Considering Nitrox Certification

[boulderjohn]

Please allow me to address the issue of "the small number of studies" that report no benefit to nitrox in terms of fatigue.

I have only read one such study, and the last time someone mentioned the "body of studies" that show this, I asked for that body, and it turned out that poster had only encountered that same one as well. If there are more than taht one in existence, I would like to see them.

The reason is that the one I saw was so very poorly designed as to be worthless. I don't recall the exact details, but they had some (not that many) divers do 2 total dives to pretty shallow levels for fairly short periods of time and then report how they felt.

If you want to check a difference in fatigue, you have to push things bit farther than that. I would not have felt remotely tired on either air or nitrox on the profiles they used, so I don't see how any conclusion could have been drawn.

I would like to see a study with divers doing 4 dives per day on a liveaboard, for 6 days. I have done such a trip both ways, and for me there was a world of difference--not even close.

Of course, my experience alone is what is called "anecdotal evidence" and thus has no scientific validity.

Thus, unless someone shows me something different, I would say that there is no scieintific evidence on either side of the question.

 

[Rhone Man]

Whilst we are all busy hijacking this post, I was recently reminded of another controversial issue about Nitrox that has yet to be resolved by a definitive study - whether Nitrox assists in reducing narcosis.

It seems to be an article of faith in North America that Nitrox does not reduce narcosis. Equally it seems to be an article of faith in Europe that it does. It is certainly an article of faith with Rhone Man that it doesn't really make that much difference either way because you can't really use Nitrox at a depth where this would make a significant difference. But if we are going to hijack this thread, let's do it right...

 

[boulderjohn]

But if we are going to hijack this thread, let's do it right...

I'm always up for a good challenge!

I often dive nitrox in the 100-130' range, and that is where I have observed narcosis symptoms, on both air and nitrox.

 

[aubie85]

Based on that, yes, the Nitrox cert would definately be worth it. You might also want to see if your medical insurance will cover a test to see if you have a PFO, which is a condition in which your heart, under heavy strain like the valsalva, will shunt blood (and bubbles) from the right side of the heart directly to the left side bypassing the natural filtering action on the lungs. Although we only see PFO's in 20% of the general population, 80% of those who have experienced type 1 DCS have one. It pre-disposes you to DCS. If it turns out you do have a PFO, Nitrox may not make a difference.

Bruce

Wow. That sounds serious. I will definately have to check that out when I get health insurance. For now, I will have to ride it out.

 

[aubie85]

Please allow me to address the issue of "the small number of studies" that report no benefit to nitrox in terms of fatigue.

I have only read one such study, and the last time someone mentioned the "body of studies" that show this, I asked for that body, and it turned out that poster had only encountered that same one as well. If there are more than taht one in existence, I would like to see them.

The reason is that the one I saw was so very poorly designed as to be worthless. I don't recall the exact details, but they had some (not that many) divers do 2 total dives to pretty shallow levels for fairly short periods of time and then report how they felt.

If you want to check a difference in fatigue, you have to push things bit farther than that. I would not have felt remotely tired on either air or nitrox on the profiles they used, so I don't see how any conclusion could have been drawn.

I would like to see a study with divers doing 4 dives per day on a liveaboard, for 6 days. I have done such a trip both ways, and for me there was a world of difference--not even close.

Of course, my experience alone is what is called "anecdotal evidence" and thus has no scientific validity.

Thus, unless someone shows me something different, I would say that there is no scieintific evidence on either side of the question.

I wonder what the "p" values were for those studies, geez, I hope @ least < 0.1 My research professor would find that amusing anyway. She would be so proud of me

On a more serious note, I wonder how significant the sample sizes were, or if they were 'pilot' studies, or high attrition rates. I will have to look into that.

 

[aubie85]

Given the great advice provided, I GUESS you guys can hijack my thread. I'll pretend I didn't notice...........

 

[aubie85]

I'm always up for a good challenge!

I often dive nitrox in the 100-130' range, and that is where I have observed narcosis symptoms, on both air and nitrox.

Did they try to give the critters air?

 

[DandyDon]

I was going to say "Just pay the $100, do the classroom, get the card, so you'll have it when you need it" as I do to any diver. So much cheaper and easier than when I got my card. But yeah, if you've been hit, get the card and dive the voodoo gas!

Wow. That sounds serious. I will definately have to check that out when I get health insurance. For now, I will have to ride it out.

You do have DAN insurance right?

 

[40Fathoms]

Nitrox definitely has its advantages, which is why people use it. I do hear a lot of divers making claims on Nitrox that are not true, even heard some say that it enables you to go deeper (!) than air.

Nitrox is great for longer lasting dives and shorter surface intervals, however you pay a price for that in terms of depth, as you cannot go as deep with Nitrox as with air due to O2 toxicity. Also, you need to check your own mix and accept responsibility for it.

So, if you're at a point where you end your dives when your dive table or computer says you have to due to nitrogen buildup, and not because you run out of air, Nitrox is great. Also, if you have days that are very dive intensive with multiple dives pr. day (like on a liveaboard) it's perfect.

If, however, you go through a tank of gas quickly enough to have that as the determining factor as to when you end your dives, Nitrox is not for you just yet.

As for the stuff on it being better for you, that you should be able less tired and so on, there's no evidence to back it up, not even from military divers using 100 % oxygen rebreathers.

 

[Cave Bum]

Whilst we are all busy hijacking this post, I was recently reminded of another controversial issue about Nitrox that has yet to be resolved by a definitive study - whether Nitrox assists in reducing narcosis.

The answer to that is NO...

Narcosis is an effect of how 'heavy' the gas is, the molecular weight. In nitrox you replace nitrogen, a fairly heavy gas with oxygen an equally heavy gas. Trimix reduces narcosis because it uses helium a much lighter gas. If I remember correctly, it has to do with short circuiting the synapses but don't quote me on that.

Bruce