title: Cerebral circulation during acute microgravity induced by free drop in anesthetized rats.
abstract: To evaluate changes in the cerebral circulation during acute microgravity (microG), 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 microG induced by free drop, then calculated arterial pressure at the eye level (AP(eye)) and cerebral perfusion pressure (CPP = AP(eye)-ICP), and estimated CPP-CFV relationship. The rats were placed in the flat and the 30 degrees head-up positions. In the head-up position, ICP, AP(eye), and CPP were significantly increased by 2.2 +/- 0.4, 12.3 +/- 2.0, and 10.1 +/- 1.7 mmHg respectively during microG, whereas the CFV did not change significantly. In the flat position, none of these variables were significantly affected by microG. The slope of the CPP-CFV relationship was decreased only in the head-up position, suggesting that the cerebrovascular resistance was increased by microG. These findings indicate that the change in gravitational (hydrostatic) pressure is a key factor in understanding the changes in cerebral circulation during acute microG.
authors.affiliation: Department of Physiology, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu, 500-8705 Japan. a2001072@hotmail.com
authors.forename: Taro Miyahara
authors.initials: TM
authors.lastname: Gotoh
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Fujiki
authors.forename: Tomoko
authors.initials: T
authors.lastname: Matsuda
authors.forename: Shuang
authors.initials: S
authors.lastname: Gao
authors.forename: Hironobu
authors.initials: H
authors.lastname: Morita
mesh_terms: D000818:Animals; D001011:Aorta / Q000502:physiology; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002560:Cerebrovascular Circulation; D003964:Diaphragm; D007427:Intracranial Pressure; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014893:Weightlessness / Q000009:adverse effects*