Abstract
The amplitudes of the first and second heart sounds were recorded during quiet natural breathing in 31 normal subjects. A total of 3,656 and 3,016 heart beats were available at the apex and pulmonic areas respectively. The in tensities of the first and second heart sounds were found to be increased during expiration. This respiratory tendency in the heart sounds was less prominent during the transitional phase between expiration and inspiration. Therefore we suggest that respiratory changes in heart sounds should be evaluated with a heart beat located at or close to the center of each inspiration and expiration. Respiratory alteration in the intensity of heart sounds is one of the commonest auscultatory pitfalls. Auscultatory evaluation of the intensity of heart sounds should thus be performed carefully, with the respiratory changes kept in mind.
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