Working Toward Human Hibernation During Long Term Spaceflight

Editor’s note: As we start to move off-world on longer space missions, the issue of crew health, food, life support, and overall safety becomes a pressing issue. If you can do what science fiction movies often do and put the crew into some form of hibernation or “suspended animation” then you could conceivably address those issues. You could also have this option as a way to deal with severe injuries or illness during the mission that the crew does not have the capability of addressing. The notion of sending humans to distant worlds is quickly limited by the realities of human life span and life support requirements. Anything that serves to lessen those life support needs and/or extend a human’s life span will serve to enable more distant exploration missions by humans than might otherwise be the case.

Hibernation is a widespread and highly efficient mechanism to save energy in mammals. However, one major challenge of hibernation is maintaining blood circulation at low body temperatures, which strongly depends on the viscoelastic properties of red blood cells (RBCs).

Here, we examined at physiologically relevant timescales the thermomechanical properties of hundreds of thousands of individual RBCs from the hibernating common noctule bat (Nyctalus noctula), the nonhibernating Egyptian fruit bat (Rousettus aegyptiacus), and humans (Homo sapiens). We exposed RBCs to temperatures encountered during normothermia and hibernation and found a significant increase in elasticity and viscosity with decreasing temperatures.

Our data demonstrate that temperature adjustment of RBCs is mainly driven by membrane properties and not the cytosol while viscous dissipation in the membrane of both bat species exceeds the one in humans by a factor of 15. Finally, our results show that RBCs from both bat species reveal a transition to a more viscous-like state when temperature decreases.

This process on a minute timescale has an effect size that is comparable with fluctuations in RBC viscoelasticity over the course of the year, implying that environmental factors, such as diets, have a lower impact on the capability of RBCs to respond to different temperatures than general physical properties of the cell membrane.

In summary, our findings suggest membrane viscoelasticity as a promising target for identifying mechanisms that could be manipulated to ensure blood circulation at low body temperatures in humans, which may be one first step toward safe synthetic torpor in medicine and space flight.

• Thermomechanical properties of bat and human red blood cells—Implications for hibernation, PNAS via PubMed
• Thermomechanical properties of bat and human red blood cells—Implications for hibernation, PNAS

Astrobiology, Space Medicine,