Effect of intermittent hypoxic training on orthostatic tolerance in humans before and after simulated microgravity

About authors

Burnazyan Federal Medical Biophysical Center of the Federal Medical and Biological Agency, Moscow, Russia

Correspondence should be addressed: Vladimir P. Katuntsev
Dyshinskaya,14, kv. 82, 111024, Moscow; ur.xednay@takpv

About paper

Acknowledgement: the authors thank all volunteers who participated in this study.

Author contribution: Katuntsev VP conceived and designed the study, wrote the manuscript; Sukhostavtseva TV collected and analyzed the obtained data, performed statistical analysis and edited the manuscript; Kotov AN collected and analyzed the obtained data and performed statistical analysis; Baranov MV collected and analyzed the obtained data and edited the manuscript.

Compliance with ethical standards: the study was approved by the Ethics Committee of Federal Research Clinical Center of FMBA (Protocol № 1 dated February 7, 2019) and conformed with the principles of biomedical ethics laid out in the Declaration of Helsinki (the 1964 version and subsequent updates); voluntary informed consent was obtained from each study participant.

Received: 2020-10-07 Accepted: 2020-11-23 Published online: 2020-12-14

Reduced orthostatic tolerance (OT) is a serious concern facing space medicine. This work sought to evaluate the effects of intermittent hypoxic training (IHT) on OT in humans before and after 3 days of head-down bed rest (HDBR) used to model microgravity. The study was carried out in 16 male volunteers aged 18 to 40 years and included 2 series of experiments with 11-day and 21-day IHT administered on a daily basis. During the first IHT session, the concentration of oxygen in the inspired gas mixture was 10%; for other sessions it was adjusted to 9%. OT was assessed by a 20-minute-long orthostatic tilt test (OTT) conducted before and after HDBR. Before HDBR, orthostatic intolerance was observed in 3 participants, while after HDBR, it was observed in 9 of 16 volunteers (p < 0.05). During OTT conducted after HDBR, the heart rate (HR) exceeded control values by 26.8% (p < 0.01). Preexposure to any of the applied IHT regimens led to a reduction in the number of volunteers with orthostatic intolerance. After the 11-day IHT program, there was a less pronounced increase in HR during OTT before HDBR; with the extended IHT regimen, less pronounced changes were observed for HR, systolic, diastolic and mean blood pressure (BP). The increase in HR during OTT after HDBR was significantly lower in the group that had completed the 11-day IHT program, while BP remained stable. The changes in HR and systolic BP were less pronounced in the group that had completed the 21-day IHT program than in the control group (p < 0.05). Thus, IHT reduced the risk of orthostatic disorders and mitigated changes in cardiovascular parameters during the orthostatic test.

Keywords: intermittent hypoxic training, orthostatic tolerance, head-down bed rest, blood pressure, heart rate