Nitrox and Fatigue: the Evidence

[dmaziuk]

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

No, I am being perpetually amazed. In this instance, the post I was replying to says, in the 2nd paragraph

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.

And the next post form the same author is

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.

So you see, "you don't metabolize more oxygen" yet at the same time the excess oxygen does not get "delivered to the lungs, exchanged to gas, and exhaled" because "your tissues clean it all up". That is the magic of nitrox. Isn't that amazing?

 

[dmaziuk]

While I'm not familiar with the goat study (which I find interesting) ...

It seems it has rotated out of my PubMed search history by now. I could still find it I think: the link was posted by somebody (@huwporter?) in one of the gradient-factors-algorithm-bickering threads not too long ago... But here's one that's called simply "oxygen bends" and another that cites startistics
https://www.physiology.org/doi/abs/10.1152/jappl.1955.7.6.639
Probabilistic models of the role of oxygen in human decompression sickness. - PubMed - NCBI

 

[jgttrey]

No, I am being perpetually amazed. In this instance, the post I was replying to says, in the 2nd paragraph



And the next post form the same author is



So you see, "you don't metabolize more oxygen" yet at the same time the excess oxygen does not get "delivered to the lungs, exchanged to gas, and exhaled" because "your tissues clean it all up". That is the magic of nitrox. Isn't that amazing?

No, you're not getting it.

It is well understood that the reason we do not worry about O2 from a decompression perspective is that on any sort of a normal dive profile, we metabolize it, so it does not accumulate in the way that inert gases do.

That metabolic need is not impacted, at least not in any material way, by the richness of the mix. On my rebreather, I have to inject the same number of additional O2 molecules to maintain my setpoint at a given depth whether that setpoint is .7 or 1.3. Ask anyone with a CMF valve on their rebreather - by design it delivers a constant, unchanging, flow of O2 molecules (CMF = constant mass flow) at just less than the diver's metabolic need at any depth up to the limits of the valve.

I am simply noting, in answer to your speculations about why your goats' symptoms of "O2 bends" cleared quickly, the likely answer is that oxygen was metabolized in situ rather than having to go the long way out through the lungs. That is, of course, my own speculation, but it seems reasonable.

I am not saying one metabolizes more O2 in this scenario, just that I would imagine the body is metabolizing the O2 already in the tissues rather than having to get everything from the lungs. If your hemoglobin is saturated with O2 being offgassed, then it wouldn't be binding with add'l O2 in your lungs. Metabolic need remains constant.

There is no "magic" to nitrox except to those that don't understand it.

 

[huwporter]

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.)

Et Voila:

http://www.ultimatedivelog.com/articles/25.pdf

 

[jgttrey]

Interesting read. Goats were on EAN64 at 150' for an hour and then surfaced at 75'/min.

This was my favorite quote: "When working with goats, in high tensions of oxygen under pressure, scrupulous care must be taken that no ‘live’ electric wires are left inside the chamber lest the bold and never failing search of these animals for new dietetic sensations causes a ‘short’ with sparking."

This was my second: "The signs developed by these animals were undoubtedly those of severe decompression sickness, caused by the presence of bubbles in the body. As these signs were only transient it is reasonable to conclude that the bubbles were largely reabsorbed in this short interval. It is common experience that decompression sickness of this severity, due to bubbles mainly composed of nitrogen, does not pass off rapidly in this dramatic fashion without recompression, owing to the lack of solubility and resistance to metabolism of this gas. There is no reason to inculpate carbon dioxide in the formation of these bubbles and it is reasonably certain that oxygen was responsible. Further the use of this gas in body metabolism would account for the remarkable relief of these animals."

 

[formernuke]

I haven't read everything here but my thought is they didnt take into account multiple days of multiple dives. I went on a dive trip a while back 1 week 4-5 dives a day every day. I dove nitrox and felt really good every day after the dives, would I felt any different on regular air I don't know for sure but it was worth the extra couple hundred for the nitrox addition just in case.

