcotic 20% oxygen-80% helium (heliox) mixture in a hyperbaric chamber at 6.5, 8.3 and 10 atmospheres absolute (ATA), The subjects responded under controlled accuracy conditions to visually presented male or female names in an oddball paradigm. Single-trial analysis revealed a strong relationship between RT and P300 latency, both of which were slowed in a dose-related manner by hyperbaric air but not by heliox. A clear-cut dose-response relationship could not be established for P300 amplitude. These results indicate that P300 latency indexes nitrogen narcosis and are interpreted as support for the slowed processing model of inert gas narcosis.

Adaptation to Deep Water Habitat

Effects of hypoxia on ionic regulation, glycogen utilization and antioxidative ability in the gills and liver of the aquatic air-breathing fish Trichogaster microlepis

Chun-Yen Huang, Hui-Chen Lina, Cheng-Huang Lin
Comparative Biochemistry and Physiology, Part A 179 (2015) 25–34
http://dx.doi.org/10.1016/j.cbpa.2014.09.001

We examined the hypothesis that Trichogaster microlepis, a fish with an accessory air-breathing organ, uses a compensatory strategy involving changes in both behavior and protein levels to enhance its gas exchange ability. This compensatory strategy enables the gill ion-regulatory metabolism to maintain homeostasis during exposure to hypoxia. The present study aimed to determinewhether ionic regulation, glycogen utilization and antioxidant activity differ in terms of expression under hypoxic stresses; fish were sampled after being subjected to 3 or 12 h of hypoxia and 12 h of recovery under normoxia. The air-breathing behavior of the fish increased under hypoxia. No morphological modification of the gills was observed. The expression of carbonic anhydrase II did not vary among the treatments. The Na+/K+-ATPase enzyme activity did not decrease, but increases in Na+/K+-ATPase protein expression and ionocyte levels were observed. The glycogen utilization increased under hypoxia as measured by glycogen phosphorylase protein expression and blood glucose level, whereas the glycogen content decreased. The enzyme activity of several components of the antioxidant system in the gills, including catalase, glutathione peroxidase, and superoxidase dismutase, increased in enzyme activity. Based on the above data, we concluded that T. microlepis is a hypoxia-tolerant species that does not exhibit ion-regulatory suppression but uses glycogen to maintain energy utilization in the gills under hypoxic stress. Components of the antioxidant system showed increased expression under the applied experimental treatments.

Divergence date estimation and a comprehensive molecular tree of extant cetaceans

Michael R. McGowen , Michelle Spaulding, John Gatesy
Molecular Phylogenetics and Evolution 53 (2009) 891–906
http://dx.doi.org/10.1016/j.ympev.2009.08.018

Cetaceans are remarkable among mammals for their numerous adaptations to an entirely aquatic existence, yet many aspects of their phylogeny remain unresolved. Here we merged 37 new sequences from the nuclear genes RAG1 and PRM1 with most published molecular data for the group (45 nuclear loci, transposons, mitochondrial genomes), and generated a supermatrix consisting of 42,335 characters. The great majority of these data have never been combined. Model-based analyses of the supermatrix produced a solid, consistent phylogenetic hypothesis for 87 cetacean species. Bayesian analyses corroborated odontocete (toothed whale) monophyly, stabilized basal odontocete relationships, and completely resolved branching events within Mysticeti (baleen whales) as well as the problematic speciose clade Delphinidae (oceanic dolphins). Only limited conflicts relative to maximum likelihood results were recorded, and discrepancies found in parsimony trees were very weakly supported. We utilized the Bayesian supermatrix tree to estimate divergence dates among lineages using relaxed-clock methods. Divergence estimates revealed rapid branching of basal odontocete lineages near the Eocene–Oligocene boundary, the antiquity of river dolphin lineages, a Late Miocene radiation of balaenopteroid mysticetes, and a recent rapid radiation of Delphinidae beginning [1]10 million years ago. Our comprehensive,  time calibrated tree provides a powerful evolutionary tool for broad-scale comparative studies of Cetacea.

Mitogenomic analyses provide new insights into cetacean origin and evolution

Ulfur Arnason, Anette Gullberg, Axel Janke
Gene 333 (2004) 27–34
http://dx.doi.org:/10.1016/j.gene.2004.02.010

The evolution of the order Cetacea (whales, dolphins, porpoises) has, for a long time, attracted the attention of evolutionary biologists. Here we examine cetacean phylogenetic relationships on the basis of analyses of complete mitochondrial genomes that represent all extant cetacean families. The results suggest that the ancestors of recent cetaceans had an explosive evolutionary radiation 30–35 million years before present. During this period, extant cetaceans divided into the two primary groups, Mysticeti (baleen whales) and Odontoceti (toothed whales). Soon after this basal split, the Odontoceti diverged into the four extant lineages, sperm whales, beaked whales, Indian river dolphins and delphinoids (iniid river dolphins, narwhals/belugas, porpoises and true dolphins). The current data set has allowed test of two recent morphological hypotheses on cetacean origin. One of these hypotheses posits that Artiodactyla and Cetacea originated from the extinct group Mesonychia, and the other that Mesonychia/Cetacea constitutes a sister group to Artiodactyla. The current results are inconsistent with both these hypotheses. The findings suggest that the claimed morphological similarities between Mesonychia and Cetacea are the result of evolutionary convergence rather than common ancestry.

The order Cetacea traditionally includes three suborders: the extinct Archaeoceti and the recent Odontoceti and Mysticeti. It is commonly believed that the evolution of ancestral cetaceans from terrestrial to marine (aquatic) life was accompanied by a fast and radical morphological adaptation. Such a scenario may explain why it was, for a long time, difficult to morphologically establish the position of Cetacea in the mammalian tree and even to settle whether Cetacea constituted a monophyletic group.

Biochemical analyses in the 1950s  and 1960s had shown a closer relationship between cetaceans and artiodactyls (even-toed hoofed mammals) than between cetaceans and any other eutherian order and karyological studies in the late 1960s and early 1970s unequivocally supported cetacean monophyly (Arnason, 1969, 1974). The nature of the relationship between cetaceans and artiodactyls was resolved in phylogenetic studies of mitochondrial (mt) cytochrome b (cytb) genes (Irwin and Arnason, 1994; Arnason and Gullberg, 1996) that placed Cetacea within the order Artiodactyla itself as the sister group of the Hippopotamidae (see also Sarich, 1993). The Hippopotamidae/ Cetacea relationship was subsequently supported in studies of nuclear data (Gatesy et al., 1996; Gatesy, 1997) and statistically established in analysis of complete mt genomes (Ursing and Arnason, 1998). The relationship has also been confirmed in analyses of combined nuclear and mt sequences (Gatesy et al., 1999; Cassens et al., 2000) and in studies of short interspersed repetitive elements (SINEs). Artiodactyla and Cetacea are now commonly referred to as Cetartiodactyla.

Previous analyses of the complete cytb gene of more than 30 cetacean species (Arnason and Gullberg, 1996) identified five primary lineages of recent cetaceans, viz., Mysticeti and the four odontocete lineages Physeteridae (sperm whales), Platanistidae (Indian river dolphins), Ziphiidae (beaked whales) and Delphinoidea (iniid river dolphins, porpoises, narwhals and dolphins). However, these studies left unresolved the relationships of the five lineages as well as those between the three delphinoid families Monodontidae (narwhals, belugas), Phocoenidae (porpoises) and Delphinidae (dolphins). Similarly, the relationships between the four mysticete families Balaenidae (right whales), Neobalaenidae (pygmy right whales), Eschrichtiidae (gray whales) and Balaenopteridae (rorquals) were not conclusively resolved in analyses of cytb genes.

Fig. (not shown). Cetartiodactyl relationships and the estimated times of their divergences. The tree was established on the basis of maximum likelihood analysis of the concatenated amino acid (aa) sequences of 12 mt protein-coding genes. Length of alignment 3610 aa. Support values for branches A–H are shown in the insert.
Cetruminantia (branch A) receives moderate support and Cetancodonta (B) strong support. Cetacea (C) splits into monophyletic Mysticeti (baleen whales) and monophyletic Odontoceti (toothed whales). Odontoceti has four basal lineages, Physeteridae (sperm whales: represented by the sperm and pygmy sperm whales), Ziphiidae (beaked whales: bottlenose and Baird’s beaked whales), Platanistidae (Indian river dolphins: Indian river dolphin) and Delphinoidea. Delphinoidea encompasses the families Iniidae (iniid river dolphins: Amazon river dolphin, La Plata dolphin), Monodontidae (narwhals/belugas: narwhal), Phocoenidae (porpoises: harbour porpoise) and Delphinidae (dolphins: white-beaked dolphin). The common odontocete branch and the branches separating the four cetacean lineages are short. These relationships are therefore somewhat unstable (cf. Section 3.1 and Table 1). Iniid river dolphins (F) are solidly nested within the Delphinoidea (E). Thus, traditional river dolphins (Platanistidae + Iniidae) do not form a monophyletic unit. Molecular estimates of divergence times (Sanderson 2002) were based on two calibration points, A/C-60 and O/M-35 (cf. Section 3.2). Due to the short lengths of internal branches, some estimates for these divergences overlap. NJ: neighbor joining; MP: maximum parsimony; LBP: local bootstrap probability; QP: quartet puzzling. The bar shows the number of aa substitutions per site.

The limited molecular resolution among basal cetacean lineages has been known for some time. Studies of hemoglobin and myoglobin (Goodman, 1989; Czelusniak et al., 1990) have either joined Physeteridae and Mysticeti to the exclusion of Delphinoidea (myoglobin data) or Mysticeti and Delphinoidea to the exclusion of Physeteridae (hemoglobin data). Thus, neither of the data sets identified monophyletic Odontoceti by joining the two odontocete lineages (Physeteridae and Delphinoidea) to the exclusion of Mysticeti. A similar instability was recognized and cautioned against in analyses of some mt data, notably, sequences of rRNA genes (Arnason et al., 1993b). The suggestion (Milinkovitch et al., 1993) of a sister group relationship between Physeteridae and the mysticete family Balaenopteridae (rorquals) was based on a myoglobin data set (which joins Physeteridae and Mysticeti to the exclusion of Delphinoidea) that was complemented with partial data of the mt 16S rRNA gene.

The cetancodont divergence times calculated using A/C-60 and O/M-35 as references have been included in Fig. 1. As a result of the short branches separating several cetacean lineages, the estimates of these divergences overlap. The same observation has been made in calculations based on SINE flanking sequences (Nikaido et al., 2001). There is a general consistency between the current and the flanking sequence datings, except for those involving the Balaenopteridae, which are somewhat younger in our analysis than in the SINEs study. The currently estimated age of the divergence between Hippopotamus and Cetacea (c53.5 MYBP) is consistent with the age (>50 MY) of the oldest archaeocete fossils identified so far (Bajpai and Gingerich, 1998). This suggests that the ages allocated to the two references, A/C-60 (the divergence between ruminant artiodactyls and cetancodonts) and O/M-35 (the divergence between odontocetes and mysticetes) are reasonably accurate.

The dating of the divergence between the blue and fin whales is of interest regarding hybridization between closely related mammalian species. Previous molecular analyses (Arnason et al., 1991b; Spilliaert et al., 1991) demonstrated the occurrence of hybridization between these two species. These studies, which were based on three hybrids (one female and two males), showed that either species could be the mother or father in these hybridizations. The two male hybrids had rudimentary testes, whereas the female hybrid was in her second pregnancy. This suggests that the blue and fin whales may be close to the limit for permissible species hybridization among mammals.

The current data set has allowed examination of the coherence between the molecular results and two prevalent morphological hypotheses related to cetacean evolution. The first hypothesis, which in essence originates from Van Valen (1966, 1968), postulates that monophyletic Artiodactyla and monophyletic Cetacea evolved separately from the extinct Palaeocene group Mesonychia. This hypothesis was recently reinforced in a morphological study (Thewissen et al., 2001) that included mesonychians, two archaeocete taxa (Ambuloocetus and Pakicetus) and some extant and fossil artiodactyls. The study of Thewissen et al. (2001) showed a sister group relationship between monophyletic Artiodactyla and monophyletic Cetacea, with Mesonychia as the basal sister group of Artiodactyla/Cetacea, a conclusion consistent with the palaeontological age of Mesonychia relative to that of Artiodactyla and Cetacea. The second hypothesis favours a sister group relationship between Mesonychia and Cetacea with the Mesonychia/Cetacea clade as the sister group of monophyletic Artiodactyla (O’Leary and Geisler, 1999; see also Gatesy and O’Leary, 2001).

Although the position of Mesonychia differs in the two morphological hypotheses, both correspond to a sister group relationship between Cetacea and monophyletic Artiodactyla among extant cetartiodactyls. Thus, both hypotheses can be tested against the current data set. The result of such a test has been included in Table 1, topology (m)(not shown). As evident, both these morphological hypotheses are incongruent with the mitogenomic findings.

Morphological studies have not provided an answer to the question whether mysticetes and odontocetes had separate origins among the archaeocetes (Fordyce and de Muizon, 2001). However, the long common cetacean branch and the short branches separating the five extant cetacean lineages strongly suggest an origin of modern cetaceans from the same archaeocete group (probably the Dorudontidae).

The limbs of Ambulocetus constitute somewhat of an evolutionary enigma. As evident in Thewissen et al.’s (1994) paper, Ambulocetus has very large hind limbs compared to its forelimbs, a difference that is less pronounced in later silhouette drawings of the animal. It is nevertheless evident that evolution from the powerful hindlimbs of Ambulocetus to their rudimentation in archaeocetes constitutes a remarkable morphological reversal if Ambulocetus is connected to the cetacean branch after the separation of the hippopotamid and cetacean lineages.

For natural reasons, systematic schemes have traditionally been based on external morphological characteristics. The rates of morphological and molecular evolution are rarely (if ever) strictly correlated, however, and this may give rise to inconsistency between traditional systematics and molecular findings. The emerging consensus that the order Cetacea resides within another traditional order, Artiodactyla, makes apparent the incongruity in cetartiodactyl nomenclature (Graur and Higgins, 1994). In this instance, a possible solution for maintaining reasonable consistency between nomenclature and phylogeny would be to recognize Cetartiodactyla as an order with three suborders: Suina, Tylopoda and Cetruminantia. According to such a scheme, Cetacea would (together with the Hippopotamidae) constitute a parvorder within the infraorder Cetancodonta.

Cytochrome b and Bayesian inference of whale phylogeny

Laura May-Collado, Ingi Agnarsson
Molecular Phylogenetics and Evolution 38 (2006) 344–354
http://dx.doi.org//10.1016/j.ympev.2005.09.019

In the mid 1990s cytochrome b and other mitochondrial DNA data reinvigorated cetacean phylogenetics by proposing many novel

and provocative hypotheses of cetacean relationships. These results sparked a revision and reanalysis of morphological datasets, and the collection of new nuclear DNA data from numerous loci. Some of the most controversial mitochondrial hypotheses have now become benchmark clades, corroborated with nuclear DNA and morphological data; others have been resolved in favor of more traditional views. That major conflicts in cetacean phylogeny are disappearing is encouraging. However, most recent papers aim specifically to resolve higher-level conflicts by adding characters, at the cost of densely sampling taxa to resolve lower-level relationships. No molecular study to date has included more than 33 cetaceans. More detailed molecular phylogenies will provide better tools for evolutionary studies. Until more genes are available for a high number of taxa, can we rely on readily available single gene mitochondrial data? Here, we estimate the phylogeny of 66 cetacean taxa and 24 outgroups based on Cytb sequences. We judge the reliability of our phylogeny based on the recovery of several deep-level benchmark clades. A Bayesian phylogenetic analysis recovered all benchmark clades and for the Wrst time supported Odontoceti monophyly based exclusively on analysis of a single mitochondrial gene. The results recover the monophyly, with the exception of only one taxa within Cetacea, and the most recently proposed super- and subfamilies. In contrast, parsimony never recovered all benchmark clades and was sensitive to a priori weighting decisions. These results provide the most detailed phylogeny of Cetacea to date and highlight the utility of both Bayesian methodology in general, and of Cytb in cetacean phylogenetics. They furthermore suggest that dense taxon sampling, like dense character sampling, can overcome problems in phylogenetic reconstruction.

Some long standing debates are all but resolved: our understanding of deeper level cetacean phylogeny has grown strong. However, the strong focus of most recent studies, aiming specifically to resolve these higher level conflicts by adding mostly characters rather than taxa, has left our understanding of lower level relationships among whale species lagging behind. Mitogenomic data, for example, is available only for 16 cetacean species, and no molecular study to date has included more than 33 cetaceans. It seems timely to focus on more detailed (genus, and species level) molecular phylogenies. These will provide better tools for detailed evolutionary studies, and are necessary to test existing morphological phylogenetic hypotheses, and current cetacean classification.

We judge the reliability of our phylogeny based on the recovery of the previously mentioned benchmark clades, in addition to the less controversial clades Perissodactyla, Euungulata (sensu Waddell et al., 2001; Perissodactyla+ Cetartiodactyla), Cetacea, and Mysticeti. Because Cytb is thought to be most reliable at lower taxonomic levels (due to high substitution rates), recovering ‘known’ deeper clades gives credibility to these new findings which have not been addressed by studies using few taxa. We compare the performance of Bayesian analyses versus parsimony under four different models, and briefly examine the sensitivity of the results to taxon sampling. We use our results to discuss agreement and remaining conflict in cetacean phylogenetics, and provide comments on current classification.

The Bayesian analysis recovered all seven benchmark clades. Support for five of the benchmark clades is high (100 posterior probabilities) but rather low for Cetancodonta (79) and marginal for the monophyly of Odontoceti. The analysis also recovered all but one family level, and most sub- and superfamily level cetacean taxa. The results broadly corroborate current cetacean classiffcation, while also pointing to some lower-level groups that may need redefinition.

Many recent cetacean phylogenetic studies include relatively few taxa, in part due to a focus on generating more characters to resolve higher level phylogenetics. While addressing crucial questions and providing the backbone for lower level phylogenies, such studies have limited utility for classification, and for comparative evolutionary studies. In some cases sparse taxon sampling may also confound the results. Of course, taxon sampling is usually simply constrained by the availability of character data, but for some reason many studies have opted to include only one, or a few outgroup taxa, even if many are available.

We find that as long as outgroup taxon sampling was extensive, Bayesian analyses of Cytb recovered all the a priori identified benchmark clades. When only a few outgroups were chosen, however, the Bayesian analysis negated Odontoceti monophyly, as have many previous parsimony analyses of mitochondrial DNA. Furthermore, in almost every detailed comparison possible our results mirror the findings O’Leary et al. (2004), the most ‘character-complete’ (but including relatively few cetacean taxa) analysis to date (37,000 characters from morphology, SINE, and 51 gene fragments). This result gives credibility to our findings, including previously untested lower level clades.

  • Monophyly and placement of Mysticeti (baleen whales).
  • Monophyly of Odontoceti (toothed whales)
  • Delphinoids
  • River Dolphins
  • Beaked and sperm whales

A major goal of phylogenetics is a phylogeny of life (i.e., many taxa), based on multiple lines of evidence (many characters of many types). However, when phylogenies based on relatively few characters can be judged reliable based on external evidence (taxonomic congruence with other phylogenies using many characters, but few taxa), they seem like very promising and useful ‘first guess’ hypotheses. The evolution of sexual dimorphism, echolocation, social behavior, and whistles and other communicative signals, and major ecological shifts (e.g., transition to fresh water) are among the numerous interesting questions in cetacean biology that this phylogeny can help answer.

