Mechanisms of mechanical heart valve cavitation in an electrohydraulic total artificial heart

Until now, we have estimated cavitation for mechanical heart valves (MHV) mounted in an electrohydraulic total artificial heart (EHTAH) with tap water as a working fluid. However, tap water at room temperature is not a proper substitute for blood at 37 degrees C. We therefore investigated MHV cavitation using a glycerin solution that was identical in viscosity and vapor pressure to blood at body temperature. In this study, six different kinds of monoleaflet and bileaflet valves were mounted in the mitral position in an EHTAH, and we investigated the mechanisms for MHV cavitation. The valve closing velocity, pressure drop measurements, and a high-speed video camera were used to investigate the mechanism for MHV cavitation and to select the best MHV for our EHTAH. The closing velocity of the bileaflet valves was slower than that of the monoleaflet valves. Cavitation bubbles were concentrated on the edge of the valve stop and along the leaflet tip. It was established that squeeze flow holds the key to MHV cavitation in our study. Cavitation intensity increased with an increase in the valve closing velocity and the valve stop area. With regard to squeeze flow, the Björk-Shiley valve, because it is associated with slow squeeze flow, and the bileaflet valve with low valve closing velocity and small valve stop areas are better able to prevent blood cell damage than the monoleaflet valves.