Effect of structural compliance on cavitation threshold measurement of mechanical heart valves

An in vitro study was designed to evaluate the effect of structural compliance on cavitation threshold measurements of mechanical heart valves. Using a dual channel high speed video image analysis method, the experiment was carried out in a pulse duplicator under a single, simulated physiologic condition. Each valve was mounted on a compliance adjustable fixture. One video camera served as a displacement monitor, while the other monitored cavitation bubbles at the inflow side of the valve. On-line adjustment of the mounting compliance allowed for cavitation threshold detection with respect to compliance without influencing the testing condition. Visible cavitation bubbles disappeared when the compliance was increased. Ten 29 mm mitral valves, including two each of St. Jude Medical, Carbomedics, Edwards-Duromedics (ED), Edwards Tekna (ET) and Medtronic-Hall (MH) were tested. All the bileaflet valves tested in this study showed similar cavitation thresholds at a compliance range of 0.5-0.65 mil/lb at a dp/dt of 4,000 mmHg/sec (averaged dp/dt during valve closure). Under the same dp/dt, MH monoleaflet valves showed a higher compliance range of 3.5-3.8 mil/lb to achieve the cavitation threshold. This study demonstrated that the mounting compliance of the valve must be known and well controlled in order to quantify the cavitation threshold with respect to dp/dt. In addition, the more compliant sewing ring of the ET valve may be responsible for higher cavitation thresholds with respect to dp/dt as observed in previous studies. The present in vitro study suggests that the investigation of the sewing structural compliance may be essential for the evaluation of in vivo cavitation potential.