Overnight recordings of intracranial pressure and electroencephalography in neurosurgical patients. Part II: Changes in intracranial pressure during sleep.

Changes in intracranial pressure (ICP) during sleep were investigated in 37 patients with chronic intracranial hypertension or chronic hydrocephalus, in whom episodic pressure waves characterized by A-waves or episodic B-waves were seen in Part I of this paper. The patients were conscious, and sleep stages including REM sleep were observed in all of them. During non-REM sleep, ICP significantly rose in Stage II on many occasions, and was always lower in Stage IV than in other sleep stages. A marked elevation of ICP was seen in REM sleep. ICP changes during REM sleep were characterized by frequent appearances of the pressure waves; 88.9% of A-waves and 95.1% of episodic B-waves appeared during REM sleep. The initiation of REM sleep scored on EEG began 1 to 2 minutes prior to or at the onset of the episodic pressure waves. The episodic pressure waves are assumed to be induced by the intracranial conditions in REM sleep, when increased brain activity and reduced sympathetic tone are known to occur simultaneously.