Abstract
To evaluate changes in the cerebral circulation during acute microgravity (μG), we measured intracranial pressure (ICP), aortic pressure at the diaphragm level, and cerebral flow velocity (CFV) in anesthetized rats (n = 5) during 4.5 s of μG induced by free drop, then calculated arterial pressure at the eye level (APeye) and cerebral perfusion pressure (CPP = APeye−ICP), and estimated CPP–CFV relationship. The rats were placed in the flat and the 30° head-up positions. In the head-up position, ICP, APeye, and CPP were significantly increased by 2.2 ± 0.4, 12.3 ± 2.0, and 10.1 ± 1.7 mmHg respectively during μG, whereas the CFV did not change significantly. In the flat position, none of these variables were significantly affected by μG. The slope of the CPP–CFV relationship was decreased only in the head-up position, suggesting that the cerebrovascular resistance was increased by μG. These findings indicate that the change in gravitational (hydrostatic) pressure is a key factor in understanding the changes in cerebral circulation during acute μG.
