air vs nitrox

[Darnold9999]

Not empirical at all, but on my last trip did the whole trip on 32% 27 dives 6 days mostly 60 - 90 feet - the last couple of days I was going up and down the ladder like I had lost 20 years. The previous trip on 21% I was up and down the ladder like I had added 10 years.

Had absolutely no expectations re "feeling better" on nitrox, did it for the longer bottom times and less N loading for multi dive days. Dive profiles were similar. At the time I put it down to that fact that I was having a great time, but on reflection I had a great time the previous trip as well. Lots of other factors were different, but none that seem to be significant to me except the change from air to Nitrox but who knows for sure. Without a double blind study you just can't know.

No wait ... I was diving a BP/W not a BC on the second trip thats it I'm sure ... less resistance in the water

Will I dive Nitrox on local single or 2 tank dives - probably not, will I dive Nitrox on multiday trips - absolutely - I am on the wrong side of 50 so every little bit helps. Do I think it helps with fatigue on such trips - don't know for sure, but I now think it does make a difference for me.

 

[Kim]

My take,
More O2 in gas volume, leaves less space for N2. N2 is associated with causing DCS. Less N2 means less potential for DCS.

Tiredness partially can come from fysiological effort to absorb/release N2 from tissues (metabolism uses energy).... hence, less N2 absorbed/released, is less energy used, means less tired?

:06:

That's my take as well. For the older diver the fact that you are absorbing less N2 to begin with, therefore have less to get rid of, is very beneficial. As older divers are supposedly more prone to DCS the further you can stay away from it the better.
Personally I feel much better diving Nitrox on multiple day/repetive diving (liveaboard style). Maybe it's just my mind...I dunno. I DO know though that the amount of N2 flushing in and out of my body is a lot less than the air divers doing the same profiles on liveaboard guided dives.

 

[String]

The "divers" didn't have any physical exertion during the simulation. I believe that one reason Nitrox might lessen fatigue is that it adds extra oxygen during exertion.

Not really, you only use 4-5% of the oxygen in normal air. Most of that increased oxygen in nitrox is just breathed straight back out as bubbles on open circuit. The reason for more oxygen is a side effect from wanting less nitrogen in the mix. Thats what nitrox is intended for - less nitrogen uptake NOT more oxygen for the diver.

It makes intuitive sense - football players breath O2 on the sidelines to help them 'get their wind back' faster.

..and im sure i saw a study somewhere that conclusively proved that had no effect too.

 

[Thalassamania]

im sure i saw a study somewhere that conclusively proved that had no effect too.

Correct

 

[trigfunctions]

I disagree that increased O2 concentration in the air cannot have an effect on O2 uptake, and thus decrease fatigue. O2 is routinely administered as a medical therapy to people with lung problems. On the flip side, we can't breath air with 15% O2 for very long, despite the fact that we only use 4-5% of the O2 in regular air.

I think the jury is still out as to whether there is a measurable effect on fatigue - one or two studies aren't conclusive proof of anything. However, I don't think the concept that increased O2 concentration can decrease fatigue can be completely written off at this point.

 

[String]

Medicine wise the increased O2 helps more to be absorbed into the bloodstream to help tissues that need it get it. This really shouldnt be an issue with a healthy diver. In either case the partial pressures when diving would have more an an effect than this.

 

[Hickdive]

Were you all ascending at the same rate? Or was the marine coming up faster than everyone else?

... Bob (Grateful Diver)

I wasn't diving with him so I made no direct observations of his ascents. However all the divers had computers with ascent rate warnings, all the dives required stops, none of the people he was diving with complained about his ascents and, finally, he wouldn't have been on the trip if he couldn't control his ascents or do stops properly.

I would say, on that basis, he was not ascending too quickly.

 

[String]

Has he ever been tested for pfo?

 

[lamont]

My experience has been that fixing my ascent rates helped a lot, but eliminating diving on air completely eliminated the subclinical DCS issues that i had in some cases. There were sometimes with perfectly decent profiles and 2-2-2 to the surface on air that i went home and curled up on the couch and passed out with mild feverish symptoms. Those ended when I started diving nitrox on every dive. You can blame placebo effect all you want, but that is suspect to me because it was after building up some data that I noticed the correlation between air and not feeling well. I've also had subclinical DCS issues on very weenie dives (e.g. 70 for 10 mins, gentle slope up to 40 for about 30 mins and then 2-2-2 on air) while more aggressive dives (large numbers of 35 mins @ 100 with varying deco profiles) on EAN32 were not problematic.

I suspect that the effects of enriched O2 on bubble elimination in the free phase (and not nitrogen loading alone) is more effective than even the O2 window models predict. Most people in this thread have stuck with the haldanian tissue loading explanations for why nitrox can't be any better than air, but we know those models are only half the story at best.

I haven't been tested for a PFO, but even the presence of one wouldn't explain what I experience because a PFO doesn't know if you're diving air or nitrox, and would only care about more or less bubbles...

YMMV

 

[bperrybap]

So, back to the orignal question posted from the begining.

I'm not seeing how the study cited applies in anyway to
the original question. From reading the study it appears
that they only did a single dive, and it was a simulated dive at that.

scientists from the Royal Hospital in Adelaide subjected a group of
divers to a 60 foot dive for 40 minutes in a dry chamber

While an interesting data point, it does not appear to answer
the question of if one could/would/should feel better after doing
multiple dives per day on multiple days.

Most folks that are reporting feeling differences are reporting
these differences for multiple dives across multiple days.

This study appears to only have tested folks on a single dive
that didn't seem too realistic, in my opinion, of a real life
dive. How many people really do such perfect square profiles
with such slow descents and linear slow ascents?
Not sure about the rest of you, but my dives are not that square.
AND on my NAUI tables that dive would be slightly off the table.

It also was only 11 people - thats a pretty small sampling.

So while it is an interesting study I'm not too convinced it
really proves anything one way or the other for multiple dives.

Perhaps, it does show that doing a single dive on Nitrox
wouldn't be a wise use of extra funds.

NOTE:
After some WEB searching I could never find the full original study
with its data to read the original text from the authors.

Anybody able to locate the original study?


--- bill