EEG spectral power and sleepiness during 24 h of sustained wakefulness in patients with obstructive sleep apnea syndrome

Objective: This study investigated if obstructive sleep apnea syndrome (OSAS) may be associated with higher activity in different frequency bands of the EEG during a sustained wakefulness paradigm. Methods: Twelve OSA patients and 8 healthy controls were studied with the Karolinska Drowsiness Test (KDT) and subjective ratings of sleepiness (VAS and KSS) conducted every hour during 24 h of sustained wakefulness. Results: The waking EEG activity, mainly in the low (0.5-7.8 Hz) and fast (12.7-29.2 Hz) frequency band, increased as time awake progressed in both groups but more obviously in OSA patients. A similar pattern was observed for rated sleepiness in both groups. Moreover, VAS ratings of alertness were closely related to the awake theta, fast alpha and beta bands in controls but not in OSA patients. Conclusions: OSAS was associated with a wake-dependent increase in low (0.5-7.8 Hz) and fast (12.7-29.2 Hz) frequency range activity. Variations in behavioural sleepiness measured by VAS ratings closely reflect most of the waking EEG parameters in controls but not in OSA patients. Significance: In a sustained wakefulness paradigm, higher activity in delta, theta and beta bands associated with OSAS indicates that OSA patients show marked signs of higher sleepiness and stronger efforts than controls to stay awake, even though they tend to underestimate their sleepiness. (c) 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.