Is this nitrogen narcosis?

[doctormike]

Are there ANY double blind studies?

I couldn't find any. I found one that showed a small improvement on cognitive performance during the dive, but not clear why.

DAN published something about this issue in 2014, asking RIchard Harris and Neal Pollack about this issue, and they agreed that there wasn't literature support for it. Not sure if there is more recent data. Paging @Dr Simon Mitchell ...

If people say they "feel" better and there is no scientific evidence to refute the potential for feeling better - then I would be inclined to believe people.

Well of course. If you feel better, you feel better. It's not really a scientific question, although it can be studied scientifically with a double blinded study.

Just be careful about terms. The burden of proof in science is on the positive. And you don't "refute the potential", unless you have identified an underlying mechanism (which hasn't been done). You can test the hypothesis, though. If randomized blinded divers claim that they feel better just as often diving air as they do nitrox, then that suggests that it's all placebo effect.

I understand that if one simply looks at an equivalent amount of super saturation of nitrogen a person is subject to (and the ascent rate) they use, then I can see why someone might suspect the placebo effect.

On the other hand, could it not be possible that a safety stop on nitrox is somewhat different in that there really is a higher partial pressure difference when using nitrox and this makes it "better" in some small way? It's more of a question than a statement.

Yes, those are interesting questions. What you really need to do is to find out of nitrox divers have less decompression stress than air divers, and if so, why? Are they using different algorithms or different conservatism factors? Do they have individual differences in their ability to offgas nitrogen? Is it a self selection process?

I'm fine with people doing whatever they want to feel better, but when advising new divers, it's important that we make it clear that just switching to nitrox and then having your dives limited by NDLs may not really give you any improvement in either DCS risk OR post-dive fatigue.

 

[doctormike]

Yeah, and there is not convincing evidence in the literature that is is not a real physiological effect.
In the absence of such convincing evidence, one way or the other, people go by how their bodies feel, and the anecdotal evidence continues to grow, while those who feel nothing just post louder and more often!

C'mon, you are a scientist!

The burden of proof is on the positive. I mean, it's fine to dive Nitrox, I always have, but not for that reason. If you run your NDLs to zero with EAN or air, you are going to have similar levels of decompression stress, you just get a longer dive on nitrox. If that's the cause of post dive fatigue (which I suspect), then you need to say why nitrox helps, and when it won't.

Why does the anecdotal evidence of people who think that it makes them less tired convince you, while you dismiss the anecdotal evidence of those who don't? Now if you could compare those two groups...

 

[Storker]

The burden of proof is on the positive

Sure.

But then there's a bit of a difference between what I'd state as a scientist and recommend to others, and what I'd do myself. In this particular case, I'd follow what my anecdotal evidence indicated, while taking all necessary precautions while telling other what they should do. And I distinctly prefer diving EAN32 unless the MOD says I'd rather use some other mix.

For some reason, I'm reminded of a certain hyperbaric scientist who won't give any definitive recommendations, but is quite clear about which gradient factors he himself chooses to follow.

 

[doctormike]

Sure.

But then there's a bit of a difference between what I'd state as a scientist and recommend to others, and what I'd do myself. In this particular case, I'd follow what my anecdotal evidence indicated, while taking all necessary precautions while telling other what they should do. And I distinctly prefer diving EAN32 unless the MOD says I'd rather use some other mix.

For some reason, I'm reminded of a certain hyperbaric scientist who won't give any definitive recommendations, but is quite clear about which gradient factors he himself chooses to follow.

Sure, I was just responding to point out that just because the literature hasn’t been able to disapprove a hypothesis doesn’t mean that the hypothesis is correct.

And I can totally understand not recommending specific gradient factors in his situation. People get bent all the time, and he has a lot of influence. Someone just needs to decide that it was those specific numbers that caused the injury and it’s a lot of unnecessary trouble for him.

 

[Jayfarmlaw]

I'll volunteer for the double blind study...all I need is tropical warm water and a plane ticket. A chartered liveaboard would be cheaper and probably easier logistics wise. It's for science after all....

I can fly out of OKC or DFW... to make it easier, I can round up several other divers to round out the sample size!

