Microgravity increases core body temperature: IIST model

The Hindu

04-05-2025

The Voyager 1 spacecraft was 25 billion km away in February, somewhere in the outer edge of the solar system. It's the farthest a human-made spacecraft has gone from the earth. The hope is that in the distant future, a human astronaut will be able to go where Voyager 1 has been — a journey that could take several years of spaceflight.
An important factor that determines an astronaut's well-being on such journeys is thermoregulation: their body's capacity to maintain a stable internal temperature. In the unique microgravity environment of space, this process faces significant challenges.
Now, researchers at the Indian Institute of Space Science and Technology (IIST), Thiruvananthapuram, have published a study reporting that 'microgravity consistently increases core body temperature, with fluid shifts playing a crucial role in thermal balance,' in the words of Shine S.R., a professor of aerospace engineering at IIST and an author of the study.
Human bodies respond differently to temperature changes based on age, fitness level, and body fat, among other parameters. In environments with near-zero gravity like space, the human body changes significantly, affecting bones, muscles, the heart, the immune system, metabolism, even individual cells. Some of the resulting complications can be severe, so space agencies and astronauts continuously monitor the spacefarer's body temperature.
Scientists using a computer model to evaluate the body's ability to regulate temperature in specific conditions must also account for 'physiological changes observed in space, including blood shifts, metabolic variations, muscle atrophy, and environmental influences'.
Shine said his team has developed a 3D computational model of human thermoregulation that 'incorporates these changes to simulate the effects of microgravity on thermoregulation, including blood redistribution, reduced blood volume, changes in metabolism, and alterations in bone and muscle mass'.
According to Chithramol M.K., PhD student at IIST and first author of the study, the team's studies were limited by sufficient as well as accessible data on metabolic changes. In situations where data was unavailable, she said they tested how different factors changed their results and used their 'best judgment and standard engineering practices' to assess their impact.
The model uses mathematical equations to track how heat moves through the body in three dimensions, and accounts for mechanisms like sweating and shivering, the impact of clothing, heat generated by vital organs, and other factors that have a say on how a body regulates its temperature.
Each factor is modeled separately and then combined to understand the overall impact of microgravity on thermoregulation.
The team published its findings with the model in Life Sciences in Space Research on March 29.
'Our findings reveal that the redistribution of blood from the lower limbs to the upper body in microgravity environments significantly impacts the body's temperature distribution,' Shine and Chithramol said.
Specifically, the researchers reported that while the feet and hands become cooler as the body spends more time in microgravity, the head, abdomen, and the core get warmer.
The model also indicated that when astronauts exercise in space, their body temperature rises faster than it does on the earth.
Over 2.5 months in microgravity, considering 30% lower sweating and 36% higher metabolism, the core body temperature may increase to around 37.8° C from 36.3° C before flight. If one were exercising in the same conditions, the temperature would be closer to 40° C.
The researchers were able to confirm their model was able to predict real outcomes by using it to simulate astronauts' body temperature onboard the USSR's and Russia's erstwhile Mir space station and onboard the International Space Station, then compared its output to official reports. They matched.
Most current models that predict how bodies regulate temperature mostly use data from non-Indian populations. Different body types and physiological processes modulate thermoregulation differently; a model specific to one population group may fail to predict specific outcomes when applied to another group.
As thermoregulation models indicate how a person responds to temperature changes, they are also used in many everyday situations. For example, clothiers use such models to fine-tune how their products keep people warm or cool. Architects use such models to design buildings to lower heat stress of their occupants. In medicine, especially during heart surgeries, thermoregulation models predict how a patient's body temperature changes, helping both doctors and patients avoid complications.
According to the IIST team, these models calculate the universal thermal climate index — a number that indicates how hot or cold it feels outside by considering factors like wind, humidity, and sunlight.
Shine said, 'These models are valuable tools for enhancing safety, comfort, and performance in diverse real-world scenarios' in addition to astronaut health and safety in microgravity environments. 'Take our model, for example: while [it] was developed with the human space program in mind, we have also realised its potential in various everyday situations on earth.'
Shreejaya Karantha is a freelance science writer.