Autonomic Cardiovascular Responses to Orthostatic Stress After a Short Artificial Gravity Exposure

Intermittent artificial gravity (AG) training over days and weeks has been shown to improve the human orthostatic tolerance limit (OTL) and improve cardiovascular regulation in response to orthostatic stress. Effects of a single AG exposure are currently unknown.

We tested cardiovascular responses to orthostatic stress in 16 hypovolemic subjects (9 men and 7 women), once following a single, short (∼90 min) bout of AG and once following a similar period of head-down bed rest (HDBR). Hypovolemia was produced by intravenous furosemide infusion (20 mg) and orthostatic stress was produced by combined 70° head-up tilt (HUT) and progressively increasing lower body negative pressure until symptoms of presyncope developed. To assess reflex-induced changes in cardiovascular regulation, heart rate and blood pressure variability were analyzed by spectral analysis and baroreflex activity was evaluated by transfer function analysis.

Compared to HDBR, a short AG exposure increased men's low frequency (0.04-0.15 Hz) power of systolic blood pressure (SBPLF), but did not change women's SBPLF responses to orthostatic stress. In response to 70° HUT, compared to supine, low frequency phase delay (PhaseLF) between systolic blood pressure and RR intervals increased by ∼20% following HDBR, but did not change following AG, reflecting improved baroreflex activity at a milder level of orthostatic stress after AG.

These results indicate that a short bout of AG increased both sympathetic and baroreflex responsiveness to orthostatic stress in hypovolemia-induced, cardiovascular-deconditioned men and women, which may contribute to the AG-induced improvement of OTL shown in our previous reports.Zhang Q, Evans JM, Stenger MB, Moore FB, Knapp CF. Autonomic cardiovascular responses to orthostatic stress after a short artificial gravity exposure. Aerosp Med Hum Perform. 2017; 88(9):827-833.