Female exposure to high G: Chronic adaptations of cardiovascular functions

Victor A. Convertino, Lloyd D. Tripp, David A. Ludwig, Juano Duff, Tamara L. Chelette

Research output: Contribution to journalArticle

35 Scopus citations

Abstract

Introduction: Exposure to microgravity is associated with increased leg venous compliance and reductions in cardiac output, baroreflex functions, and tolerance to orthostatism. However, the effects of chronic exposure to high- G environments are unknown. In addition, there is evidence that females have lower orthostatic tolerance than males, although the underlying mechanisms are unclear. Therefore, we tested the hypotheses that high-G training will enhance baroreflex and orthostatic functions and that females will demonstrate similar adaptations compared with males. Methods: Calf venous compliance, baroreflex function, and orthostatic performance were measured in six men and seven women before and after repeated exposures on the centrifuge (G-training) for 4 wk, 3 times/wk, with gradual levels of G starting with +3 Gz without G-suit protection during week I and advancing to +9 Gz with G- suit protection by the end of week 4. Calf venous compliance was measured by occlusion plethysmography using impedance rheographic recordings of volume change. Baroreflex function was assessed from beat-by-beat changes in heart rate (HR) and mean arterial pressure (MAP) that were measured before, during, and after a Valsalva maneuver strain at 30 mmHg expiratory pressure. The orthostatic performance of reflex responses was assessed from beat-by-beat changes in HR, MAP, stroke volume (SV), cardiac output (Q; by impedance plethysmography), and systemic peripheral resistance during the last 10 cardiac beats of a 4-min squat position and during the initial 10 cardiac beats in a standing position. Results: G-training increased calf compliance in both men and women. SV and Q were increased during the squat-to-stand test in the males, but not in the females, following G-training and provided protection against the development of acute hypotension in the men. Conclusions: G-training caused adaptations in orthostatic functions opposite to those observed following exposure to microgravity environments. However, adaptations to G-training were limited in females, a finding that may provide a physiological basis for their lower simulated combat tracking performance during simulated aerial combat maneuvers compared with males.

Original languageEnglish (US)
Pages (from-to)875-882
Number of pages8
JournalAviation Space and Environmental Medicine
Volume69
Issue number9
StatePublished - Sep 1 1998

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health

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    Convertino, V. A., Tripp, L. D., Ludwig, D. A., Duff, J., & Chelette, T. L. (1998). Female exposure to high G: Chronic adaptations of cardiovascular functions. Aviation Space and Environmental Medicine, 69(9), 875-882.