In Vitro Fluid Dynamics of St. Jude, Ionescu-Shiley and Carpentier-Edwards Aortic Heart Valve Prostheses
In the study reported here the in vitro fluid dynamic characteristics of the St. Jude (mechanical bi-leaflet), Carpentier-Edwards (porcine) and Ionescu-Shiley (calf pericardial) aortic valve prostheses were investigated. The experiments conducted were (a) pressure drop measurements, (b) preliminary photography of the opening of the tissue valve leaflets, and (c)velocity and shear stress measurements. The pressure drop, velocity and shear stress measurements were conducted under steady flow conditions, while the preliminary photography studies were conducted under steady and pulsatile flow conditions. The pressure drop results indicated that the St. Jude and Hall-Kaster valves have the lowest pressure drops compared to any of the other valves used clinically at present. The two bioprostheses had larger pressure drops than would be expected for their basic designs. The smaller sizes of the Carpentier-Edwards valve had excessively large pressure-drops. The photographs of the opening of the valve leaflets indicated that the two bioprostheses do not open as ideally as the natural aortic valve. It was also observed that the Ionescu-Shiley aortic valves opened more symmetrically and with reproducability than the corresponding Carpentier-Edwards valves.
Detailed velocity and shear stress measurements were made with a laser-Doppler anemometer system. These measurements indicated that the flow that emerged from the leaflets of both types of tissue valves was jet-like and could lead to turbulent shear stresses on the order of 1000–3000 dynes /cm2. Such turbulent shear stresses could be harmful to blood components. The jet type flow could also damage the the wall of the ascending aorta. Velocity measurements in the immediate downstream vicinity of the St. Jude valve showed that the flow field which emerged from the valve was centralized. The velocity measurements also indicated that there was a region of flow separation adjacent to the vessel wall and immediately downstream from the sewing ring. Such a region of flow separation could lead to excessive tissue overgrowth along the aortic side of the sewing ring. All three types of valve designs, however, created relatively low wall shear stresses on the order of 100–600 dynes/cm2. This result is definitely a positive aspect of these valves when you consider that most of the rigid aortic prostheses we have studied created wall shears on the order of 1000–3000 dynes/cm2.
KeywordsHeart Valve Valve Leaflet Prosthetic Heart Valve Turbulent Shear Stress Pressure Drop Measurement
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