I was in the gym's steam-room today and a thought occurred to me: have I truly thwarted all possible mechanisms for maintaining thermal homeostasis?

There's sweating, which is thwarted because the steam-room's atmosphere is as close to 100% humidity as possible, so there's almost no evaporative cooling.

There's convection, which is thwarted because the ambient temperature is above normal body temperature.

And I can't get rid of heat by exhaling, because every lungful of air I inhale is already above normal body temperature.

I think that, eventually, I should go into hyperthermia, but beside the above, are there any other last-ditch attempts to lower core temperature that my body could take?

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    $\begingroup$ Thermotaxis? :) $\endgroup$ Dec 21 '11 at 1:32

Another factor at play here is the cardiovascular system. Biro, Masudo, et al (2003) wrote an article about the benefits of the induction of systemic vasodilation for those with congestive heart failure. This may be a short-term adaptation of the body stemming from the reduced ability to sweat in those conditions, or it may be a harbinger of the more serious circulation changes below.

Epstein and Roberts (2011) explain how the eventual results of heatstroke (which isn't the phenomenon that you are describing, but a sauna might induce some of the features of these same pathways) can cause a circulatory collapse due to an initial overtaxing of the circulatory system to compensate as well as the activation of certain heat shock proteins.

There are a lot of other references out there on sauna physiology, but many are not in evidence-based journals, so you can make your own decisions on those.

One factor that I didn't find mentioned explicitly was the basal metabolic rate. It's probably safe to assume that the body will limit its own processes and reactions which produce heat. I'm not clear on the extent to which factors such as the level of interleukins, etc. would play a role as they do in fever regulation.


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