EFFECTS OF TILTING DISK HEART-VALVE GAP WIDTH ON REGURGITANT FLOW-THROUGH AN ARTIFICIAL-HEART MITRAL-VALVE

While many investigators have measured the turbulent stresses associat ed with forward flow through tilting disk heart valves, only recently has attention been given to the regurgitant jets formed as fluid is sq ueezed through the gap between the occluder and housing of a closed va lve. The objective of this investigation was to determine the effect o f gap width on the turbulent stresses of the regurgitant jets through a Bjork-Shiley monostrut tilting disk heart valve seated in the mitral position of a Penn State artificial heart. A 2 component laser-Dopple r velocimetry system with a temporal resolution of 1 ms was used to me asure the instantaneous velocities in the regurgitant jets in the majo r and minor orifices around the mitral valve. The gap width was contro lled through temperature variation by taking advantage of the large di fference between the thermal expansion coefficients of the Delrin occl uder and the Stellite housing of Bjork-Shiley monostrut valves. The tu rbulent shear stress and mean (ensemble averaged) velocity were incorp orated into a model of red blood cell damage to assess the potential f or hemolytic damage at each gap width investigated. The results reveal ed that the minor orifice tends to form stronger jets during regurgita nt flow than the major orifice, indicating that the gap width is not u niform around the circumference of the valve. Based on the results of a red blood cell damage model, the hemolytic potential of the mitral v alve decreases as the gap width increases. This investigation also est ablished that the hemolytic potential of the regurgitant phase of valv e operation is comparable to, if not greater than, the hemolytic poten tial of forward flow, consistent with experimental data on hemolysis.