Intracranial pressure in the normal monkey while awake and asleep

Intracranial pressure (ICP) was recorded continuously by telemetry in seven normal monkeys trained to eat, sleep, and live in a primate chair. Electroencephalography, electromyography, and blood pressure were also measured by conventional means. During wakefulness and all stages of sleep except desynchronized sleep, the ICP record showed small short-term variations in pressure. However, during desynchronized sleep, the mean ICP rose on the average to 170 +/- 6 mm H2O above the ICP levels in the other states of sleep, and the pulsation pressure variation increased by a factor of three. The episodes occurred 10 +/- 2 times during the night and lasted for 6.8 +/- 1.4 minutes, during which the average systemic blood pressure decreased by 19 +/- 1.6 mm Hg. These ICP waves occurring during desynchronized sleep resemble the plateau waves described by Lundberg, but are of smaller magnitude and they appear to be a normal characteristic of sleep in the macaque monkey. Bilateral sympathectomy of the superior cervical ganglia in four of the monkeys did not alter significantly the duration, amplitude, or frequency of occurrence of the ICP waves during desynchronized sleep.