Deep-diving sea lions exhibit extreme bradycardia in long duration dives

Birgitte I. McDonald1, and Paul J. Ponganis
The Journal of Experimental Biology (2014) 217, 1525-1534 http://dx.doi.org:/10.1242/jeb.098558

Heart rate and peripheral blood flow distribution are the primary determinants of the rate and pattern of oxygen store utilization and ultimately breath-hold duration in marine endotherms. Despite this, little is known about how otariids (sea lions and fur seals) regulate heart rate (fH) while diving. We investigated dive fH in five adult female California sea lions (Zalophus californianus) during foraging trips by instrumenting them with digital electrocardiogram (ECG) loggers and time depth recorders. In all dives, dive fH (number of beats/duration; 50±9 beats min−1) decreased compared with surface rates (113±5 beats min−1), with all dives exhibiting an instantaneous fH below resting (<54 beats min−1) at some point during the dive. Both dive fH and minimum instantaneous fH significantly decreased with increasing dive duration. Typical instantaneous fH profiles of deep dives (>100 m) consisted of:

(1) an initial rapid decline in fH resulting in the lowest instantaneous fH of the dive at the end of descent, often below 10 beats min−1 in dives longer than 6 min in duration;
(2) a slight increase in fH to ~10–40 beats min−1 during the bottom portion of the dive; and
(3) a gradual increase in fH during ascent with a rapid increase prior to surfacing.

Thus, fH regulation in deep-diving sea lions is not simply a progressive bradycardia. Extreme bradycardia and the presumed associated reductions in pulmonary and peripheral blood flow during late descent of deep dives should

(a) contribute to preservation of the lung oxygen store,
(b) increase dependence of muscle on the myoglobin-bound oxygen store,
(c) conserve the blood oxygen store and
(d) help limit the absorption of nitrogen at depth.

This fH profile during deep dives of sea lions may be characteristic of deep-diving marine endotherms that dive on inspiration as similar fH profiles have been recently documented in the emperor penguin, another deep diver that dives on inspiration.

The resting ƒH measured in this study (54±6 beats min−1) was lower than predicted for an animal of similar size (~80 beats min−1 for an 80 kg mammal). In part, this may be due to the fact that the sea lions were probably sleeping. The resting ƒH in our study was also lower than previous measurements in captive juvenile California sea lions (87±17 beats min−1, average mass 30 kg)  and wild Antarctic fur seals (78±5 beats min−1, body mass 30–50 kg). However, we found a significant negative relationship between mass and resting ƒH even with our small sample size of five sea lions (resting ƒH = –0.58 Mb +100.26, r2=0.81, F1,3=12.37, P=0.039). For a 30 kg sea lion, this equation predicts a resting ƒH of 83 beats min−1, which is similar to what was measured previously in juvenile sea lions, suggesting this equation may be useful in estimating resting ƒH in sea lions.

The sea lions exhibited a distinct sinus arrhythmia fluctuating between a minimum of 42±9 and a maximum of 87±12 beats min−1, comparable to the sinus arrhythmias described in other diving birds and mammals, including sea lions. The minimum instantaneous ƒH during the sinus arrhythmia was similar to the mean minimum ƒH in dives less than 3 min (37±7 beats min−1), indicating that in dives less than 3 min (estimated cADL), ƒH only decreased to levels observed during exhalation at rest. This is consistent with observations in emperor penguins and elephant seals, where it was proposed that in dives shorter than the aerobic dive limit (ADL) the reduction in ƒH is regulated by a mechanism of cardiorespiratory control similar to that governing the respiratory sinus arrhythmia, with a further reduction only occurring in dives longer than the ADL.

Fig. 3. (not shown) Instantaneous fH and dive depth profiles of a California sea lion (CSL12_2). Data are from (A) a short, shallow dive (1.3 min, 45 m), (B) a mid-duration dive (4.8 min, 239 m) and (C) a long-duration dive (8.5 min, 305 m). Minimum instantaneous fH reached 37 beats min−1 in the short dive
(A) 19 beats min−1 in the mid-duration dive
(B) and 7 beats min−1 in the long duration dive
(C) Prominent features typical of mid- and long-duration dives include

  • a surface interval tachycardia (pre- and post-dive);
  • a steady rapid decrease in fH during initial descent;
  • a gradual decline in fH towards the end of descent with the lowest fH of the dive at the end of descent;
  • a slight increase and sometimes variable fH during the bottom portion of the dive; and
  • a slow increase in fH during ascent,
  • often ending in a rapid increase just before surfacing.

We obtained the first diving ƒH data from wild sea lions on natural foraging trips, demonstrating how they regulate ƒH over a range of dive durations. Sea lions always decreased dive ƒH from surface ƒH values; however, individual sea lions exhibited different dive ƒH, accounting for a significant amount of the variation in the relationship between dive duration and ƒH (intra-individual correlation: 75–81%)). The individual differences in dive ƒH exhibited in this study suggest that different dive capacities of individual sea lions may partially account for the range of dive strategies exhibited in a previous study (Villegas-Amtmann et al., 2011). Despite the individual differences in ƒH, the pattern of the dive ƒH response was similar in all the sea lions. As predicted, sea lions only consistently displayed a true bradycardia on mid- to long- duration dives (>4 min) (Fig. 5A). Additionally, as seen in freely diving phocids, dive ƒH and minimum ƒH were negatively related to dive duration, with the longest duration dives having the lowest dive ƒH and displaying the most intense bradycardia, often below 10 beats min−1 (Fig. 5A,B).

Profiles of mean fH at 10 s intervals of dives

Profiles of mean fH at 10 s intervals of dives

Fig 4.  Profiles of mean fH at 10 s intervals of dives for (A) six duration categories and (B) five depth categories. Standard error bars are shown. Data were pooled from 461 dives performed by five sea lions. The number of dives in each category and the number of sea lions performing the dives in each category are provided in the keys.

The mild bradycardia and the dive ƒH profiles observed in the shorter duration dives (<3 min) were similar to those observed in trained juvenile California sea lions and adult Stellar sea lions, but much more intense than ƒH observed in freely diving Antarctic fur seals. Surprisingly, although dive ƒH of trained Steller sea lions was similar, Steller sea lions regularly exhibited lower minimum ƒH, with minimum ƒH almost always less than 20 beats min−1 in dives less than 2 min in duration. In the wild, California sea lions rarely exhibited a minimum ƒH less than 20 beats min−1 in similar duration dives (Fig. 5B), suggesting greater blood oxygen transport during these natural short-duration dives.

Fig. 5. (not shown)  fH decreases with increasing dive duration. Dive duration versus (A) dive fH (total number of beats/dive duration), (B) minimum instantaneous fH and (C) bottom fH (total beats at bottom of dive/bottom time) for California sea lions (461 dives from five sea lions).

Although California sea lions are not usually considered exceptional divers, they exhibited extreme bradycardia, comparable to that of the best diving phocids, during their deep dives. In dives greater than 6 min in duration, minimum ƒH was usually less than 10 beats min−1 and sometimes as low as 6 beats mins−1 (Fig. 5B), which is similar to extreme divers such as emperor penguins (3 beats min−1), elephant seals (3 beats min−1), grey seals (2 beats min−1) and Weddell seals (<10 beats min−1), and even as low as what was observed in forced submersion studies. Thus, similar to phocids, the extreme bradycardia exhibited during forced submersions is also a routine component of the sea lion’s physiological repertoire, allowing them to perform long-duration dives.

While the degree of bradycardia observed in long dives of California sea lions was similar to the extreme bradycardia observed in phocids, the ƒH profiles were quite different. In general, phocid ƒH decreases abruptly upon submergence. The intensity of the initial phocid bradycardia either remains relatively stable or intensifies as the dive progresses, and does not start to increase until the seal begins its ascent. In contrast, the ƒH profiles of sea lions were more complex, showing a more gradual decrease during descent, with the minimum ƒH of the dive usually towards the end of descent (Figs 3, 6). There was often a slight increase in ƒH during the bottom portion of the dive, and as soon as the sea lions started to ascend, the ƒH slowly started to increase, often becoming irregular during the middle of ascent, before increasing rapidly as the sea lion approached the surface.

Fig. 6. (not shown) Instantaneous fH and dive depth profiles of the longest dive (10.0 min, 385 m) from a California sea lion (CSL12_1). During this dive, instantaneous fH reached 7 beats min−1 and was less than 20 beats min−1 for over 5.5 min. Post-dive fH was high in the first 0.5–1 min after surfacing, but then declined to ~100 beats min−1 towards the end of the surface interval.

Implications for pulmonary gas exchange

The moderate dive ƒH in short, shallow dives compared with the much slower ƒH of deep long-duration dives suggests more pulmonary blood flow and greater potential for reliance on lung O2. Most of these dives were to depths of less than 100 m (well below the estimated depth of lung collapse near 200 m), so maintenance of a moderate ƒH during these dives may allow sea lions to maximise use of the potentially significant lung O2 stores (~16% of total body O2 stores) throughout the dive. This is supported by venous blood O2 profiles, where, occasionally, there was no decrease in venous blood O2 between the beginning and end of the dive; this can only occur if pulmonary gas exchange continues throughout the dive. Greater utilization of the lung O2 store in sea lions is consistent with higher dive ƒH in other species that both dive on inspiration and typically perform shallow dives (dolphins, porpoises, some penguin species), and in deeper diving species when they perform shallow dives (emperor penguins).

In deeper dives of sea lions, although ƒH was lower and bradycardia more extreme, the diving ƒH profiles suggest that pulmonary gas exchange is also important. In long-duration dives, even though ƒH started to decrease upon or shortly after submergence, the decrease was not as abrupt as in phocids. Additionally, in long deep dives, despite having overall low dive ƒH, there were more heart beats before resting ƒH was reached compared with short, shallow dives. In dives less than 3 min in duration, there were ~10–15 beats until instantaneous ƒH reached resting values. In longer duration dives (>3 min), there were usually ~30–40 beats before instantaneous ƒH reached resting values. We suggest the greater number of heart beats early in these deeper dives enables more gas exchange and blood O2 uptake at shallow depths, thus allowing utilisation of the postulated larger respiratory O2 stores in deeper dives The less abrupt decline in ƒH we observed in sea lions is similar to the more gradual declines documented in emperor penguins and porpoises, where it has also been proposed that the gradual decrease in ƒH allows them to maximise pulmonary gas exchange at shallower depths. However, as sea lions swam deeper, ƒH decreased further (Figs 3, 6), and by 200 m depth (the approximate depth of lung collapse, instantaneous ƒH was 14 beats min−1. Such an extreme decline in ƒH in conjunction with increased pulmonary shunting due to lung compression at greater depths will result in minimization of both O2 and N2 uptake by blood, even before the depth of full lung collapse (100% pulmonary shunt) is reached.

Implications for blood flow

ƒH is often used as a proxy to estimate blood flow and perfusion during diving because of the relative ease of its measurement. This is based on the assumption that stroke volume does not change during diving in sea lions, and, hence, changes in ƒH directly reflect changes in cardiac output. As breath-hold divers maintain arterial pressure while diving, changes in cardiac output should be associated with changes in peripheral vascular resistance and changes in blood flow to tissues. In Weddell seals, a decrease in cardiac output of ~85% during forced submersions resulted in an 80–100% decrease in tissue perfusion in all tissues excluding the brain, adrenal glands and lung. Sea lions exhibited extremely low instantaneous ƒH values that often remained low for significant portions of the dive (Figs 4, 6), suggesting severe decreases in tissue perfusion in dives greater than 5 min in duration. In almost all dives greater than 6 min in duration, instantaneous ƒH reached 10 beats min−1, and stayed below 20 beats min−1 for more than a minute. At a ƒH of 20 beats min−1, cardiac output will be ~36% of resting cardiac output and only about 18% of average surface cardiac output. At these levels of cardiac suppression, most of this flow should be directed towards the brain and heart.

Conclusions

We successfully obtained diving ƒH profiles from a deep-diving otariid during natural foraging trips. We found that

(1) ƒH decreases during all dives, but true and more intense bradycardia only occurred in longer duration dives and
(2) in the longest duration dives, ƒH and presumed cardiac output were as low as 20% of resting values.

We conclude that, although initial high ƒH promotes gas exchange early in deep dives, the extremely low ƒH in late descent of deep dives (a) preserves lung O2, (b) conserves blood O2, (c) increases the dependence of muscle on myoglobin-bound O2 and (d) limits N2 absorption at depth. This ƒH profile, especially during the late descent/early bottom phase of deep dives is similar to that of deep-diving emperor penguins, and may be characteristic of deep diving endotherms that dive on inspiration.

Dive duration was the fixed effect in all models, and to account for the lack of independence caused by having many dives from the same individual, individual (sea lion ID) was included as a random effect. Covariance and random effect structures of the full models were evaluated using Akaike’s information criterion (AIC) and examination of residual plots. AICs from all the tested models are presented with the best model in bold.

Additionally, dives were classified as short-duration (less than 3 min, minimum cADL), mid-duration (3–5 min, range of cADLs) or long-duration (>5 min) dives. Differences in pre-dive ƒH, dive ƒH, minimum ƒH, post-dive ƒH, and heart beats to resting between the categories were investigated using mixed effects ANOVA, followed by post hoc Tukey tests. In all models, dive duration category was the fixed effect and individual (sea lion ID) was included as a random effect. Model fit was accessed by examination of the residuals. All means are expressed ±s.d. and results of the Tukey tests were considered significant at P<0.05. Statistical analysis was performed in R.

Investigating Annual Diving Behaviour by Hooded Seals (Cystophora cristata) within the Northwest Atlantic Ocean

Julie M. Andersen, Mette Skern-Mauritzen, Lars Boehme
PLoS ONE 8(11): e80438. http://dx.doi.org:/10.1371/journal.pone.0080438

With the exception of relatively brief periods when they reproduce and molt, hooded seals, Cystophora cristata, spend most of the year in the open ocean where they undergo feeding migrations to either recover or prepare for the next fasting period. Valuable insights into habitat use and diving behavior during these periods have been obtained by attaching Satellite Relay Data Loggers (SRDLs) to 51 Northwest (NW) Atlantic hooded seals (33 females and 18 males) during icebound fasting periods (200422008). Using General Additive Models (GAMs) we describe habitat use in terms of First Passage Time (FPT) and analyze how bathymetry, seasonality and FPT influence the hooded seals’ diving behavior described by maximum dive depth, dive duration and surface duration. Adult NW Atlantic hooded seals exhibit a change in diving activity in areas where they spend .20 h by increasing maximum dive depth, dive duration and surface duration, indicating a restricted search behavior. We found that male and female hooded seals are spatially segregated and that diving behavior varies between sexes in relation to habitat properties and seasonality. Migration periods are described by increased dive duration for both sexes with a peak in May, October and January. Males demonstrated an increase in dive depth and dive duration towards May (post-breeding/pre-molt) and August–October (post-molt/pre-breeding) but did not show any pronounced increase in surface duration. Females dived deepest and had the highest surface duration between December and January (post-molt/pre-breeding). Our results suggest that the smaller females may have a greater need to recover from dives than that of the larger males. Horizontal segregation could have evolved as a result of a resource partitioning strategy to avoid sexual competition or that the energy requirements of males and females are different due to different energy expenditure during fasting periods.

Novel locomotor muscle design in extreme deep-diving whales

P. Velten, R. M. Dillaman, S. T. Kinsey, W. A. McLellan and D. A. Pabst
The Journal of Experimental Biology 216, 1862-1871
http://dx.doi.org:/10.1242/jeb.081323

Most marine mammals are hypothesized to routinely dive within their aerobic dive limit (ADL). Mammals that regularly perform deep, long-duration dives have locomotor muscles with elevated myoglobin concentrations that are composed of predominantly large, slow-twitch (Type I) fibers with low mitochondrial volume densities (Vmt). These features contribute to extending ADL by increasing oxygen stores and decreasing metabolic rate. Recent tagging studies, however, have challenged the view that two groups of extreme deep-diving cetaceans dive within their ADLs. Beaked whales (including Ziphius cavirostris and Mesoplodon densirostris) routinely perform the deepest and longest average dives of any air-breathing vertebrate, and short-finned pilot whales (Globicephala macrorhynchus) perform high-speed sprints at depth. We investigated the locomotor muscle morphology and estimated total body oxygen stores of several species within these two groups of cetaceans to determine whether they

(1) shared muscle design features with other deep divers and
(2) performed dives within their calculated ADLs.

Muscle of both cetaceans displayed high myoglobin concentrations and large fibers, as predicted, but novel fiber profiles for diving mammals. Beaked whales possessed a sprinterʼs fiber-type profile, composed of ~80% fast-twitch (Type II) fibers with low Vmt. Approximately one-third of the muscle fibers of short-finned pilot whales were slow-twitch, oxidative, glycolytic fibers, a rare fiber type for any mammal. The muscle morphology of beaked whales likely decreases the energetic cost of diving, while that of short-finned pilot whales supports high activity events. Calculated ADLs indicate that, at low metabolic rates, both beaked and short-finned pilot whales carry sufficient onboard oxygen to aerobically support their dives.

Serial cross-sections of the m. longissimus dorsi of Mesoplodon densirostris

Serial cross-sections of the m. longissimus dorsi of Mesoplodon densirostris

Fig. Serial cross-sections of the m. longissimus dorsi of Mesoplodon densirostris (A–D) and Globicephala macrorhynchus (E–H). Scale bars, 50μm. Muscle sections stained for the alkaline (A,E) and acidic (B,F) preincubations of myosin ATPase were used to distinguish Type I and II fibers. Muscle sections stained for succinate dehydrogenase (C,G) and α-glycerophosphate dehydrogenase (D,H) were used to distinguish glycolytic (gl), oxidative (o) and intermediate (i) fibers.

Previous studies of the locomotor muscles of deep-diving marine mammals have demonstrated that these species share a suite of adaptations that increase onboard oxygen stores while slowing the rate at which these stores are utilized, thus extending ADL. Their locomotor muscles display elevated myoglobin concentrations and are composed predominantly of large Type I fibers. Vmt are also lower in deep divers than in shallow divers or athletic terrestrial species. The results of this study indicate that beaked whales and short-finned pilot whales do not uniformly display these characteristics and that each possesses a novel fiber profile compared with those of other deep divers.

The phylogeny of Cetartiodactyla: The importance of dense taxon sampling, missing data, and the remarkable promise of cytochrome b to provide reliable species-level phylogenies

Ingi Agnarsson, Laura J. May-Collado
Molecular Phylogenetics and Evolution 48 (2008) 964–985
http://dx.doi.org:/10.1016/j.ympev.2008.05.046

We perform Bayesian phylogenetic analyses on cytochrome b sequences from 264 of the 290 extant cetartiodactyl mammals (whales plus even-toed ungulates) and two recently extinct species, the ‘Mouse Goat’ and the ‘Irish Elk’. Previous primary analyses have included only a small portion of the species diversity within Cetartiodactyla, while a complete supertree analysis lacks resolution and branch lengths limiting its utility for comparative studies. The benefits of using a single-gene approach include rapid phylogenetic estimates for a large number of species. However, single-gene phylogenies often differ dramatically from studies involving multiple datasets suggesting that they often are unreliable. However, based on recovery of benchmark clades—clades supported in prior studies based on multiple independent datasets—and recovery of undisputed traditional taxonomic groups, Cytb performs extraordinarily well in resolving cetartiodactyl phylogeny when taxon sampling is dense. Missing data, however, (taxa with partial sequences) can compromise phylogenetic accuracy, suggesting a tradeoff between the benefits of adding taxa and introducing question marks. In the full data, a few species with a short sequences appear misplaced, however, sequence length alone seems a poor predictor of this phenomenon as other taxa.

The mammalian superorder Cetartiodactyla (whales and eventoed ungulates) contains nearly 300 species including many of immense commercial importance (cow, pig, and sheep) and of conservation interest and aesthetic value (antelopes, deer, giraffe, dolphins, and whales) (MacDonald, 2006). Certain members of this superorder count among the best studied organisms on earth, whether speaking morphologically, behaviorally, physiologically or genetically. Understanding the interrelationships among cetartiodactyl species, therefore, is of obvious importance with equally short sequences were not conspicuously misplaced. Although we recommend awaiting a better supported phylogeny based on more character data to reconsider classification and taxonomy within Cetartiodactyla, the new phylogenetic hypotheses provided here represent the currently best available tool for comparative species-level studies within this group. Cytb has been sequenced for a large percentage of mammals and appears to be a reliable phylogenetic marker as long as taxon sampling is dense. Therefore, an opportunity exists now to reconstruct detailed phylogenies of most of the major mammalian clades to rapidly provide much needed tools for species-level comparative studies.

Our results support the following relationship among the four major cetartiodactylan lineages (((Tylopoda ((Cetancodonta (Ruminantia + Suina))), with variable support. This arrangement has not been suggested previously, to our knowledge (see review in O’Leary and Gatesy, 2008 and discussion).

