Leaders in Pharmaceutical Business Intelligence (LPBI) Group

ONE Critical Medical Device: Aortic Valve Prosthesis — The Inventor Perspective on Design

Author: Carl Goosen, Goosen Enterprises, LLC, CEO

The Aortic Prosthesis

For 18 months after he started using my mitral valve, Christiaan Barnard demanded an aortic prosthesis.”Everybody uses the same valve and just changes the sewing ring” My reply: That is not the way to go.Just look at the natural valves, they have opposite functions. The aortic has high pressure and high velocity, the mitral low pressure and velocity” When I try to solve a problem, I have found it is better to leave it on the “corner of my mind “ and the answer will hit me suddenly.

In our day it was normal to have only one car. My wife needed it and I decided to walk the mile and a half to work. As I walked up the hill to the hospital with the winter sun beating on my neck, it hit me. It was a Thursday and we did not have a case. I stood still and sketched my idea on the back of a cigarette carton. I have lost the souvenir long since. On Sunday evening I was sewing the cushion on a complete new aortic prosthesis.

Barnard had an engineer brother attached to the Salt River Railway workshops capable of the most sophisticated engineering. They built complete steam locomotives. I believe they had a staff of about a thousand. He was in charge of a program trying to prevent smokestacks from starting fires in the countryside. He had connection with the Minister of Railways who gave them permission to make the valve ostensibly as an emergency life saving device. I sat for 3 hours with engineers and draftsmen turning my design into reality. Finally I passed the drawings and gave over control to 15 top tool and die makers and 5 machinists. They worked round the clock in 8-hour shifts while I cat-napped in an office. The molds for the silicone poppets and the manufacture of the stainless steel frames were ready by 4pm Sunday. By evening I had the poppets ready and vulcanized. I sewed on the sewing cushions and assembled the first units (3 sizes). Surgery was done Monday at 8 am.This is the original design which was used for many years. We have discovered patients who had long term survival with no problems. ( Both had been anticoagulated unnecessarily) in whom the valve had functioned perfectly. One in Bloemfontein South Africa had the valve explanted in error since a new (other) valve did not relieve her rheumatic heart ( the reason for her original valve implant) The valve had functioned well for 34 years. I have this valve in my possession and believe it can outlive any patient.

The other long term was found in Athens, Greece. She had her valve for 37 years when first reported. Her valve was shown to be functioning perfectly. She had surgery scheduled for mitral stenosis at the 38 year mark but succumbed to a botched intubation. We were not able to receive the specimen. ( Enclosed X-rays show perfect function of my valve) Both these patients had my valve inserted by Christiaan Barnard at the Groote Schuur Hospital, Cape Town, South Africa in 1970.

It is time to discuss the reason for my aortic valve design. Everything begins with the Starr-Edwards ball-in-cage design. The primary lesion is aortic stenosis. The maximum orifice that can be squeezed out of the space is the question. Early models of the S-E had problems where the ball got stuck with fatal results. I thought of enlarging the orifice and having projections into it to stop the ball from sticking but under constant pressure to get somewhere, abandoned it. Enlarging the ball diameter and using a segment of a sphere seemed a good idea. Since the required flow is about 80 cc in about three-tenths of a second a streamlined poppet becomes essential. I achieved this by mounting a cone on a segment of a sphere. To control the poppet it has two poles. These are held in place by two small rings held by arms above and below. These guide poles assist in the streamline by steering the flow during systole and pulling it together in the ventricle. I also liked the streamline to feed the coronary flow entry during diastole.

This is a very brief summary which should be exposed to qualified engineers .

Carl Goosen