Expiratory pharyngeal airway obstruction during sleep: a multiple element model.

OBJECTIVE/HYPOTHESIS: In patients with obstructive sleep apnea and snoring, airway obstruction during sleep is not limited to inspiration but may also occur with expiration. The aim of this study was to assess the segmental mechanics of expiratory obstruction.

DESIGN: Experimental study of a convenience sample of 20 patients with snoring and mild obstructive sleep apnea.

METHODS: During sedated sleep, airflow, airway pressure measurements (supraglottic, oropharyngeal, nasopharyngeal, and nasal mask), and either supraglottic/retroglossal or retropalatal areas were simultaneously measured. Nasal continuous positive airway pressures were experimentally adjusted during single breath tests (SBTs) to modify upper airway size. Airway mechanics were evaluated during pressure drops on expiration.

RESULTS: The predominant level of expiratory obstruction was supraglottic/retroglossal level alone (65%) or combined supraglottic/retroglossal and retropalatal (17.6%). In nonobstructed SBTs, compliance curves derived from supraglottic/retroglossal and retropalatal pressures were similar but diverged in obstructed breaths. Compliance during expiration was greater in the supraglottic/retroglossal segment compared to the retropalatal segment. Retropalatal cross-sectional size was smaller during early and late expiration on obstructed than on nonobstructed breaths independent of airway pressure measures. The rate of expiratory collapse was increased at all time points measured (P <.005) in the retropalatal segment on obstructed as compared with nonobstructed breaths.

CONCLUSIONS: During expiration, the supraglottic/retroglossal level is obstructed more frequently and has greater compliance than the retropalatal segment. Failure of upstream pressures to describe pharyngeal obstruction supports a multi-element model of collapse. Segments interact during expiration, with increased retropalatal collapse on obstructed as compared with nonobstructed breaths. Increased collapse on expiration provides a mechanism for increased obstruction on subsequent inspiratory breaths.