title: The relationship between widespread changes in gravity and cerebral blood flow.
abstract: OBJECTIVE
  We investigated the dose-effect relationship between wide changes in gravity from 0 to 2.0 Gz (Δ0.5 Gz) and cerebral blood flow (CBF), to test our hypothesis that CBF has a linear relationship with levels of gravity.
  
  
  METHODS
  Ten healthy seated men were exposed to 0, 0.5, 1.0, 1.5, and 2.0 Gz for 21 min, by using a tilt chair and a short-arm human centrifuge. Steady-state CBF velocity (CBFV) in the middle cerebral artery by transcranial Doppler ultrasonography, mean arterial pressure (MAP) at the heart level (MAPHeart), heart rate, stroke volume, cardiac output and respiratory conditions were obtained for the last 6 min at each gravity level. Then, MAP in the middle cerebral artery (MAPMCA), reflecting cerebral perfusion pressure, was estimated.
  
  
  RESULTS
  Steady-state CBFV decreased stepwise from 0.5 to 2.0 Gz. Steady-state heart rate, stroke volume, estimated MAPMCA and end-tidal carbon dioxide pressure (ETCO2) also changed stepwise from hypogravity to hypergravity. On the other hand, steady-state MAPHeart and cardiac output did not change significantly. Steady-state CBFV positively and linearly correlated with estimated MAPMCA and ETCO2 in most subjects.
  
  
  CONCLUSIONS
  The present study demonstrated stepwise gravity-induced changes in steady-state CBFV from 0.5 to 2.0 Gz despite unchanged steady-state MAPHeart. The combined effects of reduced MAPMCA and ETCO2 likely led to stepwise decreases in CBFV. We caution that a mild increase in gravity from 0 to 2.0 Gz reduces CBF, even if arterial blood pressure at the heart level is maintained.
authors: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Oyaguchi-Kamimachi, Itabashi-ku, Tokyo, 173-8610, Japan.
authors: Yojiro
authors: Y
authors: Ogawa
authors: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Oyaguchi-Kamimachi, Itabashi-ku, Tokyo, 173-8610, Japan.
authors: Ryo
authors: R
authors: Yanagida
authors: Division of Anesthesiology, Department of Anesthesiology, Nihon University School of Medicine, Tokyo, 173-8610, Japan.
authors: Kaname
authors: K
authors: Ueda
authors: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Oyaguchi-Kamimachi, Itabashi-ku, Tokyo, 173-8610, Japan.
authors: Ken
authors: K
authors: Aoki
authors: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Oyaguchi-Kamimachi, Itabashi-ku, Tokyo, 173-8610, Japan. iwasaki.kenichi@nihon-u.ac.jp.
authors: Ken-Ichi
authors: K
authors: Iwasaki
mesh_terms: D000328:Adult; D002498:Centrifugation; D002560:Cerebrovascular Circulation; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects; D018472:Hypogravity / Q000009:adverse effects; D007564:Japan; D008297:Male; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult
keywords: Centrifugation; Cerebral circulation; Hypergravity; Hypogravity; Transcranial Doppler ultrasonography