Fatigue and nitrox

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Valéry;5008624:
Well let's say that those dives are between 30 and 40m (a small part of the dive is at this depth), reef, swimming 90% of the time and the speed is a little more than normal, duration between 30 and 40 mins.

Not to much deco 15mins (or less) rarely 20mins or more. Gas is Air even for deco. We dive at a club and we all have different level so we all dive with air to be at the same time on the boat, but this should be fixed as next season there will be more advanced divers.

If I don’t succeed in fixing the problem, I'll post several profile dives as soon as possible.


My X1 is new and I haven’t logged any thing interesting on it yet. The problem started before I bought it, I use to dive and follow my instructor deco who has a VRX set to 0.

Just for interest, & as you have logged some dives on the X1, you could have a look at the ascent rates at the steepest parts of the profile on those you have logged. (I'v assumed you've uploaded to a PC)

Now that you have the X1 what settings do you use. Or does "I haven't logged anything interesting yet", mean you haven't used it for these sort of dives yet.

When I do no stop dives I set mine to 0 conservatism. For the sort of deco dives you've described & as you've been fatigued, I'd suggest using a conservatism of 2.
 
Just for interest, & as you have logged some dives on the X1, you could have a look at the ascent rates at the steepest parts of the profile on those you have logged. (I'v assumed you've uploaded to a PC)

Now that you have the X1 what settings do you use. Or does "I haven't logged anything interesting yet", mean you haven't used it for these sort of dives yet.

When I do no stop dives I set mine to 0 conservatism. For the sort of deco dives you've described & as you've been fatigued, I'd suggest using a conservatism of 2.

I've logged 2 dives with it but I was so happy using it that I don't remember how I felt after the dive:)
One dive was with the 3 setting on vpm-b the other dive the setting was on 1, I'm still a little confused with how fast I'm out of water comparing to the VR of the other divers in my group.
In my ascent rate I've sometimes been faster than 10m/min.

On my next dives I'll try cons 4 and some deep stop (keeping bubble small, you know)during the way out and I think I'll stay a litle longer around 6m. Just to see if it works.

I remember 1 dive beeing very hard on swiming to the point that I had to slow down to catch my breath, it was a dive with a maximum depth of 27m and we stayed in the NDL. The dive lasted 47mins. After this dive I felt very good like I never dived, since this dive I started focusing on how to improve what I was doing wrong in those deco dive...
 
Bubbletrubble:
What I wrote places the burden of proof on the person hypothesizing that nitrogen loading does not affect a diver's post-dive fatigue level. Your simplification places the burden of proof on the person hypothesizing that the nitrogen loading increases post-dive fatigue. The difference is in how the statement was phrased.

The burden of proof always lies on the side making a claim.

You guys are arguing a point that neither of you can win until more research is done.
 
Let us look at those two multilevel dives :

A) Air. First dive of the day. 20 minutes at 28 meters, then 20 minutes at 14 meters, then 10 minutes at 4.5 meters and exit.

B) Nitrox 32. First dive of the day. 20 minutes at 34 meters, then 20 minutes at 17 meters, then 10 minutes at 6 meters and exit.

Both are close to the No Deco Limit (could even lead to deco with some computers). Both lead to the same intake of Nitrogen, so I believe I would feel tired the same after each of them.

Now let us look at gas consumption, assuming a SAC of 15 liters/minute.
Dive A) represents 2078 liters of air. Dive B) represents 2370 liters of Nitrox 32.
The classic Al80 tank offers 2280 liters of gas (11.4 liters x 200 bars).

So I am led to think that for dive B) the diver won't go so close to the NDL and will dive more conservatively than the suggested profile because he is more likely to be limited in gas. For example he may actually stay only 15 minutes at 34 meters, instead of 20 minutes. Hence he will reduce Nitrogen intake.

In other words, maybe sometimes Nitrox reduces fatigue because we don't go as close to the NDL as we do with air, given the tank we dive with (very often an Al80).

I am well aware this is only an example, not a demonstration.
 
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Kinda an odd way of demonstrating it, but yeah, I agree.

The bottom line is that EAN32 (32% nitrox) has an equivalent narcotic depth (END) of 80% - that is, if two divers do exactly the same profile and one is on air (21%) and the other on nitrox I (32%), then the person on 32% has 20% less exposure to nitrogen... Resulting in less narcosis, a longer NDL, shorter surface intervals, and the like.

Alternatively - what usually happens - is that the dive profile is the same as before (because of the limiting tank size), but the diver is simply not as close to his NDLs as he would be on air.

...Which reduces fatigue - and is especially more obvious during dives which are closer to the diver's limits (NDLs).
 
Kinda an odd way of demonstrating it, but yeah, I agree.

The bottom line is that EAN32 (32% nitrox) has an equivalent narcotic depth (END) of 80% - that is, if two divers do exactly the same profile and one is on air (21%) and the other on nitrox I (32%), then the person on 32% has 20% less exposure to nitrogen... Resulting in less narcosis, a longer NDL, shorter surface intervals, and the like.

