SPECTRAL COMPOSITION OF HEART SOUNDS BEFORE AND AFTER MECHANICAL HEART-VALVE IMPLANTATION USING A MODIFIED FORWARD-BACKWARD PRONYS METHOD

This paper investigates the impact of the lung-thorax and heart-valve system on the overall spectral composition of the externally recorded heart sounds. The study concentrates in the case of the first and the second heart sounds for normal patients and patients before and after implantation of a mechanical valve in the mitral or aortic position. T he analysis is performed using a modified forward-backward overdetermi ned Prony's method (MFBPM) which uses a forward-backward mean filter a nd a modified procedure for estimating the position of the signal pole s. In terms of the normalized cross-correlation coefficient, this meth od has an average modeling accuracy of 99,62% for representing the fir st and second heart sounds and an average least square time-domain err or of 0.43%. Results obtained from 40 subjects show that the condition of the native mitral or aortic valve affects mostly the distribution of the amplitudes of the spectral components, whereas the number of th e spectral components or their respective relative energy remains more or less unchanged. It has been found that the amplitudes of frequency components in the range 120-250 Hz are more affected by abnormalities of native mitral valves. Furthermore, in the case of the second heart sound the region 250-400 Hz has been found to be more affected by abn ormalities in the aortic valve. It has also been found that the mechan ical prosthetic heart valve affects mostly the spectrum beyond 400 Hz. A clear difference has been observed in the frequency spectrum above 400 Hz between both normally and abnormally functioning native valves and normally functioning mechanical valves. Preliminary results in som e malfunctioning cases of mechanical prosthesis suggest that spectral components beyond 400 Hz can be used to monitor the condition of these prostheses.