Cardiovascular Responses to Artificial Gravity are Modulated by Radius of Rotation and Exercise

Abstract

Artificial gravity (AG) training improves orthostatic tolerance (Aviat Space 2004;75:–8), but AG protocols have not been optimized. We therefore investigated regulatory responses to variations of posture, exercise, Gz level and radius of rotation (the latter two measured at the foot). Results presented are from 4 protocols that address radius and exercise effects only. Protocol A: After 10 min supine control, 12 healthy men (age 35 ± 9 yrs, wt 82.8 ± 7.9 kg) were exposed to rotational 1 Gz (2.5 m radius) for 2 min followed by 20 min of alternating between 1 and 1.25 Gz. Blood samples were taken pre and post spin. Protocol B: Subjects repeated A, but lower limb exercise (70% of V02max) preceded the ramps to 1.25 Gz. Protocol C: Same as A but radius of rotation was 8.3 m. Protocol D: Same as B but at 8.3 m. RESULTS: For the 8 subjects who completed all 4 protocols, we observed the following increases from control: Heart Rate (HR, bpm) A: 4, B: 40, C: 15, D: 45; Hematocrit (HCT, %) A: 2.0, B: 3.5, C: 2.4, D: 4.3; Aldosterone (pg/ml) A: 0, B: 121, C: 32, D: 115; and Plasma Renin Activity (PRA, ng/ml/h) A: 0.18, B: 1.12, C: 1.29, and D: 1.12. Our data suggest that HR, HCT and aldosterone were primarily influenced by exercise and secondarily by radius while PRA was influenced by both. We conclude that an optimal AG training countermeasure should involve exercise and maximal radius of rotation. Supported by NASA EPSCoR WKU52611 and NASA Ames Res. Center.