Is this nitrogen narcosis?

[Storker]

I've followed quite a few of these "does nitrox make you feel better" threads, and if there's ever been suggested a hypothesis for why "nitrox makes you feel better", it has been reduced N2 loading and reduced decompression stress. Which is a rather plausible hypothesis with solid backing in what we know about basic decompression science.

What you seem to be implying is that someone apparently seems to ascribe some other magical properties to nitrox, but I can't for my life remember that anyone has done that. I'd really like a link to such an argument if you have that.

 

[Dominik_E]

It stands to reason however that for many real profiles, people will simply incur more stress due to radical oxygen species for reduced decompression stress. The most simple explanation, and one that is not in conflict with any scientific study, for the many people that feel less tired with Nitrox is placebo effect. Which is actually not even a problem. Feeling good is a subjective thing. If you feel better when using Nitrox, simply do it...

 

[Storker]

It stands to reason however that for many real profiles, people will simply incur more stress due to radical oxygen species for reduced decompression stress.

I'd really like to read the study linking radical oxygen species stress to post-dive lethargy. Where and when was it published? And which radical oxygen species are responsible?

 

[Dominik_E]

The ROS typically discussed in this context would superoxide(s) and to some extend the hydroxyl ion.

Potential (!, this is important, as with many other topics, it will be very hard to arrive at high statistical confidence) pO2 influence on post-dive alertness parameters is discussed in:

Lafère P, Balestra C, Hemelryck W, Donda N, Sakr A, Taher A, Marroni S, Germonpré P. Evaluation of critical flicker fusion frequency and perceived fatigue in divers after air and enriched air nitrox diving. Diving Hyperb Med. 2010 September; 40(3): 114-8.

This paper, and also the one that drives at least a small and potentially not yet lethal nail into the coffin of believe in Nitrox as an objective way to less fatigue under identical profiles:

Harris RJD, Doolette DJ, Wilkinson DC, Williams DJ. Measurement of fatigue following 18 msw dry chamber dives breathing air on enriched air nitrox. Undersea Hyperb Med. 2003; 30(4): 285-91.

have of course already been quoted in this discussion.

Note that the rationale of ROS inhibiting neurotransmission can actually be used in *both* directions: also inhibitory aspects can be inhibited (double negative), thus increasing perceived wakefulness and other things. So, when asking if anyone has ever ascribed "other magical properties" to Nitrox, maybe this is what you were in reality looking for? Maybe a useful analogy may be what alcohol does to different people. You can argue until the sheep come home whether having a drink makes one tired or awake. And the same will potentially go for Nitrox, confounded by the fact that not much of what we are discussing is actually _proven_.

As I said, if you like your Nitrox, why not dive it? If I have to do a late night drive on the Autobahn, I have a habit of buying and eating chocolate containing caffeine. I even know that it will do next to nothing for me but placebo. It still helps.

 

[Lorenzoid]

You're basing your conclusion on a huge and untested assumption there.

NDL isn't the only thing which can limit bottom time, particularly on OC single tank. Gas may just as well limit bottom time. Also, a diver who switches from air to EAN32 may very well go from being saturation limited to being gas limited.

Not just that but also consider the typical vacation dive where divers are instructed to limit their dive time to 50 minutes or some similar number.

 

[MrBigfins]

My limited understanding is that the best possible correlation between nitrox and reduced fatigue is ascent. Nitrox has a lower partial pressure and therefore allows for more efficient off gassing on ascent. The I feel reason that studies may have missed the mark on showing the benefit or lack thereof, is that in tests they are reasonable and conservative profiles and ascents. More aggressive dive profiles, or increased ascent rate may better show the benefits of EANX or lack thereof.

 

[Dominik_E]

Such studies are normally done by agencies that use scuba divers on specific missions. Thus they will test profiles that are more or less similar to their real life situations. Very aggressive profiles will anyhow bend a lot of divers, which only further complicates the problem of disentangling different effects. And very aggressive profiles are neither used by the agencies nor by us sports divers in real life (normally). So I do not think such a study will happen soon, nor would be useful...

 

[almostDIR]

Such studies are normally done by agencies that use scuba divers on specific missions. Thus they will test profiles that are more or less similar to their real life situations. Very aggressive profiles will anyhow bend a lot of divers, which only further complicates the problem of disentangling different effects. And very aggressive profiles are neither used by the agencies nor by us sports divers in real life (normally). So I do not think such a study will happen soon, nor would be useful...

If one is having serious buoyancy problems or runs out of air at depth and needs to do CESA or buoyant ascent by dropping weights, then it is very easy for a vacation diver to get into Polaris style super aggressive profiles getting almost into deco and then shooting up to the surface fast enough to get a nosebleed

for some vacation divers I know it is relatively "normal" to run out of air, maybe once in couple of dozen dives or so I believe

 

[Dominik_E]

Well that may be, but such a messed up ascent will not be a good experimental set up to answer the question of post-dive tiredness. That manifest DCS risk under identical profiles will be smaller with Nitrox is well tested...

 

[ScubaPink]

Well, this won’t answer the question re Nitrox reducing post-dive fatigue,I think it is kind of interesting... I can say that I never experienced post-dive fatigue and I also never used Nitrox. (Did not get the cert). I drove 3.5 hours to the dive site, and went on the first a.m. boat (left at 7:30) so I had to get up at 3:30 in the morning. We would dive 2 dives and be back at the dock around 12:30. We would follow the dive with some drinking and not get home until 6 or 7pm and I still did not get tired. So, I wonder why it makes some tired and others, not? Also, I actually did go past my limits and did a deco dive and it was also the same dive where I experienced narcosis. So, I learned I was susceptible to that...even though, there were other dives when I went past the 60ft (way past) on air and did not experience narcosis. Even after getting narced I STILL wasn’t tired after the dive. Lol