Alternatively - what usually happens - is that the dive profile is the same as before (because of the limiting tank size), but the diver is simply not as close to his NDLs as he would be on air.

...Which reduces fatigue - and is especially more obvious during dives which are closer to the diver's limits (NDLs).

What makes you think that O2 is noticeably less narcotic than N2?
This is a topic still subject to debate.

To quote a post made by Rick Murchison:
"Whan I see "END" I read "Equivalent Narcotic Depth," and figure that at (100% - He%) * ATA. In other words, both Nitrogen and Oxygen count full measure for loopiness.
If you really want to shave nits, the narcotic effect of oxygen is probably a bit less than nitrogen, (even though it has about twice the lipid solubility, so you'd expect it to be twice as narcotic, its tissue titres tend to be lower than an inert gas would be as it's a metabolized gas that's also scavenged by hemoglobin - in rats the brain tissue titre's about a sixth what you'd expect were the gas inert, which should more than compensate for the increased narcosis expected by lipid solubility) and the narcotic effects of Helium + Oxygen may still be a bit less, maybe.... but it ain't enough to spit at, so prudence dictates "it is best not to assume reduced narcosis for the oxygen fraction of the mix" (Uncle Ricky's Rule).
Of course if you stick to HeliAir it's a moot point :)
I don't use the term "Equivalent Nitrogen Depth" because we already define that as "EAD" - "Equivalent Air Depth," making the term redundant and unnecessary, and confusing as well..."

or from TSandM
"GUE counts oxygen and nitrogen as narcotic."

or from wedivebc
"So does IANTD."

Normally only the He % is used as a narcosis reductor.
 
What makes you think that O2 is noticeably less narcotic than N2?
This is a topic still subject to debate.

Fair enough - EAD. I like that term better. :) Great point!
 
But, if memory serves, there is no clinical or experimental evidence that oxygen is narcotic.
 
Other than for "Harris RJD, Doolette DJ, Wilkinson DC, Williams DJ.
Measurement of fatigue following 18 msw dry chamber dives breathing air or enriched air nitrox. Undersea Hvperb Med. 2003:30(4):285-90," which used simulated dives and had some serious methodological problems (e.g., the EANx divers had shorter total immersion and decompression times than the air dives with which they were compared), the following piece is only published science on the topic of which I am aware.

Seems that EAN may in fact reduce subjective and objective fatigue in divers, although more research obviously is needed.


“Abstract

Lafere P, Balestra C, Hemelryck W, Donda N, Sakr A, Taher A, Marroni S, Gerrnonpre P.

Evaluation of critical flicker fusion frequency and perceived fatigue in divers after air and enriched air nitrox diving.

Diving and Hyperbaric Medicine. 2010;40(3): 114-8.)

Introduction: Many divers report less fatigue following dives breathing enriched air nitrox (EANx) compared with breathing air. A reduction of post-dive fatigue with EANx would suggest a pathological origin, possibly the presence of asymptomatic nitrogen bubbles in the body after a dive.

Method: We studied fatigue in 219 healthy divers performing either an air (n = 121) or EA x32 (oxygen 32%, nitrogen 68%; n = 98) dive to 21.2 ± 4 metres' sea water for 43.3 ± 8.6 minutes in tropical open-water conditions. Divers were assessed pre-dive and 30-60 minutes after surfacing using a visual analog scale (VAS) offatigue and critical flicker fusion frequency (CFFF).

Results: The two groups were comparable in sex ratio, age and diving experience. The change in perceived fatigue level after a single dive was significantly lower when EANx was breathed compared to air dives (VAS; P < 0.001). Compared to pre-dive, CFFF decreased by 6% in the air group (P < 0.01) but increased by 4% in the EANx group (P < 0.05). The post-dive difference between the two groups was highly significant (P < 0.001).

Conclusions: Three hypotheses should be considered to explain the difference in post-dive fatigue and alertness between the air and EA x groups: a nitrogen effect, an oxygen effect and a bubble effect. These involve complex phenomena in the functional modifications of the nervous system in hyperbaric environments according to the type of gas used for the dive, and more research will be required to elucidate them.”

Regards,

DocVikingo
 
Well, one of the mechanisms for the claimed and controversial effect of less fatigue felt when diving with enriched air (nitrox) was the higher Oxygen pressure in the gas mix.

The other possible mechanism for a decrease in perceived fatigue would be nitrogen loading.

There is a real big problem with the increased oxygen pressures having a beneficial effect. The vast majority of the oxygen delivered to the body's tissues at sea level is transported by hemoglobin to the tissues by way of the circulatory system. The problem is at sea level, the hemoglobin in the blood comes out with something like 99.5% saturation. Breathing even pure oxygen at sea level will not increase the amount of oxygen delivered to your tissues to any significant degree. I know, professional foot ball players often like to breathe pure oxygen at the sidelines. If it makes them happy, so what?

But if there is any benefit to diving nitrox on perceived fatigue, I don't think that it is likely to be caused by increased oxygen tension. It is more likely to be the decreased nitrogen loading. But if you are still pushing your no dec limits, how would nitrox benefit you? You are still getting the same nitrogen loading. You just get it faster using air.
 
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