Relationships among clades within Cetancodonta are identical to those found by May-Collado and Agnarsson (2006).

Within Ruminantia all our analyzes suggest the following relationships among families: (((((Tragulidae((((Antilocapridae(((Giraffidae(( Cervidae(Moschidae + Bovidae))))) with relatively high support, supporting the subdivision of Ruminantia into Tragulina and Pecora.
In the rare cases where our results are inconsistent with benchmark clades, ad hoc explanations seem reasonable. The placement of M. meminna (Tragulidae) within Bovidae is likely an artifact of missing data, although remarkably it is the only conspicuous misplacement of a species across the whole phylogeny at the family level (while three species appear to be misplaced at the subfamily level within Cervidae in the full analysis, see Fig. 5a). This is supported by the fact that the placement of Moschiola receives low support, and the removal of Moschiola prior to analysis increases dramatically the support for clades close to where it nested (not shown, analysis available from authors), suggesting it had a tendency to ‘jump around’. Two other possibilities cannot be ruled out, however. One, that possibly the available sequence in Genbank may be mislabeled. And second, it should be kept in mind that the validity of Tragulidae has never been tested with molecular data including more than two species.

Oxygen and carbon dioxide fluctuations in burrows of subterranean blind mole rats indicate tolerance to hypoxic–hypercapnic stresses

Imad Shams, Aaron Avivi, Eviatar Nevo
Comparative Biochemistry and Physiology, Part A 142 (2005) 376 – 382
http://dx.doi.org:/10.1016/j.cbpa.2005.09.003

The composition of oxygen (O2), carbon dioxide (CO2), and soil humidity in the underground burrows from three species of the Israeli subterranean mole rat Spalax ehrenbergi superspecies were studied in their natural habitat. Two geographically close populations of each species from contrasting soil types were probed. Maximal CO2 levels (6.1%) and minimal O2 levels (7.2%) were recorded in northern Israel in the breeding mounds of S. carmeli in a flooded, poor drained field of heavy clay soil with very high volumetric water content. The patterns of gas fluctuations during the measurement period among the different Spalax species studied were similar. The more significant differentiation in gas levels was not among species, but between neighboring populations inhabiting heavy soils or light soils: O2 was lower and CO2 was higher in the heavy soils (clay and basaltic) compared to the relatively light soils (terra rossa and rendzina). The extreme values of gas concentration, which occurred during the rainy season, seemed to fluctuate with partial flooding of the tunnels, animal digging activity, and over-crowded breeding mounds inhabited by a nursing female and her offspring. The gas composition and soil water content in neighboring sites with different soil types indicated large differences in the levels of hypoxic–hypercapnic stress in different populations of the same species. A growing number of genes associated with hypoxic stress have been shown to exhibit structural and functional differences between the subterranean Spalax and the aboveground rat (Rattus norvegicus), probably reflecting the molecular adaptations that Spalax went through during 40 million years of evolution to survive efficiently in the severe fluctuations in gas composition in the underground habitat.

map of the studied sites

map of the studied sites

Schematic map of the studied sites: S. galili (2n =52): 1— Rehania (chalk); 2— Dalton (basaltic); S. golani (2n =54): 3— Majdal Shams (terra tossa); 4—Masa’ada (basaltic soils); S. carmeli (2n =58): 5— Al-Maker (heavy clay); 6— Muhraqa (terra rossa).

Comparison of gas composition (O2 and CO2) and water content between light and heavy soils inhabited by S. carmeli

Comparison of gas composition (O2 and CO2) and water content between light and heavy soils inhabited by S. carmeli

Comparison of gas composition (O2 and CO2) and water content between light and heavy soils inhabited by S. carmeli, Al-Maker (heavy soil) and Muhraqa (light soil). AverageTSD of measurements in the burrows of approximately 10 animals at a given date is presented. **p <0.01, T-test and Mann– Whitney test).

Subterranean mammals, which live in closed underground burrow systems, experience an atmosphere that is different from the atmosphere above-ground. Gas exchange between these two atmospheres depends on diffusion through the soil, which in turn, depends on soil particle size, water content, and burrow depth. Heavy soils (clay and basaltic), hold water and have little air space for gas diffusion. A large deviation from external gas composition is found in the burrows of Spalax living in these soil types. The maximal measured concentration of CO2 was 6.1% in Spalax breeding mounds, which is one of the highest concentrations among studied mammals in natural conditions. At the same time 7.2% O2 was measured in water saturated heavy clay soil

seasonal variation from August to March in mean O2, CO2, and soil water content

seasonal variation from August to March in mean O2, CO2, and soil water content

Example of seasonal variation from August to March in mean O2, CO2, and soil water content (VWC) in the Al-Maker population (2n =58, heavy soil). Values are presented as mean TSD.

In this study new data were presented for a wild mammal that survives in an extreme hypoxic–hypercapnic environment. Interestingly, the very low concentrations of O2 experienced by Spalax are correlated with the expression pattern of hypoxia related genes.  So far, we have shown higher and longer-term mRNA expression of erythropoietin, the main factor that regulates the level of circulating red blood cells, in subterranean Spalax compared to the above-ground rat in response to hypoxic stress, as well as differences in the response of erythropoietin to hypoxia in different populations of Spalax experiencing different hypoxic stress in nature. We also demonstrated that erythropoietin pattern of expression is different in Spalax than in Rattus throughout development, a pattern suggesting more efficient hypoxic tolerance in Spalax starting as early as in the embryonic stages. Furthermore, vascular endothelial growth factor (VEGF), which is a critical angiogenic factor that responds to hypoxia, is constitutively expressed at maximal levels in Spalax muscles, the most energy consuming tissue during digging. This level is 1.6-fold higher than in Rattus muscles and is correlated with significantly higher blood vessel concentration in the Spalax muscles compared to the Rattus muscles. Likewise, myoglobin the globin involved in oxygen homeostasis in skeletal muscles, exhibits different expression pattern under normoxia and in response to hypoxia in Spalax muscles compared to rat muscles as well as between different populations of Spalax exposed to different hypoxic stress in nature (unpublished results). Similarly, neuroglobin, a brain-specific globin involved in reversible oxygen binding, i.e., presumably in cellular homeostasis, is expressed differently in the Spalax brain compared to Rattus brain. Like erythropoietin and myoglobin also neuroglobin is expressed differently in Spalax populations experiencing different oxygen supply (unpublished results). Furthermore, Spalax p53 harbors two amino acid substitutions in its binding domain, which are identical to mutations found in p53 of human cancer cells. These substitutions endow Spalax p53 with several-fold higher activation of cell arrest and DNA repair genes compared to human p53 and favor activation of DNA repair genes over apoptotic genes. The study of specific tumoral variants indicates that such preference of growth arrest over apoptosis possibly results as a response to the hypoxic environmental stress known in tumors. Differences in the structure of other molecules related to homeostasis, namely, hemoglobin, haptoglobin (Nevo, 1999), and cytoglobin (unpublished) were also observed in Spalax.

Stress, adaptation, and speciation in the evolution of the blind mole rat, Spalax, in Israel

Eviatar Nevo
Molecular Phylogenetics and Evolution 66 (2013) 515–525
http://dx.doi.org/10.1016/j.ympev.2012.09.008

Environmental stress played a major role in the evolution of the blind mole rat superspecies Spalax ehrenbergi, affecting its adaptive evolution and ecological speciation underground. Spalax is safeguarded all of its life underground from aboveground climatic fluctuations and predators. However, it encounters multiple stresses in its underground burrows including darkness, energetics, hypoxia, hypercapnia, food scarcity, and pathogenicity. Consequently, it evolved adaptive genomic, proteomic, and phenomic complexes to cope with those stresses. Here I describe some of these adaptive complexes, and their theoretical and applied perspectives. Spalax mosaic molecular and organismal evolution involves reductions or regressions coupled with expansions or progressions caused by evolutionary tinkering and natural genetic engineering. Speciation of Spalax in Israel occurred in the Pleistocene, during the last 2.00–2.35 Mya, generating four species associated intimately with four climatic regimes with increasing aridity stress southwards and eastwards representing an ecological speciational adaptive trend: (Spalax golani, 2n = 54?S. galili, 2n = 52?S. carmeli, 2n = 58?S. judaei, 2n = 60). Darwinian ecological speciation occurred gradually with relatively little genetic change by Robertsonian chromosomal and genic mutations. Spalax genome sequencing has just been completed. It involves multiple adaptive complexes to life underground and is an evolutionary model to a few hundred underground mammals. It involves great promise in the future for medicine, space flight, and deep-sea diving.

Stress is a major driving force of evolution (Parsons, 2005; Nevo, 2011). Parsons defined stress as the ‘‘environmental factor causing potential injurious changes to biological systems with a potential for impacts on evolutionary processes’’. The global climatic transition from the middle Eocene to the early Oligocene (45–35 Ma = Million years ago) led to extensive convergent evolution underground of small subterranean mammals across the planet (Nevo, 1999; Lacey et al., 2000; Bennett and Faulkes, 2000; Begall et al., 2007). The subterranean ecotope provided small mammals with shelter from predators and extreme aboveground climatic stressful fluctuations of temperature and humidity. However, they had to evolve genomic adaptive complexes for the immense underground stresses of darkness, energy for burrowing in solid soil, low productivity and food scarcity, hypoxia, hypercapnia, and high infectivity. These stresses have been described in Nevo (1999, 2011) and Nevo et al. (2001); and Nevo list of Spalax publication at http://evolution.haifa.ac.il with many cited references relevant to these stresses).

blind subterranean mole rat of the Spalax ehrenbergi superspecies

blind subterranean mole rat of the Spalax ehrenbergi superspecies

The blind subterranean mole rat of the Spalax ehrenbergi superspecies in Israel. An extreme example of adaptation to life underground

Circadian rhythm and genes

adaptive circadian genes. We identified the circadian rhythm of Spalax
(Nevo et al., 1982) and described, cloned, sequenced, and expressed several circadian genes in Spalax. These include Clock, MOP3, three Period (Per), and cryptochromes (Avivi et al., 2001, 2002, 2003). The Spalax circadian genes are differentially conserved, yet characterized by a significant number of amino acid substitutions. The glutamine-rich area of Clock, which is assumed to function in circadian rhythmicity, is expanded in Spalax compared with that of mice and humans and is different in amino acid composition from that of rats. All three Per genes of Spalax oscillate with a periodicity of 24 h in the suprachaismatic nucleus, eye, and Harderian gland and are expressed in peripheral organs. Per genes are involved in clock resetting. Spalax Per 3 is unique in mammals though its function is still unresolved. The Spalax Per genes contribute to the unique adaptive circadian rhythm to life underground. The cryptochrome (Cry) genes, found in animals and plants, act both as photoreceptors and as ingredients of the negative feedback mechanism of the biological Clock. The CRY 1 protein is significantly closer to the human homolog than to that of mice, as was also shown in parts of the immunogenetic system. Both Cry 1 and Cry 2 mRNAs were found in the SCN, eye, harderian gland, and in peripheral tissues. Remarkably, the distinctly hypertrophied harderian gland is central in Spalax’s unique underground circadian rhythmicity (Pevet et al., 1984).

  • Spalax eye mosaic evolution
  • Gene expression in the eye of Spalax
  • Brain evolution in Spalax to underground stresses
  • Spalax: four species in Israel

The morphological, physiological, and behavioral Spalax eye patterns are underlain by gene expression representing regressive and progressive associated transcripts. Regressive transcripts involve B-2 microglobulin, transketolase, four keratins, alpha enolase, and different heat shock proteins. Several proteins may be involved in eye degeneration. These include heat shock protein 90alpha (hsp90alpha), found also in the blind fish Astyanax mexicanus, two transcripts of programmed cell death proteins, oculospanin, and peripherin 2, both belonging to the Tetraspanin family, in which 60 different mutations cause eye degeneration in humans. Several progressive transcripts in the Spalax eye are found in the retina of many mammals involving gluthatione, peroxidase 4, B spectrin, and Ankyrin; the last two characterize rod cells in the retina. Some transcripts are involved in metabolic processing of retinal, a vertebrate key component in phototransduction, and a relative of vitamin A.

cross section of the developing eye of the mole rat

cross section of the developing eye of the mole rat

Light micrographs showing cross section of the developing eye of the mole rat Spalax ehrenbergi. (A) Optic cup and lens vesicle initially develop normally (x100). (B) Eye at a later embryonic stage. Note appearance of iris-ciliary body rudiment (arrows), and development of the lens nucleus (L). ON, optic nerve (x100). (C) Eye at a still later fetal stage. Note massive growth of the iris-ciliary body complex colobomatous opening (arrow) (x100). (D) Early postnatal stage. The iris-ciliary body complex completely fills the chamber. The lens is vascularized and vacuolated (x100). (E) Adult eye. Eyelids are completely closed and pupil is absent. Note atrophic appearance of the optic disc region (arrow) (x65). (F) Higher magnification of the adult retina. The different retinal layers are retained: PE, pigment epithelium: RE, receptor layer; ON, outer nuclear layer: IN, inner nuclear layer; GC, ganglion cell layer (x500) (from Sanyal et al., 1990, Fig. 1).

The brains of subterranean mammals underwent dramatic evolution in accordance with underground stresses for digging and photoperiodic perception associated with vibrational, tactile, vocal, olfactory, and magnetic communication systems replacing sight, as is seen in Spalax. The brain of Spalax is twice as large as that of the laboratory rat of the same body size. The somatosensory region in the isocortex of Spalax is 1.7 times, the thalamic nuclei 1.3 times, and the motor cortex 3.1 times larger than in the sighted laboratory rat Rattus norvegicus matched to body size.

The ecological stress determinant in Spalax brain evolution is highlighted by the four species of the Spalax ehrenbergi superspecies in Israel. They differentiated chromosomally (by means of Robertsonian mutations and fission), allopatrically, and clinally southwards into four species associated with different climatic regimes, following the gradient of increasing aridity stress and decreasing predictability southwards towards the desert: Spalax galili (2n = 52) ->S. golani (2n = 54)->S. carmeli (2n = 58)->S. judaei (2n = 60), and eastwards S. galili ->S. golani (2n = 52–>54) (Fig. 2). This chromosomal speciation trend southwards is associated with the regional aridity stress southwards (and eastwards) in Israel, budding new species adapted genomically, proteomically, and phenomically (i.e., in morphology, physiology, and behavior) to increasing stresses of higher solar radiation, temperature, and drought southwards (Nevo, 1999; Nevo et al., 2001; Nevo
list of Spalax at http://evolution.haifa.ac.il). A uniquely recent discovery of incipient sympatric ecological speciation at a microscale in Spalax triggered by local stresses occurs within Spalax galili.

retinal input to primary visual structures in Spalax

retinal input to primary visual structures in Spalax

Relative degree of retinal input to primary visual structures in Spalax, hamster, rat, and Spalacopus cyanus (South American Octodontidae, ‘‘coruro’’). These rodents are of similar body size (120–140 g). B. Relative degree of change in the proportions of retinal input to different primary visual structures in Spalax compared with measures obtained in other rodents. A relative progressive development in Spalax is seen in structures involved in photoperiodic and neuroendocrine functions (SCN, BNST).The main regressive feature is the drastic relative reduction of retinal input to the superior colliculus. The main regressive feature is the drastic reduction of retinal input to the superior colliculus. The relative size of other visual structures in Spalax is modified compared to that of the other species. c. Comparison of the absolute size (volume, mm3 x 10-4) of visual structures in Spalax and other rodents. The size of the SCN is equivalent in all species. The vLGN and dLGN are reduced by 87–93% in Spalax. The retino-recipient layers of the superior colliculus are reduced by 97%. Abbreviations: SCN: suprachiasmatic nucleus; BNST: bed nucleus of the stria terminalis; dLGN: dorsal lateral geniculate nucleus; SC: superior colliculus [From Cooper et al., 1993 (Fig 3)].

Subterranean life has a high energetic cost if an animal has to burrow in order to obtain its food. For a 150 g Thomomys bottae, burrowing 1 m may be 360–3400 times more expensive energetically than moving the same distance on the surface (Vleck, 1979). Mean rates of oxygen consumption during burrowing at 22 oC are from 2.8 to 7.1 times the RMR. Vleck developed a model examining the energetics of foraging by burrowing and found that, in the desert, Thomomys adjusts the burrow segment length to minimize the cost of burrowing. Since burrowing becomes less economic as body size increases, Vleck (1981) predicted that the maximum possible body size that a subterranean mammal can attain depends on a balance between habitat productivity and the cost of burrowing in local soils. Vleck’s cost of burrowing hypothesis has been verified in multiple cases. Heth (1989) demonstrated longer burrows in the rendzina soil and shorter ones in the terra rossa soil, associating lower productivity in the former for Spalax.

Food is a limiting factor for subterranean mammals. The abundance and distribution of food explain some of the ecological, physiological, and behavioral characteristics of subterranean mammals. In a field test of Spalax foraging strategy, we concluded that Spalax was a generalist due to the constraints of the subterranean ecotope. Restricted foraging time primarily during the winter when soil is wet, and the high energetic investment of tunneling to get to food items is significantly reduced than in summertime.
We also identified a decrease in the basic metabolic rate towards the desert, i.e., economizing energetics. The maintenance of adequate O2 transport in a subterranean mammal confronting hypoxia requires adaptation along the O2 transport system, achieved by increasing the flow of O2 in the convection systems (ventilation and perfusion) and by reduction of oxygen pressure (PO2) gradients at the diffusion barriers (lung blood, blood-tissue (Arieli, 1990). The PO2 gradient between blood capillaries and respiring mitochondria capillaries is large, and any adaptation at this level could be significant for O2 transport. Reduction of diffusion distance in a muscle can be achieved, like in Spalax, by increasing the number of capillaries that surround muscle fiber or by reducing fiber areas.

Geographic distribution in Israel of the four chromosomal species belonging to the S. ehrenbergi superspecies

Geographic distribution in Israel of the four chromosomal species belonging to the S. ehrenbergi superspecies

Geographic distribution in Israel of the four chromosomal species belonging to the S. ehrenbergi superspecies that are separated by narrow hybrid zones (2n = 52, 54, 58, and 60, now named as S. galili, S. golani, S. carmeli, and S. judaei, respectively; see Nevo et al., 2001).

Spalacid evolution, based on mtDNA, is driven by climatic oscillations and stresses. The underground ecotope provided subterranean mammals with shelter from extreme climate (temperature and humidity) fluctuations, and predators. However, they had to extensively and intensively adapt to the multiple underground stresses (darkness, energetic, low productivity and
food scarcity, hypoxia, hypercapnia, and high infectivity). All subterranean mammals, including spalacids as an extreme case, share convergent molecular and organismal adaptations to their shared unique underground ecotope. Evolution underground, as exemplified here in spalacids, led to mosaic molecular and organismal evolutionary syndromes to cope with multiple stresses.

Speciation involves all rates – from gradual to rapid. Subterranean mammals, with the spalacid example discussed above, provide uniquely rich evolutionary global tests of speciation and adaptation, convergence, regression, progression, and mosaic evolutionary processes. Adaptation and speciation underground was one of the most dramatic natural experiments verifying Darwinian evolution.

The Spalax genome sequencing has just been completed. It is being analyzed and will soon be published in 2012. This will be a milestone in understanding how numerous mammals across the globe, who found underground shelter from climatic fluctuations and stresses above ground, cope with the new suite of stresses they encountered underground, demanding a new engineering overhaul on all organizational levels, selecting for adaptive complexes to cope with the new underground stresses. The main current and future challenges are to compare and contrast genome sequences and identify the genomic basis of adaptation and speciation.

This global Cenozoic experiment could answer the following open questions: How heterozygous is the whole genome? How prevalent are retrotransposons and what is their functional role? How many genes are involved in the Spalax genome and how are they regulated? What are the genic and regulatory networks resisting the multiple stresses underground? How much of the Spalax genome is conserved and how much is reorganized to cope with the underground stresses? How is the solitary blind mole rat, Spalax, different from the social naked mole rat Heterocephalus? How are the processes of reduction, expansion, and genetic tinkering and engineering reflected across the genome? How effective is copy number variation in regulation? Is there similarity in the transcriptomes of subterranean mammals? How could we harness the rich genome repertoire of Spalax to revolutionize medicine, especially in the realm of hypoxia tolerance and the related major diseases of the western world, e.g., cancer, stroke, and cardiovascular diseases? What is the phylogenetic origin of Spalax? How much of the Spalax genome represents its phylogenetic roots and how much of coding and noncoding genomic regions are shared with other subterranean mammals across the globe in adapting to life underground?

