Three-component laser Doppler velocimetry measurements in the regurgitant flow region of a Björk-Shiley monostrut mitral valve.

Three-dimensional laser Doppler velocimetry measurements were acquired in a mock-circulatory loop proximal to a Björk-Shiley monostrut valve in the mitral position, and synchronous ensemble-averaging was applied to form an "average" beat. Two axial locations in the regurgitant flow region of the valve (in the minor orifice) were mapped, and maximum Reynolds shear stresses were calculated. A large spike in regurgitant flow was noted at the beginning of systole, which may be the squeeze flow phenomenon computed by other researchers. A region of sustained regurgitant flow 50 msec later was the focus of this study. Maximum velocities of approximately 3.7 mps were noted, and maximum Reynolds shear stresses of approximately 10,000 dyne/cm2 were calculated. Comparisons were made of two-dimensional (ignoring tangential component) versus three-dimensional shear stresses, and, in this case, in regions of high stress, the differences were insignificant. This suggests that the tangential component of velocity can probably be ignored in similar measurements where the tangential velocity is likely to be small.