Have a good weekend guys!
Jay

 

[doctormike]

I'll volunteer for the double blind study...all I need is tropical warm water and a plane ticket. A chartered liveaboard would be cheaper and probably easier logistics wise. It's for science after all....

Awesome, thanks so much for volunteering! Now we just need someone to write up the grant proposal… Either of you guys in?

 

[Barnaby'sDad]

I can see that there is a lot of enthusiasm for nitrox diving here, which is fine, but I think that for the OP, as a new diver, he should realize a couple of things.

1) Post dive tiredness is likely a subclinical form of DCS. It's sort of arbitrary where you draw the line between decompression stress and decompression sickness, but it's a continuum, ranging from tiredness to mild skin bends to life threatening injury. Everyone has pointed out that you should not be going into deco or caves at this point, but clearly you did incur some decompression stress by going into deco, even though you followed the instructions of your dive computer (the "magic bracelet").

2) While nitrox does reduce nitrogen loading for the same dive when compared to air, just "diving nitrox" doesn't reduce decompression stress unless you dive air tables (or set your computer to air). Of course, if you do this, you still need to respect the MOD and O2 clock for what you are actually breathing. If you choose to take advantage of the longer NDLs with nitrox by setting your computer to your actual mix, you are trading away that reduction in decompression stress.

3) Although many people will swear that they feel less tired after diving nitrox (and I certainly believe what people say about their own bodies), there is not convincing evidence in the literature for that as a real physiological effect. Two possibilities of course would be that diving nitrox with air tables would give you less decompression stress (see #1), or the psychological (placebo) effect. A hard thing to measure objectively, and not many double blinded studies.

I’ve read plenty of similar accounts to mine. On the flip side, I’ve read plenty of posts where people say that there’s no proof that there’s a difference. It works for me, so I’ll continue to dive it.

I set my computer to the blend that I’m diving. I don’t run a cushion (ex. Use the air setting). I do set my computer to the most conservative setting though.

Just saying that IF someone is following their dive plan, computer, etc. and they feel fatigue after diving...there’s no reason for that person to not consider taking the Nitrox course and trying it out.

Edit: Something else to ponder on a Saturday afternoon. Do some people feel better on Nitrox not because it’s a higher percentage of oxygen than standard diving air, but because it’s better/more pure gas? I’m referring to how...in the case of my partial pressure blended tanks...the blending air is hyper air/run through an additional cleaning filter vs. standard diving air.

Probably just another can of worms there. I imaging that the answer to that is “no,” but ...you never know.

 

[kafkaland]

guys

I’d do the writing for a nice tropical dive vacation. Now we just need an agency that is sure to fund this...

 

[RyanT]

No, not a chance. It happens during a dive, at depth, not after the dive.

Quite often (at least for us rec divers), the cure against nark is ascending just a few meters.

Some evidence suggests this is not true.

Persistence of critical flicker fusion frequency impairment after a 33 mfw SCUBA dive: evidence of prolonged nitrogen narcosis?

Regardless, I feel pretty confident that the OP's post-dive experience was not from narcosis.

 

[doctormike]

Just saying that IF someone is following their dive plan, computer, etc. and they feel fatigue after diving...there’s no reason for that person to not consider taking the Nitrox course and trying it out.

Totally agree. But the caveat should be that if they still feel tired, they should consider subclinical DCS and back off the N2 loading.

Everybody's physiology is different. Any modern dive computer running any algorithm should provide a recreational diver with an acceptably low DCS rate, but that doesn't mean that they aren't giving people decompression stress which isn't enough for a chamber ride but which might be the cause of their fatigue. In that case, instead of just relying on switching to Nitrox and eliminating the safety advantage by diving Nitrox tables, they might want to dial back their overall exposure, by manipulating conservatism or just not running the NDL down to zero.

Edit: Something else to ponder on a Saturday afternoon. Do some people feel better on Nitrox not because it’s a higher percentage of oxygen than standard diving air, but because it’s better/more pure gas? I’m referring to how...in the case of my partial pressure blended tanks...the blending air is hyper air/run through an additional cleaning filter vs. standard diving air.

Probably just another can of worms there. I imaging that the answer to that is “no,” but ...you never know.

An excellent point! Something to put in the grant proposal...