The Atmospheric Environment of the Fossorial Mole Rat (Spalax Ehrenbergi): Effects of Season, Soil Texture, Rain, Temperature and Activity

  1. Arieli
    Comp Biochen Physiol. 1978; 63A:569-5151. The fossorial mole rat (Spalax ehrenbergi) may inhabit heavy soil with low gas permeability.
  2. Air composition in burrows in heavy soil deviates from atmospheric air more than that of burrows in light soil.
  3. In winter and spring O2 and CO2 concentrations in breeding mounds were 16.5% O2 and 2.5-3x CO2 and the extreme values measured were 14.0% O2 and 4.8% Cot.
  4. Hypoxia and hypercapnia in the burrow develop shortly after rain and when ambient temperature drops.
  5. Composition of the burrows air is influenced by the solubility of CO2 in soil water and by faster penetration of oxygen than outflowing of CO2.

Hypo-osmotic stress-induced physiological and ion-osmoregulatory responses in European sea bass (Dicentrarchus labrax) are modulated differentially by nutritional status

Amit Kumar Sinha, AF Dasan, R Rasoloniriana, N Pipralia, R Blust, G De Boeck
Comparative Biochemistry and Physiology, Part A 181 (2015) 87–99
http://dx.doi.org/10.1016/j.cbpa.2014.11.024

We investigated the impact of nutritional status on the physiological, metabolic and ion-osmoregulatory performance of European sea bass (Dicentrarchus labrax)when acclimated to seawater (32 ppt), brackishwater (20 and 10 ppt) and hyposaline water (2.5 ppt) for 2 weeks. Following acclimation to different salinities, fish were either fed or fasted (unfed for 14 days). Plasma osmolality, [Na+], [Cl−] and muscle water contentwere severely altered in fasted fish acclimated to 10 and 2.5 ppt in comparison to normal seawater-acclimated fish, suggesting ion regulation and acid–base balance disturbances. In contrast to feed-deprived fish, fed fish were able to avoid osmotic perturbation more effectively. This was accompanied by an increase in Na+/K+-ATPase expression and activity, transitory activation of H+-ATPase (only at 2.5 ppt) and down-regulation of Na+/K+/2Cl− gene expression. Ammonia excretion rate was inhibited to a larger extent in fasted fish acclimated to low salinities while fed fish were able to excrete efficiently. Consequently, the build-up of ammonia in the plasma of fed fish was relatively lower. Energy stores, especially glycogen and lipid, dropped in the fasted fish at low salinities and progression towards the anaerobic metabolic pathway became evident by an increase in plasma lactate level. Overall, the results indicate no osmotic stress in both feeding treatments within the salinity range of 32 to 20 ppt. However, at lower salinities (10–2.5 ppt) feed deprivation tends to reduce physiological, metabolic, ion-osmo-regulatory and molecular compensatory mechanisms and thus limits the fish’s abilities to adapt to a hypo-osmotic environment.

The absence of ion-regulatory suppression in the gills of the aquatic air-breathing fish Trichogaster lalius during oxygen stress

Chun-Yen Huang, Hsueh-Hsi Lin, Cheng-Huang Lin, Hui-Chen Lin
Comparative Biochemistry and Physiology, Part A 179 (2015) 7–16
http://dx.doi.org/10.1016/j.cbpa.2014.08.017

The strategy for most teleost to survive in hypoxic or anoxic conditions is to conserve energy expenditure, which can be achieved by suppressing energy-consuming activities such as ion regulation. However, an air-breathing fish can cope with hypoxic stress using a similar adjustment or by enhancing gas exchange ability, both behaviorally and physiologically. This study examined Trichogaster lalius, an air-breathing fish without apparent gill modification, for their gill ion-regulatory abilities and glycogen utilization under a hypoxic  treatment. We recorded air-breathing frequency, branchial morphology, and the expression of ion-regulatory proteins (Na+/K+-ATPase and vacuolar-type H+-ATPase) in the 1st and 4th gills and labyrinth organ (LO), and the expression of glycogen utilization (GP, glycogen phosphorylase protein expression and glycogen content) and other protein responses (catalase, CAT; carbonic anhydrase II, CAII; heat shock protein 70, HSP70; hypoxia-inducible factor-1α, HIF-1α; proliferating cell nuclear antigen, PCNA; superoxidase dismutase, SOD) in the gills of T. lalius after 3 days in hypoxic and restricted conditions. No morphological modification of the 1st and 4th gills was observed. The air breathing behavior of the fish and CAII protein expression both increased under hypoxia. Ion-regulatory abilities were not suppressed in the hypoxic or restricted groups, but glycogen utilization was enhanced within the groups. The expression of HIF-1α, HSP70 and PCNA did not vary among the treatments. Regarding the antioxidant system, decreased CAT enzyme activity was observed among the groups. In conclusion, during hypoxic stress, T. lalius did not significantly reduce energy consumption but enhanced gas exchange ability and glycogen expenditure.

The combined effect of hypoxia and nutritional status on metabolic and ionoregulatory responses of common carp (Cyprinus carpio)

Sofie Moyson, HJ Liew, M Diricx, AK Sinha, R Blusta, G De Boeck
Comparative Biochemistry and Physiology, Part A 179 (2015) 133–143
http://dx.doi.org/10.1016/j.cbpa.2014.09.017

In the present study, the combined effects of hypoxia and nutritional status were examined in common carp (Cyprinus carpio), a relatively hypoxia tolerant cyprinid. Fish were either fed or fasted and were exposed to hypoxia (1.5–1.8mgO2 L−1) at or slightly above their critical oxygen concentration during 1, 3 or 7 days followed by a 7 day recovery period. Ventilation initially increased during hypoxia, but fasted fish had lower ventilation frequencies than fed fish. In fed fish, ventilation returned to control levels during hypoxia, while in fasted fish recovery only occurred after reoxygenation. Due to this, C. carpio managed, at least in part, to maintain aerobic metabolism during hypoxia: muscle and plasma lactate levels remained relatively stable although they tended to be higher in fed fish (despite higher ventilation rates). However, during recovery, compensatory responses differed greatly between both feeding regimes: plasma lactate in fed fish increased with a simultaneous breakdown of liver glycogen indicating increased energy use, while fasted fish seemed to economize energy and recycle decreasing plasma lactate levels into increasing liver glycogen levels. Protein was used under both feeding regimes during hypoxia and subsequent recovery: protein levels reduced mainly in liver for fed fish and in muscle for fasted fish. Overall, nutritional status had a greater impact on energy reserves than the lack of oxygen with a lower hepatosomatic index and lower glycogen stores in fasted fish. Fasted fish transiently increased Na+/K+-ATPase activity under hypoxia, but in general ionoregulatory balance proved to be only slightly disturbed, showing that sufficient energy was left for ion regulation.

The effect of temperature and body size on metabolic scope of activity in juvenile Atlantic cod Gadus morhua L.

Bjørn Tirsgaard, Jane W. Behrens, John F. Steffensen
Comparative Biochemistry and Physiology, Part A 179 (2015) 89–94
http://dx.doi.org/10.1016/j.cbpa.2014.09.033

Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20 °C) and wet body mass (BM) (~30–460 g) on standard metabolic rate (SMR, mg O2 h−1), maximum metabolic rate (MMR, mg O2 h−1) and metabolic scope (MS, mg O2 h−1) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82–0.92). Q10 values were 1.8–2.1 at temperatures between 5 and 15 °C but higher (2.6–4.3) between 2 and 5 °C and lower (1.6–1.4) between 15 and 20 °C in 200 and 450 g cod. MMR increased with temperature in the smallest cod (50 g) but in the larger cod MMR plateaued between 10, 15 and 20 °C. This resulted in a negative correlation between the optimal temperature for MS (Topt) and BM, Topt being respectively 14.5, 11.8 and 10.9 °C in a 50, 200 and 450 g cod. Irrespective of BM cold water temperatures resulted in a reduction (30–35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450 g), caused by plateauing of MMR at 10 °C and above. Warm temperatures thus seem favorable for smaller (50 g) juvenile cod, but not for larger conspecifics (200 and 450 g).

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Altitude Adaptation

Writer and Curator: Larry H. Bernstein, MD, FCAP 

 

Introduction

Land adapted animals depend on respiration for oxygen supply, but have adapted to altitudes that have difference oxygen contents.  In this discussion we explore how animals have adapted to oxygen supply in different terrestrial habitats, and also how humans adjust to short term changes in high and extreme altitudes.

High-altitude adaptation is an evolutionary modification in animals, most notably in birds and mammals, by which species are subjected to considerable physiological changes to survive in extremely high mountainous environments. As opposed to short-term adaptation, or more properly acclimatization (which is basically an immediate physiological response to changing environment), the term “high-altitude adaptation” has strictly developed into the description of an irreversible, long-term physiological responses to high-altitude environments, associated with heritable behavioral and genetic changes. Perhaps, the phenomenon is most conspicuous, at least best documented, in human populations such as the Tibetans, the South Americans and the Ethiopians, who live in the otherwise uninhabitable high mountains of the Himalayas, Andes and Ethiopia respectively; and this represents one of the finest examples of natural selection in action.

Oxygen, essential for animal life, is proportionally abundant in the atmosphere with height from the sea level; hence, the highest mountain ranges of the world are considered unsuitable for habitation. Surprisingly, some 140 million people live permanently at high altitudes (>2,500 m) in North, Central and South America, East Africa, and Asia, and flourish very well for millennia in the exceptionally high mountains, without any apparent complications. This has become a recognized instance of the process of Darwinian evolution in humans acting on favorable characters such as enhanced respiratory mechanisms. As a matter of fact, this adaptation is so far the fastest case of evolution in humans that is scientifically documented. Among animals only few mammals (such as yak, ibex, Tibetan gazelle, vicunas, llamas, mountain goats, etc.) and certain birds are known to have completely adapted to high-altitude environments.

These adaptations are an example of convergent evolution, with adaptations occurring simultaneously on three continents. Tibetan humans and Tibetan domestic dogs found the genetic mutation in both species, EPAS1. This mutation has not been seen in Andean humans, showing the effect of a shared environment on evolution.

At elevation higher than 8,000 metres (26,000 ft), which is called the “death zone” in mountaineering, the available oxygen in the air is so low that it is considered insufficient to support life. And higher than 7,600 m is seriously lethal. Yet, there are Tibetans, Ethiopians and Americans who habitually live at places higher than 2,500 m from the sea level. For normal human population, even a brief stay at these places means mountain sickness, which is a syndrome of hypoxia or severe lack of oxygen, with complications such as fatigue, dizziness, breathlessness, headaches, insomnia, malaise, nausea, vomiting, body pain, loss of appetite, ear-ringing, blistering and purpling and of the hands and feet, and dilated veins. Amazingly for the native highlanders, there are no adverse effects; in fact, they are perfectly normal in all respects. Basically, the physiological and genetic adaptations in these people involve massive modification in the oxygen transport system of the blood, especially molecular changes in the structure and functions hemoglobin, a protein for carrying oxygen in the body. This is to compensate for perpetual low oxygen environment. This adaptation is associated with better developmental patterns such as high birth weight, increased lung volumes, increased breathing, and higher resting metabolism.

http://en.wikipedia.org/wiki/High-altitude_adaptation

Acute Mountain Sickness: Pathophysiology, Prevention, and Treatment

Chris Imraya, Alex Wright, Andrew Subudhie,, Robert Roache
Progress in Cardiovascular Diseases 52 (2010) 467–484
http://dx.doi.org:/10.1016/j.pcad.2010.02.003

Barometric pressure falls with increasing altitude and consequently there is a reduction in the partial pressure of oxygen resulting in a hypoxic challenge to any individual ascending to altitude. A spectrum of high altitude illnesses can occur when the hypoxic stress outstrips the subject’s ability to acclimatize. Acute altitude-related problems consist of the common syndrome of acute mountain sickness, which is relatively benign and usually self-limiting, and the rarer, more serious syndromes of high-altitude cerebral edema and high-altitude pulmonary edema. A common feature of acute altitude illness is rapid ascent by otherwise fit individuals to altitudes above 3000 m without sufficient time to acclimatize. The susceptibility of an individual to high altitude syndromes is variable but generally reproducible. Prevention of altitude-related illness by slow ascent is the best approach, but this is not always practical. The immediate management of serious illness requires oxygen (if available) and descent of more than 300 m as soon as possible. In this article, we describe the setting and clinical features of acute mountain sickness and high altitude cerebral edema, including an overview of the known pathophysiology, and explain contemporary practices for both prevention and treatment exploring the comprehensive evidence base for the various interventions.

Acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) strike people who travel too fast to high altitudes that lie beyond their current level of acclimatization. Understanding AMS and HACE is important because AMS can sharply limit recreation and work at high altitude. The syndromes can be identified early and reliably without sophisticated instruments, and when AMS and HACE are recognized early, most cases respond rapidly with complete recovery in a few hours (AMS) to days (HACE).

High-altitude headache (HAH) is the primary symptom of AMS. High-altitude headache in AMS usually occurs with some combination of other symptoms.
These are –  insomnia, fatigue (beyond that expected from the day’s activities), dizziness, anorexia, and nausea. The headache often worsens during the night and with exertion. Insomnia is the next most frequent complaint. Poor sleep can occur secondary to periodic breathing, severe headache, dizziness, and shortness of breath, among other causes. Anorexia and nausea are common, with vomiting reported less frequently in trekkers to 4243 m.

AMS is distinguished only by symptoms. The progression of AMS to HACE is marked by altered mental status, including impaired mental capacity, drowsiness, stupor, and ataxia. Coma may develop as soon as 24 hours after the onset of ataxia or change in mental status. The severity of AMS can be scored using the Lake Louise Questionnaire, or the more detailed Environmental Symptoms Questionnaire, or by the use of a simple analogue scale. Today, more than 100 years after the first clear clinical descriptions of AMS and HACE, we have advanced our understanding of the physiology of acclimatization to high altitude, and the pathophysiology of AMS and HACE.

As altitude increases, barometric pressure falls (see Fig ). This fall in barometric pressure causes a corresponding drop in the partial pressure of oxygen (21% of barometric pressure) resulting in hypobaric hypoxia. Hypoxia is the major challenge humans face at high altitude, and the primary cause of AMS and HACE. It follows that oxygen partial pressure is more important than
geographic altitude, as exemplified near the poles where the atmosphere is thinner and, thus, barometric pressure is lower. Lower barometric pressure at the poles can result in oxygen partial pressures that are physiologically equivalent to altitudes 100 to 200 m higher at more moderate latitudes. We define altitude regions as high altitude (1500-3500 m), very high altitude (3500-5500 m), and extreme altitude (>5500 m).

Neurological consequences of increasing altitude

Neurological consequences of increasing altitude

Neurological consequences of increasing altitude: The relation among altitude (classified as high [1500–3500 m], very high [3500-5500 m] and extreme [>5500 m]), the partial pressure of oxygen, and the neurological consequences of acute and gradual exposure to these pressure changes. Neurological consequences will vary greatly from person to person and with rate of ascent. HACE is far more common at higher altitudes, although there are case reports of HACE at 2500 m.

It is important for any discussion of AMS and HACE to have as a starting point an understanding of acclimatization. The process of acclimatization involves a series of adjustments by the body to meet the challenge of hypoxemia. While we have a general understanding of systemic changes associated with acclimatization, the underlying molecular and cellular processes are not yet fully described. Recent findings suggest that the process may be initiated by widespread molecular up-regulation of hypoxia inducible factor-1. Downstream processes ultimately act to offset hypoxemia, including elevated ventilation leading to a rise in arterial oxygen saturation (SaO2), a mild diuresis and contraction of plasma volume such that more oxygen is carried per unit of blood, elevated blood flow and oxygen delivery, and eventually a greater circulating hemoglobin mass. Acclimatization can be viewed as the end-stage process of how humans can best adjust to hypoxia. But optimal acclimatization takes from days to weeks, or perhaps even months.

The initial and immediate strategy to protect the body from hypoxia is to increase ventilation. This compensatory mechanism is triggered by stimulation of the carotid bodies, which sense hypoxemia (low arterial PO2), and increase central respiratory drive. This is a fast response, occurring within minutes of exposure to hypoxia persisting throughout high altitude exposure. This is why one cautions against the use of respiratory depressants such as alcohol and some sleeping medications, which can depress the hypoxic drive to breathe and may thus worsen hypoxemia. Pharmacological simulation of this natural process by acetazolamide, a respiratory stimulant and mild diuretic, largely protects from AMS and HACE by stimulating acclimatization. Circulatory responses are key to improving oxygen delivery, and are likely regulated by marked elevations in sympathetic activity. Field experience suggests that a marked elevation in early morning resting heart rate is a sign of challenges to acclimatization, perhaps secondary to increased hypoxemia, or dehydration. For the pathophysiology of AMS and HACE responses of the cerebral circulation are especially important. Maintenance of cerebral oxygen delivery is a critical factor for survival at high altitude. The balance between hypoxic vasodilation and hypocapnia-induced vasoconstriction determines overall cerebral blood flow (CBF). In a classic study, CBF increased 24% on abrupt ascent to 3810 m, and then returned to normal over 3 to 5 days. Recent studies, largely using regional transcranial Doppler measures of CBF velocity as a proxy for CBF, report discernible individual variation in the CBF response to hypoxia. All advanced brain imaging studies to date have shown both elevations in CBF in hypoxic humans and striking heterogeneity of CBF distribution in the hypoxic brain, with CBF rising up to 33% in the hypothalamus, and 20% in the thalamus with no other significant changes. Also, it is becoming clear that cerebral autoregulation, the process by which cerebral perfusion is maintained as blood pressure varies, is impaired in hypoxia. Thus, hypoxia modulates cerebral autoregulation and raises interesting questions about the importance of this process in AMS and acclimatization, since it appears to be a uniform response in all humans made hypoxemic. Further, hematocrit and hemoglobin concentration are elevated after 12 to 24 hours of hypoxic exposure due to a fall in plasma volume, but after several weeks,  plasma volume returns to near sea level values. Normalization of plasma volume coupled with an increase in red cell mass secondary to the hypoxia stimulated erythropoiesis leads to an increase in total blood volume after several weeks of acclimatization. Adequate iron stores are required for adequate hematologic acclimatization to high altitude. Acclimatization, then, is a series of physiological responses to hypoxia that serve to offset hypoxemia, improve systemic oxygen delivery, and avoid AMS and HACE. When acclimatization fails, or the challenge of hypoxia is too great, AMS and HACE can develop.

AMS occurs in susceptible individuals when ascent to high altitude outpaces the ability to acclimatize. For example, most people ascending very rapidly to high altitude will get AMS. The symptoms, although often initially incapacitating, usually resolve in 24 to 48 hrs. The incidence and severity of AMS depend on the rate of ascent and the altitude attained, the length of time at altitude, the degree of physical exertion, and the individual’s physiological susceptibility. The chief significance of AMS is that planned activities may be impossible to complete during the first few days at a new altitude due to symptoms. In addition, in a few individuals, AMS may progress to life-threatening HACE or HAPE. At 4000 m and above, the incidence of AMS ranges from 50% to 65% depending on the rate and mode of ascent, altitude reached, and sleeping altitude. A survey of 3158 travelers visiting resorts in the Rocky Mountains of Colorado revealed that 25% developed AMS, and most decreased their daily activity because of their symptoms.

Singh et al. proposed that the high-altitude syndromes are secondary to the body’s responses to hypobaric hypoxia, not due simply to hypoxemia. They based this conclusion on 2 observations:

  • there is a delay between the onset of hypoxia and the onset of symptoms after ascent (from hours to days), and
  • not all symptoms are immediately reversed with oxygen.

On the other hand, scientists have long assumed that AMS and HACE are due solely to hypoxia, based largely on 2 reports:

  • the pioneering experiments of Paul Bert and
  • the Glass House experiment of Barcroft.

