抄録
Space sickness is believed to be related to the cephalad fluid shift and elevated intracranial pressure (ICP) during early microgravity exposure. Recently, we have reported elevation of ICP and cerebral perfusion pressure (CPP) although cerebral flow velocity (CFV) did not change during microgravity induced by free drop. We hypothesized that resistance of cerebral blood vessel increased to counteract against increase in cerebral blood flow (CBF) due to cephalad fluid shift. To test the hypothesis, we measured abdominal aortic pressure (AAP), carotid arterial and venous pressure (CAP and CVP, respectively), CBF (n = 10), and muscle blood flow (MBF) (n = 6) during microgravity induced by parabolic flight. The rats were set at horizontal prone (Flat) and 30-degree head-up whole body tilting (HUT) positions. With HUT, CVP increased by 1.9 mmHg during microgravity, compared to 1G condition. CAP raised by 15 mmHg although AAP rose by only 8 mmHg right after induction of microgravity. Similarly, in spite of increase in MBF up to 160%, only 115% increase in CBF was observed. With Flat position, no significant change was shown during microgravity. These results indicate that cephalad fluid shift due to acute microgravity exposure cause sudden increase in peripheral blood flow but change in CBF is counteracted by cerebral hemodynamic autoregulation. [Jpn J Physiol 54 Suppl:S92 (2004)]
