In vitro pulsatile flow measurements in the vicinity of mechanical heart valves in the mitral flow chamber.

A three-beam laser Doppler anemometer system was used to study the flow fields created by various types of mitral heart valve prostheses under conditions of physiological pulsatile flow. The prosthetic valves studied were the Beall caged-disc valve, Björk-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 elevated turbulent shear stresses and regions of flow separation and/or stagnation. The maximum turbulent shear stresses measured were 1900 dynes/cm2 for the Beall valve, 380 dynes/cm2 for the Björk-Shiley valve, 1800 dynes/cm2 for the Medtronic-Hall valve, and 770 dynes/cm2 for the St. Jude valve. These elevated turbulent shear stresses could cause sublethal and/or lethal damage to red cells and platelets. The regions of flow separation and/or stagnation could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on clinically recovered prosthetic valves.