Physiological responses to sustained recumbency and hypoxia; implications for future planetary habitats

It is envisaged that the breathing gas in future human-use habitats on the Moon and Mars will have low partial pressure of oxygen (hypoxia). Thus, the atmospheric pressure in such habitats needs to be reduced to inhibit decompression sickness in conjunction with repeated excursions (EVAs; extravehicular activities) to the face of the Moon/Mars. Information is scarce regarding physiological responses to sustained exposure to hypoxia and reduced gravity. To investigate the combined effects of hypoxia and musculoskeletal and cardiovascular unloading (simulating reduced gravity) healthy individuals (n=14) were exposed to three 21-day interventions in a crossed and balanced, latin-squared fashion: (i) hypoxia (corresponding to an altitude of 4000 m) and sustained horizontal recumbency (bedrest), (ii) hypoxia and ambulation, and (iii) normoxia and bedrest, interventions being separated by 4-month washout periods. Several physiological systems were investigated both as regards function and morphology. The interactive effects of hypoxia and bedrest varied. For instance, hypoxia exaggerated the bedrest-induced drops in plasma volume, cardiac output and aerobic exercise capacity. By contrast, hypoxia countered the bedrest-induced reduction in orthostatic tolerance, whereas it did not affect the bedrest-induced decreases in postural muscle mass and strength, or in insulin sensitivity and glucose tolerance.

The lecture will give an overview of the study background, experimental design and of some of its main results.

Coffee and cake will be available for the first 30 attendees at 15:00, warmly welcome!