Nocturnal Sleep Determinants For Excessive Daytime Sleepiness In Obstructive Sleep Apnea Syndrome

Purpose: 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 SaO2 < 95%, lower nocturnal SaO2 during separate rapid eye movement sleep(REM) and non-rapid eye movement sleep (NREM) periods, and lower total mean and minimum SaO2 during total recording period; 2) shortened latency to sleep and to rapid eye movement sleep, and increased total sleep time and sleep efficiency; 3) increases in the brief arousal index, duration of sleep stage 1 and a trend of decrease in the percentage of slow wave sleep (p<0.081). In addition, stepwise logistic regression analysis showed that the arousal index, the time length of SaO2 < 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.