Spectral Characteristics of Mechanical Heart Valve Closing Sounds
Peter Johansen MSc, Mads Lomholt MD, Hans Nygaard DMSc

In-vivo evaluation of cavitation near mechanical heart valves has been based on high-pass filtering of pressure fluctuations in order to remove the mechanical resonance components of the closing sound. This study presents a method to determine the optimal cut-off frequency, based on an airflow-controlled, non-cavitating set-up. As the valves were operated in air, the surrounding mediašs impact on resonance was investigated, and the observed change in resonance between water and air for a simple harmonic system was used to correct the valve findings. Five different valves were evaluated. The closing sounds were recorded, and spectral characteristics deduced. The frequency corresponding to 97.5% of the closing sound signal energy ranged from 40.9 to 65.8 kHz. In conclusion, this method can be used to determine the frequency signature of different valves, and can provide the information needed to design the optimal high-pass filter when evaluating cavitation.