Tissue stress associated with bubble formation; potential benefits of diving enriched air

[Bob DBF]

I did not say "if I don't, nobody does". What I said is you may be wrong in your generalizations. I'll be convinced by results of a blind (or even better, a double-blind) test, supported by of fatigue actually measured after dives.

Well the problem is that what I and others call fatigue after a dive is not what the last study I saw considers fatigue. They did however find in their double blind study that divers felt better after the dives after diving nitrox, but attributed it to less decompression stress rather than fatigue. Since it was not the focus of their study it was just an interesting bit that they stumbled upon, but was the result of a double blind study.

Measurement of Fatigue following 18 msw Open Water Dives Breathing Air or EAN36.

Another discussion can be found at Why Nitrox? and it is only 5 pages.

The chances of a double blind study to answer this question is rather slim. Most have made up their own minds from personal experience and the study would effect few. I don't use Nitrox for a three tank day, but multi dives on a multi day trip makes a difference to me. As I get older it makes a more noticeable difference. Whether it reduces fatigue or decompression stress is irrelevant to me as I feel better.


Bob

 

[tarponchik]

Well the problem is that what I and others call fatigue after a dive is not what the last study I saw considers fatigue. They did however find in their double blind study that divers felt better after the dives after diving nitrox, but attributed it to less decompression stress rather than fatigue. Since it was not the focus of their study it was just an interesting bit that they stumbled upon, but was the result of a double blind study.

Measurement of Fatigue following 18 msw Open Water Dives Breathing Air or EAN36.

Another discussion can be found at Why Nitrox? and it is only 5 pages.

The chances of a double blind study to answer this question is rather slim. Most have made up their own minds from personal experience and the study would effect few. I don't use Nitrox for a three tank day, but multi dives on a multi day trip makes a difference to me. As I get older it makes a more noticeable difference. Whether it reduces fatigue or decompression stress is irrelevant to me as I feel better.


Bob

Thank you, Bob. This is exactly what I was looking for. They have not found statistically significant correlation between fatigue and the type of gas the divers were breathing. Moreover, if you look at their numbers, fatigue ratings were slightly worse in EAN36 divers (34.7 ± 4.6) vs. air divers (30.8 ± 3.7). They got statistically significant differences in DHS, however. Such result can be expected, though utility of DHS for monitoring decompression stress has been questioned.

 

[Bob DBF]

My point is that whatever their definition of fatigue is, they excluded the DHS results that showed that the divers using Nitrox felt better after those on air. Even if it is not decompression stress, it is something.

The study you cite is using dive working professionals, the job they do includes more than diving and their diving is not recreational, this might impact the survey differently than a rec diver. Too many variables spoil the soup.


Bob

 

[MaxBottomtime]

There was a second study involving actual dives in water. Results showed no difference in fatigue between the eleven divers tested.
http://archive.rubicon-foundation.o.../123456789/8005/AAUS_2008_1-11.pdf?sequence=1

I just realized this study was already posted. The other one was done in a chamber with similar results.

 

[tarponchik]

My point is that whatever their definition of fatigue is, they excluded the DHS results that showed that the divers using Nitrox felt better after those on air. Even if it is not decompression stress, it is something.

The study you cite is using dive working professionals, the job they do includes more than diving and their diving is not recreational, this might impact the survey differently than a rec diver. Too many variables spoil the soup.


Bob

They dropped DHS because they did not believe in its direct connection to fatigue. And they also argued that "It was not apparent whether post-dive fatigue was induced through decompression stress or energy expenditure." After all, the divers in their test swam in 12 C waters. Like you said, too many variables spoil the soup. Also, note this paragraph: "Three participants felt they would be able to determine which gas they were breathing during a test session. Only 1 of 3 guessed correctly. One commented that his breathing rate was better during one test session and, therefore, he assumed he was breathing EAN36. The data did not support this conjecture; the diver actually consumed 249.75 L (8.82 ft3 ) more gas during the EAN test session." So here they had a NITROX fan who honestly believed in his case but got it all wrong. Which is basically what I said earlier: people come to wrong conclusions based on their small stats, and once they make such conclusions they become biased and disregard any evidence to the contrary of their bias.

 

[Centrals]

If divers believe Nitrox do them wonder, I see no reason to dispute with them. But I only use it to extend the bottom time. And as far as I am concern, longer surface interval is very much preferred.

 

[KenGordon]

If divers believe Nitrox do them wonder, I see no reason to dispute with them. But I only use it to extend the bottom time. And as far as I am concern, longer surface interval is very much preferred.

That is ok, but if they believe that they can tell how much deco stress they have by 'feelings' and choose to dive more aggressively because they do not have the feelings yet then they might get a surprise about how being bent really feels.

Believing in fairies on your own is ok, pushing that belief is something else.

 

[DevonDiver]

I don't know anyone who would (now,) choose to dive more aggressively because of positive post-dive vitality.

But I do know many that'll assume less than optimal decompression if their relative vitality was depressed post-dive.

I think... I hope.... The situation has changed a lot since the days of tech divers accepting a little 'fizz' whilst striving for a bare minimal deco