Severe Hypotension During the Decreasing Phase of G(z) Stress in Anesthetized Rats Wearing an Anti-G Suit

• Published in: Aviation, space, and environmental medicine space, and environmental medicine, 2011-11, Vol.82 (11), p.1030-1036
• Main Authors: Maruyama, Satoshi, Kemueiyama, Takehito, Manabe, Tomoko, Takahata, Tomofumi, Shoji, Ichiro, Nlshida, Yasuhiro
• Format: Article
• Language: English
• Subjects: Aviation; Blood flow; Brain; Hemodynamics; Hypotension; Mathematical analysis; Rats; Stresses
• ISSN: 0095-6562
• DOI: 10.3357/ASEM.2870.2011

Introduction: Physiological responses to +G(Z) stress have been reported in several studies. However, no reports exist on differences in arterial pressure responses between increasing and decreasing C phases. We hypothesized that +G(Z) 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 +G(Z) magnitude, hemodynamic changes, renal sympathetic nerve activity (RSNA), and aortic blood flow (AoBF) were estimated in anesthetized rats to analyze the effects of +G(Z) stress and/or an anti-G support on arterial pressure at a level of the brain (APLB). The rats were exposed to +G(Z) 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 G phase at +5 G(z) was significantly deeper than that in the increasing G phase (47.5 plus or minus 7.7 vs. 29.6 plus or minus 3.0 mmHg). RSNA responses to G(z) loads were greater in the decreasing G than in the increasing G phase (129.7 plus or minus 8.6 vs. 147.3 plus or minus 10.4%). Both AoBF and calculated vascular resistance were suppressed more significantly in the decreasing G than in the increasing G phase (38.3 plus or minus 4.4 vs. 34.4 plus or minus 3.4 ml times min(-1), 1.44 plus or minus 0.22 vs. 1.09 plus or minus 0.14 mmHg times min(-1) times ml(-1)). Discussion: We conclude that transient excessive decreasing G hypotension may occur during the decreasing G phase, which may be due to anti-G suit functioning.