Velocity measurements were made in vitro using a laser-Doppler anemometer downstream from prosthetic aortic heart valves with distinctly different designs. The valves studied were an Ionescu-Shiley tri-leaflet bioprosthesis, a Björk-Shiley convexo-concave tilting-disc prosthesis, a Smeloff caged-ball prosthesis, and a St. Jude bi-leaflet prosthesis. Velocity measurements were made in steady and in pulsatile flow using a Newtonian fluid with a viscosity of 0.001 kg/ms. Velocity components in all three coordinate directions were measured at 305 locations distibuted systematically across a cross section of the flow system at an axial distance of 31.8 mm downstream from the valve mount. This systematic approach to the data acquisition allowed a detailed analysis of the disturbed flow fields generated by each of the four valves. Large shear stresses were estimated in the bulk flow which were potentially hemolytic and which could potentially activate platelet chemical-release reactions.
A well-controlled, comparative analysis of the steady-flow and pulsatile-flow velocity results revealed that measurements made in steady flow could be used to approximate the dynamics of pulsatile flow during the middle of the pulse cycle only. Shear stresses estimated for steady flow were found to be an upper bound on those estimated for pulsatile flow.
A comparison of the pressure-drop and regurgitant-flow characteristics of these four valves showed that there was a significant range in the hydrodynamic performance of these prostheses. The St. Jude prosthesis generated the lowest pressure drop among the four valves studied while the Smeloff prosthesis generated the largest. The St. Jude prosthesis also allowed the least amount of regurgitant flow of the three valve designs which, when closed, did not totally occlude their orifice for flow. Because it has a totally-occluding design, the lonescu-Shiley bioprosthesis allowed the least regurgitant flow of the valves studied. The Smeloff prosthesis allowed the largest amount of regurgitant flow of the valves studied.
