Nitrox and Fatigue: the Evidence

[Storker]

Deep diver use helium to reduce the nitrogen concentration

Since they do it to reduce narcosis and gas density, not to reduce inert gas tissue loading (AFAIK), I didn't want to bring trimix into the discussion. That's quite another topic IMNSHO.

 

[potato cod]

You seem to know enough about o2 that I'm sure you realize that your body can only metabolize a certain amount of oxygen.

I'll be the first to admit that I know very little about this. I'm no physiologist, I was just speculating about the fact that there are lots of older divers with various underlying medical challenges as well as more fit divers and not many studies to date. It just piqued my curiosity about whether there might be some going on, maybe just with some conditions. I was thinking about a woman at works that walks around with an O2 bottle all day for medical reasons--of which I know next to nothing, but there must be some reason supplemental O2 matters for some people. But your point about only being able to metabolize a small fraction of the O2 we breathe probably means there is little effect for most of us.

This effective % Oxygen thing is a funky measurement and confusing to me. We ought to use partial pressure of oxygen as the actual % Oxygen in the air is pretty much constant value of about 21% at all altitudes.

Yeah, I just like this measurement because while the partial pressure remains 21%, I think this provides some frame of reference for why being at higher altitudes feels relatively more difficult. And summiting Kilimanjaro! That's awesome!

 

[dmaziuk]

The study on supplemental O2 on exercise looked at athletes using it after or in between short bouts of exertion for recovery (football and soccer). But diving is a little different because you breathe the enriched 02 air continuously while you are not exercising, so there may be more time with higher blood saturation levels.

Fixed it for ya.

 

[dmaziuk]

No-one - except you - have said anything about magical effects of increased oxygen concentrations

Not entirely true: there is a cite from back when, where they managed to bend goats on oxygen and commented -- in a scientific paper no less, -- that the result was nothing short of magical. DCS symptoms, once they finally managed to produce them, cleared within minutes of appearing. (I can probably dig up the link if you ask nicely.)

The best I could find is the speculation is that a) oxygen "doesn't bubble as much" and/or b) oxygen bubbles are not recognized as foreign bodies and thus don't provoke immune response, i.e. no clinical DCS.

Then there's Schreiner's magic by which %O2 is simply subtracted from the gas contributing to tissue loading. Since, as @MaxBottomtime pointed out, the amount of O2 you metabolize is pretty much fixed, as far as our dive computers are concerned all this extra oxygen just vanishes. That's pretty magical I think.

And last but no least: "woodoo gas".

 

[dmaziuk]

Since they do it to reduce narcosis and gas density, not to reduce inert gas tissue loading

Nitpick: no MOD for He. But you knew that.

 

[jgttrey]

The best I could find is the speculation is that a) oxygen "doesn't bubble as much" and/or b) oxygen bubbles are not recognized as foreign bodies and thus don't provoke immune response, i.e. no clinical DCS.

I'm sure if you O2 saturated enough, and ascended like a bullet, you could generate some O2 bubbles. After all, it's just the gas laws at work and you can only metabolize so much at a time.

The difference as you know is that the O2 will be metabolized. Your tissues clean it up, which is not the case for helium or nitrogen, which must be delivered through the venous system to the lungs, exchanged into gas, and exhaled. While I'm not familiar with the goat study (which I find interesting), I suspect the reason it clears up so fast is that your tissues "consume" those O2 bubbles.

Medical O2 bottles is a different deal. If you think about folks with COPD, their lungs are not exchanging gases as they should - not getting a full breath, so their blood oxygen levels are low. For them, normal breathing is like breathing at altitude. Supplemental oxygen helps get those blood O2 levels up. But, once your body is getting the O2 it needs to satisfy its metabolic needs, there's no need for more (unless you're trying to displace something else that is bad, like nitrogen or CO).

 

[dmaziuk]

The difference as you know is that the O2 will be metabolized.

That's exactly why it's magic: extra O2 will be metabolized simply because you're breathing nitrox at pressure. All without extra energy source, sink, or waste disposal.

 

[jgttrey]

That's exactly why it's magic: extra O2 will be metabolized simply because you're breathing nitrox at pressure. All without extra energy source, sink, or waste disposal.

I'm not sure I'm following you. You don't metabolize any more or less oxygen at depth or depending on whether it is nitrox, air or pure O2. You use XYZ molecules per minute depending on your metabolic needs, regardless of the mix you are breathing. You don't use more just because the mix is rich. I'm not sure if you're saying something different, but I'm not understanding your post.

 

[BlueTrin]

I'm not sure I'm following you. You don't metabolize any more or less oxygen at depth or depending on whether it is nitrox, air or pure O2. You use XYZ molecules per minute depending on your metabolic needs, regardless of the mix you are breathing. You don't use more just because the mix is rich. I'm not sure if you're saying something different, but I'm not understanding your post.

From his history of posting I am pretty sure he’s being sarcastic.

 

[BRT]

Deep divers use helium to reduce the nitrogen concentration, as long as the oxygen partial pressure is not exceeding safe level at depth.

Maximum operating depth - Wikipedia[/QUOTE
4. Decreased inert gas content in the breathing gas.
Helium doesn't change much in the inert gas category, other than reducing narcosis. I think you know this.