Nitrox vs Air

[mikeb663]

These threads are always soooooo amusing! String . . . enjoy your air! I'm done with this thread:

 

[mooney]

The status quo remains until proven otherwise. Its how standard scientific method and peer review works.

Otherwise i could quite happily state "I have pink fairies living at the bottom of my garden that only i can see and talk to" and pass it off as true unless you can prove otherwise.

FWIW there have been some small scale studies and all have failed to find any reduction in fatigue (however you attempt to quantify that) over a placebo. But that isn't relevant to the above. Its a very difficult thing to test and measure but there is currently no evidence supporting a reduction in fatigue nor in fact is there any postulated mechanism as to why it would that stands up to any scrutiny. However placebo effect is known to and scientifically proven to have a physical effect on a person.

Shouldn't matter if there is scientific evidence of it or not. If an individual feels less fatigued after diving Nitrox, whether it's just in his head(PLACEBO) or not shouldn't matter. He personally feels less fatigued, doesn't matter if 1000 other divers (including me) don't notice a difference. If I run a 4 minute mile after drinking Gatorade and 4:30 after drinking only water, you aren't going to convince me that the drinks are the same, scientific evidence or not....it's up to the individual abut how his body feels and nobody but that individual can back up or deny the claims.

By the way, in aviation it is well known and published and in some cases in regulations that increased levels of O2 decrease fatigue and increase alertness etc (when feeling fatigued i regularly take a few hits from the O2 mask and it does wonders), and athletes routinely suck O2 to increase energy, so why wouldn't it be the same for a diver?

String, if you told me that you feel less fatigued after running 3 miles than after swimming 1000 meters, I wouldn't say that's BS because there is no scientific evidence to back that up, I would assume that you know your body and are able to make a rational decision on your own as to wether you are fatigued or not. Fatigue affects everyone differently, and 1 aspect of being fatigued is that you may not even know you are fatigued! Kind of like the narcosis or being drunk argument...

 

[Hammerhead]

It gets me more time underwater in the typical dives I do. That's good enough for me.

Funnily enough, some people I know claim there are tangible advantages in *ahem* "getting wood" after multiple dives with nitrox versus multiple air dives.

Needless to say, this has never been an issue for me.

 

[Tigerman]

Thats generally more an issue with and/or for the other part of the.. needy party

 

[Jaeger45]

Problem comparing dives done on two separate days means you cant account for variation of daily conditions, like eating, drinking, possible beginning sickness etc...

That's where randomization and adequate sample size takes over, along with subsequent statistical analysis for variation within the group.

If your test group has two subjects, it stands to reason that they could be coming down with a virus. If your test group has 200 subjects, it becomes much less likely that they ALL are coming down with a virus (and your null hypothesis group isn't).

 

[Jaeger45]

Research by Harris, et al (2003) supports the idea that the reduction fatigue experienced when using Nitrox is solely due to the reduction in subclinical DCS rather than any inherent property of Nitrox. In their double blinded, randomized controlled study 11 divers breathed either air or EAN36 during an 18m dry chamber dive for a bottom time of 40 minutes. Two periods of exercise were performed during the dive. Divers were assessed before and after each dive using a range of performance measuring tests. Diving to 18m produced no measurable difference in fatigue, attention levels or ability to concentrate following dives using either breathing gas. As a result of this and other research the current thinking at this time is that there is no difference in terms of fatigue between diving air and Nitrox."

Glad to see an actual relevant study cited! Could only get the abstract on PubMed, not the full text. However:

The results stated would seem to support an alternate hypothesis: no difference in fatigue between diving air and diving nitrox would suggest placebo effect as a cause for reported decrease in fatigue, rather than any actual effect.

At best, a sample size of 11 divers (if a crossover study), or more likely 5-6 divers per group, would seem to be vastly underpowered to detect a small, subjective difference between groups. While it's good to see someone doing actual research, I would hesitate to draw any conclusions from this study, other than to state that this study did not find a difference.

 

[DaleC]

Some other things I note that I think may affect the outcome.

1. The general fitness level of the study group. If they were all fit (as in a Navy) then the exertion level may not trigger a response. The general fitness level of todays recreational diver is sub optimal (age, obesity poor cardio) and fatigue may be more easily induced and differenciated within this second group.

2. The exertion threshold may not be high enough. It may be that that particular exercise, at that depth, does not trigger a great enough exertion level to register a difference. Perhaps higher exertion over a longer testing period may though.

If subclinical DCS is the root cause of fatigue (and so reduced by EAN use) then the study may not have been enough to induce subclinical DCS in this group for those two reasons.

 

[oldogre]

Just to toss in another variable "age". As we age lung efficiency decreases, at 78 I use Nitrox if possible, is this correct?

 

[Token]

Would it be correct to say that using Nitrox would increase your margin of safety if you used it on the last day of diving before flying? If so, this by itself would be a pretty good justification for its use...

 

[DandyDon]

Would it be correct to say that using Nitrox would increase your margin of safety if you used it on the last day of diving before flying? If so, this by itself would be a pretty good justification for its use...

I don't think so. It wouldn't hurt, but with hits being so rare - DAN does not support Nitrox use for safety margins. It's most beneficial on deeper, square bottom profiles like many wreck dives, but the Nx divers generally just stay down longer and surface with similar computer readings as the Air divers who surface earlier - which negates any safety ideas as well as sub-clinical DCS relieve.

Simply put: Nitrox lets you stay down longer without pissing off your computer.