Sleep apnea, narcolepsy, and dreaming: regional cerebral hemodynamics.

Regional cerebral flow after inhalation of xenon 133 as well as polysomnography were recorded during daytime sleep and the awake state in patients with narcolepsy and sleep apnea. Brainstem-cerebellar (BSC) gray matter blood flow (Fg) values in the awake state were reduced below normal (p less than 0.05) in both narcolepsy and sleep apnea; in sleep apnea, bihemispheric Fg values were also reduced in the awake state. After sleep onset, Fg paradoxically increased in narcolepsy but decreased further in sleep apnea. Maximal regional Fg changes occurred in BSC regions in both groups of patients. Oral administration of methylphenidate hydrochloride (Ritalin) increased resting Fg values in awake narcoleptics, particularly in BSC regions, but attentuated Fg increases during sleep onset. Regional Fg values during visual dreaming or hypnagogic hallucinations in narcoleptics were maximally increased in right parietooccipital regions. In narcoleptics, impaired control of sleep-wake and REM mechanisms is attentuated by methylphenidate. In patients with sleep apnea, brainstem functional activity is low in the awake state but becomes critically reduced during sleep, culminating in apnea-stimulated arousal followed by repetitive cycles as sleep recurs.