Daytime sleepiness and EEG spectral analysis in apneic patients before and after treatment with continuous positive airway pressure

Background: Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent apneas during sleep, resulting in repetitive hypoxemic episodes and interruptions of the normal sleep pattern. A previous study showed EEG slowing tie, a higher ratio of delta + theta frequencies to alpha + beta frequencies on EEG) during rapid eye movement (REM) sleep and wakefulness in untreated OSAS patients. Study and objectives: To determine whether EEG slowing is reversible with continuous positive air pressure (CPAP) treatment and to verify whether the persistence of excessive daytime sleepiness (EDS) is correlated with residual slowing of the EEG. Patients: Ten healthy subjects (9 men and 1 woman) and 14 patients with moderate-to-severe OSAS (13 men and 1 woman) were studied before and after 6 months of treatment with CPAP. Results: Untreated OSAS patients showed EEG slowing in frontal and central cortical regions during both wakefulness and during REM sleep compared to healthy control subjects. This EEG slowing was found to be independent of time spent with arterial oxygen saturation < 90%, severity of OSAS, or mean sleep latency as determined by the multiple sleep latency test. CPAP treatment was found to correct the EEG slowing for both REM sleep and wakefulness. Daytime sleepiness also greatly improved with treatment, but some degree of somnolence remained. Conclusion: CPAP treatment was found to correct the EEG slowing that was observed in untreated OSAS patients. Persistent EDS may be related to persistent obesity after CPAP treatment.