On the closing sounds of a mechanical heart valve

In the 1994 Replacement Heart Valve Guidance of the U.S. Food and Drug Administration (FDA), in-vitro testing is required to evaluate the potential for cavitation damage of a mechanical heart valve (MHV). To fulfill this requirement, the stroboscopic high-speed imaging method is commonly used to visualize cavitation bubbles at the instant of valve closure. The procedure is expensive; it is also limited because not every cavitation event is detected, thus leaving the possibility of missing the whole cavitation process. As an alternative, some researchers have suggested an acoustic cavitation-detection method, based on the observation that cavitation noise has a broadband spectrum. In practice, however, it is difficult to differentiate between cavitation noise and the valve closing sound, which may also contain high-frequency components. In the present study, the frequency characteristics of the closing sound in air of a Bjork-Shiley Convexo-Concave (BSCC) valve are investigated. The occluder closing speed is used as a control parameter, which is measured via a laser sweeping technique. It is found that for the BSCC valve tested, the distribution of the sound energy over its frequency domain changes at different valve closing speeds, but the cut-off frequency remains unchanged at 123.32 +/- 6.12 kHz. The resonant frequencies of the occluder are also identified from the valve closing sound.