Calculating deco and mix

[Bismark]

If you want a real chuckle read this:
2000-11 Out The Oxygen Window

The agency whom shall not be mentioned strikes again.....

 

[do it easy]

To me, it has always seemed that the "oxygen window" explanation was just a shorthand or a lazy man's way to explain offgassing using high FO2 mixes.

I agree! I don't think the concept is anymore complicated than perfusion and it certainly doesn't require a 5 page explanation to boil it down to a level that is applicable to divers. Anesthesiologists might need to study it in more detail.

In my little mind, the analogy is similar to rinsing soapy dishes- you can use water or you can use alcohol, but as long as the rinse doesn't contain any soap, either will get the soap bubbles out just as fast as the other. Now if you have soapy dishes with alcohol, and you want to get both out, then using the cleanest water available will be the fastest.

The 1.6 ppO2 is the finger that is pointing to the moon. If you are breathing a gas that has a 1.6 ppO2, then you are minimizing the inert gasses in the mixture.

I just happened to find that whatever basis it came from, the numbers and strageties we covered with GUE work for me, my teams and a lot of other people and are about as simple and easy to use as I think we are going to get. SO I use them

This is the short and skinny of it.

 

[Charlie99]

If you want a real chuckle read this:
2000-11 Out The Oxygen Window

The agency whom shall not be mentioned strikes again.....

Do you disagree any of the facts or analysis of the article? It looks to be a pretty straightforward, relatively lucid explanation.

I certainly hope that you aren't making fun of the EAD of negative 33'. That's a good, simple way to estimate the effect of breathing 100% O2. Your ambient pressure is whatever depth you are at (hopefully 20' or shallower if you are not in a dry habitat or chamber), while your equivalent air depth is -33'.

That's about as simple of a description of the Oxygen Window that you can have.

From my take on it, your explanation <post #19 above> is correct but incomplete. I will chime back in by monday with either some new stuff or my head on a platter.......

I look forward to hearing your take on it after further review. There's a bunch of stuff on air breaks, vasoconstriction, etc., but those are just subtle 2nd order effects. I've never seen a coherent explanation of any "oxygen window" effect other than the reduction of inert partial pressure while not reducing total inspired pressure.

 

[TSandM]

The explanation of the oxygen window in the 2000-11 article is a correct one.

The "oxygen window" that GUE talks about is a phenomenon where you breathe in three gases, but offgas two, and somehow, the space the oxygen was occupying is available to be occupied by inert gas. This has never made any sense to me, since it violates Dalton's law that gases behave in liquids as though they were alone. It does seem to make some kind of sense to sit a short time where the gradient is maximized by the switch to a low inert gas mix, but not because it can crawl out into the "oxygen spaces" in the blood.

 

[wedivebc]

I certainly hope that you aren't making fun of the EAD of negative 33'. That's a good, simple way to estimate the effect of breathing 100% O2. Your ambient pressure is whatever depth you are at (hopefully 20' or shallower if you are not in a dry habitat or chamber), while your equivalent air depth is -33'.

That's about as simple of a description of the Oxygen Window that you can have.
.

No matter what you call it, it's still gas gradient. Oxygen window just sounds more mysterious

 

[Bismark]

Do you disagree any of the facts or analysis of the article? It looks to be a pretty straightforward, relatively lucid explanation.

I certainly hope that you aren't making fun of the EAD of negative 33'. That's a good, simple way to estimate the effect of breathing 100% O2. Your ambient pressure is whatever depth you are at (hopefully 20' or shallower if you are not in a dry habitat or chamber), while your equivalent air depth is -33'.

That's about as simple of a description of the Oxygen Window that you can have.

I look forward to hearing your take on it after further review. There's a bunch of stuff on air breaks, vasoconstriction, etc., but those are just subtle 2nd order effects. I've never seen a coherent explanation of any "oxygen window" effect other than the reduction of inert partial pressure while not reducing total inspired pressure.

How about this part?
quote: "The biggest oxygen window comes from 100 percent oxygen".



