Use of the fast Fourier transform in the frequency analysis of the second heart sound in normal man

Abstract

The second heart sounds of 26 normal, young males, recorded at the aortic and pulmonary areas, were analysed for their frequency content by means of the fast Fourier transform. For both locations of measurement, peaks were observed in the frequency spectra in the lowfrequency range (10–80 Hz), the medium-frequency range (80–220 Hz), and the high-frequency range (220–400 Hz). In both the aortic and pulmonary areas, 25 of the 26 subjects had at least two peaks in the 80–400 Hz range, and a majority had one peak in the low-frequency range. A correlation coefficient of 0·75 was obtained between the medium frequency peaks in the aortic and pulmonary areas. The average frequency spectrum obtained for the entire study at each area indicates that the attenuation characteristics are nonlinear in the region of 10–160 Hz. For 160–400 Hz the attenuation in the pulmonary area is about 18 dB per octave and in the aortic area about 23 dB per octave. The observed peaks are probably related to the fluid-dynamic events causing the second heart sound. Thus important diagnostic information can probably be obtained from frequency analysis studies of cardiovascular sounds, and these studies will help in understanding the basic mechanisms which produce the sounds.