Implications of sex differences in orthostatic tolerance during exposure to acute artificial gravity

Development of countermeasures to minimise spaceflight deconditioning is of paramount importance, such as the short-arm human centrifuge (SAHC); however, sex differences in cardiovascular responses should be considered. 20 participants (female = 10, male = 10) conducted an identical centrifugation protocol of 10-min phases of standing (NG), 1Gz centrifugation (1GRF), and 2Gz centrifugation (2GRF). Separated by 10-min each in hot (29.1 ± 0.8 °C) conditions, and either normoxia (PO₂ = 133 mmHg) or hypoxia (PO₂ = 92 mmHg). Haemodynamics, microvascular blood flow (arm and leg) and temperatures (skin and gastrointestinal) were continuously recorded. At 2GRF, females lasted 2.7 ± 1.6 min less than males. Arm blood flow significantly decreased, and leg blood flow increased, in 2GRF (p > 0.001); with higher female leg blood flow in 2GRF (p = 0.002). 2GRF altered all haemodynamic variables and females exhibited significantly higher heart rate, and lower stroke volume index (p < 0.001). Female participants exhibited greater cardiovascular strain, and encountered pre-syncopal symptoms earlier, during 2GRF. Future research should consider individualised and tolerable gravitational loads.