BACKGROUND

Excessive daytime sleepiness (EDS) is the major complaint in subjects with obstructive sleep apnea syndrome (OSAS). However, EDS is not universally present in all patients with OSAS. The mechanisms explaining why some patients with OSAS complain of EDS whereas others do not are unknown.

OBJECTIVE

To investigate polysomnographic determinants of excessive daytime sleepiness (EDS) in a large multicenter cohort of patients with obstructive sleep apnea (OSAS).

METHODS

All consecutive patients with an apnea-hypopnea index greater than 5h(-1) who were evaluated between 2003 and 2005. EDS was assessed using the Epworth Sleepiness Scale (ESS), and patients were considered to have EDS if the ESS was >10.

RESULTS

A total of 1649 patients with EDS ((mean [+/-SD] Epworth 15+/-3) and 1233 without EDS (Epworth 7+/-3) were studied. Patients with EDS were slightly younger than patients without EDS (51+/-12 vs 54+/-13 years, p<0.0001), had longer total sleep time (p<0.007), shorter sleep latency (p<0001), greater sleep efficiency (p<0.0001) and less NREM sleep in stages 1 and 2 (p<0.007) than those without EDS. Furthermore, patients with EDS had slightly higher AHI (p<0.005) and arousal index (p<0.001) and lower nadir oxygen saturation (p<0.01).

CONCLUSIONS

Patients with OSAS and EDS are characterized by longer sleep duration and increased slow wave sleep compared to those without EDS. Although patients with EDS showed a mild worsening of respiratory disturbance and sleep fragmentation, these results suggest that sleep apnea and sleep disruption are not the primary determinants of EDS in all of these patients.