The protective mechanism is modulated by sympathetic vasoconstriction and parasympathetic heart rate (HR) increase. The average of relaxed G tolerance (RGT) is from 4.5 to 6G, determined at a gradual onset rate (GOR) run. Several studies have indicated that the majority of military aircrew have experienced visual disturbances 2, 3 and that approximately 10–20% of them have suffered GLOC episodes in flight 4, 5.īaroreflex, a cardiovascular response, will be fully activated to restore blood pressure and to enhance G tolerance when aircrews are subjected to sustained G stress. Pilots can develop visual disturbances, low cerebral oxygen saturation and, if without proper protection, G-induced loss of consciousness (GLOC). Orthostatic stress induced by G force decreases the mean arterial pressure and blood flow velocity, leading to blood being retained in the lower extremities 1. Military pilots who fly high-performance aircrafts are frequently exposed to large head-to-toe gravito-inertial (G) forces. Nonetheless, good AGSM performance seemed to reduce the negative effect of weak HR responses on the dependent variable. We speculate that low AGSM effectiveness and a small HR increase were separately associated with failure of high-G challenge. The negative effect of a smaller HR increase on the outcome was likely to be affected by improved AGSM effectiveness (adjusted OR 1.26, 95% CI 0.65–2.42). The adjusted OR of 9G profile disqualification was 2.93 (95% CI 1.19–7.20) for participants with smaller HR increases and lower AGSM effectiveness. Trainees with HR increases of less than 20% in the first five seconds also had higher odds of 9G profile intolerance (adjusted OR 1.83, 95% CI 1.09–3.07). Subjects with an AGSM effectiveness of less than 2.5G had a 2.14-fold higher likelihood of failing in the 9G profile. A total of 530 attempts for the 9G profile were extracted to clarify the association of interest. We assessed the combined effect of HR and AGSM on the outcome of 9G profile exposure. Previous studies reported the main effects of HR only or AGSM only on G tolerance. The anti-G straining manoeuvre (AGSM) is the crucial technique for withstanding a high-G load. Increased heart rate (HR) is a reaction to head-to-toe gravito-inertial (G) force.
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