Why Nitrox?

[tursiops]

Can you provide any citations?

i guess not.

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[MaxBottomtime]

There was one study on Nitrox which determined there was no difference in how tired you are after using air or Nitrox.

However, I tracked down the study and I felt it had no bearing on the discussions of the subject. I had a link to it in another discussion but have had too many Longboard's to try to find it. The study was done in a chamber using one tank, having the subjects exercise and ask them how tired they were. Since I don't notice any positive effects until after 3 or so tanks on the first day of a live aboard, I would agree with them on one tank but disagree with extending the findings past the first tank.



Bob
---------------
I may be old, but I'm not dead yet.

Another test was published in 2008 using 36% and having eleven dives make two repetitive air dives and two repetitive EAN36 dives to eighteen meters in water on separate, nonconsecutive days. The results confirmed the earlier study.
Measurement of Fatigue following 18 msw Open Water Dives Breathing Air or EAN36.

 

[scjoe]

Uh! Hmm, glad to know this. I'll throw all my materials out about hemoglobin and oxygen toxicity. LOL (FOR YOU NEW GUYS, THIS IS SARCASM!)

Two years ago a friend of mine had to do his dive master swims. The first swim was 900' in nothing but swim suit. The second swim was 1800' in Mask Fins and Snorkel. The third swim was 1800' in full scuba on the surface, and the fourth swim was 1800' in full scuba underwater. The resting period between these skills is less than 5 minutes. So, he does swim 1. 5 minutes or less after completing swim 1, he must start swim 2, 5 minutes or less after completing swim 2, he must start swim three, etc. etc. As you can imagine, this is pretty exhausting. But, what's interesting is that on Swim 4 and Swim 5, even though he had WAY more drag by being in full scuba as opposed to being in just a mask, fins and snorkel, the candidate shaved almost 8 minutes off his time. How did he do this? He had already swam almost a mile, and on his last dive, after what seemed like forever swimming, he shaved 8 minutes off his time. Well, he was diving with a bottle of pure oxygen.

I've seen people repeat this *cheat* several times over the years. It works every time.

Your friend was obviously dogging the early swims in anticipation of the later swims.

 

[Bob DBF]

Another test was published in 2008 using 36% and having eleven dives make two repetitive air dives and two repetitive EAN36 dives to eighteen meters in water on separate, nonconsecutive days. The results confirmed the earlier study.
Measurement of Fatigue following 18 msw Open Water Dives Breathing Air or EAN36.

Thanks, didn't run across this study before. I skimmed it but will read it all later. As I said before, I don't feel the positive effects until I'm outside the range of the study.

What i found interesting was

Divers did tend to be more fatigued after diving; however, breathing gas
mixture exhibited no statistically significant effect. Participants did have significantly lower
Diver Health Survey scores upon the conclusion of EAN36 test sessions, possibly indicative
of reduced decompression stress.

The way I read it, they saw some indication of a positive effect however, it was not significant enough to be considered a finding in the study. Also it sounds like they are trying to separate "reduced decompression stress" from fatigue when interpreting the Diver Health Survey scores. Personally I wouldn't know one from the other, I just feel better.



Bob
-----------------------------
The day I can't dive anymore, I will really need some other good reasons to stay alive. DarkAbyss

 

[BRT]

I'm not sure that 18 meter dives for total time of 30 minutes is the same as 1 hour dives with a maximum depth of 25 meters. It would be hard to get a separation of data between air and 36% in dives like that. Just what is the "Diver Health Survey" they talked about?

 

[MaxBottomtime]

The entire study and results are available at http://archive.rubicon-foundation.o.../123456789/8005/AAUS_2008_1-11.pdf?sequence=1

 

[scubadada]

Sorry, you dive nitrox to maximize your NDL and dive it to the limit, just like you would dive air. Why would you have any less dive stress with the same nitrogen loading and exposure? Maybe I'm wrong and other divers don't push nitrox limits.

 

[dfx]

What i found interesting was
The way I read it, they saw some indication of a positive effect however, it was not significant enough to be considered a finding in the study. Also it sounds like they are trying to separate "reduced decompression stress" from fatigue when interpreting the Diver Health Survey scores. Personally I wouldn't know one from the other, I just feel better.

As a completely unqualified opinion, I'd say their point was that you don't feel "decompression stress". DHS is merely means to quantify how likely you are to come down with DCS.

 

[Bob DBF]

As a completely unqualified opinion, I'd say their point was that you don't feel "decompression stress". DHS is merely means to quantify how likely you are to come down with DCS.

My question would be how do you not feel it and yet it is noticeable enough enough to change your answers on a survey question. And my point would be that if I feel less tired (my evaluation with no medical training) on Nitrox after 3 or 4 dives, how would I know or possibly care what was actually causing it to happen. In other words I tell you I feel tired and then you tell me its sub-clinical DCS. I say OK, but I still feel tired.

As for the DHS predicting DCS in recreational divers see Diver Health Survey score and probability ... [Diving Hyperb Med. 2012] - PubMed - NCBI. The conclusion was "Utility of the DHS for monitoring daily decompression stress among occupational divers working in the recreational diving industry in New Zealand remains unproven."

In all it is an interesting topic and I hope to be around to hear the conclusion, but I doubt that it will change my habits.


Bob
-------------------------------
There is no problem that can't be solved with a liberal application of sex, tequila, money, duct tape, or high explosives, not necessarily in that order.