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...