Any reported cases of Ox Tox between 1.4 and 1.6?

[lermontov]

Less nitrogen exposure, longer NDLs. Are you asking something else?

sorry didnt mean to direct that to you - just following on tursiops view of nitrogen decreasing rather than oxygen increasing veiw point - ive found explaining it to others in those terms is easier to understand

 

[justinthedeeps]

Re: oxygen windows
Why would oxygen metabolism somehow be relevant or magically different at 1.6 vs. 1.0 atm, or have anything to do with the off-gassing other gases?

Oxygen supply is already in excess regardless of whether it's 1.0 or 1.6 atm, the metabolic rate of oxygen consumption is independent of depth, etc etc ..

Seems like a lot of attention was placed on arterial oxygen supersaturation. Sure it creates 'ratios,' and total arterial pressure is higher, but how is this actually affecting venous gas dynamics for other gases? Bubble sizes are mentioned?

Arterial pO2 can be higher or lower, sure, but increasing paO2 ratio to CO2 (or others) seems irrelevant. Increasing arterial oxygen levels isn't 'pumping' other gases out into the veins more strongly, pretty sure it doesn't work like that (?)

If my question about 3 metres vs 6 metres is trickier than even I meant it to be, it's probably about whether total ambient pressure matters (or not) for off-gassing, once you are on pure oxygen. "Oxygen window" is not even a necessary theory

But since the thread is about 1.4 vs 1.6, the depth question still matters

 

[justinthedeeps]

Quote below from the lengthy old InDepth article, which while making a strong honest effort to be clear and understandable, still does not quite seem to show or prove that venous ppN2/He is somehow actually off-gassing better on "deeper oxygen" (vs shallower oxygen)

Breathing oxygen at a deeper depth has the advantage of a greater hydrostatic pressure to hold dissolved gas in solution.

This sounds like the opposite of what we are trying to do in decompression, which is to let dissolved gas exit the body.

Also irrelevant anyway, since off-gassing is about non-oxygen gradients, according to everything else?

 

[boulderjohn]

If my question about 3 metres vs 6 metres is trickier than even I meant it to be, it's probably about whether total ambient pressure matters (or not) for off-gassing, once you are on pure oxygen. "Oxygen window" is not even a necessary theory

IF you correctly understand that it is the level of inspired nitrogen that affects the rate at which nitrogen off-gases, then, no, once you are one pure oxygen, the PO2 does not matter. The oxygen window theory held that higher PO2s created something called an oxygen vacancy that allowed nitrogen to leave the system more quickly. I would love to explain why that was supposed to happen, but it made no sense whatsoever to me when I read the explanation 14 years ago, and I am having a hard time remembering the full explanation.

 

[crofrog]

The Oxygen Window

As we breathe, the inspired gas partial pressures (O2, N2, CO2 and H2O vapor) within the alveolar sacs of the lung are in a dynamic balance with the dissolved gas tensions in the blood flowing through the lung.

www.dansa.org

A different explanation

 

[boulderjohn]

As Mark Powell explained in Deco for Divers, the phrase "oxygen window" is used in three different ways in diving. Two of them work. The one that was introduced in this thread does not.

 

[crofrog]

As Mark Powell explained in Deco for Divers, the phrase "oxygen window" is used in three different ways in diving. Two of them work. The one that was introduced in this thread does not.

Can you be less vague?

 

[inquis]

A different explanation

I agree with all the physiology that DAN (SA) article lays out, but their conclusion (bolded below) does NOT follow. Here's the final section:

So, what is the oxygen window? Essentially, it is the 'missing' gas tension created by the conversion of oxygen to carbon dioxide (as a result of their different solubility in blood); this allows more nitrogen (or inert gas) to be dissolved in venous blood to take 'in its place' and increases the rate of nitrogen (or inert gas) gas elimination

This conclusion implicitly assumes the total gas tension must equal the ambient pressure (i.e., there is "more room"), which they already said will LAG. Furthermore, their claim that the rate of inert gas elimination increases is explicitly contradicted by Dr. Brian (see any of the above links) who states (bolding mine):

The reality is that at any given ambient pressure, regardless of the size of the oxygen window, as long as there is no inspired He, the rate of He off-gassing will be unchanged.

N2 & He are effectively interchangeable in that sentence, given they are both inert / non-metabolic gases.

 

[boulderjohn]

Can you be less vague?

I'd love to, but my copy of Deco for Divers has eluded me. I was hoping to quote it, but all I have is a distant memory.

 

[scubadada]

The first definition for the oxygen window is described at the end of chapter 2 of Deco for Divers, pp 57-59. The second and third definitions are discussed at the end of chapter 5, pp 131-135.

There is a summary table on page 135

1. Drop in partial pressure between arterial and venous systems. Benefit, reduces bubbling.

2. Reduced inspired pressure of inert gas due to increased oxygen content in the breathing mixture. Benefit, greater inert gas gradient gives faster off-gassing.

3. Increased drop in partial pressure between arterial and venous side as a result of breathing high partial pressure of oxygen. Benefit, reduces bubbling to a greater degree.

I would encourage you to read the entire sections.