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Richard Pyle wrote: > Are you sure about that? I have always read that O2 is a vasoconstrictor > - not an inhibitor of vasodialation. People don't lose arms & legs in > chambers because: > 1) vasoconstriction does not equate to zero blood flow (as pointed out by > Prime Rat); and > 2) there is so much dissolved oxygen in the blood & tissues during > hyperoxia that the tissues do not get hypoxic (if they did, the > vasoconstriction effect would reduce, and the tissues would get the needed > blood flow). A thought about this occured to me while I was in the shower this morning (yes, thinking best in the shower is, unfortunately, about the only thing I have in common with Mr. Mickey Mouse, Michael Eisner): If increased O2 levels really result in significant vasoconstriction, thast would imply that diving Nitrox using EAD (Equavallent Air Depth) and an air table would be extremely dangerous. In fact, we would see substantially more DCS incidents in EANx/EAD/Air table divers vs Air/Table divers. (This would be due to vasoconstriction imparing offgassing.) Perhaps one could argue that any vasoconstriction effect would also impair tissue loading, but I would argue (and, in fact, do :-) that the time delay before the O2 level increased to the point where vasoconstriction manifested would permit significant tissue loading to occur according to the non-vasoconstriction model. Do I believe that vasoconstriction is an issue? Not really, but it sounds interesting. I had not included it in the model I built earlier, as at the time the vasoconstriction effect of O2 was not quantifiable and did not seem very large. One thing is for sure: the interaction of pressure and O2 on the diver seems more interesting and complicated every day -- and I think the complex interactions are way beyond our capability to reason about using just calculators. Remember, the problem here is essentially one of linear diffusion through a moving fluid, with feedback. Not simple at all. -frank -- fhd@pa*.co* | One man's knowledge is another man's trivia. 1 212 559 5534 | 1 917 992 2248 | 1 718 746 7061 |
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