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Dave Story
> 
> Julius Loennechen
> > 
> > [....] The +oxygen
> > window+ is the non-inert part of a breathing mix which does not contribute
> > to bubble formation. It is, slightly simplified, the partial pressure of
> > oxygen at a given depth. 
> 
> This is not my definition of "oxygen window."  The oxygen window is
> the "inherent unsaturation" of the tissues brought about by the
> consumption of O2 in the metabolic process.  Simply stated: you inhale
> ~21% O2 and exhale only 16% O2.  The difference is not completely made
> up in CO2 produced.  Hence you have an "inherent unsaturation" or
> "oxygen window" into which you can eliminate inert gases, since you
> have a below normal pressure of gases in your venous blood.

The Jan/Feb '93 issue of Alert Diver has an article on the oxygen
window by Richard Vann, Ph.D. A highlighted part on page 15 reads:

"Oxygen increases the nitrogen gradient between lungs and tissue
which makes perfusion more efficient in removing nitrogen. The
reduced tissue nitrogen also increases the gradient for the diffusion
of nitrogen from the bubble back into tissue. This gradient between
nitrogen in the bubble and in tissue is known as the oxygen window."

It also has an interesting explanation of the chemistry of bubbles,
pointing out that the elimination of gas in a bubble is slower
than the elimination of dissolved gas. He adds:

"In repetitive diving, this might lead to an accumulation of
inert gas not expected by a Haldane decompression model which
assumes gas to remain dissolved."

John Crea's modification of the Buhlmann model attempts to
compensate for this by using longer halftimes for tissues
which are off-gassing.

Bill Mayne

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