When these assumptions were tested in a laboratory setting to study symptom responses to hypobaric hypoxia (simulated high altitude), hypoxia alone, and hypobaric normoxia, AMS occurred soonest and with greater severity with simulated altitude, compared with either normobaric hypoxia or normoxic hypobaria.  In 2 studies, one in normobaric hypoxia found no MRI signs of vasogenic edema but suggested that AMS was associated with “cytotoxic edema”, whereas a comparable study in hypobaric hypoxia found combined vasogenic and intracellular edema. The conclusions from the 2 studies have very different implications for refining a theory of the pathophysiology of AMS. Although the studies were not designed for a direct comparison between hypobaria and hypoxia, the discrepancy points out an assumption about normobaric hypoxia and the pathophysiology of AMS that may warrant further investigation.

Our central hypothesis regarding the pathophysiology of AMS, and by extension of HACE, is that it is centered on dysfunction within the brain. This is not a new idea, but it is one of current intense interest thanks to advances in brain imaging and neuroscience techniques. Barcroft, writing in 1924, argued that the brain’s response to hypoxia was central to understanding the pathophysiology of mountain sickness.

A low ventilatory response to hypoxia coupled with increased symptoms of AMS led to intensive investigation of a link between the chemical control of ventilation and the pathogenesis of AMS. The results of these investigations suggest that for most people, the ventilatory response to hypoxia has little predictive value for AMS risk. Only if the extremes of ventilator responsiveness are contrasted can accurate predictions be made, where those with extremely low ventilatory drives being more likely to suffer AMS. At the extreme end of the distribution (i.e., for very high responses), the protective role of a brisk hypoxic ventilatory response may be due to increased arterial oxygen content and cerebral oxygen delivery despite mild hypocapnic cerebral vasoconstriction.

Hansen and Evans were the first to publish a comprehensive hypothesis of the pathophysiology of AMS centered on the brain. Their theory posited that compression of the brain, either by increased cerebral venous volume, reduced absorption of cerebral spinal fluid, or increased brain-tissue hydration (edema), initiates the development of the symptoms and signs of AMS and HACE. Ross built on these ideas with his “tight fit hypothesis,” published in 1985, and others have developed these ideas into a series of testable hypotheses congruent with today’s knowledge of AMS and HACE. The tight fit hypothesis states that expanded intracranial volume (due to the reasons put forth by Hansen and Evans, or other causes) plus the volume available for intracranial buffering of that expanded volume would predict who would get AMS. Greater buffering capacity leads to AMS resistance, lower buffering capacity, or a ‘tight fit’ of the brain in the cranial vault, would lead to greater AMS susceptibility. Overall, it is clear that brain volume increases in humans on exposure to hypoxia. It is less certain whether this elevation in brain volume plays a role in AMS.

Hackett’s pioneering MRI study in HACE, with marked white matter edema suggestive of a vasogenic origin, has led to a decade of studies looking for a similar finding in AMS. In moderate to severe AMS, all imaging studies have shown some degree of cerebral edema. But in mild to moderate AMS, admittedly an arbitrary and subjective distinction, brain edema is present in some MRI studies of AMS subjects, but not in all. It seems reasonable to conclude from the available data that the increase in brain volume observed is at least partially due to brain edema, and that earlier studies missed the edema more for technical than physiological reasons. It is less clear whether the brain edema is largely of intracellular or vasogenic origin, and what role if any it plays in the pathophysiology of AMS.

Although we support transcranial doppler for many investigations in integrative physiology, the complex interplay of hypoxia and hypocapnia that is present in acutely hypoxic humans may present a situation where whole brain imaging is a more reliable and accurate tool to discern the role of CBF in the onset of AMS. To date, no brain imaging studies have addressed global cerebral perfusion in AMS.

The management of AMS and HACE is based on our current understanding of the physiological and pathophysiological responses to hypoxia. Hypoxia itself, however, does not immediately lead to AMS as there is a delay of several hours after arrival at high altitude before symptoms develop. Increased knowledge of hypoxic inducible factor and cytokines that alter capillary permeability may lead to the discovery of new drugs for the prevention and alleviation of AMS and HACE.

Much work has focused on the role of vascular endothelial growth factor (VEGF), a potent permeability factor up-regulated by hypoxia. Some studies have found no evidence of an association of changes in plasma concentrations of VEGF and AMS, whereas others support the hypothesis that VEGF contributes to the pathogensis of AMS. Clearly a better understanding of the mechanisms of increased capillary permeability of cerebral capillaries will greatly enhance the management of AMS and HACE.

Flying high: A theoretical analysis of the factors limiting exercise performance in birds at altitude

Graham R. Scott, William K. Milsom
Respiratory Physiology & Neurobiology 154 (2006) 284–301
http://dx.doi.org:/10.1016/j.resp.2006.02.012

The ability of some bird species to fly at extreme altitude has fascinated comparative respiratory physiologists for decades, yet there is still no consensus about what adaptations enable high altitude flight. Using a theoretical model of O2 transport, we performed a sensitivity analysis of the factors that might limit exercise performance in birds. We found that the influence of individual physiological traits on oxygen consumption (˙VO2 ) during exercise differed between sea level, moderate altitude, and extreme altitude. At extreme altitude, hemoglobin (Hb) O2 affinity, total ventilation, and tissue diffusion capacity for O2 (DTO2) had the greatest influences on VO2; increasing these variables should therefore have the greatest adaptive benefit for high altitude flight. There was a beneficial interaction between DTO2 and the P50 of Hb, such that increasing DTO2 had a greater influence on VO2 when P50 was low. Increases in the temperature effect on P50 could also be  beneficial for high flying birds, provided that cold inspired air at extreme altitude causes a substantial difference in temperature between blood in the lungs and in the tissues. Changes in lung diffusion capacity for O2, cardiac output, blood Hb concentration, the Bohr coefficient, or the Hill coefficient likely have less adaptive significance at high altitude. Our sensitivity analysis provides theoretical suggestions of the adaptations most likely to promote high altitude flight in birds and provides direction for future in vivo studies.

The bird lung is unique among the lungs of air-breathing vertebrates, with a blood flow that is crosscurrent to gas flow, and a gas flow that occurs unidirectionally through rigid parabronchioles. As such, bird lungs are inherently more efficient than the lungs of other air-breathing vertebrates (Piiper and Scheid, 1972, 1975). While this may partially account for the greater hypoxia tolerance of birds in general when compared to mammals (cf. Scheid, 1990), its presence in all birds excludes the crosscurrent lung as a possible adaptation specific to high altitude fliers. Similarly, an extremely small diffusion distance across the blood–gas interface compared to other air breathers seems to be a characteristic of all bird lungs, and not just those of high fliers (Maina and King, 1982; Powell and Mazzone, 1983; Shams and Scheid, 1989). Partly because of this small diffusion distance, the inherent O2 diffusion capacity across the gas–blood interface (DLO2) is generally high in birds. Interestingly, pulmonary vasoconstriction does not appear to increase during hypoxia in bar-headed geese (Faraci et al., 1984a). This may be a significant advantage during combined exercise and severe hypoxia, and suggests that regulation of lung blood flow could be important in high altitude birds. In addition, the CO2/pH sensitivity of ventilation is commonly assessed by comparing the isocapnic and poikilocapnic hypoxic ventilatory responses; however, the isocapnic ventilatory responses to hypoxia of both low and high altitude birds have not been compared. In this regard, the ventilator response in high altitude birds may also depend on their capacity to maintain intracellular pH during alkalosis, or to buffer changes in extracellular pH due to hyperventilation. It therefore remains to be conclusively determined whether high altitude fliers have a greater capacity to increase ventilation during severe hypoxia.

After diffusing into the blood in the lungs, oxygen is primarily circulated throughout the body bound to hemoglobin. A high cardiac output is therefore important for exercise at high altitude to supply the working muscle with adequate amounts of O2. Indeed, animals selectively bred for exercise performance have higher maximum cardiac outputs, as do species that have evolved for exercise performance. Whether cardiac output limits exercise performance per se, however, is less clear; other factors may limit intense exercise, and in more athletic species (or individuals) cardiac output may be higher simply out of necessity. Excessive cardiac output may even be detrimental if blood transit times in the lungs or tissues are substantially reduced. Unfortunately, very little is known about cardiac performance in high flying birds. Both the high altitude bar-headed goose and the low altitude pekin duck can increase cardiac output at least five-fold during hypoxia at rest (Black and Tenney, 1980), but no comparison of maximum cardiac performance has been made between high and low altitude birds.

Once oxygenated blood is circulated to the tissues, O2 moves to the tissue mitochondria, the site of oxidative phosphorylation and oxygen consumption. Transport of oxygen from the blood to the mitochondria involves several steps. Oxygen must first dissociate from Hb and diffuse through the various compartments of the blood, but in both birds and mammals the conductances of these steps are high, and are unlikely to impose much of a limitation to O2 transport. In contrast, diffusion across the vascular wall and through the extracellular spaces is thought to provide the most sizeable limitation to O2 transport. Consequently, the size of the capillary–muscle fiber interface is an extremely important determinant of a muscle’s aerobic capacity. Finally, oxygen diffuses across the muscle fiber membrane and moves through the cytoplasm until it associates with cytochrome c oxidase, the O2 acceptor in the mitochondrial electron transport chain. Myoglobin probably assists intracellular O2 transport, so diffusion through the muscle likely provides very little resistance to O2 flux.

It is obvious that the ability of some bird species to fly at extreme altitudes is poorly understood. The adaptive benefit of high hemoglobin oxygen affinity is well established, but its relative importance is unknown. Some evidence suggests that traits increasing oxygen diffusion capacity in flight muscle are adaptive in high fliers as well, but the adaptive significance of differences in the respiratory and cardiovascular systems of high altitude fliers is not clear. The remainder of this study assesses these possibilities using theoretical sensitivity analysis, and explores potential adaptations for high altitude flight in birds.

Oxygen transport in birds

Oxygen transport in birds

Oxygen transport in birds. The crosscurrent parabronchial lung is unidirectionally ventilated by air sacs, and oxygen diffuses into blood capillaries from air capillaries (not shown) all along the length of the parabronchi. Oxygen is then circulated in the blood, and diffuses to mitochondria in the tissues. The rate of oxygen transport at both the lungs and tissues can be calculated using the Fick equation, and the amount of O2 transferred from the lungs into the blood can be calculated using an oxygen conservation equation.

Oxygen tensions in the lung

Oxygen tensions in the lung

Oxygen tensions in the lung (A) and tissue (B) capillaries during normoxia. In the crosscurrent avian lung, PO2 varies in two dimensions: PO2 increases along the path of blood flow through the lungs, but does not increase by as much at the end of the parabronchi as at the start (gas PO2 decreases along the length of the parabronchi). In the tissues, blood PO2 decreases continuously along the capillary length as O2 diffuses to tissue mitochondria. To reach a solution, our model iterates between gas transport calculations in the lungs (A) and tissues (B) until a stable result is reached.

varying different biochemical features of hemoglobin (Hb) on oxygen consumption

varying different biochemical features of hemoglobin (Hb) on oxygen consumption

The effects of varying different biochemical features of hemoglobin (Hb) on oxygen consumption during exercise in normoxia (PIO2 of 150 Torr; red), moderate hypoxia (84 Torr; green dashed), and severe hypoxia (30 Torr; dark blue). (A) P50, the PO2 at 50% Hb saturation; (B and C) Bohr coefficient (φ); and (D and E) Hill coefficient (n) (see Section 2 for a mathematical description of each). In (B)–(E), the effects of each variable were assessed at the P50 of pekin ducks (40 Torr; B and D) as well as the P50 of bar-headed geese (25 Torr; C and E).

Unlike in vivo studies, theoretical sensitivity analyses allow individual physiological variables to be altered independently so their individual effects on oxygen consumption can be assessed. By applying this analysis to hypoxia in birds, we feel we can predict which factors most likely limit oxygen consumption and exercise performance. As a consequence, our analysis identifies which steps in the oxygen cascade can provide the basis for adaptive change in birds that evolved for high altitude flight, namely ventilation and tissue diffusion capacity.

Since our interest was in the factors limiting exercise performance at altitude, the starting data for our model were obtained from previous studies on pekin ducks near maximal oxygen consumption. These ducks were exercising on a treadmill, however, and were not flying. Unfortunately, to the best of our knowledge only one previous study has made all the required measurements for this analysis during flight, and this was only done in normoxia (in pigeons, Butler et al., 1977). Pekin ducks are the only species for which we could find all the required measurements for our analysis during exercise in both normoxia and hypoxia. Only the lung and tissue diffusion capacities remained to be calculated in our analysis, but previous experimental determinations of DLO2 in pekin ducks were similar to the values calculated in this study (Scheid et al., 1977). Similar values for DTO2 are not available.

The physiological variables limiting exercise performance in birds during moderate hypoxia are similar to those limiting performance in normoxia. DTO2 continues to pose the greatest limitation, and limitations imposed by the circulation (˙Q and CHb) are still greater at a lower P50. Unlike normoxia, however, ˙VO2 in moderate hypoxia appears to be limited less by the circulation and more by respiratory variables, as is also the case in humans (Wagner, 1996). The most substantial difference between severe hypoxia and normoxia/moderate hypoxia is in the effects of altering ventilation. Ventilation appears to become a major limitation to exercise performance at extreme altitude. DTO2 also appears to limit ˙VO2 in severe hypoxia, but only at lower P50 values. This is not entirely unsurprising: in severe hypoxia the venous blood of pekin ducks (a species which has a higher P50) is almost completely deoxygenated in vivo, so there are no possible benefits of increasing DTO2 . At the lower P50, there is a substantially higher arterial oxygen content, so more oxygen can be removed, and increasing DTO2 can have a greater influence. In humans during severe hypoxia, DTO2, DLO2, and ˙V have the greatest influence on exercise performance.

Tissue diffusion capacity should also be adaptive in high altitude birds with a high hemoglobin O2 affinity. In the present study, a simultaneous decrease in P50 (from 40 to 25 Torr) and increase in DTO2 (twofold) increased ˙VO2 by 51%. Thus, in high flying birds that are known to have a low P50, such as the barheaded goose and Ruppell’s griffon (Gyps rueppellii), increases in flight muscle diffusion capacity should be of extreme importance. This suggestion is supported by research demonstrating greater muscle capillarization in bar-headed geese than in low altitude fliers, as the size of the capillary–muscle fiber interface is known to be the primary structural determinant of O2 flux into the muscle.

Our analysis suggests that an enhanced capacity to increase ventilation should also benefit birds significantly in severe hypoxia, and could therefore be an important source of adaptation for high altitude flight. This is likely true regardless of P50; although there is a small amount of interaction between P50 and ventilation, increasing ˙V always had a substantial effect on oxygen consumption. Data from the literature addressing this possibility have unfortunately been inconclusive. Both bar-headed geese and pekin ducks can effectively increase ventilation, thus reducing the inspired-arterial O2 difference, during severe poikilocapnic hypoxia at rest, as well as during moderate poikilocapnic hypoxia and running exercise.

oxyhemoglobin dissociation curve

oxyhemoglobin dissociation curve

In contrast to the Bohr effect and Hill coefficient, the temperature effect on Hb-O2 binding affinity may have a substantial effect on oxygen consumption, and may therefore be a source of adaptive change for high altitude flight. An effect of temperature on ˙VO2 may arise if hyperventilation during flight at extreme altitude cools the pulmonary blood. This would reduce the P50 of Hb in the lungs, and thus facilitate oxygen uptake. When this blood enters the exercising muscles it would then be rewarmed to body temperature, and oxygen would be released from Hb. Our modelling suggests that a temperature effect on Hb could significantly enhance ˙VO2 . The greater the difference in temperature between blood in the lungs and in the muscles, and the greater the temperature effect on Hb-O2 binding, the greater the increase in ˙VO2 . At normal levels of temperature sensitivity, the increase in ˙VO2 was approximately 5% for every 1 ◦C difference. It could be adaptive at high altitude to alter the magnitude of the temperature effect on Hb while allowing lung temperature to fall. At present, however, it is unknown whether the Hb of high altitude birds has a heightened sensitivity to temperature, or whether pulmonary blood is actually cooled during high altitude flight.

Using a theoretical sensitivity analysis that allows individual physiological variables to be altered independently, we have identified the factors most likely to limit oxygen consumption and exercise performance in birds, and by extension, the physiological changes that are likely adaptive for high altitude flight. The adaptive benefits of some of these changes, in particular hemoglobin oxygen affinity, are already well established for high flying birds. For other traits, such as an enhanced hypoxic ventilatory response or O2 diffusion capacity of flight muscle, adaptive differences have not been conclusively recognized in studies in vivo. Furthermore, the beneficial interaction between increasing DTO2 and decreasing hemoglobin P50 has not yet been demonstrated in vivo. Our theoretical analysis suggests that changes in these respiratory processes could also adapt birds to environmental extremes, and future studies should explore these findings.

Adaptation and Convergent Evolution within the Jamesonia-Eriosorus Complex in High-Elevation Biodiverse Andean Hotspots

Patricia Sanchez-Baracaldo, Gavin H. Thomas
PLoS ONE 9(10): e110618. http://dx.doi.org:/10.1371/journal.pone.0110618

The recent uplift of the tropical Andes (since the late Pliocene or early Pleistocene) provided extensive ecological opportunity for evolutionary radiations. We test for phylogenetic and morphological evidence of adaptive radiation and convergent evolution to novel habitats (exposed, high-altitude paramo habitats) in the Andean fern genera Jamesonia and Eriosorus. We construct time-calibrated phylogenies for the Jamesonia-Eriosorus clade. We then use recent phylogenetic comparative methods to test for evolutionary transitions among habitats, associations between habitat and leaf morphology, and ecologically driven variation in the rate of morphological evolution. Paramo species (Jamesonia) display morphological adaptations consistent with convergent evolution in response to the demands of a highly exposed environment but these adaptations are associated with microhabitat use rather than the paramo per se. Species that are associated with exposed microhabitats (including Jamesonia and Eriorsorus) are characterized by many but short pinnae per frond whereas species occupying sheltered microhabitats (primarily Eriosorus) have few but long pinnae per frond. Pinnae length declines more rapidly with altitude in sheltered species. Rates of speciation are significantly higher among paramo than non-paramo lineages supporting the hypothesis of adaptation and divergence in the unique Pa´ramo biodiversity hotspot.

AltitudeOmics: Rapid Hemoglobin Mass Alterations with Early Acclimatization to and De-Acclimatization from 5,260 m in Healthy Humans

Benjamin J. Ryan, NB Wachsmuth, WF Schmidt, WC Byrnes, et al.
PLoS ONE 9(10): e108788. http://dx.doi.org:/10.1371/journal.pone.0108788

It is classically thought that increases in hemoglobin mass (Hb mass) take several weeks to develop upon ascent to high altitude and are lost gradually following descent. However, the early time course of these erythropoietic adaptations has not been thoroughly investigated and data are lacking at elevations greater than 5,000 m, where the hypoxic stimulus is dramatically increased. As part of the AltitudeOmics project, we examined Hb mass in healthy men and women at sea level (SL) and 5,260 m following 1, 7, and 16 days of high altitude exposure (ALT1/ALT7/ALT16). Subjects were also studied upon return to 5,260 m following descent to 1,525 m for either 7 or 21 days. Compared to SL, absolute Hb mass was not different at ALT1 but increased by 3.7-5.8% (mean 6 SD; n = 20; p<0.01) at ALT7 and 7.6-6.6% (n = 21; p=0.001) at ALT16. Following descent to 1,525 m, Hb mass was reduced compared to ALT16 (-6.0+3.7%; n = 20; p = 0.001) and not different compared to SL, with no difference in the loss in Hb mass between groups that descended for 7 (-6.3+3.0%; n = 13) versus 21 days (-5.7+5.0; n = 7). The loss in Hb mass following 7 days at 1,525 m was correlated with an increase in serum ferritin
(r =20.64; n = 13; p,0.05), suggesting increased red blood cell destruction. Our novel findings demonstrate that Hb mass increases within 7 days of ascent to 5,260 m but that the altitude-induced Hb mass adaptation is lost within 7 days of descent to 1,525 m. The rapid time course of these adaptations contrasts with the classical dogma, suggesting the need to further examine mechanisms responsible for Hb mass adaptations in response to severe hypoxia.

