POSTURE-DEPENDENT CHANGE OF TRACHEAL SOUNDS AT STANDARDIZED FLOWS IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

Background: The ability of awake subjects,vith obstructive sleep apnea (OSA) to dilate their pharynx during inspiration may be defective. Ai rflow through a relatively more narrow pharyngeal passage should lead to increased flow turbulence and hence to louder respiratory sounds. W e therefore studied the increase of tracheal sound intensity (TSI) in the supine position as an indicator of abnormal pharyngeal dynamics in patients with documented OSA. Subjects ana methods: Sound was recorde d with a contact sensor at the suprasternal notch in ? patients with O SA (age, 52 +/- 8 years; body mass index, 29.0 +/- 3; apnea-hypopnea i ndex, 58 +/- 17; means +/- SD), and in 8 control subjects, including o bese subjects and snorers (age, 39 +/- 8 years; body mass index, 28.6 +/- 4). Subjects breathed through a pneumotachograph and aimed at targ et flows of 1.5 to 2 L/s, first sitting, then supine. Flow and sound s ignals were digitized at a 10-KHz rate. Fourier analysis was applied t o sounds within the target now range and average power spectra were ob tained. Spectral power was calculated for frequency bands 0.2 to 1, 1 to 2, and 2 to 3 KHz. Results: In the supine position, OSA patients ha d a significantly greater increase of inspiratory TSI than control sub jects: 7.5 +/- 1.2 dB vs 1.7 +/- 3.4 dB (p < 0.001); 6.6 +/- 1.7 dB vs 1.3 +/- 3.9 dB (p < 0.005); and 12.2 +/- 3.2 dB vs 5.6 +/- 3.1 dB (p < 0.001) at low, medium, and high frequencies, respectively. Expirator y TSI also increased in supine subjects, but the change was significan tly greater in OSA subjects only at high frequencies. These findings c onfirm our earlier observations that did not include obese subjects or snorers among control subjects. Summary: Measuring posture effects on tracheal sounds is noninvasive and requires little time and effort. T he greater increase of inspiratory TSI in supine OSA patients compared to subjects without OSA suggests a potential value for daytime acoust ic screening.