Effects of daily artificial gravity training on orthostatic tolerance following 60-day strict head-down tilt bedrest

Abstract

Purpose Orthostatic intolerance commonly occurs following immobilization or space flight. We hypothesized that daily artificial gravity training through short-arm centrifugation could help to maintain orthostatic tolerance following head-down tilt bedrest, which is an established terrestrial model for weightlessness. Methods We studied 24 healthy persons (eight women; age 33.3 ± 9.0 years; BMI 24.3 ± 2.1 kg/m2) who participated in the 60-days head-down tilt bedrest (AGBRESA) study. They were assigned to 30 min/day continuous or 6 × 5 min intermittent short-arm centrifugation with 1Gz at the center of mass or a control group. We performed head-up tilt testing with incremental lower-body negative pressure until presyncope before and after bedrest. We recorded an electrocardiogram, beat-to-beat finger blood pressure, and brachial blood pressure and obtained blood samples from an antecubital venous catheter. Orthostatic tolerance was defined as time to presyncope. We related changes in orthostatic tolerance to changes in plasma volume determined by carbon dioxide rebreathing. Results Compared with baseline measurements, supine and upright heart rate increased in all three groups following head-down tilt bedrest. Compared with baseline measurements, time to presyncope decreased by 323 ± 235 s with continuous centrifugation, by 296 ± 508 s with intermittent centrifugation, and by 801 ± 354 s in the control group (p = 0.0249 between interventions). The change in orthostatic tolerance was not correlated with changes in plasma volume. Conclusions Daily artificial gravity training on a short-arm centrifuge attenuated the reduction in orthostatic tolerance after 60 days of head-down tilt bedrest.

Impact of daily artificial gravity on autonomic cardiovascular control following 60-day head-down tilt bed rest

“…Regardless of the mechanism driving the relative increase in sympathetic activity, be it secondary to reduced cardiac preload or to impaired vascular sympathetic transduction, the reserve of the autonomic nervous system to respond to additional hemodynamic stresses could be reduced. Indeed, while daily artificial gravity at least partly preserved orthostatic tolerance, time to presyncope was numerically reduced in all three groups (28).…”

“…Supine blood pressure variability (lf-SBP), which is mediated through sympathetic modulation of vascular tone, was lower before than after bedrest, (Figure 2B). The participant tolerated 17 min head-up tilt before bedrest and only 6 min of passive upright tilt following bedrest as described previously (28). The orthostatic decrease of RRI was 273 ms before and 335 ms bpm after bedrest consistent with increases in sympathetic efferent activity and post bedrest postural tachycardia.…”