The PlanHab Project
The aim of PlanHab is to investigate the combined effects of hypoxia and sustained recumbency (bedrest) on human physiological systems as they relate to life in space planetary habitats and also specific clinical populations (chronic obstructive pulmonary disease, congestive heart failure, obesity). Bedrest is commonly used to simulate the biological effects of reduced gravity, or the zero gravity astronauts experience when they fly long-duration spaceflights.
It is anticipated that the partial pressure of oxygen inside future planetary habitats will be lower than our current atmospheric air (i.e. the astronauts will live and work in a hypoxic environment). Prolonged exposure to low / zero gravity will result in the deconditioning of several vital physiological systems, which may become a threat to the health of the astronaut over the long term. However, it is presently unknown how exposure to both reduced gravity and hypoxia will affect human health. Therefore, this study is an applied space-science project with a basic science question:
what will happen to our bodies in this kind of extreme environment?
This study is being conducted at the Olympic Sport Centre Planica, in Rateče, Slovenia. The Olympic centre is capable of housing up to 20 subjects simultaneously, and can simulate any altitude along the entire floor and in each room individually. During the course of this study, subjects will remain in a horizontal position (bedrest) or be able to walk around (i.e. ambulatory), but remain confined to the floor for 21 days. The level of hypoxia will be maintained at 12.5 kPa (corresponding to a high-altitude of 4 000 m above sea level). This study will be conducted using a repeated-measures cross-over design with each subject completing three trials: hypoxic bedrest, normoxic bedrest, and hypoxic ambulation. In between trials, the subjects will have a wash-out period of about 3 months and then return to complete the rest of the trials.
The project will investigate the interactions between hypoxia and unloading in regards to several physiological responses. Since the proposed levels of unloading and hypoxia will be exaggerated compared to those encountered during real-life missions on the moon or planets like Mars, these interactions may be larger than what would occur in a real planetary habitat. One problem associated with the design of human habitats concerns the environmental control and life support system, which, for both technical and medical safety reasons, is desired to have a low operating pressure. A low operating pressure within the planetary habitat will reduce the potential risk of decompression sickness during extravehicular activities.
Implications for Society
Knowledge concerning the combined effects of hypoxia and unloading / inactivity is important for both space science as well as people here on Earth. Individuals who suffer from chronic hypoxia due to diseases like chronic obstructive pulmonary disease or congestive heart failure are very limited in their physical capacity. These individuals are commonly restricted to an inactive lifestyle and so they may also suffer from inactivity-related complications like skeletal muscle atrophy and bone demineralisation. Thus, this research will also assist us to better understand the pathophysiology of these clinical conditions.
Therefore, the principle objective of PlanHab is to evaluate the combined and interactive effects of hypoxia and bedrest on the physiology of the human body. To a large extent, basic core data will be collected corresponding to bedrest experiments already conducted by the European Space Agency and National Aeronautics & Space Agency. Our 21-day project corresponds to a medium-term bedrest study according to ESA standards; therefore our data will be readily comparable to core data collected from previous bedrest studies. Some of the main topic areas include:
• cardiovascular and respiratory functions
• musculoskeletal functions
• haematological and immunological functions
• oxidative stress and thermogenesis
• thermoregulatory functions and circadian rhythm
• sleep disorders and altitude sickness