Abstract
We studied 15 men (8 treatment, 7 control) before and after 21 days of 6º head-down tilt to determine whether daily, 1-h exposures to 1.0 Gz (at the heart) artificial gravity (AG) would prevent bed rest-induced cardiovascular deconditioning. Testing included echocardiographic analysis of cardiac function, plasma volume (PV), aerobic power (VO2pk) and cardiovascular and neuroendocrine responses to 80º head-up tilt (HUT). Data collected during HUT were ECG, stroke volume (SV), blood pressure (BP) and blood for catecholamines and vasoactive hormones. Heart rate (HR), cardiac output (CO), total peripheral resistance, and spectral power of BP and HR were calculated. Bed rest decreased PV, supine and HUT SV, and indices of cardiac function in both groups. Although PV was decreased in control and AG after bed rest, AG attenuated the decrease in orthostatic tolerance [pre- to post-bed rest change; control: −11.8 ± 2.0, AG: −6.0 ± 2.8 min (p = 0.012)] and VO2pk [pre- to post-bed rest change; control: −0.39 ± 0.11, AG: −0.17 ± 0.06 L/min (p = 0.041)]. AG prevented increases in pre-tilt levels of plasma renin activity [pre- to post-bed rest change; control: 1.53 ± 0.23, AG: −0.07 ± 0.34 ng/mL/h (p = 0.001)] and angiotensin II [pre- to post-bed rest change; control: 3.00 ± 1.04, AG: −0.63 ± 0.81 pg/mL (p = 0.009)] and increased HUT aldosterone [post-bed rest; control: 107 ± 30 pg/mL, AG: 229 ± 68 pg/mL (p = 0.045)] and norepinephrine [post-bed rest; control: 453 ± 107, AG: 732 ± 131 pg/mL (p = 0.003)]. We conclude that AG can mitigate some aspects of bed rest-induced cardiovascular deconditioning, including orthostatic intolerance and aerobic power. Mechanisms of improvement were not cardiac-mediated, but likely through improved sympathetic responsiveness to orthostatic stress.
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Acknowledgments
The authors gratefully acknowledge the support of the UTMB GCRC nursing staff, the Short Radius Centrifuge team, the subjects who participated in the study and JSC Cardiovascular Laboratory team members that participated in data collection and reduction, particularly Christine Ribeiro, Shang-Jin Shi, Ph.D., Timothy Matz, David Martin, and Natalia Arzeno-González. We would also like to thank Alan Feiveson, Ph.D., for statistical support. This study was supported by the NASA Human Research Program, and conducted at the NIH-funded [M01 RR 0073] GCRC at UTMB, Galveston, TX.
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Communicated by Dag Linnarsson.
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Stenger, M.B., Evans, J.M., Knapp, C.F. et al. Artificial gravity training reduces bed rest-induced cardiovascular deconditioning. Eur J Appl Physiol 112, 605–616 (2012). https://doi.org/10.1007/s00421-011-2005-1
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DOI: https://doi.org/10.1007/s00421-011-2005-1