Comparison of the lung sound frequency spectra of infants and adults

Auscultation of the infant chest reveals lung sounds that seem different from those of adults. To characterize this subjective difference, we compared the phonopneumographic median frequencies of lung sounds of seven full-term and six premature infants with those of seven adults free of cardiopulmonary disease. The median frequencies over the upper lobes for the adults, term infants, and premature infants were 282 +/- 63(SD) Hz, 383 +/- 80 Hz, and 483 +/- 86 Hz, respectively. At this location the differences among the three groups were significant (p less than 0.01). Over the lower lobes, the median frequencies for the adults, term infants, and premature infants were 243 +/- 56 Hz, 386 +/- 76 Hz, and 390 +/- 63 Hz, respectively. Here the difference between the adults and both groups of infants was significant (p less than 0.01), but that between the term and premature infants was not. We conclude that the normal lung sounds of newborn infants contain higher-frequency components than those of adults. We postulate that this difference is the result of less filtering of the lung sound in infants. This difference should be considered when lung sounds of infants are described or assessed for the presence of abnormalities.