Is this nitrogen narcosis?

[tursiops]

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...

I understand statistics and hypothesis testing. I also understand that many useful discoveries start as anecdotal evidence....after all, the hypothesis comes from observations, almost always. And I agree that this particular hypothesis is very difficult to test. But I'm a little tired of people saying, "I don't feel better after a Nitrox dive and there is no proof I should, so therefore no one feels better, it is all a myth."

I do not dive to my NDL limits on a recreational dive, with or without Nitrox. So I suppose, given my typical profiles, I am ongassing less nitrogen when using Nitrox, and maybe that is why I feel better when using it. I could accomplish the same thing by using air on much shorter dives, but why would I want to? My two strongest pieces of personal evidence are: (1) many once-a-day air dives off Oahu to 90 ft (on the Mahi wreck) that inevitably pooped me, and (2) many multi-day multi-dive Nitrox dives on liveaboards and shore resorts that do not poop me.

 

[doctormike]

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.

I can only see the abstract, but I don't see why they conclude that that measurement change has to be due to narcosis. That CFFF seems to be a measurement of visual persistence, but it looks like it is used to measure the brain's processing speed. To determine that this was a narcosis issue and not related to decompression stress, pulmonary changes, immersion reactions or anything else, I would think that the obvious experiment would be a control group breathing trimix, right? There was no control group, they just used the pre dive measurements for each diver as their own controls.

Still, a pretty interesting study!

 

[doctormike]

And I agree that this particular hypothesis is very difficult to test. But I'm a little tired of people saying, "I don't feel better after a Nitrox dive and there is no proof I should, so therefore no one feels better, it is all a myth."

I didn't say that, and no one in this tread said that.

And no one said that you didn't feel better diving nitrox. Of course, I believe you. Why would anyone lie about that?

I'm just saying that we might want to figure out WHY many people feel better with nitrox. If you are comparing similar profiles where the only difference is your mix, then I would suggest that you probably feel better because you are incurring less decompression stress. That's not saying that it's a myth that you feel better.

What I suspect MIGHT be a myth, and which apparently the experts in that DAN article also doubt, is that nitrox causes less fatigue for the SAME amount of N2 loading. In other words, if you control for decompression stress, there isn't much evidence to support EAN as an independent variable.

 

[Graeme Fraser]

Putting the nitrox debate aside for a moment, I'm surprised how early on in the first dive your DC exceeded NDL even on a very conservative setting. Do you know what algorithm the Garmin is running? Also, how long was your surface interval?

Obviously everyone's physiology is different, but this looks like a pretty conservative profile and, although you definitely shouldn't have gone into deco, at least you did observe your obligations.

 

[tursiops]

I didn't say that, and no one in this tread said that.

And no one said that you didn't feel better diving nitrox. Of course, I believe you. Why would anyone lie about that?

I'm just saying that we might want to figure out WHY many people feel better with nitrox. If you are comparing similar profiles where the only difference is your mix, then I would suggest that you probably feel better because you are incurring less decompression stress. That's not saying that it's a myth that you feel better.

What I suspect MIGHT be a myth, and which apparently the experts in that DAN article also doubt, is that nitrox causes less fatigue for the SAME amount of N2 loading. In other words, if you control for decompression stress, there isn't much evidence to support EAN as an independent variable.

No, no one here has said that, but it is as pretty good paraphrase of innumerable other threads. I agree with your thinking. I'll put it this way: I feel less tired after a recreational dive with Nitrox than after a similar dive on air. And that improvement grows with multi- day diving and multi-dive days. I have no idea if I am abnormally susceptible to subclinical DCS, but this is certainly consistent. My deco dives are always padded with additional O2 near and at the surface.

 

[Diver below 83]

I did notice I felt slightly more fresh after my Nitrox dives compared to my air dives. But it wasn’t a huge difference. But I also didn’t get close to my NDL

 

[JackD342]

Putting the nitrox debate aside for a moment, I'm surprised how early on in the first dive your DC exceeded NDL even on a very conservative setting. Do you know what algorithm the Garmin is running? Also, how long was your surface interval?

Obviously everyone's physiology is different, but this looks like a pretty conservative profile and, although you definitely shouldn't have gone into deco, at least you did observe your obligations.

Garmin site says it is Bühlmann zhl-16c.

I tried working backwards from that 1st profile. It looks like the deco indicator kicked in just about minute 14. Using DSAT tables, that would be for a depth somewhere between 110ft and 120ft. The Pelagic PZ+ algorithm would kick it in for a dive somewhere between 100ft and 110ft. The average depth to that point certainly does not appear even close to those depths. That "highly conservative" setting may really affect the limits severely, or perhaps this was not the 1st dive in the series that week.

 

[Bob DBF]

The studies were looking for reduced fatigue and found none. The first was a chamber dive, the second I saw was actually diving, multiple dives over time. I believe it was double blind. The second found divers felt consistently better after the dives, however it was not due to reduced fatigue. I'm figuring that scientific fatigue has a different definition than I use. Although the feeling better was scientificly notacable, it didn't count because they were studying fatigue, but they did note it might have to do with decompression stress, another study would have to be done to find out.

Good luck with your grant.


Bob

 

[doctormike]

I'll put it this way: I feel less tired after a recreational dive with Nitrox than after a similar dive on air.

So that's the key question. When you say "similar" do you mean similar in terms of actual profile, or similar in terms of N2 loading (e.g. two dives where you are limited by NDL=0 based on a computer set to your actual mix). If the former, I would say that supports the subclinical DCS model of post-dive fatigue.

It's also interesting that the evolving model of the pathophysiology of decompression stress at the tissue level seems to be more focused on inflammation rather than simply the assumption that bubbles themselves cause local microcirculation issues.

Interesting discussion!

 

[tursiops]

So that's the key question. When you say "similar" do you mean similar in terms of actual profile, or similar in terms of N2 loading (e.g. two dives where you are limited by NDL=0 based on a computer set to your actual mix). If the former, I would say that supports the subclinical DCS model of post-dive fatigue.

Yes, the former. Similar profiles.