Changes in cerebral blood flow velocity in healthy young men during overnight sleep and while awake.

Using transcranial Doppler ultrasonography, we measured in 6 healthy young men cerebral blood flow velocity (CBFV) in the middle cerebral artery as well as oxygen saturation by a non-invasive method. Continuous recordings were taken starting from a point before the onset of sleep, throughout the duration of normal nighttime sleep, ending after awakening. During stages 2, 3 and 4, CBFV was approximately 15% lower than during the waking period preceding sleep. CBFV during rapid eye movement sleep did not differ from the presleep waking value, whereas the postsleep waking value was 6.6% lower. In 5 subjects CBFV showed a transient rise after sleep onset. Oxygen saturation was lower during sleep than during waking.