title: Severe hypotension during the decreasing phase of Gz stress in anesthetized rats wearing an anti-G suit.
abstract: BACKGROUND
  Physiological responses to +Gz stress have been reported in several studies. However, no reports exist on differences in arterial pressure responses between increasing and decreasing G phases. We hypothesized that +Gz stress and/or an anti-G support might disturb the circulation system and cause potential brain hypoperfusion, even if the anti-G support protects against G-induced loss of consciousness.
  
  
  METHODS
  Dependency of +Gz magnitude, hemodynamic changes, renal sympathetic nerve activity (RSNA), and aortic blood flow (AoBF) were estimated in anesthetized rats to analyze the effects of +Gz stress and/or an anti-G support on arterial pressure at a level of the brain (APLB). The rats were exposed to +Gz using a centrifuge for small animals while wearing an anti-G suit.
  
  
  RESULTS
  APLB remained at the control level while the anti-G suit was inflated. However, a decrease in APLB was observed twice during increasing and decreasing G phases using the anti-G suit. Hypotension in the decreasing C phase at +5 Gz was significantly deeper than that in the increasing G phase (47.5 +/- 7.7 vs. 29.6 +/- 3.0 mmHg). RSNA responses to Gz loads were greater in the decreasing G than in the increasing G phase (129.7 +/- 8.6 vs. 147.3 +/- 10.4%). Both AoBF and calculated vascular resistance were suppressed more significantly in the decreasing G than in the increasing G phase (38.3 +/- 4.4 vs. 34.4 +/- 3.4 ml x min(-1), 1.44 +/- 0.22 vs. 1.09 +/- 0.14 mmHg x min(-1) x ml(-1)).
  
  
  CONCLUSIONS
  We conclude that transient excessive decreasing G hypotension may occur during the decreasing G phase, which may be due to anti-G suit functioning.
authors.affiliation: Department of Physiology, National Defense Medical College, Tokorozawa, Saitama, Japan. dr21048@ndmc.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Maruyama
authors.forename: Takehito
authors.initials: T
authors.lastname: Kemuriyama
authors.forename: Tomoko
authors.initials: T
authors.lastname: Manabe
authors.forename: Tomofumi
authors.initials: T
authors.lastname: Takahata
authors.forename: Ichiro
authors.initials: I
authors.lastname: Shoji
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nishida
mesh_terms: D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D000818:Animals; D002498:Centrifugation; D006112:Gravitation; D005676:Gravity Suits; D007022:Hypotension / Q000503:physiopathology*; D007668:Kidney / Q000294:innervation; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D014520:Urethane / Q000008:administration & dosage
chemical_list: D018686:Anesthetics, Intravenous; D014520:Urethane