EFFECT OF LOWER-BODY NEGATIVE-PRESSURE ON CEREBRAL-CIRCULATION

This experiment was performed to study the effects of lower body negat ive pressure (LBNP) on cerebral circulation. Cerebral hemodynamics wer e monitored continuously and noninvasively in eight subjects at 30 mmH g of LBNP for 25 minutes by following items: 1) the carotid Doppler fl owmeter which measures the carotid blood flow, 2) the transcranial Dop pler sonography which measures the flow velocity of the middle cerebra l artery, 3) the near infrared spectrophotometer which measures the ox ygenated and deoxygenated hemoglobin in the brain. The mean flow veloc ity of the middle cerebral artery and the blood flow of the common car otid artery significantly decreased during LBNP, even though the mean arterial blood pressure was well maintained. The oxygenated hemoglobin was significantly increased during LBNP, while the deoxygenated hemog lobin was not changed significantly. Our results suggest that exposure to moderate LBNP (30 mmHg) decreased the cerebral blood flow with the vasodilatation on the arterial side of the brain.