Core body temperatures in astronauts on the international space station
- Paper number
IAC-17,A1,2,16,x37788
- Author
Prof.Dr. Hanns-Christian Gunga, Germany
- Year
2017
- Abstract
Endothermic organisms such as humans have a core body temperature (CBT) of about 37 °C, which is controlled by the hypothalamus with slightly undulating circadian rhythm changes. Even mild CBT deviations impair physiological functions, leading to changes in physical and mental performance, while more severe deviations (<33 °C or >40 °C) may have life-threatening consequences. Several factors, including exercise intensity, environmental conditions, and hydration, determine the extent, duration, and health risks associated with exercise-induced hyperthermia. Heat exchange between an organism and its environment occurs by way of conduction, convection, radiation, and evaporation. Under terrestrial thermoneutral and resting conditions this happens mainly by radiation and convection. It has been assumed that in space these mechanisms of heat exchange are challenged due to a lack of convective heat transfer, diminished production, and/or efficiency of evaporation. Several authors have touched on the issue of thermoregulation in weightlessness, either in sleep or in circadian rhythm-related studies, but it should be of particular interest during vigorous exercise where >80% of energy expenditure is converted to heat. To address the question of impaired thermoregulation in space a joint international research project called Thermolab was conducted in close cooperation with the German Aerospace Agency (DLR), the European Space Agency (ESA), and the National Aeronautics and Space Administration (NASA). The overarching aim of this initiative was to continuously monitor the changes of CBT during exercise before, during, and after long-term stays on the International Space Station (ISS). Due to impaired heat exchange mechanisms in microgravity, we hypothesize that CBT increases faster and reaches a higher maximum during physical exercise in space than on ground. We found that astronauts’ CBT, indeed, rises higher and faster during short-term exercise on the International Space Station (P<0.05) than under same conditions on Earth, in some instances exceeding 40 °C. Surprisingly, resting temperatures gradually increased by 1.0 °C while in space and only returned to baseline 30 days after landing (P<0.05). Increased interleukin-1 receptor antagonist levels were associated with the latter changes (P<0.05). Since already slight core body temperature changes can impair physical and cognitive functions, these findings have an impact on astronauts’ health and future space missions. This research was supported by DLR/BMWi Projects 50WB0223, 50WB0724, and 50WB1030.
- Abstract document
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