Pulsatile flow velocity and shear stress measurements on the St. Jude bileaflet valve prosthesis.

The velocity and turbulent shear stress fields in the immediate vicinity of the St. Jude bileaflet valve were measured under pulsatile flow conditions with a two-dimensional laser Doppler anemometer system. The valve was studied in both aortic and mitral positions. In both positions, the valve created relatively centralized flow fields. However, a major portion of the flow occurred through the two side orifices. Regions of flow separation were observed adjacent to the valve sewing ring in the area of the valve pivot (hinge) mechanism. Elevated turbulent shear stresses were measured in both positions. Peak values of 760 dynes/cm2 and 2 000 dynes/cm2 were observed in the mitral and aortic flow chambers, respectively. Such turbulent shears could cause sublethal and/or lethal damage to blood elements. The regions of flow separation adjacent to the pivot mechanism could lead to tissue overgrowth and/or thrombus formation, which in turn could impede proper motion of the valve leaflets.