Effect of systolic duration on mechanical heart valve cavitation in a pneumatic ventricular assist device: using a monoleaflet valve.

The cavitation intensity of a mechanical heart valve (MHV) may differ according to the geometry of the blood pump and driving mechanism. Our group is currently developing a pneumatic ventricular assist device (VAD), and the effects of different operating conditions on MHV cavitation in our pneumatic VAD were investigated. Tests were conducted under physiological pressure at heart rates ranging from 60 to 90 beats/min and at a systolic duration ranging from 38% to 43%. The valve-closing velocity was measured using a charge-coupled device (CCD) laser displacement sensor, and images of MHV cavitation were recorded using a high-speed video camera. A miniature pressure sensor was mounted 10 mm away from the inlet valve surface. The data were stored at a 1-MHz sampling rate using a digital oscilloscope. The pressure signal was band-pass filtered between 35 and 200 kHz using a digital filter. The cavitation bubbles were concentrated at the inlet valve stop, and were caused mainly by the squeeze flow. The band-pass filtered root mean squared (RMS) pressure and cavitation cycle duration increased with the closing velocity of the inlet valve. At a low heart rate and low systolic duration, the inlet valve closed before the outlet valve opened, which caused no cavitation bubbles to form around the valve stop.