Hypersomnolence and neurocognitive performance in sleep apnea.

Two symptom clusters are prominent obstructive sleep apnea syndrome: excessive daytime sleepiness and neurocognitive difficulties. This article reviews studies that have attempted to determine the etiology and interrelation of these two symptom clusters. The research has clearly determined that the cause of the daytime sleepiness of obstructive sleep apnea syndrome is the fragmentation of sleep by the brief arousals that terminate each apneic event rather than the nocturnal hypoxemia that also occurs in obstructive sleep apnea syndrome. However, the daytime sleepiness and nocturnal hypoxemia appear to both contribute to the neurocognitive impairments of obstructive sleep apnea syndrome, and each seems to affect specific aspects of neurocognitive performance. The extent to which treatment reverses the neurocognitive impairments of obstructive sleep apnea syndrome is yet to be fully determined. The initial study suggests that the impairments are not completely reversed with treatment.