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Wil, you write:
> Is a trimix dive ever actually able to induce a useful oxygen window
> during the course of a typical decompression schedule ?
>
> I am talking here about the real oxygen window that operates between a
> bubble / tissue or bubble / blood interface rather than the concentration
> gradient it is often mistaken to be.
>
Chuck,
The much maligned term "Oxygen window" actually refers to a popular theme
from the 70's (supersaturation theory) that has to do with optimizing the
total tissue saturation. It's based on the idea that deeper tissues
naturally run an O2 partial-pressure deficit, and that that deficit
can be filled by inert gasses during deco. Under normal pressures, this
deficit plays a significant part in drawing O2 into the tissues,
due to the gradient differential. Note that the true definition
of "oxygen window" has nothing to do with either inert gas partial pressure
gradients or bubble formation, as popular banter would suggest.
> It seems that our practice of maintaining relatively high PPO2 during deco
> would serve to keep the oxygen tissue tensions higher than that of any
tissue
> bound bubbles and the drop in venous PPO2 such a small percentage of the
total
> that there would be little or no opportunity to diffuse any O2 out of
bubbles
> in either environment during an ascent after the first gas switch.
Chuck, in all honesty, you're mixing terms and concepts here in a way that
frankly makes little sense. Among other things, arterial, venous,
or any other O2 tensions have little or nothing to do with the real
issue, which is inert gas management (whether bubble, microbubble, or
theoretically potential bubble). Diffusing O2 out of bubbles
is the least of worries.
Regards,
-Will
========================
Well, one thing is for sure in the world of diving. Just about half the
terms in use have been maligned to the point of meaninglessness.
I have seen 4 definitions of the O2 window :
1 The drop in tissue PPO2 resulting from the metabolism of O2
2 The change in inert gas partial pressure gradient across
a bubble/tissue interface due to O2 metabolism
3 The drop in total venous dissolved gas pressure due to
O2 metabolism
4 The partial pressure of the inspired O2
The top 3 refer to specific features of the process associated with the
O2 window but non by itself does it justice. The fourth is wrong.
My post was based on no. 2 alone with no further explanation and
you are right; it is misleading.
I will reorganize it and post something more intelligible.
Chuck Boone
--
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