h a l f b a k e r yExpensive, difficult, slightly dangerous, not particularly effective... I'm on a roll.
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Welll.....the problem with this idea is that it taps into an
artery (and presumably a biggie, if it's to have much effect). |
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Your arterial blood is at a pretty constant temperature
anyway, unless you're in real difficulty. So trying to adjust
its temperature would be either pointless or dangerous. |
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Dangerous? very (maybe not so much with more
research into how to do this safely). Pointless? no.
Since blood circulates through the entire body it has
the potential to act as a coolant or heating fluid. I
believe it would be quite effective. |
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Excellent! Now if I can only figure out how to float around the room, I'll feel like the Baron in the movie "Dune" (only with fewer complexion problems). Bun! [+] |
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//Since blood circulates through the entire body it has the
potential to act as a coolant or heating fluid.// Not
"potential." It already works this way, with skin as the
heat exchanger. |
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[MB] dropping the temperature of arterial blood is a pretty
commonplace occurrence: happens when the arterial
blood enters the capillaries. I'd rephrase your criticism as
"Altering core [as opposed to peripheral] body
temperature would be dangerous." Nonetheless, it's
occasionally done, typically by means of gastric lavage,
though ventilation with warmed air, or as an incidental
effect of laparotomy. |
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All of those methods work better than this idea, but none
of them *look* as good. Extracorporeal circulation is a
well-developed technology, so this should be feasible.
Probably could be made portable, but if not, portable
intraaortic baloon pumps exist, and could presumably be
used to heat or cool cool arterial blood in situ. |
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I don't think this method would actually make people
comfortable. I think that: in hot weather, it would make
you shiver violently and feel horribly cold, whereas, in cold
weather, you might *feel* OK, but you'd still need warm
clothing to avoid frostbite. |
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//I don't think this method would actually make
people comfortable. |
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We won't know until we try (not me). Also why
would you "shiver violently?" Maybe if you
adjusted your temperature wrong .... but just
crank it back up a little until you are comfortable. |
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I
was thinking about the frostbite problem too, but
I
decided that it would not be a problem either .. |
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from wikipedia: "At or below 0 °C (32 °F), blood
vessels close to the skin start to constrict. The
same response may also be a result of exposure to
high winds. This constriction helps to preserve
core body temperature. In extreme cold, or when
the body is exposed to cold for long periods, this
protective strategy can reduce blood flow in some
areas of the body to dangerously low levels. This
lack of blood leads to the eventual freezing and
death of skin tissue in the affected areas." |
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If core body temperature is normal with no signs
of dropping, the body will
have no reason to use this protective strategy of
restricting blood flow. If blood flow is not
restricted, there is no worry of frostbite. I admit
I may be wrong about this, because the wind may
be the main trigger for the constriction (not
temperature). In that case, just go out dressed
in nothing but thin wind proof jacket and you'll be
fine against frostbite (even if it's -60C) |
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//If core body temperature is normal with no signs of
dropping, the body will have no reason to use this protective
strategy of restricting blood flow.// |
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I am pretty sure that the constriction of peridermal blood
vessels does not happen in response to changes in core
temperature, but in response to skin temperature. |
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anno extensively edited as the original included factually
incorrect material and faulty reasoning. The following is
better, I hope. |
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re: shivering: I think I may have been talking through my
hat. |
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Re: frostbite:" What's the rate of bloodflow through your
fingertips?
What's the rate of heat loss at an ambient temp of, say -
50C, if the fingertips are, say, 0C? What's the specific heat
of blood? Now, how hot would the blood flowing through
the fingertips have to be, to keep them above freezing? I
don't know any of these numbers: I merely intuit that the
necessary blood temperature would be dangerously high
for every other part of the body. |
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Pace [MB] it appears (<link>) that constriction of
peridermal blood vessels DOES happen in response to
changes in core temperature. However, for frostbite, it's
more important that "Local cooling of the skin [also]
produces a powerful localized vasoconstriction that can
decrease skin blood flow essentially to zero." So there's a
positive feedback effect which makes it even harder to
prevent frostbite by heating blood. |
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There's a way to test it, though. This is best done in
somewhere with 1) cold winters and 2) high rates of
alcoholism. First, find a volunteer with, say, pneumonia,
or anything that'll cause a high fever. Next, administer
enough vodka to cause A) peripheral vasodilation and B)
unconsciousness. Finally, recover your research subject
from the snowbank where he or she has passed out.
IMPORTANT: do this prior to the onset of hypothermia. (A
rectal thermometer will help with monitoring core body
temperature. That's why unconsciousness is essential.) I
hypothesize that frostbite will occur. |
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