TIME-FREQUENCY ANALYSIS OF THE NOISE PRODUCED BY THE CLOSING OF ARTIFICIAL-HEART VALVES - AN IN-VITRO STUDY

Clinical investigations showed that patients with an implanted mechani cal heart valve are sometimes disturbed by the noise produced by the v alve closing. The aim of this study was to investigate the noise gener ated by mechanical artificial heart valves with reference to the one p roduced by biological valves. This type of biological valve was used a s a standard because it does not disturb the patient. We used an in vi tro approach with a cardiovascular simulator. The noise signal was rec orded simultaneously using a hydrophone and an accelerometer. During e ach cardiac cycle, because of the shortness of the signal (15-25 ms) a nd of the transient state, rapid frequency dynamics limited the useful ness of stationary analysis techniques for the first heart sound. Ther efore, a time-frequency technique was much more convenient than a clas sic Fourier analysis. We used a discrete wavelet transform that pointe d out the time fluctuation of each frequency component. Globally, mech anical valves produced a high sound level within the octave bandwidths centered on 64 Hz up to 512 Hz, while the amplitude of these componen ts decreased rapidly for the biological valve. (C) 1998 IPEM. Publishe d by Elsevier Science Ltd. All rights reserved.