title: Acute hemodynamic responses in the head during microgravity induced by free drop in anesthetized rats.
abstract: To examine acute hemodynamic responses to microgravity (microG) in the head, we measured carotid artery pressure (CAP) and jugular vein pressure (JVP) to calculate cephalic perfusion pressure (CPP = CAP - JVP) and recorded images of microvessels in the iris to evaluate capillary blood flow velocity (CBFV) and capillary diameter (CD) in anesthetized rats during 4.5 s of microG induced by free drop. Rats were placed in 30 degrees head-up whole body-tilted (HU, n = 7) or horizontal (flat, n = 6) position. In the flat group, none of the measured variables was significantly affected by microG, whereas in the HU group, CAP, JVP, and CPP increased, respectively, by 23.4 +/- 2.6, 1.3 +/- 0.2, and 22.9 +/- 3.1 mmHg, and CBFV and CD increased, respectively, by 33 +/- 8 and 9 +/- 3%, showing an increase in capillary blood flow. To further examine the mechanisms underlying these CAP and JVP increases, another experiment was performed in which CAP and JVP were measured in anesthetized rats (n = 6) during a postural change from HU to flat. In these animals, the change in JVP was similar to that observed during actual microG, but no change in CAP was seen, indicating that the JVP increase during actual microG is caused by disappearance of the gravitational pressure gradient in the head-to-foot axis, whereas the CAP increase is not. In conclusion, actual microG elicits an increase in CPP due to a greater increase in CAP than JVP, resulting in increased capillary blood flow. Although the increase in JVP is explained by the disappearance of gravitational pressure gradient in the head-to-foot axis as a result of microG, the larger increase in CAP is not.
authors.affiliation: Department of Physiology, Gifu University School of Medicine, 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: Kunihiko
authors.initials: K
authors.lastname: Tanaka
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: D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002196:Capillaries / Q000033:anatomy & histology / Q000502:physiology; D002339:Carotid Arteries / Q000502:physiology; D003326:Coronary Circulation / Q000502:physiology; D006257:Head / Q000098:blood supply*; D006321:Heart / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D007498:Iris / Q000098:blood supply; D007601:Jugular Veins / Q000502:physiology; D008297:Male; D008833:Microcirculation / Q000502:physiology; D009333:Neck / Q000502:physiology; D011187:Posture / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000502:physiology; D014893:Weightlessness / Q000009:adverse effects*