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 obstructive sleep apnoea (OSA). EDS is a high-risk factor for accidents at work and on the road. Thirty untreated patients with different levels of severity of OSA were studied concerning night sleep and EDS. The criterion for severity was the respiratory disturbance index (RDI): 15 patients were classified as 'moderately' apnoeic (RDI < 40), 15 as 'severely' apnoeic (RDI > 40). Following night-time polysomnography, objective and subjective aspects of EDS were studied. To assess objective EDS the Maintenance of Wakefulness Test (MWT) and a computer-based vigilance performance test were used. Subjective EDS was determined using the Stanford Sleepiness Scale (SSS), the Epworth Sleepiness Scale (ESS) and the Visual Analogue Scales for Performance (VAS-P) and Tiredness (VAS-T). Well-being was assessed using the Scale of 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 shorter in the severe apnoea group. Vigilance testing revealed no group differences. Patients with moderate apnoea described themselves as more impaired in all subjective scales, but only SSS scores reached statistical significance. Our results suggest that there is no simple correlation between polysomnographic and respiratory sleep variables at night on the one hand, and the extent of EDS on the other hand. Furthermore, subjective and objective evaluation of EDS does not yield the same results. New approaches which allow a more detailed analysis of night sleep and daytime function are required to identify high-risked patients.