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Reading the stuff previously posted on the Oxygen Window - especially Bill
Wolk's postings which are very helpful - it almost all makes sense, except
that I can't quite understand why the high ppO2 in the blood helps the
Nitrogen come out of the cells. I understand the advantages of 100% O2 over
80/20, but can't fully see why breathing 100% O2 at 20' is better than
breathing 100% O2 at 10'. I accept that it has proven to be better, but
would like to understand the theory as to why.

Bill Wolk defined the Oxygen Window as used in diving theory as "the
difference between the concentration of inert gas dissolved in tissue vs.
the concentration of oxygen and inert gas in arterial blood". Breathing an
elevated ppO2 forces extra O2 to dissolve into the blood plasma, in addition
to that normally carried bound to Hemoglobin. So far I'm with the program.

But what I can't see is how this additional O2 affects the N2 coming out of
the tissues. When there is no N2 in the arterial blood anyway, why does
forcing additional O2 into it make a difference?

According to Henry's law the amount of Nitrogen that will dissolve into the
blood is affected only by the partial pressure of the Nitrogen itself, so
increasing the ppO2 will have no effect on that. A previous posting (which I
can't find now, but I don't think anyone argued against it) indicated that
increased ppO2 will tend to block the Nitrogen molecules from coming out of
the cells by osmosis.

The only beneficial effect of the additional O2 that I can see is that
(again from a previous Bill Wolk posting) "the additional osmotic pressure
forces O2 into the surrounding tissue, which has the effect of oxygenating
tissue and reducing swelling and clotting -- essentially, healing the
cellular damage caused by deco diving". Is that the only benefit of the
higher ppO2, or is there something other way in which it aids off-gassing
N2?

Anyone care to explain?
Ian



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