 

[dmaziuk]

I am simply noting, in answer to your speculations about why your goats' symptoms of "O2 bends" cleared quickly, the likely answer is that oxygen was metabolized in situ rather than having to go the long way out through the lungs. That is, of course, my own speculation, but it seems reasonable.

Let's say for simplicity we metabolize 1L of O2 per minute (usually cited number is between 0.25L at rest and up to 4L during heavy exercise). So in order for all dissolved oxygen to metabolize, it needs to come in at the rate of 1L/min or less. If your ~6L lungs are filled with 32% O2 at, say, 4 atmospheres, you have ~8L of O2 pushing its way into your tissues. I wouldn't know off the top of my head how much gets there how fast, but it seems to me once (if) you've more than 1L/min getting in, it's magic time.

I.e. the hard limit on how much O2 you can metabolize doesn't change just because you're metabolizing dissolved oxygen instead of heme-bound stuff. So what the "it's metabolized" argument really says is, we never get enough O2 dissolved in our tissues, to go over that hard limit. That may well be true but I've never seen the numbers anywhere.

 

[jgttrey]

"Magic time"? I still don't understand what you mean by this. The same effect happens on air. We use about 5% O2 and exhale about 15 or 16% just sitting here.

I suspect if we did the math, we'd find that metabolizing 1L/min, to take your example, is sufficient to clear large amounts of O2 from your system, such that it takes an extreme example of O2 saturation and rapid ascent, like your goats, to overwhelm the body's ability to metabolize O2 and result in bubbling. On a normal dive, whatever O2 is dissolved in solution is utilized by the body and a corresponding lesser amount is being stripped out by the lungs from your inhaled gas - the hemoglobin is already bound to O2 from your tissues.

 

[dmaziuk]

"Magic time"? I still don't understand what you mean by this. The same effect happens on air. We use about 5% O2 and exhale about 15 or 16% just sitting here.

Yep: nitrox or air, you metabolize some pretty much fixed amount of oxygen that is relatively small compared to the amount that gets into your lungs. And it gets progressively relatively smaller as gas pressure and/or oxygen content goes up. The part you do not metabolize either does not dissolve in your tissue, or it does not bubble on the way out. That's the magic.

The non-magical explanation is that it is all metabolized and I'd like to see a numerical guesstimate of "all". Especially when you up the O2% in the breathing mix and the "all" gets bigger, while the metabolized part remains constant.

 

[jgttrey]

The part you do not metabolize either does not dissolve in your tissue, or it does not bubble on the way out. That's the magic.

Your goat study shows this isn't true - that with sufficient extreme conditions, O2 does bubble out. There's no question that it dissolves in tissues. That's a simple function of the gas laws. O2 is a gas like any other.

The likely explanation, which is the same one the authors of the study suggested, is that that offgassed O2 was metabolized quickly so that any DCS symptoms cleared quickly.

Especially when you up the O2% in the breathing mix and the "all" gets bigger, while the metabolized part remains constant.

That's the point of disagreement about the "magic": the "all" is not getting bigger.

You are assuming that the amount of O2 absorbed into the blood as it passes through the lungs remains constant and equal to the metabolic need and therefore there is some mystery about how you could metabolize the "extra" O2 being offgassed since we know the metabolic rate is not going to increase. I do not believe that is correct.

If your blood/hemoglobin is saturated with O2 being offgassed, you will not be taking on as much O2 from whatever it is you are breathing. The hemoglobin is already bound up with O2 coming out of your tissues as you ascend.

In theory, those bent goats were not only metabolizing the offgassed O2, and therefore absorbing less "new" O2 from the inspired gas while this was going on, but probably even exhaling it too (just as you would with offgassed inert gases). Put another way, the body is preferentially metabolizing the in situ O2 in place of binding "fresh" O2 from what you are breathing.