What Do Ya Know About Body Temp?

I am going to take a guess and say that body temperature isn't something you normally think about ( I know when I roll out of bed in the morning... my body temperature isn't exactly the first thing on my mind... its usually the thought "Damn it, morning already?" ). We don't NEED to think about it much, since since temperature is pretty well regulated after all, especially here on earth with our great atmosphere! So perhaps lets begin by discussing it just a bit.

You are all familiar with just how important our body temperature is to how we feel right? You know that the average human body temperature is 37 °C and we've likely all been sick and had a slightly elevated temperature and felt awful, or been outside unprepared in the winter and experienced a slightly lowered body temperature (the beginnings of hypothermia).

Maintaining a body temperature right around that 37 °C mark is extremely important for a variety of things including our abilities to accomplish both physical or mental tasks (AKA, its important for literally every aspect of our existence!). [2], [3]. If our body temperatures get too high, or too low... well you know the result... (gulp) death.

So how do we achieve this very specific body temperature? Well a portion of the brain called the hypothalamus does the heavy lifting for you. It causes us to give off less heat when our body temperatures drift too low, and to further give off more heat and utilize the exaporation of sweat to cool things down when it drifts too high. [4] It is recommended that for any worker, doing a job that their core body temperature not exceed 38 °C, so we really only have a 1 °C window.

On earth our atmosphere does a good job allowing for effective heat transfer, however in space things are a bit different for the astronauts. In fact there is another contributing factor to effective transfer of heat away from our bodies that we on earth all take for granted.

Gravity

Up in space there is a distinct lack of gravity, and the result is a recipe for reduced heat transfer away from the body (evaporation of sweat... not so easy in zero gravity!) [5] However, does this reduced heat transfer ability actually cause drastic changes to astronauts core body temperatures?

The Data

Okay so this study was simple enough to perform, just monitor the body temperature of astronauts on long space flight missions on a daily basis. Which is precisely what was done:

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Reproduced from [1] Figure 1

In the image to the left we are looking at reported core body temperature (CBT) readings for the astronauts. Pre, is the value prior to the initiation of the space flight (the greyed box), and the values after the greyed box (+1 etc) are days back on earth after the space mission. What we can see from this figure is that the astronauts core body temperature, at rest, was raised by around 1 °C after by 75 days of space flight (so a good length for a mission). This is within the recommended guidelines for people who are actively engaged in work on earth and likely does not pose a significant health risk. (three *'s above the data point indicates a p<0.001, so relatively good statistical significance that the rise is indeed a real phenomenon and not due to just noise in the data). We also see in this data that upon returning to earth, the astronauts body temperature quickly returns to the pre-mission levels.

In the image to the right, we are looking at reported core body temperature readings for the astronauts during exercise. We can see that while still on earth, during exercise the astronauts body temperatures increased by about 1.5 °C from at rest levels, and that exercising in space resulted in a significant further increase in the body temperatures, with some astronauts reporting core body temperature readings exceeding 40 °C, which would be a 3 °C or greater increase. To make matters worse, the intensity of the exercise the astronauts were doing during the space fight was significantly lower then what was done for the "pre-flight" baseline.

This is a bit troubling, as it has been determined elsewhere that [6] exposure of the brain to temperatures of 44 °C can cause lasting damage, and these astronauts were pushing values exceeding 40 °C with out even working as hard as they could be! This means its a potential that the astronauts could experience body temperatures that were far too high quite easily.

TL;DR

Our body temperatures are highly regulated, with an optimal temperature of around 37 °C. Here the authors report that regulation of body temperatures is much more difficult in outer space based on data collected from astronauts during space flight. An increase in body temperature was observed both during activity in space and also during rest. As such the authors have coined the term "space fever" to describe the phenomenon. The increased body temperatures that astronauts are experiencing have the potential to cause health issues that may remain even after they are no longer participating in space flights. So the question we are left with now is... what do we do with this information? How can we better protect our astronauts bodies during space flights?

Sources

Image Sources

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What Happens To An Astronauts Body Temperature During A Long Space Flight?