In vitro pulsatile flow velocity and turbulent shear stress measurements in the vicinity of mechanical aortic heart valve prostheses.

A two-dimensional laser Doppler anemometer system was used to study the velocity and turbulent shear stress fields created by various types of mechanical aortic heart valve prostheses under physiological pulsatile flow conditions. The prosthetic valves studied were the Starr-Edwards caged ball valve, Bjork-Shiley tilting disc valve, Medtronic-Hall tilting disc valve, and St. Jude bileaflet valve. The results indicate that all four prosthetic valve designs studied create very disturbed flow fields with regions of flow separation and/or stagnation and regions of elevated turbulent shear stress. The maximum values of the mean turbulent shear stresses measured during peak systole were 1200 dynes/cm2 for the Starr-Edwards valve, 1600 dynes/cm2 for the Bjork-Shiley valve, 1000 dynes/cm2 for the Medtronic-Hall valve, and 1050 dynes/cm2 for the St. Jude valve. The corresponding values during the deceleration phase were about 800, 600, 450 and 800 dynes/cm2, respectively. These elevated turbulent shear stresses could cause sublethal and/or lethal damage to blood elements, and, together with the regions of flow separation and/or stagnation, could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on the clinically recovered prosthetic valves.