Effect of Posture on Airway Resistance in Obstructive Sleep Apnea-Hypopnea Syndrome by Means of Impulse Oscillation

Abstract

Background: There is more than one mechanism which contributes to the increases in upper airway resistance in obstructive sleep apnea and hypopnea syndrome. Impulse oscillation provides a convenient way of noninvasive monitoring and differentiating the contributions of airway resistance. Objective: To evaluate the effect of posture on airway resistance in obstructive sleep apnea-hypopnea syndrome (OSAHS) by means of impulse oscillation. Methods: Ten subjects without OSAHS proved by polysomnography served as controls, 14 patients with mild or moderate OSAHS and another 20 severe OSAHS patients were studied. All subjects underwent an overnight sleep study. Airway resistance was measured by impulse oscillometry, and spirometry was performed in the seated position and then in the supine position while awake. Results: Compared with controls, the severe and the mild-moderate OSAHS groups had significantly bigger changes in Zrs, Rrs5, R20 and R35 due to posture. There were also significant differences in R10, R15 and R25 between the severe OSAHS and the control groups. Besides, the group differences between the severe and the mild-moderate groups regarding the magnitude of this change were not significant. The correlation coefficients between apnea/hypopnea index and Zrs, R5 and R20 in supine position were 0.487, 0.486 and 0.485, respectively. Conclusion: The magnitude of change in airway resistance due to posture is bigger in OSAHS than in non-OSAHS. Zrs, R5 and R20 in supine position were associated moderately with apnea/hypopnea index.