Frequency distribution of the heart sounds in normal man

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Abstract
The magnitude of the heart sounds at various frequencies was studied in 11 normal young men over three areas of the praecordium by using a new calibrated system. The average slope of attenuation for the first heart sound was found to be −6·5 dB per octave at the apex and −7·5 dB per octave at the midpraecordium. A slower decline was found for the second heart sound as the average slope of attenuation of the aortic component at the second left interspace was −6 dB per octave up to 80 Hz and no slope existed between 80 and 140 Hz. The pulmonary component of the second sound at the second left interspace had an overall slope of −3·5 dB per octave. A relative 'peaking' was found in all subjects at different frequencies with the first heart sound usually peaking at lower frequency than the second. Marked variability existed in the slope of attenuation and in the relative peaking between the various subjects. These data are discussed both in terms of physiological considerations and in terms of practical application to the design of equipment.

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