Cardiovascular adjustments for life at high altitude

Roger Hainsworth, Mark J. Drinkhill
Respiratory Physiology & Neurobiology 158 (2007) 204–211
http://dx.doi.org:/10.1016/j.resp.2007.05.006

The effects of hypobaric hypoxia in visitors depend not only on the actual elevation but also on the rate of ascent. There are increases in sympathetic activity resulting in increases in systemic vascular resistance, blood pressure and heart rate. Pulmonary vasoconstriction leads to pulmonary hypertension, particularly during exercise. The sympathetic excitation results from hypoxia, partly through chemoreceptor reflexes and partly through altered baroreceptor function. Systemic vasoconstriction may also occur as a reflex response to the high pulmonary arterial pressures. Many communities live permanently at high altitude and most dwellers show excellent adaptation although there are differences between populations in the extent of the ventilatory drive and the erythropoiesis. Despite living all their lives at altitude, some dwellers, particularly Andeans, may develop a maladaptation syndrome known as chronic mountain sickness. The most prominent characteristic of this is excessive polycythemia, the cause of which has been attributed to peripheral chemoreceptor dysfunction. The hyperviscous blood leads to pulmonary hypertension, symptoms of cerebral hypoperfusion, and eventually right heart failure and death.

High altitude places are not only destinations of adventurous travelers, many people are born, live their lives and die in these cold and hypoxic regions. According to WHO, in 1996 there were approximately 140 million people living at altitudes over 2,500m and there are several areas of permanent habitation at over 4,000 m. These are in three main regions of the world: the Andes of South America, the highlands of Eastern Africa, and the Himalayas of South-Central Asia. This review is concerned with the effects of exposure to high altitude on the cardiovascular system and its autonomic control, in visitors, and the means by which the permanent high altitude dwellers have adapted to their environment.

For visitors the period of initial adaptation, i.e. the first days and weeks following arrival at attitude, is a critical time since it is during this period that acute mountain sickness and/or pulmonary edema may occur. The processes of adaptation occurring during this initial period may well determine the individual’s ability to continue to function normally. Recent studies in animals and man have highlighted the role of the autonomic nervous system in adaptation and in particular the importance of sympathetic activation of the cardiovascular system following high altitude exposure.

An increase in resting heart rate in response to acute hypoxia has been
described in several species including man. Vogel and Harris (1967)
investigated the effects of simulated exposure to high altitude in man
at pressures equivalent to 600, 3,400 and 4,600m using a hypobaric
chamber. Each level of chamber pressure was developed over a 30 min
period andwas maintained for 48 h in an attempt to simulate expedition
conditions. After 10 h at the equivalent of 3,400 m resting
heart rate was significantly increased and by 40 h it had increased by
16% from the resting value at 600 m. At 4,600 m it increased by 34%.
Similar findings, an increase in heart rate of 18%, were shown following
ascent to 4,300 m for periods up to 5 weeks. However, this study also
demonstrated that the rate of ascent also influenced the magnitude of
the heart rate increase. A gradual increase in altitude over a period
of 2 weeks resulted in the resting heart rate increasing by 25%
compared with an abrupt ascent which resulted in an increase of
only 9%. As subjects acclimatize at altitudes up to about 4,500 m
much of the increase in heart rate is lost and resting heart rates
return towards their sea level values. Acute hypoxia also causes
increases in cardiac output both at rest and for given levels of
exercise compared with values during normoxia.

The effect of hypoxia on the pulmonary circulation is dramatic
resulting in pulmonary hypertension caused by an increase in
pulmonary vascular resistance. The onset has been shown in man
to be very rapid, reaching a maximum within 5 min. Zhao et al.
(2001) demonstrated that breathing 11% oxygen for 30 min
increased mean pulmonary artery pressure by 56%, from 16 to
25 mmHg. The effect of hypoxia on the pulmonary circulation is
even more pronounced during exercise, as demonstrated in studies
carried out on subjects of Operation Everest II. Resting pulmonary
artery pressure increased from 15 mmHg at sea level to 34 mmHg
at the equivalent of 8,840 m. During near maximal exercise at
8,840 m it increased from the sea level value of 33–54 mm Hg.
In the short term the mechanism of this pulmonary artery vaso-
constriction has been shown to involve inhibition of O2 sensitive
K+ channels leading to depolarization of pulmonary artery smooth
muscle cells and activation of voltage gated Ca2+ channels. This
causes Ca2+ influx and vasocon-striction. This process is
immediately reversed by breathing oxygen.

Healthy high altitude residents show excellent adaptation to their
environment. These adaptations are likely to be associated with
altered gene expression as the expression of genes associated with
vascular control and reactions to hypoxia have been found to be high
in altitude dwellers. Different communities, however, seem to adopt
different adaptation strategies. For example Andeans hyperventilate
to decrease end-tidal and arterial CO2 levels to as low as 25 mmHg
and have hemoglobin levels well above those in sea-level people.
Tibetans Hyperventilate but have normal hemoglobin levels below
4,000 m. Ethiopian highlanders, on the other hand, have CO2 and
hemoglobin levels similar to those of sea-level dwellers.

Blood volumes are larger in high altitude dwellers. In Andeans this
is due to large packed cell volumes whereas in Ethiopians it was the
plasma volumes that were large. Probably as the result of the large
blood volumes, tolerance to orthostatic stress was greater than that
in sea-level residents.

CMS is a condition frequently found in long term residents of high
altitudes, particularly in the Andes where it is a major public health
problem. It also occurs in residents on the Tibetan plateau, although
not in Ethiopians. Patients with CMS develop excessive polycythemia
and various clinical features including dyspnea, palpitations, insomnia,
dizziness, headaches, confusion, loss of appetite, lack of mental
concentration and memory alterations. Patients may also complain
of decreased exercise tolerance, bone pains, acral paresthesia and
occasionally hemoptysis. The impairment of mental function may
be reversed by phlebotomy. Physical examination reveals cyanosis,
due to the combination of polycythemia and low oxygen saturation,
and a marked pigmentation of the skin exposed to the sun.
Hyperemia of conjunctivae is characteristic and the retinal vessels
are also dilated and engorged. The second heart sound is frequently
accentuated and there is an increased cardiac size, mainly due to
right ventricular hypertrophy. As the condition progresses, overt
congestive heart failure becomes evident, characterized by dyspnea
at rest and during mild effort, peripheral edema, distension of
superficial veins, and progressive cardiac dilation.

The major mechanism for the control of blood pressure is through
regulation of peripheral vascular resistance, but most studies have
examined only the control of heart rate. We have recently studied
the responses of forearm vascular resistance to carotid baroreceptor
stimulation in high altitude residents with and without CMS, both at
their resident altitude and shortly after descent to sea level. Results
showed that baroreflex “set point” was higher in CMS, but only at
altitude. At sea level, values were similar.

The chronic hypoxia at high altitude stresses many of the body’s
homeostatic mechanisms. There have been many investigations
which have examined the effects on respiration. However, cardio-
vascular effects are no less important and it is largely through effects
on the cardiovascular system that both acute and chronic mountain
sickness are caused. The hypoxia exerts both direct and reflex effects.
In the lung it causes vasoconstriction and pulmonary hypertension.
The sympathetic nervous system is excited partly through a central
effect of the hypoxia, through stimulation of chemoreceptors and
possibly pulmonary arterial baroreceptors and altered systemic
baroreceptor function. In some individuals the excessive hemopoiesis
causes increased blood viscosity and tissue hypoperfusion leading
to the syndrome of chronic mountain sickness.

New Insights in the Pathogenesis of High-Altitude Pulmonary Edema

Urs Scherrer, Emrush Rexhaj, Pierre-Yves Jayet, et al.
Progress in Cardiovascular Diseases 52 (2010) 485–492
http://dx.doi.org:/10.1016/j.pcad.2010.02.004

High-altitude pulmonary edema is a life-threatening condition occurring in predisposed but otherwise healthy individuals. It therefore permits the study of underlying mechanisms of pulmonary edema in the absence of confounding factors such as coexisting cardiovascular or pulmonary disease, and/or drug therapy. There is evidence that some degree of asymptomatic alveolar fluid accumulation may represent a normal phenomenon in healthy humans shortly after arrival at high altitude. Two fundamental mechanisms then determine whether this fluid accumulation is cleared or whether it progresses to HAPE: the quantity of liquid escaping from the pulmonary vasculature and the rate of its clearance by the alveolar respiratory epithelium. The former is directly related to the degree of hypoxia induced pulmonary hypertension, whereas the latter is determined by the alveolar epithelial sodium transport. Here, we will review evidence that, in HAPE-prone subjects, impaired pulmonary endothelial and epithelial NO synthesis and/or bioavailability may represent a central underlying defect predisposing to exaggerated hypoxic pulmonary vasoconstriction and, in turn, capillary stress failure and alveolar fluid flooding. We will then demonstrate that exaggerated pulmonary hypertension, although possibly a condition sine qua non, may not always be sufficient to induce HAPE and how defective alveolar fluid clearance may represent a second important pathogenic mechanism.

Cerebral Blood Flow at High Altitude

Philip N. Ainslie and Andrew W. Subudhi
High Altitude Medicine & Biology 2014; 15(2): 133–140
http://dx.doi.org:/10.1089/ham.2013.1138

This brief review traces the last 50 years of research related to cerebral blood flow (CBF) in humans exposed to high altitude. The increase in CBF within the first 12 hours at high altitude and its return to near sea level values after 3–5 days of acclimatization was first documented with use of the Kety-Schmidt technique in 1964. The degree of change in CBF at high altitude is influenced by many variables, including arterial oxygen and carbon dioxide tensions, oxygen content, cerebral spinal fluid pH, and hematocrit, but can be collectively summarized in terms of the relative strengths of four key integrated reflexes:

  • hypoxic cerebral vasodilatation;
  • 2) hypocapnic cerebral vasoconstriction;
  • 3) hypoxic ventilatory response; and
  • 4) hypercapnic ventilatory response.

Understanding the mechanisms underlying these reflexes and their interactions with one another is critical to advance our understanding of global and regional CBF regulation. Whether high altitude populations exhibit cerebrovascular adaptations to chronic levels of hypoxia or if changes in CBF are related to the development of acute mountain sickness are currently unknown; yet overall, the integrated CBF response to high altitude appears to be sufficient to meet the brain’s large and consistent demand for oxygen.

Relative to its size, the brain is the most oxygen dependent organ in the body, but many pathophysiological and environmental processes may either cause or result in an interruption to its oxygen supply. As such, studying the brain at high altitude is an appropriate model to investigate both acute and chronic effects of hypoxemia on cerebrovascular function. The cerebrovascular responses to high altitude are complex, involving mechanistic interactions of physiological, metabolic, and biochemical processes.

This short review is organized as follows: An historical overview of the earliest CBF measurements collected at high altitude introduces a summary of reported CBF changes at altitude over the last 50 years in both lowlanders and high-altitude natives. The most tenable candidate mechanism(s) regulating CBF at altitude are summarized with a focus on available data in humans, and a role for these mechanisms in the pathophysiology of AMS is considered. Finally, suggestions for future directions are provided.

Angelo Mosso (1846–1910) is undoubtedly the forefather of high altitude cerebrovascular physiology. In order to pursue his principal curiosity of the physiological effects of hypobaria, Mosso built barometric chambers and was reported to expose himself pressures as low as 192 mmHg (equivalent to > 10,000 m). He was also responsible for the building of the Capanna Margherita laboratory on Monta Rosa at 4,559 m. In both settings, Mosso utilized his hydrosphygmomanometer to measure changes in ‘‘brain pulsations’’ in patients that had suffered removal of skull sections, due to illness or trauma. Indicative of changes in CBF, these recordings preceded the next estimates of CBF in humans by some 50 years.

At sea level, Kety and Schmidt (1945) were the first to quantify human CBF using an inert tracer (nitrous oxide, N2O) combined with arterial and jugular venous sampling. This method for the measurement of global CBF is based on the Fick principle, whereby the integrated difference of multiple arterial and venous blood samples during the first 10 or more minutes after the sudden introduction into the lung of a soluble gas tracer is inversely proportional to cerebral blood flow.  In 1948, they showed that breathing 10% oxygen increased CBF by 35%; however, it was not until 1964 that the first measurements of CBF were made in humans at high altitude. The motivation for these high altitude experiments was stimulated, in part, from the earlier discovery of the brain’s ventral medullary cerebrospinal fluid (CSF) pH sensors in animals. Following the location of these central chemoreceptors, Severinghaus and colleagues examined in humans the role of CSF pH and bicarbonate in acclimatization to high altitude (3,810 m) at the White Mountain (California, USA) laboratories (Severinghaus et al., 1963). A year later, at the same location, John Severinghaus performed his seminal study of CBF at high altitude. He was joined by Tom Hornbein—shortly after his first ascent of Everest by the West Ridge—who was part of the research team and also volunteered for the study (Fig.). The results showed clear time dependent changes in CBF during acclimatization to high altitude (HA).

the Kety-Schmidt nitrous oxide method of measuring CBF

the Kety-Schmidt nitrous oxide method of measuring CBF

  • From left to right, Larry Saidman (administering the gas), Tom Hornbien (volunteer), Ed Munson (drawing jugular venous blood samples), and John Severinghaus. Here (1964) the Kety-Schmidt nitrous oxide method of measuring CBF is used. The subject breathed about 15% N2O for 15 min while arterial and jugular venous blood was frequently sampled. (B) Results from Severinghaus et al. (1966). Graphs shows that CBF as estimated by cerebral A-VO2 differences from sea level controls increased about 24% within hours of arrival at 3810 m, and fell over 4 days to about 13% above control. CBF by the N2O method was increased by 40% on day 1, and returned to 6% above control on day 4. However, the N2O method data had greater variance. Acute normoxia on day 1 and day 4 returned CBF to sea level values within 15 min. Photograph courtesy of Dr. John W Severinghaus.

Native Tibetan (or Himalayan) and Andean populations arrived approximately 25,000 and 11,000 years ago, suggesting that these populations either carried traits that allowed them to thrive at high altitude or were able to adapt to the environment. The physiological and genetic traits associated with native high-altitude populations have been elegantly reviewed (Beall, 2007; Erzurum et al., 2007; Frisancho, 2013). As such, this topic is briefly summarized here with the focus on CBF at altitude in context of Andean and Tibetan high-altitude residents.

In general, native Andeans have lower CBF values compared to sea level natives. The first evidence suggesting lower flow was reported in 8 Peruvian natives living at 4300m altitude in Cerro de Pasco (Milledge and Sørensen, 1972). The authors found the mean arterial–venous oxygen content difference across the brain was 7.9 – 1 vol%, about 20% higher than the published sea level mean of 6.5 vol%. They suggested that CBF probably was proportionately about 20% below sea level normal values, assuming that brain metabolic rate was normal, and postulated that the mechanism might be high blood viscosity given the high hematocrit (58 – 6%) in these subjects. However, since the cerebral metabolic rate for oxygen (CMRO2) is constant even in severe hypoxia (Kety and Schmidt 1948b; Ainslie et al. 2013), the inverse linear relationship between CBF and arterial–venous oxygen content differences could also explain the reduction in CBF, as less flow would be needed to match the oxygen demand of the brain when arterial content is elevated. A similar study (Sørensen et al., 1974), using arterio-venous differences combined (in a subgroup) with a modified version of Kety–Schmidt method (krypton instead of N2O,) conducted in high-altitude residents in La Paz in Bolivia at 3800 m, also reported a 15%–20% reduction in CBF (with a reported average hematocrit of 50%) compared to a sea level control group.

Percent changes in cerebral blood flow

Percent changes in cerebral blood flow

Percent changes in cerebral blood flow (D%CBF, graph A), arterial oxygen content (Cao2, graph B), and cerebral oxygen delivery (CDO2, graph C) with time at high-altitude from seven studies at various altitudes and durations. Severinghaus et al. (1966) studied CBF using the Kety-Schmidt technique in five subjects brought rapidly by car to 3810 m. Using the Xe133 method, Jensen et al. (1990) measured CBF in 12 subjects at 3475 m. Huang et al. (1987) measured ICA and VA blood velocities as a metric of CBF on Pikes Peak (4300 m). Baumgartner et al. (1994) studied 24 subjects who rapidly ascended to 3200m by cable car, slept one night at 3600 m, and ascended by foot to 4559m the next day. Cerebral blood flow was estimated by transcranial Doppler ultrasound. About two-thirds of the subjects developed symptoms of AMS, data included are the mean of all subjects. Lucas et al. (2011) employed an 8–9 day ascent to 5050m and estimated changes in CBF by transcranial Doppler ultrasound of the middle cerebral artery. Willie et al. (2013) following the same ascent measured flow (Duplex ultrasound; and TCCD) in the ICA and VA and estimated global flow from: 2*ICA + 2* VA. The same methodological approach was used time Subudhi upon rapid ascent via car and oxygen breathing to 5240 m (Subudhi et al. 2013). Cao2 was calculated from: (1.39 · [Hb] · SaO2) + Pao2 *0.003. In some studies [Hb] data were not available, and typical data from previous studies over comparable time at related elevation were used. In other studies, Pao2 was not always reported; therefore, Sao2 was used to estimate Pao2 via (Severinghaus, 1979).

Only two studies have measured serial changes in CBF during progressive ascent to high altitude, but the findings may help explain small discrepancies between studies. In 2011, Wilson et al. (2011) measured diameter and velocity in the MCA (using transcranial color-coded Duplex-ultrasound, TCCD) following partial acclimation to 5300m (n = 24), 6400 m (n = 14), and 7950m (n = 5). Remarkable elevations (200%) in flow in the MCA occurred at 7950 m. Notably, the authors estimated *24% dilation of the MCA occurred at 6400 m. Dilation of the MCA further increased to *90% at 7950m (Fig.) and was rapidly reversed with oxygen supplementation (Fig.). Cerebral oxygen delivery and oxygenation were maintained by commensurate elevations of CBF even at these extreme altitudes. In another recent study, CBF and MCA diameter were measured at 1338 m, 3440 m, 4371 m, and over time at 5050 m (Willie et al., 2013). Dilation of the MCA was observed upon arrival at 5050 m with subsequent normalization of CBF and MCA diameter by days 10–12. Such findings are consistent with unchanged diameter following 17 days at 5400m (Wilson et al., 2011). It is important to note that according to Poiseuille’s Law, flow is proportional to radius raised to the fourth power. Therefore, consistent with previous concerns about TCD (Giller, 2003), that the MCA dilates at such levels of hypoxemia indicates that previous studies using TCD at altitude may have underestimated flow (see previous Fig.) and thus may explain differences between studies. These findings are particularly important because they suggest regional regulation of CBF occurs in both large and small cerebral arteries.

Changes in blood flow in the middle cerebral artery (MCA) upon progressive ascent to 7950 m

Changes in blood flow in the middle cerebral artery (MCA) upon progressive ascent to 7950 m

Changes in blood flow in the middle cerebral artery (MCA) upon progressive ascent to 7950 m. Data were collected following partial acclimation to 5300 m (n = 24), at 6400 m (n = 14), and at 7950 m (n = 5). Remarkable elevations (200%) in flow in the MCA occurred at 7950 m following removal of breathing supplementary oxygen and breathing air for 20 min. Dilation (*24%) of the MCA occurred at 6400 m, which was further increased to 90% at 7950 m. Oxygen supplementation at this highest altitude rapidly reversed the observed MCA vessel dilation (denoted by blue triangle). Elevations in CBF via cerebral vasodilation were adequate to maintain oxygen delivery, even at these extreme altitudes. Modified from Wilson et al. (2011).

Summary of the major factors acting to increase ( plus) and decrease (minus) CBF during exposure to hypoxia

Summary of the major factors acting to increase ( plus) and decrease (minus) CBF during exposure to hypoxia

Summary of the major factors acting to increase ( plus) and decrease (minus) CBF during exposure to hypoxia. Cao2, arterial oxygen content; CBV, cerebral blood volume; EDHF, endothelium-derived hyperpolarizing factor; ET-1, endothelin-1; HCT, hematocrit; NO, nitric oxide; O2-, superoxide; PGE, prostaglandins; SNA, sympathetic nerve activity; VAH, ventilatory acclimatization to hypoxia/altitude. Modified from Ainslie and Ogoh (2010); Ainslie et al. (2014).