I would say that this seems to be at best an oversimplification as the effect of the 02 window at 70' on 50% would be just about the same as 100% at 20'.

Also, "The nitrogen is said to be “going out the oxygen window" seems pretty silly.

You mentioned above the bit on vasoconstriction which pretty much explains why the window is only open for a period of time regardless of the depth/pp02. Then you have to "shut" the window and allow for time to recover from the vasoconstriction and then you can "reopen" the window again.

TTYL

 

[Charlie99]

You mentioned above the bit on vasoconstriction which pretty much explains why the window is only open for a period of time regardless of the depth/pp02. Then you have to "shut" the window and allow for time to recover from the vasoconstriction and then you can "reopen" the window again.

TTYL

You are confusing the main effects with 2nd order things. Vasoconstriction is a reduction in blood flow. It is a secondary issue, much like whether one is still or mildly exercising at deco stops is a secondary issue. Not a trivial issue that one can ignore, but it's not the main factor in decompression. Both vasoconstriction and exercise or the lack of it affect blood circulation levels, but don't significantly affect the partial pressures involved.

 

[gcbryan]

I posted this earlier today in another forum so I'm just cutting and pasting it here. I think Lynne and Charlie's last posts may have answered most of my questions about many of the papers on this subject not making sense.

I've read several papers on the Oxygen Window as well as several posts on this board.

If Charlie reads this post perhaps he has a simple explanation as his posts seem to be the clearest on all topics regarding decompression.

I understand that oxygen is metabolised and replaced in part by CO2 and that more O2 is used and less CO2 is exchanged thereby resulting in a "partial pressure vaccum".

What is the main benefit of this to diving? Since N2 offgassing is only affected by N2 ongassing and not other gasses how does reducing O2 levels in the blood result in faster N2 offgassing? Perhaps it doesn't and this is not the point?

I also understand that with 100% O2 you aren't taking in any more N2 so of course N2 offgassing will take less time but this is not the Oxygen Window.

Is the whole point of the Oxygen Window not that N2 will offgass faster but rather that total partial pressures will be reduced and therefore there will be less bubble formation. Is reduced bubble formation really the whole point of the Oxygen Window?
Is there a point?

 

[Charlie99]

Now that we have had fun with the Oxygen Window, we should start on Isobaric Counterdiffusion .

To me it seems that this is another case where the physics involved are quite straightforward, but that somehow the explanations of what is going on make it seem very esoteric and weird.

It really all boils down to that ongassing/offgassing of each inert gas is driven only by the relative tissue tensions and inspired partial pressure of that inert gas, ignoring all other gases.

 

[Bismark]

You are confusing the main effects with 2nd order things. Vasoconstriction is a reduction in blood flow. It is a secondary issue, much like whether one is still or mildly exercising at deco stops is a secondary issue. Not a trivial issue that one can ignore, but it's not the main factor in decompression. Both vasoconstriction and exercise or the lack of it affect blood circulation levels, but don't significantly affect the partial pressures involved.

You may have read more into this particular post than I intended. Vasoconstriction caused by 02 is simply the reason why the oxygen window is only considered useful for limited amounts of time beyond which greater effect is achieved by increasing the pressure gradient. IE: 3 or 4 minutes with 50% at 1.6 ATAs then the oxygen window is no longer as relevant as moving up and increasing the gradient--3-4 minutes being an average time for your blood supply to be processed once. It could be argued that here, the decision to move up to a higher pressure gradient rather than remain in an "oxygen window" is quite strongly related to vasoconstriction. I would argue that this has more significance than a secondary issue, however, that was not the point I was making.

In the last few hours my reading has supported your original explanation of how the Oxygen window works with a few caveats. This has been a very interesting exercise and I am waiting for a few articles, etc., from some others. Rather than keep updating things, I think it would be more prudent for me to put it all together in one package and then we can go from there. I will provide all the references I can so we can go back to primary sources for the science, etc.

I had some recent sinus surgery last week so I am out of the water for a couple of weeks. A good time to bone up on the theoretical stuff that was less than 100% clear before. What else do you want me to work on? Anything is better than work....