Velocity and Shear Stress Distribution Downstream of Mechanical Heart Valves in Pulsatile Flow

Abstract

Ten mechanical valves (TAD 27 mm): Starr-Edwards Silastic Ball, Björk-Shiley Standard, Björk-Shiley Concave-Convex, Björk-Shiley Monostrut, Hall-Kaster (Medtronic-Hall), OmniCarbon, Bicer Val, Sorin, Saint-Jude Medical and Hemex (Duromedics) are investigated in a comparative in vitro study. The velocity and turbulent shear stress profiles of the valves were determined by Laser Doppler anemometry in two different downstream axes within a model aortic root. Depending on the individual valve design, velocity peaks up to 1.5 m/s and turbulent shear stress peaks up to 150 N/m² were measured during the systolic phase. These shear stress peaks mainly occurred in areas of flow separation and intense momentum exchange. Directly downstream of the valves (measuring axis 0.55.d_Aorta) turbulent shear stress peaks occurred at peak systole and during the deceleration phase, while in the second measuring axis (1.5.d_Aorta) turbulence levels were lower. Shear stress levels were high at the borders of the fluid jets. The results are discussed from a fluid-dynamic point of view.