It is clear that many aspects of CBF regulation and brain function at high altitude warrant further investigation. Indeed, several questions remain. For example, over the period of ventilatory acclimatization (weeks to months), how do interactions between the hypoxic ventilatory response, hypercapnic ventilatoy response, hypoxic cerebral vasodilatation, and hypocapnic cerebral vasoconstriction interact to alter CBF? Furthermore, what is the role of NO and/or adenosine in mediating cerebral vasodilation at high altitude? And last, what is the time-course of recovery in CBF following descent to sea level?

 

Cognitive Impairments at High Altitudes and Adaptation

Xiaodan Yan
High Alt Med Biol. 15:141–145, 2014
http://dx.doi.org:/10.1089/ham.2014.1009

High altitude hypoxia has been shown to have significant impact on cognitive performance. This article reviews the aspects in which, and the conditions under which, decreased cognitive performance has been observed at high altitudes. Neural changes related to high altitude hypoxia are also reviewed with respect to their possible contributions to cognitive impairments. In addition, potential adaptation mechanisms are reviewed among indigenous high altitude residents and long-term immigrant residents, with discussions about methodological concerns related to these studies.

The amount of cognitive impairments at high altitudes is related to the chronicity of exposure. Acute exposure usually refers to a duration of several weeks, whereas chronic exposure usually refer to ‘‘extended permanence’’ in the high altitude environment (Virue´s-Ortega and others, 2004). The altitude of ascending or residence is another factor affecting the severity of impairments. This review will first summarize the cognitive impairments in acute exposure, then talk about impairments in chronic exposure, with discussions about the effect of altitudes in corresponding sections.

 

High altitude-related neurocognitive impairments with ascending altitudes

High altitude-related neurocognitive impairments with ascending altitudes

 

 

High altitude-related neurocognitive impairments with ascending altitudes in acute high altitude exposure (Wilson and others, 2009).

human brain consumes about 20% of the total oxygen intake

human brain consumes about 20% of the total oxygen intake

The human brain consumes about 20% of the total oxygen intake, which is disproportional to its size (about 2% of the total body weight). In this figure, oxygen consumption is reflected from glucose consumption in positron emission tomography (PET) (Alavi and Reivich, 2002).

The possibility of adaptation to high altitude hypoxia has always been an intriguing issue. In the acute cases, the human body does have some capacity for acclimatization, which varies significantly for different individuals. The question is, in chronic cases, for example, does growing up at high altitude regions guarantee sufficient adaption to occur to compensate for the risk of cognitive impairments? Existing research tends to suggest that, although some level of adaptation does occur, neural and cognitive impairments are still observed in these populations who are native or long-term residents at high altitude.

Although multiple studies have suggested that growing up at high altitudes is associated with cognitive impairments, it is not to say that adaptation does not happen with prolonged chronic exposure to high altitudes. One study has revealed that as a function of the length of low altitude residence (across the range of 1–5 years), some neuroimaging parameters of original highlanders who grew up at high altitude regions had shown the trend of converging towards the patterns of original low altitude residents, although such changes were not accompanied by statistically significant changes in cognitive performance (Yan and others, 2010). It is possible that, given sufficiently long time for normoxia adaptation, the neural and cognitive impairments associated with high altitude hypoxia may be alleviated to a certain extent.

In summary, various cognitive impairments associated with high altitude hypoxia have been reported from existing studies, which are accompanied by findings about neural impairments, suggesting that these cognitive impairments have legitimate neural basis. The specific relationships between physiological symptoms and cognitive impairments appear to be complicated and require further elucidation. There are cognitive impairments associated with both acute and chronic exposure to high altitudes; however, particular caution should be taken when interpreting the findings about cognitive impairments among native high altitude residents because of the differences
in cultural and socioeconomic factors. Existing studies have suggested that there can be some level of adaptation to high altitudes, in spite of the fact that some neuronal impairment may be irreversible.

Exercise Capacity and Selected Physiological Factors by Ancestry and Residential Altitude: Cross-Sectional Studies of 9–10-Year-Old Children in Tibet

Bianba, Sveinung Berntsen, Lars Bo Andersen, Hein Stigum, et al.
High Alt Med Biol. 2014; 15:162–169
http://dx.doi.org:/10.1089/ham.2013.1084

Aim: Several physiological compensatory mechanisms have enabled Tibetans to live and work at high altitude, including increased ventilation and pulmonary diffusion capacity, both of which serve to increase oxygen transport in the blood. The aim of the present study was to compare exercise capacity (maximal power output) and selected physiological factors (arterial oxygen saturation and heart rate at rest and during maximal exercise, resting hemoglobin concentration, and forced vital capacity) in groups of native Tibetan children living at different residential altitudes (3700 vs. 4300 m above sea level) and across ancestry (native Tibetan vs. Han Chinese children living at the same altitude of 3700 m). Methods: A total of 430 9–10-year-old native Tibetan children from Tingri (4300 m) and 406 native Tibetan and 406 Han Chinese immigrants (77% lowland-born and 33% highland-born) from Lhasa (3700 m) participated in two cross-sectional studies. The maximal power output (Wmax) was assessed using an ergometer cycle. Results: Lhasa Tibetan children had a 20% higher maximal power output (watts/kg) than Tingri Tibetan and 4% higher than Lhasa Han Chinese. Maximal heart rate, arterial oxygen saturation at rest, lung volume, and arterial oxygen saturation were significantly associated with exercise capacity at a given altitude, but could not fully account for the differences in exercise capacity observed between ancestry groups or altitudes. Conclusions: The superior exercise capacity in native Tibetans vs. Han Chinese may reflect a better adaptation to life at high altitude. Tibetans at the lower residential altitude of 3700 m demonstrated a better exercise capacity than residents at a higher altitude of 4300m when measured at their respective residential altitudes. Such altitude- or ancestry-related difference could not be fully attributed to the physiological factors measured.

Group size effects on foraging and vigilance in migratory Tibetan antelope

Xinming Lian, Tongzuo Zhang, Yifan Cao, Jianping Su, Simon Thirgood
Behavioural Processes 76 (2007) 192–197
http://dx.doi.org:/10.1016/j.beproc.2007.05.001

Large group sizes have been hypothesized to decrease predation risk and increase food competition. We investigated group size effects on vigilance and foraging behavior during the migratory period in female Tibetan antelope Pantholops hodgsoni, in the Kekexili Nature Reserve of Qinghai Province, China. During June to August, adult female antelope and yearling females gather in large migratory groups and cross the Qinghai–Tibet highway to calving grounds within the Nature Reserve and return to Qumalai county after calving. Large groups of antelope aggregate in the migratory corridor where they compete for limited food resources and attract the attention of mammalian and avian predators and scavengers. We restricted our sampling to groups of less than 30 antelopes and thus limit our inference accordingly. Focal-animal sampling was used to record the behavior of the free-ranging antelope except for those with lambs. Tibetan antelope spent more time foraging in larger groups but frequency of foraging bouts was not affected by group size. Conversely, the time spent vigilant and frequency of vigilance bouts decreased with increased group size. We suggest that these results are best explained by competition for food and risk of predation.

High altitude exposure alters gene expression levels of DNA repair enzymes, and modulates fatty acid metabolism by SIRT4 induction in human skeletal muscle

Zoltan Acsa, Zoltan Boria, Masaki Takedaa, Peter Osvatha, et al.
Respiratory Physiology & Neurobiology 196 (2014) 33–37
http://dx.doi.org/10.1016/j.resp.2014.02.006

We hypothesized that high altitude exposure and physical activity associated with the attack to Mt Everest could alter mRNA levels of DNA repair and metabolic enzymes and cause oxidative stress-related challenges in human skeletal muscle. Therefore, we have tested eight male mountaineers (25–40 years old) before and after five weeks of exposure to high altitude, which included attacks to peaks above 8000 m. Data gained from biopsy samples from vastus lateralis revealed increased mRNA levels of both cytosolic and mitochondrial superoxide dismutase. On the other hand 8-oxoguanine DNA glycosylase(OGG1) mRNA levels tended to decrease while Ku70 mRNA levels and SIRT6 decreased with altitude exposure. The levels of SIRT1 and SIRT3 mRNA did not change significantly. But SIRT4 mRNA level increased significantly, which could indicate decreases in fatty acid metabolism, since SIRT4 is one of the important regulators of this process. Within the limitations of this human study, data suggest that combined effects of high altitude exposure and physical activity climbing to Mt. Everest, could jeopardize the integrity of the particular chromosome.

High-altitude adaptations in vertebrate hemoglobins

Roy E. Weber
Respiratory Physiology & Neurobiology 158 (2007) 132–142
http://dx.doi.org:/10.1016/j.resp.2007.05.001

Vertebrates at high altitude are subjected to hypoxic conditions that challenge aerobic metabolism. O2 transport from the respiratory surfaces to tissues requires matching between theO2 loading and unloading tensions and theO2-affinity of blood, which is an integrated function of hemoglobin’s intrinsic O2-affinity and its allosteric interaction with cellular effectors (organic phosphates, protons and chloride). Whereas short-term altitudinal adaptations predominantly involve adjustments in allosteric interactions, long-term, genetically-coded adaptations typically involve changes in the structure of the hemoglobin molecules. The latter commonly comprise substitutions of amino acid residues at the effector binding sites, the heme protein contacts, or at inter-subunit contacts that stabilize either the low-affinity (‘Tense’) or the high-affinity (‘Relaxed’) structures of the molecules. Molecular heterogeneity (multiple iso-Hbs with differentiated oxygenation properties) can further broaden the range of physico-chemical conditions where Hb functions under altitudinal hypoxia. This treatise reviews the molecular and cellular mechanisms that adapt hemoglobin-oxygen affinities in mammals, birds and ectothermic vertebrates at high altitude.

Vertebrate animals display remarkable ability to tolerate high altitudes and cope with the concomitant decreases in O2 tension that potentially constrain aerobic life (Monge and Leon-Velarde, 1991;Weber, 1995; Samaja et al., 2003). Compared to an ambient PO2 of approximately 160 mm Hg at sea level, inspired tension approximates only 95 mm Hg for llamas and frogs from Andean habitats above 4000 m, 45 mm Hg for bar-headed geese that fly across the Himalayas, and 33 mm Hg for Ruppell’s griffon that soars at 11,300 m over Africa’s Ivory Coast. Apart from the distinct adaptations manifest in blood’s O2-transporting properties, tolerance to decreased O2 availability may entail reconfigurations at the organ and cellular levels that include a switch to partial anaerobiosis. Driven by needs to reduce aerobic metabolic rate and maintain functional integrity (Ramirez et al., 2007), these pertain to a core triad of adaptations:

  1. metabolic suppression,
  2. tolerance to metabolite (e.g. lactate) accumulation, and
  3. defenses against increased free radicals associated with return to high O2 tensions (Bickler and Buck, 2007).

The response to oxygen lack comprises two phases

  1. defense, which includes metabolic arrest (a suppression of ATP-demand and ATP-supply) and channel arrest (decreases cell membrane permeability), and
  2. rescue, which commonly involves preferential expression of proteins that are implicated in extending metabolic down-regulation (Hochachka et al., 1996).

These responses vary greatly in different species and different tissues. Thus, although mixed-venous lactate concentrations increase strongly in sea-level as well as high-altitude acclimated pigeons that are exposed to altitude (from 1–2 mM at sea level to 5–7 mM at 9000 m) (Weinstein et al., 1985), and humans performing submaximal work at high altitude show a transient ‘lactate paradox’ (lower peak lactate levels that humans living at sea level (Lundby et al., 2000)), many species do not exhibit altitude-related changes in anaerobic metabolism.

Organismic adaptations to survive and perform physical exercise at extreme altitudinal hypoxia are diverse. In birds the undisputed high-altitude champions, where flapping flight may raise the energy demand 10–20-fold compared to resting levels (Scott et al., 2006), a highly efficient “cross-current” ventilation perfusion arrangement in the lungs may increase arterial O2 tensions above the tensions in expired air (Scheid, 1979) and drastically reduce the difference between inhalant and arterial O2 tensions (to 1 mm Hg in bar-headed geese subjected to simulated altitude of 11580 m) (Black and Tenney, 1980). The Andean frog Telmatobius culeus has a highly ‘oversized’ (folded) and vascularized skin that is ventilated by ‘bobbing’ behavior to support water(=skin) breathing. Manifold organismic adaptations moreover include combinations of increased muscle Mb concentrations (Reynafarje and Morrison, 1962) increased muscle capillarization (manifest in mammals and birds (cf. Monge et al., 1991)) and decreased red cell size (seen in amphibians but not high-altitude reptiles (Ruiz et al., 1989; Ruiz et al., 1993)). Amphibians exhibit an interspecific correlation between erythrocyte count and the degree of vascularization of respiratory surfaces and muscle tissues (Hutchison and Szarski, 1965), that reflect differences in their ability to tolerate altitudinal hypoxia.

A sensitivity analysis of the factors that may limit exercise performance identifies high Hb-O2 affinity, together with high total ventilation and high tissue diffusion capacity as the physiological traits that have greatest adaptive benefit for bird flight at extreme high altitude (Scott and Milsom, 2006). Blood O2 affinity is a combination of the intrinsic O2 affinity of the ‘stripped’ (purified) Hb molecules and the interaction of allosteric effectors (like organic phosphates, protons and chloride ions) that decrease Hb-O2 affinity inside the rbcs (Weber and Fago, 2004). Short-term adaptations in O2 affinity are commonly mediated by changes in erythrocytic effectors such as organic phosphates (2,3-diphosphoglycerate, DPG, in mammals, inositol pentaphosphate, IPP, in birds, ATP in reptiles, and ATP and DPG in amphibians), whereas long-term adaptations (that include interspecific ones that are genetically determined) commonly involve changes in Hb structure (amino acid exchanges) that alter Hb’s intrinsic O2 affinity or its sensitivity to allosteric effectors.

Vertebrate Hbs are tetrameric molecules composed of two α (or α-like) chains and two β (or β-like) chains, which in humans consist of 141 and 146 amino acid residues, respectively. Each subunit exhibits a highly characteristic “globin fold” comprised of seven or eight α-helices (labelled A, B, C, etc.) linked by nonhelical (EF, FG) segments, and N- and C-terminal extensions termed NA and HC, respectively. Individual amino acid residues are identified by their sequential positions in chain or/and the helix; thus α1131(H14)-Ser refers to Serine that is the 131st residue of α1 chain and the 14th of the H. During (de-) oxygenation Hb switches between two major structural states:

  1. the high affinity oxygenated R (relaxed) state that prevails at the respiratory surfaces, and
  2. the low affinity, deoxygenated T (tense) state that occurs predominantly in the tissues and is constrained by additional hydrogen bonds and salt bridges.

The Hbs exhibit cooperative homotropic interactions between the O2 binding heme groups (that cause the S-shaped O2 equilibrium curves and increase O2 loading and unloading for a given change in O2 tension) as well as inhibitory, heterotropic interactions between the hemes and the binding sites of effectors that decrease O2 affinity (increase the half-saturation O2 loading tension, P50) and facilitate O2 unloading.

A comparison of Hbs from different species (cf. Perutz, 1983) reveals that variation in the sensitivities to effectors correlates generally with exchanges of very few of the approximately 287 amino acid residues that comprise each αβ dimer. Thus in adult human Hb (HbA) at physiological pH, the majority of the Bohr effect (pH dependence of Hb-O2 affinity that facilitates O2 release in relatively acid working muscles) results from proton binding at the C-terminal residues of the β-chains (β146-His) (cf. Lukin and Ho, 2004). Correspondingly DPG binds to only four β-chain residues (β1-Val, β2-His, β82-Lys and β143-His), CO2 binding (carbamate formation) occurs at the uncharged amino-termini of both chains (α1-Val and β1-Val), and monovalent anions like chloride are considered to bind at one α-chain site (between α1-Val and α131–Ser) and one β-chain site (between  β82-Lys and β1-Val) (cf. Riggs, 1988).

The small number of sites that primarily determine Hb-O2 affinity and its sensitivity to effectors aligns with the neutral theory of molecular evolution (Kimura, 1979), which holds that the majority of amino acid substitutions are non-adaptive and harmless—and facilitates identification of key molecular mechanisms implicated in adaptations at altitude.

The role of effectors in altitude adaptation is aptly illustrated in humans where Hb structure (intrinsic O2 affinity) remains unchanged. Newcomers and permanent residents at moderate altitude (e.g. 2000 m) show increased DPG levels, resulting in a decreased O2 affinity that positions arterial and mixed venous O2 tensions on the steep part of the O2 equilibrium curve, increasing O2 capacitance ([1]bO2) and O2 transport, without materially compromising O2 loading (Turek et al., 1973; Mairbaurl, 1994). The increased DPG correlates with erythropoietin-mediated formation of new rbcs that have higher glycolytic rates and higher DPG and ATP levels than old rbcs. However, faster increases in P50 than in DPG level indicate contributions from other factors, such as chloride and ATP, and Mg ions that neutralize the anionic effectors (Mairbaurl et al., 1993). At higher altitudes (4559 m) increased hyperventilation that drives off CO2 causes respiratory alkalosis (Mairbaurl, 1994). The higher pH increases O2 affinity via the Bohr effect and, offsetting the effect of increased DPG, leads to a similar O2 affinity and arterio-venous O2 saturation  difference as at sea level (Fig.). O2 unloading in the tissues is moreover enhanced by metabolic acidification of capillary blood (Fig.).

Obviously right-shifted curves (that favor O2 unloading) becomes counterproductive at extreme altitudes where O2 loading becomes compromised, predicting that decreased O2 affinity becomes maladaptive under severe hypoxic stress. This is consistent with the observation that a carbamylation-induced increase in blood O2 affinity of rats (that lowers P50 from 27 to 15 mm Hg), increases survival under hypobaric hypoxia equivalent to 9200 meters’ altitude (Eaton et al., 1974). The altitude limit where increased affinity rather than a decreased affinity optimizes tissue O2 supply < 5000 m in man (Samaja et al., 2003)] depends on organismic adaptations (e.g. efficiency of gas exchange) and thus will vary between species. Mammals that permanently inhabit high altitudes and show high blood O2 affinities include the Andean rodent Chinchilla brevicaudata living at 3000–5000 m (blood P50 = 23 mm Hg compared to 38 mm Hg in the rat) (Ostojic et al., 2002). The deer mouse, Peromyscus maniculatus that occurs continuously from sea level to altitudes above 4300 m shows a strong correlation between blood O2 affinity and native altitude (Snyder et al., 1988). That genetically based differences in cofactor levels may contribute to this relationship follows from lower DPG/Hb ratios found in specimens resident, and native to, high altitude than in those from low altitude, after long-term acclimation of both groups to low altitude (Snyder, 1982).

O2 equilibrium curves of human blood illustrating the effects of increases in red cell DPG and pH at high-altitude

O2 equilibrium curves of human blood illustrating the effects of increases in red cell DPG and pH at high-altitude

 

O2 equilibrium curves of human blood illustrating the effects of increases in red cell DPG and pH at high-altitude (4559 m). Solid curves refer to arterial blood (P50 = 26  mm,upper section) and cubical venous blood (P50 = 27.5 mm Hg, lower section); their displacement reflects the Bohr effect. The broken curves depict effects of increased DPG levels (↑DPG) at unchanged pH, increased pH (↑pH) at unchanged DPG, and of decreased tissue pH (↓pH) resulting from higher degrees of metabolic acidification in the tissues. Open and shaded vertical columns indicate O2 unloaded at sea level and 4559 m, respectively, for venous O2 tensions (PvO2) of 25 and 15 mm Hg,respectively [Modified after (Mairbaurl, 1994)].

