Expiratory Breathing Sounds Characteristics During Wakefulness and Sleep in Mild and Severe Apneic Groups

Abstract

We investigated plausible changes in spectral and phasic properties of tracheal respiratory sounds from wakefulness to sleep in relation to obstructive sleep apnea (OSA). Data were tracheal expiratory breathing sounds of 30 subjects during wakefulness and sleep, both recorded in supine position. Subjects were divided into 2 groups of mild and severe OSA (15 in each group) based on their apnea/hypopnea index (AHI). Power spectral density (PSD) and phase spectrum, were estimated from each normalized expiratory sound; their characteristics were compared within and between the groups. Spectral analysis during wakefulness showed an opposite pattern between mild and severe groups in low and high frequencies. The mild group’s PSD on average was higher than that of the severe group in lower frequencies, while this pattern was reversed in high frequencies. During sleep, however, the PSD of the severe group was higher than that of mild group across the spectrum. On the other hand, during sleep, the average phase spectrum of the severe group showed larger delay than that of the mild group, especially at higher frequencies. The physiological and pathological interpretations of these findings are discussed.