Normal human sleep: regional cerebral hemodynamics

Area of Science:

• Neuroscience
• Physiology

Background:

• Regional cerebral blood flow (rCBF) regulation during sleep is not fully understood.
• Nocturnal sleep stages exhibit distinct physiological changes affecting brain function.

Purpose of the Study:

• To investigate serial changes in regional cerebral blood flow during different stages of nocturnal sleep.
• To assess cerebral vasomotor responsiveness to carbon dioxide during sleep.

Main Methods:

• 18 healthy volunteers underwent xenon-133 inhalation method for rCBF measurement.
• Polygraph recordings monitored sleep stages (I-IV, REM, wakefulness).
• Serial measurements were taken during relaxed wakefulness and sleep.

Main Results:

• Fast flow (Fg) significantly declined in hemispheric and brainstem-cerebellar (BSC) regions during stages I-IV sleep.
• BSC flow increased more than hemispheric flow upon awakening from stage IV.
• REM sleep showed diffuse increases in Fg in both hemispheric (+41%) and BSC (+47%) regions.
• A significant inverse correlation was found between end-tidal partial pressure for carbon dioxide and bihemispheric Fg reduction during sleep.

Conclusions:

• Cerebral blood flow dynamics vary significantly across sleep stages.
• Cerebral vasomotor responsiveness to carbon dioxide is impaired during both REM and non-REM sleep.
• These findings highlight altered cerebrovascular regulation during sleep.