Time-frequency analysis of transient pressure signals for a mechanical heart valve cavitation study

A series of transient pressure signals (TPSs) can be measured using a miniature pressure transducer mounted near the tip of the inflow side of a mechanical heart valve (MHV) occluder during closure. A relationship appears to exist between the intensity and pattern of the TPS and the cavitation potential of a MHV. To study the relationship between MHV cavitation and the TPSs, we installed an MHV in a valve testing chamber of a digitally controlled burst test loop. A charge coupled device (CCD) camera and a personal computer based image grabbing program was used to visualize cavitation bubbles appearing on or near the occluder surface. One bileaflet MHV was used as the model for this study. Cavitation bubbles were observed within 300 microsec of the leaflet/housing impact. The valve was tested at various driving pressures between 100 and 1,300 mmHg. MHV cavitation bubble intensities were qualitatively classified into three categories: 1) strong, 2) weak, and 3) none. Digital images of the MHV occluder inflow surface were recorded simultaneously with the TPSs. TPSs were studied by the time-frequency analysis method (spectrogram) and correlated to MHV cavitation potential. The intensity of the cavitation bubbles was found to be associated with burst test loop driving pressures during leaflet closure.