Camelids. The high blood-O2 affinities in Andean camelids (llama, vicunia, alpaca and guanaco) whose natural habitats exceed 3000 m (Bartels et al., 1963) compared to those of similarly-sized lowland mammals are well-established. In the camelids a β2His→Asn substitution deletes two of the seven DPG contacts in the tetrameric Hb, which increases blood O2 affinity by reducing the DPG effect. Although the intrinsic Hb-O2 affinity is lower in llama than in the related, lowland camel (Bauer et al., 1980), llama blood has a higher O2 affinity due to a three-fold lower DPG-binding than in camel Hb that has the same DPG binding sites as humans (Bauer et al., 1980). In vicunia, a higher O2 affinity than in llama (that has identical β-chains), correlates with the α130Ala→Thr substitution, which introduces a hydroxyl polar group that predictably reduces the chloride binding at adjacent α131Asn residue .

Sheep and goats commonly express two isoforms, HbA and HbB. The heterogeneity is controlled by two autosomal alleles with codominant expression. Whereas individuals expressing HbA have higher blood-O2 affinity than those that express HbB, heterozygotes that express both forms at equimolar concentrations in the same erythrocytes show intermediate affinity. Anemic blood loss induces switching from HbA to HbC that has a similarly high affinity. Hbs A, B and C have identical α-chains but different β[1]-chains. It appears unknown whether altitudinal exposure (which like anemia, induces tissue hypoxia) modulates Hb heterogeneity via selective expression of specific β-chains.

Compared to most mammals that possess one major adult and one major fetal Hb, yak, Poephagus (=Bos) grunniens, a native to altitudes of 3000–6000 m in Tibet, Nepal and Bhutan, has two or four major adult Hbs and two major fetal Hbs. These Hbs exhibit higher intrinsic affinities than closely-related bovine Hb, marked DPG sensitivities and, exceptional amongst mammals, differentiated O2 affinities that indicates an extended range of ambient O2 tensions (and altitudes) in which the composite Hb functions.

(Not shown).  Representation of interchain contacts considered to underly differentiated O2 affinities in Rueppell’s griffon isoHbs A, A , D and D that have identical β- chains but different α- chains. Accordingly the van der Waal’s contact between β134Ile and β1125-Asp in Hbs A , D and D stabilizes the low-affinity, T-state less strongly than the H-bond between Thr 134 and β1125-Asp and thus increases O2 affinity in Hbs A, D and D. Analogously, the hydrogen bonds between α138-β297/99 that stabilize the high-affinity oxystructure (raising O2 affinity in isoHbs D and D) cannot form in HbA and HbA that have Pro at α138.

Ostriches, the largest extant birds, exhibit a β2His→Gln exchange (that reduces phosphate interaction). They moreover ‘use’ ITP (inositol phosphate) that carries fewer negative charges, and predictably has lesser allosteric effect, than IPP (Isaacks et al., 1977), predicting a high blood O2 affinity that is compatible with ‘scaling’ and (as in elephants) increases high altitude tolerance.

Whereas some adult birds express one major iso-Hb (HbA), the majority of species, reportedly all that fly at high altitudes (Hiebl et al., 1987), also express a less abundant HbD. HbD has the same β-chains as HbA but different α-chains (αD) and exhibits higher O2 affinities (Huisman et al., 1964). There is no consistent evidence for hypoxia-induced changes in HbD expression.

An example of how “molecular anatomy is just as key to understanding molecular adaptation as phylogeny and physiological ecology” (Golding and Dean, 1998) is Hb of the high-altitude tolerant bar-headed goose that has a sharply higher blood O2 affinity than that of the closely related graylag goose that is restricted to lower altitudes (P50 = 29.7 and 39.5mmHg at 37 ◦C and pH 7.4). The Hbs differ by only four (greylag→bar-headed) amino acid exchanges: α18Gly→Ser, α63Ala→Val, β125Glu→Asp and α119Pro→Ala. The last mentioned exchange that is unique in birds, predictably increases O2 affinity, by deleting a contact between α1119 and β155 that destabilizes the T-structure (Perutz, 1983). Moreover, Andean ‘goose’ Hb that also has high blood O2 affinity shows β55 Leu→Ser that deletes the same contact. Significantly, two human Hb mutants (α119Pro–Ala and β155Met→Ser) engineered by site-directed mutagenesis to mimic the mutations found in bar-headed and Andean geese possess markedly higher O2 affinities than native HbA.

Although “the study of molecular adaptation has long been fraught with difficulties not the least of which is identifying out the hundreds of amino acid replacements, those few directly responsible for major adaptations” Hb’s adaptations to high altitude are a prime example of how “an amino acid replacement of modest effect at the molecular level causes a dramatic expansion in an ecological niche” [quotations from (Golding et al., 1998)].

However, the pathway of molecular O2 from the respiratory medium to the cellular combustion sites via the Hb molecules is regulated by a symphony of supplementary adaptations that span different levels of biological organization, each of which (according to the principle of symmorphosis) may become maximally recruited in extreme cases (as in birds actively flying above 10,000 m). Apart from hyperventilation, that appears to occur ubiquitously (and increases blood O2 affinity via increased pH), different species subjected to less extreme hypoxic stress utilize different adaptations among the arsenal of organismic, cellular and molecular strategies that favor efficient aerobic utilization of the scarce O2 available at high altitude. No clear correlations exist between the adaptive strategies recruited by different animals on the one hand, and their phylogenetic position, mode of life or ecological niches on the other. An overall limitation is that short-term adaptive adjustments in O2 affinity (that may occur within individual animals) necessarily involves rapid adaptive responses, such as changes in the levels of erythrocytic effectors, whereas the long-term acclimations that have accumulated in permanent high-altitude dwellers during evolutionary development.

Genetic Diversity of Microsatellite DNA Loci of Tibetan Antelope (Chiru, Pantholops hodgsonii) in Hoh Xil National Nature Reserve, Qinghai, China

Hui Zhou, Diqiang Li, Yuguang Zhang, Tao Yang, Yi Liu
J Genetics and Genomics (Formerly Acta Genetica Sinica) 2007; 34(7): 600-607

The Tibetan antelope (Pantholops hodgsonii), indigenous to China, became an endangered species because of considerable reduction both in number and distribution during the 20th century. Presently, it is listed as an AppendixⅠspecies by CITES and as CategoryⅠ by the Key Protected Wildlife List of China. Understanding the genetic diversity and population structure of the Tibetan antelope is significant for the development of effective conservation plans that will ensure the recovery and future persistence of this species. Twenty-five microsatellites were selected to obtain loci with sufficient levels of polymorphism that can provide in-formation for the analysis of population structure. Among the 25 loci that were examined, nine of them showed high levels of genetic diversity. The nine variable loci (MCM38, MNS64, IOBT395, MCMAI, TGLA68, BM1329, BMS1341, BM3501, and MB066) were used to examine the genetic diversity of the Tibetan antelope (n = 75) in Hoh Xil National Nature Reserve(HXNNR), Qinghai, China. The results obtained by estimating the number of population suggested that all the 75 Tibetan antelope samples were from the same population. The mean number of alleles per locus was 9.4 ± 0.5300 (range, 7–12) and the mean effective number of alleles was 6.519 ± 0.5271 (range, 4.676–9.169). The observed mean and expected heterozygosity were 0.844 ± 0.0133 (range, 0.791–0.897) and 0.838 ± 0.0132 (range, 0.786–0.891), respectively. Mean Polymorphism Information Content (PIC) was 0.818 ± 0.0158 (range, 0.753–0.881). The value of Fixation index (Fis) ranged from −0.269 to −0.097 with the mean of −0.163 ± 0.0197. Mean Shannon’s information index was 1.990 ± 0.0719 among nine loci (range, 1.660–2.315). These results provide baseline data for the evaluation of the level of genetic variation in Tibetan antelope, which will be important for the development of conservation strategies in future.

Expression profiling of abundant genes in pulmonary and cardiac muscle tissues of Tibetan Antelope (Pantholops hodgsonii)

Xiaomei Tong, Yingzhong Yang, Weiwei Wang, Zenzhong Bai, et al.
Gene 523 (2013) 187–191
http://dx.doi.org/10.1016/j.gene.2013.03.011

The Tibetan Antelope (TA), which has lived at high altitude for millions of years, was selected as the model species of high hypoxia-tolerant adaptation. Here we constructed two cDNA libraries from lung and cardiac muscle tissues, obtained EST sequences from the libraries, and acquired extensive expression data related energy metabolism genes. Comparative analyses of synonymous (Ks) and nonsynonymous (Ka) substitution rates of nucleus-encoded mitochondrial unigenes among different species revealed that many antelope genes have undergone rapid evolution. Surfactant-associated protein A (SP-A) and surfactant-associated protein B (SP-B) genes in the AT lineage experienced accelerated evolution compared to goat and sheep, and these two genes are highly expressed in the lung tissue. This study suggests that many specific genes of lung and cardiac muscle tissues showed unique expression profiles and may undergo fast adaptive evolution in TA. These data provide useful information for studying on molecular adaptation to high-altitude in humans as well as other mammals.

Exogenous Sphingosine-1-Phosphate Boosts Acclimatization in Rats Exposed to Acute Hypobaric Hypoxia: Assessment of Haematological and Metabolic Effects

Sonam Chawla, Babita Rahar, Mrinalini Singh, Anju Bansal, et al.
PLoS ONE 9(6): e98025. http://dx.doi.org:/10.1371/journal.pone.0098025

Background: The physiological challenges posed by hypobaric hypoxia warrant exploration of pharmacological entities to improve acclimatization to hypoxia. The present study investigates the preclinical efficacy of sphingosine-1-phosphate (S1P) to improve acclimatization to simulated hypobaric hypoxia. Experimental Approach: Efficacy of intravenously administered S1P in improving hematological and metabolic acclimatization was evaluated in rats exposed to simulated acute hypobaric hypoxia (7620 m for 6 hours) following S1P pre-treatment for three days. Major Findings: Altitude exposure of the control rats caused systemic hypoxia, hypocapnia (plausible sign of hyperventilation) and respiratory alkalosis due to suboptimal renal compensation indicated by an overt alkaline pH of the mixed venous blood. This was associated with pronounced energy deficit in the hepatic tissue along with systemic oxidative stress and inflammation. S1P pre-treatment improved blood oxygen-carrying-capacity by increasing hemoglobin, hematocrit, and RBC count, probably as an outcome of hypoxia inducible factor-1a mediated  erythropoiesis and renal S1P receptor 1 mediated hemoconcentation. The improved partial pressure of oxygen in the blood could further restore aerobic respiration and increase ATP content in the hepatic tissue of S1P treated animals. S1P could also protect the animals from hypoxia mediated oxidative stress and inflammation. Conclusion: The study findings highlight S1P’s merits as a preconditioning agent for improving acclimatization to acute hypobaric hypoxia exposure. The results may have long term clinical application for improving physiological acclimatization of subjects venturing into high altitude for occupational or recreational purposes.

S1P Stabilizes HIF-1a and Boosts HIF-1a Mediated Hypoxia Adaptive Responses

S1P pre-conditioning led to 1.9 fold higher HIF-1a level in the kidney tissue (p<0.001) and 1.3 fold higher HIF-1a level in the liver tissue (p<0.001) in 1 mg/kg b.w. S1P group than in hypoxia control group. However, the hypoxia control group also had 1.3 folds higher HIF-1a levels in both liver and kidney tissues than in normoxia control groups, indicating a non-hypoxic boost of HIF-1a in S1P treated animals (Figure 1a and b). Further, plasma Epo levels were also observed to be significantly higher following S1P pre-treatment compared to the hypoxia control groups (p=0.05) (Figure 1a). Epo being primarily secreted by the kidneys and its expression being under regulation of HIF-1a, the raised plasma Epo level could be attributed to higher HIF-1a level in the kidney.

Figure 1. (not shown) Effect of S1P treatment on HIF-1a accumulation and downstream gene expression. a) Renal HIF-1a accumulation and Epo accumulation in plasma. HIF-1a accumulation in the renal tissue homogenate and build-up of erythropoietin in plasma was quantified. b) Hepatic HIF-1a accumulation. c) Effect S1P pre-treatment on circulatory VEGF. Vascular endothelial growth factor (VEGF) was quantified in plasma of experimental animals. These estimations were carried out using sandwich ELISA, and were carried out in triplicates for each experimental animal. Values are representative of mean 6 SD (n = 6). Statistical significance was calculated using ANOVA/post hoc Bonferroni. NC: Normoxia control, HC: Hypoxia control, 1: 1 mg S1P/kg b.w., 10: 10 mg S1P/kg b.w., 100: 100 mg S1P/kg b.w.,  p<0.05 compared with the normoxic control, p<0.01 compared with the normoxic control, p<0.001 compared with the normoxic control,  p<0.05 compared with the hypoxic control,  p<0.01 compared with the hypoxic control,  p<0.001 compared with the hypoxic control. http://dx.doi.org:/10.1371/journal.pone.0098025.g001

Figure 2.(not shown)  Effect of S1P treatment on S1P1 expression in renal tissue. Representative immune-blot of S1P1. Densitometric analysis of blot normalized against the loading control (α-tubulin). Values are representative of mean 6 SD (n = 6). Statistical significance was calculated using ANOVA/post hoc Bonferroni. NC: Normoxia control, HC: Hypoxia control, 1: 1 mg S1P/kg b.w., 10: 10 mg S1P/kg b.w., 100: 100 mg S1P/kg b.w.,  p<0.05 compared with the normoxic control,  p<0.01 compared with the normoxic control, p<0.001 compared with the normoxic control, p< 0.05 compared with the hypoxic control, p<0.01 compared with the hypoxic control, p<0.001 compared with the hypoxic control. http://dx.doi.org:/10.1371/journal.pone.0098025.g002

Cloning of hypoxia-inducible factor 1α cDNA from a high hypoxia tolerant mammal—plateau pika (Ochotona curzoniae)

T.B. Zhao, H.X. Ning, S.S. Zhu, P. Sun, S.X. Xu, Z.J. Chang, and X.Q. Zhao
Biochemical and Biophysical Research Communications 316 (2004) 565–572
http://dx.doi.org:/10.1016/j.bbrc.2004.02.087

Hypoxia-inducible factor 1 is a transcription factor composed of HIF-1α and HIF-1β. It plays an important role in the signal transduction of cell response to hypoxia. Plateau pika (Ochotona curzoniae) is a high hypoxia-tolerant and cold adaptation species living only at 3000–5000m above sea level on the Qinghai-Tibet Plateau. In this study, HIF-1α cDNA of plateau pika was cloned and its expression in various tissues was studied. The results indicated that plateau pika HIF-1α cDNA was highly identical to those of the human (82%), bovine (89%), mouse (82%), and Norway rat (77%). The deduced amino acid sequence (822 bp) showed 90%, 92%, 86%, and 86% identities with those of the human, bovine, house mouse, and Norway rat, respectively. Northern blot analyses detected two isoforms named pLHIF-1α and pSHIF-1α. The HIF-1α mRNA was highly expressed in the brain and kidney, and much less in the heart, lung, liver, muscle, and spleen, which was quite different from the expression pattern of mouse mRNA. Meanwhile, a new variant of plateau pika HIF-1α mRNA was identified by RT-PCR and characterized. The deduced protein, composed of 536 amino acids, lacks a part of the oxygen-dependent degradation domain (ODD), both transactivation domains (TADs), and the nuclear localization signal motif (NLS). Our results suggest that HIF-1α may play an important role in the pika’s adaptation to hypoxia, especially in brain and kidney, and pika HIF-1α function pattern may be different from that of mouse HIF-1α. Furthermore, for the high ratio of HIF-1α homology among the animals, the HIF-1α gene may be a good phylogenetic performer in recovering the true phylogenetic relationships among taxa.

Comparative Proteomics Analyses of Kobresia pygmaea Adaptation to Environment along an Elevational Gradient on the Central Tibetan Plateau

Xiong Li, Yunqiang Yang, Lan Ma, Xudong Sun, et al.
PLoS ONE 9(6): e98410. http://dx.doi.org:/10.1371/journal.pone.0098410

Variations in elevation limit the growth and distribution of alpine plants because multiple environmental stresses impact plant growth, including sharp temperature shifts, strong ultraviolet radiation exposure, low oxygen content, etc. Alpine plants have developed special strategies to help survive the harsh environments of high mountains, but the internal mechanisms remain undefined. Kobresia pygmaea, the dominant species of alpine meadows, is widely distributed in the Southeastern Tibet Plateau, Tibet Autonomous Region, China. In this study, we mainly used comparative proteomics analyses to investigate the dynamic protein patterns for K. pygmaea located at four different elevations (4600, 4800, 4950 and 5100 m). A total of 58 differentially expressed proteins were successfully detected and functionally characterized. The proteins were divided into various functional categories, including material and energy metabolism, protein synthesis and degradation, redox process, defense response, photosynthesis, and protein kinase. Our study confirmed that increasing levels of antioxidant and heat shock proteins and the accumulation of primary metabolites, such as proline and abscisic acid, conferred K. pygmaea with tolerance to the alpine environment. In addition, the various methods K. pygmaea used to regulate material and energy metabolism played important roles in the development of tolerance to environmental stress. Our results also showed that the way in which K. pygmaea mediated stomatal characteristics and photosynthetic pigments constitutes an enhanced adaptation to alpine environmental stress. According to these findings, we concluded that K. pygmaea adapted to the high-elevation environment on the Tibetan Plateau by aggressively accumulating abiotic stress related metabolites and proteins and by the various life events mediated by proteins. Based on the species flexible physiological and biochemical processes, we surmised that environment change has only a slight impact on K. pygmaea except for possible impacts to populations on vulnerable edges of the species’ range
Altered mitochondrial biogenesis and its fusion gene expression is involved in the high-altitude adaptation of rat lung

Loganathan Chitra, Rathanam Boopathy
Respiratory Physiology & Neurobiology 192 (2014) 74– 84
http://dx.doi.org/10.1016/j.resp.2013.12.007

Intermittent hypobaric hypoxia-induced preconditioning (IHH-PC) of rat favored the adaption of lungs to severe HH conditions, possibly through stabilization of mitochondrial function. This is based on the data generated on regulatory coordination of nuclear DNA-encoded mitochondrial biogenesis; dynamics,and mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mt-OXPHOS) genes expression. At16th day after start of IHH-PC (equivalent to 5,000 m, 6 h/d, 2 w of treatment), rats were exposed to severe HH stimulation at 9142 m for 6 h. The IHH-PC significantly counteracted the HH-induced effect of increased lung: water content; tissue damage; and oxidant injury. Further, IHH-PC significantly increased the mitochondrial number, mtDNA content and mt- OXPHOS complex activity in the lung tissues. This observation is due to an increased expression of genes involved in mitochondrial biogenesis (PGC-1α,ERRα, NRF1, NRF2 and TFAM), fusion (Mfn1 and Mfn2) and mt OXPHOS. Thus, the regulatory pathway formed by PGC-1α/ERRα/Mfn2 axes is required for the mitochondrial adaptation provoked by IHH-PC regimen to counteract subsequent HH stress.

Molecular characteristics of Tibetan antelope (Pantholops hodgsonii) mitochondrial DNA control region and phylogenetic inferences with related species

  1. Feng, B. Fan, K. Li, Q.D. Zhang, et al.
    Small Ruminant Research 75 (2008) 236–242
    http://dx.doi.org:/10.1016/j.smallrumres.2007.06.011

Although Tibetan antelope (Pantholops hodgsonii) is a distinctive wild species inhabiting the Tibet-Qinghai Plateau, its taxonomic classification within the Bovidae is still unclear and little molecular information has been reported to date. In this study of Tibetan antelope, the complete control regions of mtDNA were sequenced and compared to those of Tibetan sheep (Ovis aries) and goat (Capra hircus). The length of the control region in Tibetan antelope, sheep and goat is 1067, 1181/1106 and 1121 bp, respectively. A 75-bp repeat sequence was found near the 5’ end of the control region of Tibetan antelope and sheep, the repeat numbers of which were two in Tibetan antelope and three or four in sheep. Three major domain regions, including HVI, HVII and central domain, in Tibetan antelope, sheep and goat were outlined, as well as other less conserved blocks, such as CSB-1, CSB-2, ETAS-1 and ETAS-2. NJ cluster analysis of the three species revealed that Tibetan antelope was more closely related to Tibetan sheep than Tibetan goat. These results were further confirmed by phylogenetic analysis using the partial control region sequences of these and 13 other antelope species. Tibetan antelope is better assigned to the Caprinae rather than the Antilopinae subfamily of the Bovidae.

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