Polysomnographic characteristics of daytime sleepiness in obstructive sleep apnea syndrome.

Objective: The study is intended to explore the nocturnal sleep determinants for excessive daytime sleepiness (EDS) in patients with obstructive sleep apnea syndrome (OSAS).

Methods: Consecutive patients (n = 182) who had an apnea/hypopnea index (AHI) greater than 5 times per hour were used in this study. EDS (n = 32) was considered present whenever the Epworth sleepiness scale (ESS) score was >10 and the multiple sleep latency test (MSLT) score was <5 min. Absence of EDS (no EDS, n = 48) was determined in patients with an ESS score of <10 and a MSLT score of >10 min.

Results: Compared to no EDS patients, EDS patients exhibited (1) greater AHI and time length of SaO(2) <95%, lower nocturnal SaO(2) during separate rapid eye movement (REM) and NREM periods, and lower total mean and minimum SaO(2) during total recording period; (2) shortened latency to sleep and to REM sleep, and increased total sleep time and sleep efficiency; and (3) increases in the brief arousal index and duration of sleep stage 1. In addition, stepwise logistic regression analysis showed that the arousal index, the time length of SaO(2) <95%, and the latency to REM were independent predictors of EDS.

Conclusions: The results suggest that EDS in OSAS patients are characterized by the following aspects of nocturnal sleep: (1) severe sleep apnea/hypopnea and hypoxemia, (2) fragmented sleep, (3) low quality of sleep, and (4) high pressure of sleep drive.