Statistical Correlation Between Transient Pressure Drop and Cavitation at Closure of a Mechanical Heart Valve

Effects of leaflet geometry on the flow field in three bileaflet valves when installed in a pneumatic ventricular assist device

Our group is currently developing a pneumatic ventricular assist device (PVAD). In this study, in order to select the optimal bileaflet valve for our PVAD, three kinds of bileaflet valve were installed and the flow was visualized downstream of the outlet valve using the particle image velocimetry (PIV) method. To carry out flow visualization inside the blood pump and near the valve, we designed a model pump that had the same configuration as our PVAD. The three bileaflet valves tested were a 21-mm ATS valve, a 21-mm St. Jude valve, and a 21-mm Sorin Bicarbon valve. The mechanical heart valves were mounted at the aortic position of the model pump and the flow was visualized by using the PIV method. The maximum flow velocity was measured at three distances (0, 10, and 30 mm) from the valve plane. The maximum flow velocity of the Sorin Bicarbon valve was less than that of the other two valves; however, it decreased slightly with increasing distance it the X-Y plane in all three valves. Although different bileaflet valves are very similar in design, the geometry of the leaflet is an important factor when selecting a mechanical heart valve for use in an artificial heart.

Effects of the driving condition of a pneumatic ventricular assist device on the cavitation intensity of the inlet and outlet mechanical heart valves

Our group is currently developing a pneumatic ventricular assist device (PVAD), and in previous studies, we reported the mechanical heart valve (MHV) cavitation intensity at the inlet valve in the PVAD only. In this study, we investigated the effect of the running conditions on the cavitation intensity both for the inlet and outlet valve in the PVAD using an acoustic signal. A 23-mm Medtronic Hall valve with an opening angle of 70 degrees was mounted in the inlet and outlet port of the PVAD after removing the sewing ring. A mini pressure sensor with high frequency was mounted 15 mm downstream from the inlet valve and downstream from the outlet valve. The pressure signal was band-pass filtered between 35 and 500 kHz using a digital filter. The band-pass filtered root mean squared (RMS) pressure was used as an index of the cavitation intensity. The RMS pressure of the inlet valve was higher than that of the outlet valve. Even if the outlet valve has a lower RMS pressure than the inlet valve, cavitation occurs. In case of a full-filling and full-ejection condition, the RMS pressure of the inlet valve was higher than that of the partial-filling and partial-ejection condition. This means that a partial-filling and partial-ejection condition is best to prevent the hemolysis caused by the cavitation phenomenon and the damage to the valve surface in our PVAD system.