OBJECTIVETo understand how sleep stage and position influence the mechanisms for pharyngeal collapse in different levels of upper airway (UA), overnight state-related changes and postural variation in obstructive sites in obstructive sleep apnea hypopnea syndrome (OSAHS) patients were studied.

METHODSFifty four OSAHS patients underwent overnight upper airway pressure monitoring during polysomnography. The lower limits of the UA obstruction were determined and their relationship with sleep stage, position, age, body mass index and apnea hypopnea index (AHI) were investigated.

RESULTSAll 54 patients had oropharynx (14 837 of the 23 172 analyzed events) and tongue base obstruction (5605/23,172), 2532 events were located at the oropharynx with extension to tongue base. Twenty nine patients has hypopharynx obstruction (105/23 172). Of the total amount of apnea hypopnea, the portions of obstruction located at tongue base level increased (t = 8.790, P = 0.000) in rapid eye movement (REM) sleep while those located at oropharynx decreased (t = -6.846, P = 0.000). Indexes of the apnea hypopnea caused by tongue base obstruction raised (t = 6.189, P = 0.000). Although the overall AHI in supine position was higher than in lateral position (t = 4.000, P = 0.000), increases in indexes of both the apnea hypopnea caused by tongue base (supine, 17.1 +/- 13.8 vs. lateral, 13.9 +/- 14.6) and oropharynx obstruction (44.3 +/- 20.3 vs. 37.2 +/- 25.9) were without significance (P > 0.05). Distribution of obstructive site varied little with different position (P > 0.05).

CONCLUSIONSUpper airway obstruction involves more than one specific site of the upper airway and the oropharynx is the most common collapse site. Obstructive sites are likely to extend to lower levels during REM sleep. Sleep position has little effect on the distribution of obstructive site.