An international team of scientists led by Professor Hanns-Christian Gunga of Charité-Universitätsmedizin Berlin has observed that astronauts run hot when exposed to weightlessness, and that, even at rest, their core body temperature is around one degree Celsius above the normal value. The results appear in the journal Scientific Reports.
Stahn et al observed for the first time a sustained increased astronauts’ core body temperature under resting conditions. Image credit: Jonny Lindner.
“Humans are endothermic organisms with a core body temperature of about 37 degrees Celsius (98.6 degrees Fahrenheit), which is controlled within a narrow range by the preoptic nucleus of the hypothalamus with slightly undulating circadian changes,” Professor Gunga and co-authors said.
“It is well known that the tight control of body temperature is a prerequisite for maintaining physical and mental performance. Severe body temperature deviations can even have life-threatening consequences.”
“During spaceflight these processes can be considerably challenged as reduced gravity impairs convective heat transfer and the efficiency of evaporation. Such deficiencies could be particularly prominent during exercise, where over 80% of energy expenditure is converted to heat.”
The researchers developed a new technology which combines a skin surface temperature sensor with a heat flux sensor, and which is capable of measuring even minor changes in arterial blood temperature.
They measured astronauts’ core body temperature before, during and after their stays on the International Space Station (ISS), taking readings both at rest and during exercise.
They found that the astronauts experienced a type of persistent fever — during exercise, the astronauts’ body temperature often exceeded 40 degrees Celsius (104 degrees Fahrenheit).
“We used forehead sensors to measure the core body temperature (the temperature of the internal body and brain) of astronauts on the ISS,” the scientists said.
“We found that the astronauts’ core body temperature did not increase suddenly, but that this increase in temperature developed gradually over 2.5 months, eventually reaching approximately 38 degree Celsius (100.4 degrees Fahrenheit).”
“Under weightless conditions, our bodies find it extremely difficult to eliminate excess heat,” Professor Gunga explained.
“The transfer of heat between the body and its environment becomes significantly more challenging in these conditions.”
“Our results will have positive implications for the health and well-being of astronauts during future long-term space missions,” he added.
“Our findings also pinpoint crucial physiological challenges for spacefaring civilizations, and raise questions about the assumption of a thermoregulatory set point in humans, and our evolutionary ability to adapt to climate changes on Earth,” the researchers concluded.
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Alexander C. Stahn et al. 2017. Increased core body temperature in astronauts during long-duration space missions. Scientific Reports 7, article number: 16180; doi: 10.1038/s41598-017-15560-w
