Analyse des bruits émis par les valves cardiaques artificielles

The aim of this study is to compare the noise emitted by mechanical artificial valves to that produced by biological ones which are not disturbing for the patients. We use an in vitro approach. The valves, in the mitral position, are placed on a cardiovascular similator composed of an elastic atrio-ventricular prosthesis and an hydrodynamic generator. This assembly generates a periodic pulsatile flow. The noise signal is recorded with a hydrophone located in the excitation tank, close to the valve. Three different prostheses have been investigated : ball, tilting disk, bileaflet valves. During each cardiac cycle, the recorded signal is composed of a short burst of large amplitude which corresponds to the valve closure, and then a low level component at much lower frequency. To analyse such a burst, a time-frequency technique is much more convenient than a classical Fourier analysis. The wavelet analysis method appeared to be very efficient : it points out the time fluctuations of each frequency component. The results obtained show the efficiency of this technique. As far as the results are concerned, it appears that mechanical valves produce a high level sound within the octave bandwidth centered at 64 Hz up to 512 Hz, while the amplitude of these components decreases rapidly for the biological valve. The sound level difference is about 20 dB