Nitrox and Fatigue: the Evidence

[BlueTrin]

Nitrox is like lime in your beer.

Finally some scientific viewpoint ...

 

[jgttrey]

….."state of scientific evidence supporting, or not, the claim that using nitrox reduces fatigue". = how people feel. How is that scientifically quantified?
I find it hard to be curious about the subject.

Well, according to the studies, by "the Multidimensional Fatigue Inventory-20, a visual analogue scale, Digit Span Tests, Stroop Tests, and Divers Health Survey (DHS)," whatever all that is.

But the point isn't how you measure. Even if it is a subjective "are you tired" sort of a thing, so long as it is 2x blind (divers and those asking questions not knowing whether they were on EAN or air) that can be done -- it is all the time.

The reason the one-off experiences are worthless isn't because they are reported subjectively, but because they are not controlled for other factors, not blind, and, probably biased due to the fact that divers that believe it makes them less fatigued probably report that more than those who think "meh." So, if you think it makes you feel better, go for it. Maybe it does. Or, maybe it is in the same category as sugar pills, oxygen bars, and homeopathic medicine. The point is personal experience from someone who knows he/she is diving nitrox is not going to tell you which it is.

Personally, I doubt it does much beyond give you more NDL, and I don't really care. I just think we ought to be clear on what is legitimate evidence and what is just SB chatter - not that I have anything against sharing personal experiences or chatter. It's SB after all. But, since we were talking about what is evidence and what isn't, that's my 0.02.

 

[MaxBottomtime]

As Lynne used to say, the Plural of Anecdote Is Not Evidence.

 

[Doc]

Did I really? I thought I posted a summary of DAN's article. We don't need any more reports of personal experiences.

Foreseeable causation, a classic “attractive nuisance” in a Torts 101 fashion.

No real damages proven. Next thread!

 

[potato cod]

Interesting conversation. 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 exercising, so there may be more time with higher blood saturation levels.

On an anecdotal level, I just spent two weeks between 9300-14000 feet. At those altitudes the effective oxygen percentage was between 14-12% vs. nearly 21% where I live. That 6-9% LOSS of 02 sure as hell mattered. Hiking felt difficult and I often found myself breathing hard and feeling light headed--and my other sport is competitive running, where we geek out on things like VO2 Max (essentially how efficiently you can take in and use oxygen). Of course this isn't totally comparable to diving where you start out at close to O2 saturation, but it does makes me wonder about how all the unknowns including base level of fitness, age, gender/size, continuously breathing O2 when diving, etc might affect things and would be interesting to see studied.

Ultimately, I dive nitrox because I am mostly a vacation diver and do multiple dives/day for multiples days in a row and it reduces my nitrogen load. If I'm less fatigued than I would be on air, great, but I rarely dive air and and can't compare.

 

[MaxBottomtime]

You seem to know enough about o2 that I'm sure you realize that your body can only metabolize a certain amount of oxygen. At a normal breathing rate we use 5-6% of the oxygen in each breath, exhaling the rest. That is great for rebreathers. Adding more oxygen to your breathing mix doesn't mean your body metabolizes any more. Nitrox replaces some of the nitrogen in our breathing gas to lower our NDLs. It doesn't mean you are getting a magical cure for fatigue, narcosis or that you will have super human strength or X-Ray vision,

 

[Dan]

Interesting conversation. 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 exercising, so there may be more time with higher blood saturation levels.

On an anecdotal level, I just spent two weeks between 9300-14000 feet. At those altitudes the effective oxygen percentage was between 14-12% vs. nearly 21% where I live. That 6-9% LOSS of 02 sure as hell mattered. Hiking felt difficult and I often found myself breathing hard and feeling light headed--and my other sport is competitive running, where we geek out on things like VO2 Max (essentially how efficiently you can take in and use oxygen). Of course this isn't totally comparable to diving where you start out at close to O2 saturation, but it does makes me wonder about how all the unknowns including base level of fitness, age, gender/size, continuously breathing O2 when diving, etc might affect things and would be interesting to see studied.

Ultimately, I dive nitrox because I am mostly a vacation diver and do multiple dives/day for multiples days in a row and it reduces my nitrogen load. If I'm less fatigued than I would be on air, great, but I rarely dive air and and can't compare.

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.

I wouldn’t survive summiting Kilimanjaro (20,000’ or 6km altitude) back in December 2014 if I breathe actual 10% Oxygen otherwise, according to Minimum Oxygen Concentration for Human Breathing What happened was I was breathing 21% oxygen at 460 mIllibars (0.46 atmosphere), as shown, below

or 0.096 atm (0.21 x 0.46 atm) oxygen partial pressure. The effective % Oxygen at that altitude is simply = the oxygen partial pressure x 100% = 0.096 x 100% = 9.6%.

Since I was only able to inhale less than half of air volume up there, than when I was at the sea level, I had to pace myself (walk slowly), balancing the low oxygen intake with low oxygen consumption my muscle needed to summit Kili, but the oxygen concentration in the air was still 21%, not 9.6%.

 

[Dan]

Nitrox replaces some of the nitrogen in our breathing gas to lower our NDLs.

You mean Nitrox increases our NDL bottom time.

 

[Storker]

It doesn't mean you are getting a magical cure for fatigue, narcosis or that you will have super human strength or X-Ray vision,

Well, now you're being silly. And this level of hyperbole doesn't reflect particularly well on you.

1. No-one - except you - have said anything about magical effects of increased oxygen concentrations In fact, it has already been pointed out upthread that we don't use nitrox for an increased oxygen concentration. We use it for a decreased nitrogen concentration. That we're using oxygen for that is purely incidental.
2. It's been proven scientifically that divers bubble post-dive, and that the amount of bubbling varies wildly from diver to diver.
3. There is strong scientific evidence that nitrogen bubbles in the tissues can provoke adverse physiological reactions.
4. Many divers believe that subclinical bubbles and decompression stress may lead to excessive post-dive lethargy, which is also supported by the latest publication cited in the OP.
5. There are several ways to decrease decompression stress, such as:
   1. Extended safety stops/deco stops
   2. Slow, controlled ascents, especially after the safety/deco stop
   3. Decreased bottom times
   4. Decreased inert gas content in the breathing gas
6. What has been argued is that by staying away from the NDL instead of riding it, the diver experiences less decompression stress, which may manifest as decreased post-dive lethargy for some divers (probably those who bubble easier). And decreasing the amount of nitrogen in your breathing gas is an effective way to stay away from the NDL without any penalty in bottom time. Given the large variation in bubble score between divers, it's not at all surprising that there is widely varying experience about the "effect" of nitrox in the diving community
7. What has not been argued - except by you - is your strawman about some kind of magical effect of increased oxygen content in the breathing gas.

And BTW, the article I'm referring to can be found in its entirety here (scroll down to download DHM J 40(3) as a PDF): DHMJ_Full Journals. The link in the OP only leads to the abstract on Researchgate.

 

[Dan]

...we don't use nitrox for an increased oxygen concentration. We use it for a decreased nitrogen concentration. That we're using oxygen for that is purely incidental.

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