Relation of intensity of cardiac sounds to age.

The absolute intensity of the first (S1), third (S3), and fourth (S4) heart sounds (in mm Hg) and the relative intensity of S4 compared with S1 were measured in 146 normal persons, aged 8 to 91 years, using an infinite time-constant, calibrated pressure mechanocardiograph applied to the chest wall with a loading pressure of 400 mm Hg. The absolute intensity of S1 (r = 0.28) and S3 (r = 0.43) decreases with age, but the absolute intensity of S4 does not increase with age (r = 0.06). Therefore, the relative intensity of S4 compared with S1 increases with age (r = 0.31). This finding may explain the increased frequency of S4 in qualitative phonocardiograms in older persons.