Cardiovascular responses to standing with and without lower body compression garments after long-duration spaceflight

Long-duration astronauts (>4 mo on the International Space Station, 87 total person-missions) participated in an orthostatic test consisting of 2 min of prone rest followed by 3.5 min of standing preflight, within hours of landing on the first day of recovery (R + 0), and 1, 3, 7, 14, and 30 days after landing. Astronauts and cosmonauts performed exercise during spaceflight and fluid loading before landing to mitigate cardiovascular deconditioning. On R + 0, astronauts participated in testing without compression garments or while wearing one of three garments designed to prevent orthostatic intolerance: Russian Kentavr, National Aeronautics and Space Administration's gradient compression garment (GCG), or SpaceX's gradient orthostatic protection garment (OPG). On R + 0, the change in mean arterial pressure (ΔMAP) from prone to standing tended to decrease without compression garments (-8 mmHg, P = 0.053) and was less in astronauts wearing the Kentavr (-5 mmHg, P = 0.02), but not in crewmembers wearing the GCG or OPG. The heart rate response from prone to standing (ΔHR) on R + 0 tended to increase in those not wearing compression garments (+11 beats/min, P = 0.051) and was greater when wearing the Kentavr (+9 beats/min, P < 0.0001) or the OPG (+10 beats/min, P = 0.003), but not different in those wearing the GCG (+1 beats/min, P = 0.74). Although ΔHR when not wearing compression garments was greater (P < 0.05) for at least 2 wk after landing, ΔMAP was not different from preflight. Wearing NASA's GCG mitigates cardiovascular stress during standing after long-duration spaceflight, and full recovery of orthostatic responses to standing without compression garments is not complete for weeks.NEW & NOTEWORTHY Cardiovascular adaptations during long-duration spaceflight increase the likelihood of orthostatic intolerance upon re-exposure to gravity, and thus, countermeasures have been developed. Here we report findings derived across four National Aeronautics and Space Administration- and Russian-sponsored studies using a brief stand test protocol to characterize the efficacy of lower body compression garments in the first hours after landing and orthostatic responses without compression garments during readaptation in the first 4 wk after long-duration spaceflight.