Fluid shear stress in prosthetic heart valves

A semiempirical approach has been developed to estimate the fluid shear stress developing between the valve seat and moving poppet during the opening sequence of an aortic ball valve and a disk valve prosthesis. The assumption of laminar quasi-steady flow is shown to be conservative. The laminar shear stresses calculated by this method are large, and exceed threshold levels for incipient hemolysis. Results are compared to a circular-orifice valve, for which much lower shear stresses are evident. Paravalvular leaks are considered as well, and shear stresses derived from a turbulent free-jet analysis indicate that such leaks could lead to incipient hemolysis if significant pressure drops occur across the leak. The overall results indicate that prosthetic heart valves tend to generate a condition of mild chronic hemolysis, a condition that may not be as innocuous as has been assumed in the past.