Polysomnographic characteristics of daytime sleepiness in obstructive sleep apnea syndrome

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

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.

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.

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.