Effect of acute exposure to hypergravity (GX vs. GZ) on dynamic cerebral autoregulation

1 Cerebral Blood Flow Research Lab, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7; 2 Deptartment of Neurotology Research, Legacy Clinical Research and Technology Center, Portland, Oregon 97232; 3 Faculty of Applied Science and Engineering, Ryerson Polytechnic University, Toronto, Ontario, Canada M5B 2K3; 4 Naval Aerospace Medical Research Laboratory, United States Navy, Pensacola, Florida 32508; 5 Life Sciences Research Laboratories, National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058 We examined the effects of 30 min of exposure to either +3G X (front-to-back) or +G Z (head-to-foot) centrifugation on cerebrovascular responses to 80° head-up tilt (HUT) in 14 healthy individuals. Both before and after +3 G X or +3 G Z centrifugation, eye-level blood pressure (BP eye ), end tidal P CO 2 (P ET CO 2 ), mean cerebral flow velocity (CFV) in the middle cerebral artery (transcranial Doppler ultrasound), cerebral vascular resistance (CVR), and dynamic cerebral autoregulatory gain (GAIN) were measured with subjects in the supine position and during subsequent 80° HUT for 30 min. Mean BP eye decreased with HUT in both the G X ( n = 7) and G Z ( n = 7) groups ( P