Tracheal and lung sounds repeatability in normal adults.

Tracheal and lung sounds measurements for clinical applications depends on their intrasubject repeatability. Our objectives were to characterize tracheal and lung sounds and to investigate the temporal variability in normal adults. Tracheal sounds were studied in 7 subjects and lung sounds in 10 adults. Acoustic measurements were done in five occasions over a month for tracheal sounds and on seven occasions over a year for lung sounds. Sounds were recorded using contact sensors on the suprasternal notch and on the posterior right lower lobe. Subjects breathed through a pneumotachograph at flows of 0.9-1.1 l/s. Signals were low-pass filtered, amplified and Fourier analysis was applied to sounds within a target flow range. We measured the frequencies below which 25% (F25), 50% (F median), 75% (F75) and 99% (SEF99) of the spectral power between 100 and 2000 Hz. There were no differences between the measurements obtained at different days comparing each subject (P = ns, ANOVA). Our results show that the spectral pattern of tracheal and lung sounds are stable with low intrasubject variability.