wrote:
: But if I go underwater, there's certainly no air there. And I can stay
: down for a while, holding my breath. How is high altitudes different?
: I would think you would rasp / fight to breath in but keep functioning
: as your body uses up the 02 in the blood from your last breath? Not
: like a sleeping gas in the movies where you just keel over as soon as
: it hits you?

Your breathe reflex is controlled by the concentration of CO2 in your blood,
not the lack of O2. If you hold your breath underwater, you increase CO2
concentration and your breathe reflex kicks in. If you go to high altitude (or
breathe any non-CO2-enriched mixture of gasses where the partial pressure of O2 is too
low to maintain adequate O2 transfer to your blood), the CO2 in your blood will
happily exchange out of your lungs. You don't feel the urge to breathe, and simply
pass out from lack of oxygen.

Different mechanisms between life-sustainment and breathe reflex.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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