Human cardiovascular adaptation to hypergravity

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2022-06, Vol.322 (6), p.R597-R608
• Main Authors: Eiken, Ola, Keramidas, Michail E, Sköldefors, Håkan, Kölegård, Roger
• Format: Article
• Language: English
• Subjects: Acceleration; Adaptation; Adaptation, Physiological - physiology; Aerospace Medicine; arterial pressure distension; arterial pressure regulation; arterial stiffness; Arteries; Arterioles; Blood pressure; Cardiovascular system; Centrifugation; Centrifuges; Distension; Exposure; G suits; gravitoinertial load; headward acceleration; Humans; Hydrostatic pressure; Hypergravity; Hypergravity - adverse effects; Male; Maneuvers; Pressure breathing; Pressure dependence; Pressure gradients; Training
• ISSN: 0363-6119; 1522-1490; 1522-1490
• DOI: 10.1152/ajpregu.00043.2022

Despite decades of experience from high-gravitoinertial (G) exposures in aircraft and centrifuges, information is scarce regarding primary cardiovascular adaptations to +Gz loads in relaxed humans. Thus, effects of G-training are typically evaluated after regimens that are confounded by concomitant use of anti-G straining maneuvers, anti-G suits, and pressure breathing. Accordingly, the aim was to evaluate cardiovascular adaptations to repeated +Gz exposures in the relaxed state. Eleven men underwent 5 wk of centrifuge G training, consisting of 15 × 40 min +Gz exposures at G levels close to their individual relaxed G-level tolerance. Before and after the training regimen, relaxed G-level tolerance was investigated during rapid onset-rate (ROR) and gradual onset-rate (GOR) G exposures, and cardiovascular responses were investigated during orthostatic provocation and vascular pressure-distension tests. The G training resulted in: ) a 13% increase in relaxed ROR G tolerance ( < 0.001), but no change in GOR G tolerance, ) increased pressure resistance in the arteries and arterioles of the legs ( < 0.001), but not the arms, and ) a reduced initial drop in arterial pressure upon ROR high G, but no change in arterial pressure under basal resting conditions or during GOR G loading, or orthostatic provocation. The results suggest +Gz adaptation via enhanced pressure resistance in dependent arteries/arterioles. Presumably, this reflects local adaptations to high transmural pressures, resulting from the +Gz-induced exaggeration of the intravascular hydrostatic pressure gradients.