Excessive daytime sleepiness in patients suffering from different levels of obstructive sleep apnoea syndrome

Excessive daytime sleepiness (EDS) is a frequent symptom of patients with o bstructive sleep apnoea (OSA). EDS is a high-risk factor for accidents at w ork and on the road. Thirty untreated patients with different levels of sev erity of OSA were studied concerning night sleep and EDS. The criterion for severity was the respiratory disturbance index (RDI): 15 patients were cla ssified as 'moderately' apnoeic (RDI < 40), 15 as 'severely' apnoeic (RDI > 40). Following night-time polysomnography, objective and subjective aspect s of EDS were studied. To assess objective EDS the Maintenance of Wakefulne ss Test (MWT) and a computer-based vigilance performance test were used. Su bjective EDS was determined using the Stanford Sleepiness Scale (SSS), the Epworth Sleepiness Scale (ESS) and the Visual Analogue Scales for Performan ce (VAS-P) and Tiredness (VAS-T). Well-being was assessed using the Scale o f Well-Being by von Zerssen (Bf-S/Bf-S'). Severe apnoea patients spent more time in stage 1 and less in slow-wave sleep. MWT latencies tended to be sh orter in the severe apnoea group. Vigilance testing revealed no group diffe rences. Patients with moderate apnoea described themselves as more impaired in all subjective scales, but only SSS scores reached statistical signific ance. Our results suggest that there is no simple correlation between polys omnographic and respiratory sleep variables at night on the one hand, and t he extent of EDS on the other hand. Furthermore, subjective and objective e valuation of EDS does not yield the same results. New approaches which allo w a more detailed analysis of night sleep and daytime function are required to identify high-risked patients.