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At 12:01 PM 10/22/00 +0700, you wrote:
>were they in a chamber for the 2.0 tests?

Obviously, but I didn't take part in that. I was just breathing argox from 
a rebreather at surface pressure while they took gas samples and drew some 
blood at regular intervals. The parameters of this test were blood fat 
contents (empty stomach/no breakfast versus a high-fat breakfast) and PO2. 
I remember the graphs from several test trials showing how the PO2 affected 
the offgassing rate of nitrogen, the faster the more hypoxic the breathing 
medium. I don't think the blood fat issue made much of a difference but 
obesity would since you'd have more slow tissues to equilibrate. I haven't 
read the final paper on this whole series of experiments and I'm sure that 
would be a good idea.

In any event, the improved offgassing is a vasodilation issue. If you 
balance this issue out against the benefit of a total absence of inert gas 
accomplished by breathing oxygen, rather than just measuring the time it 
takes to swap one inert gas for another, you'd still want hyperoxia for 
deco. In a fantasy world the best deco mix would be a mix bordering on 
hypoxic, the rest of it being an inert gas that does not dissolve in 
tissues. I don't believe this inert gas has been invented yet :-)

As an aside, if one is using a hyperoxic bottom mix to get more no-stop 
time (nitrox/ hot trimix) the vasoconstriction issue would actually provide 
another margin to DCS. So the question "What does this bode for nitrox 
diving?" should be answered by stating "It gives you a slight additional 
edge that goes beyond the EAD". Oxygen induced vasoconstriction is hardly a 
deco problem until you want to lose inert gas -- acquiring a tad less inert 
gas than calculated will not hurt. However, I'd like to repeat: The 
vasoconstriction issue is a very good reason to do backgas breaks and may 
help explain why breaks are "good" deco time. It could very well be that 
longer or more frequent backgas breaks will prove to be the best approach.

regards,

Hans

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