Spectral analysis of breath sounds in normal newborn infants

To determine whether breath sounds in newborns are different from those described in older subjects, fast Fourier transform and power spectra analysis were performed on recorded breath sounds from 14 normal newborns. A respiration-triggered sampling technique was applied to compare early, middle, and late phases of inspiration and expiration, using a thoracic impedance signal. Peak frequencies were found in the range described for normal breath sounds in older subjects, and the frequency range of breath sounds was similar to that reported for older children and adults. The difference in breath sound quality of normal newborns appears to depend on the sound intensity during expiration. In contrast to older subjects, newborns showed only slightly less sound intensity during expiration; in the late phases of inspiration and expiration this intensity was almost equal.