Benefit of Nitrox?

[Rhone Man]

Not looking to be a troll but: I read the literature and I am certainly no Luddite, but in my own mind I am pretty definitive that I feel better after diving on nitrox than I do on air. And for the record, I also suffer less from CO2 headaches (I am a terrible skip breather).

I know, I know, I know. But what can I tell you. I feel what I feel.

I won't be at all shocked (in line with much of diving medicine) if in a few years someone produces a paper which says, you know what we thought we knew? Turns out we were wrong. It is a highly inexact science after all, and we are constantly revising the state of established knowledge. For me the anecdotals and my personal experiences stack up strongly against the published research.

YMMV.

 

[scubadada]

When nitrox is used as if it were air (meaning you stay down the same amount of time you would on air), it is safer. You absorb less nitrogen, have less chance of DCS, and you may feel better afterward as a result, especially if diving multiple times. When using nitrox you can't go as deep as when using air because nitrox has more oxygen and you would absorb too much oxygen.

When nitrox is used to stay down longer then when using air, it is NOT safer but instead provides the same risk as when using air. You absorb the same amount of nitrogen and have the same chance of DCS as you would using air, except you get to stay down longer.

Gas consumption is the same on both gases. If your dives end because you run out of gas, nitrox won't let you stay down longer (but you will absorb less nitrogen). If your dives end because you have absorbed as much nitrogen as is safe, then nitrox will let you dive for longer.

It may not reduce fatigue, but it definitely reduces nitrogen uptake. What ramifications does that have? It seems reasonable that people "feel better" after using nitrox, even if they just as fatigued as they would be using air.

What does the 0.01% chance mean? DCS can be anything from unexplained fatigue, itching, joint pain, dizziness to hearing loss, paralysis, embolism, and more.

Nate,

Please stick to a topic for which you have some knowledge, experience, and expertise.

Good diving, Craig

 

[Storker]

So, scientific evidence aside, it still "seems reasonable" to you?

If you want to go all scientific on the subject: I've seen a presentation of a study where they used ultrasound imaging to detect bubbles in chamber divers. 18m, two hours, deco according to the US Navy table. None of the research subjects were bent (deliberately bending humans is poorly regarded by the research ethics committees these days), but the amount of (sub-clinical) bubbles varied from "none detectable" to "warm beer in a glass". So it's obvious that you can't prove a negative correlation, because the spread in data is huge, and most studies involve a moderate amount of subjects. You can't even conclude sensibly unless you have a bunch of subjects and seriously consider even the outliers. That no studies have found a clear correlation between nitrox and post-dive fatigue does not mean that people can't experience a real benefit from nitrox.

It may of course be pure, unadulterated placebo, but I've found that diving less aggressive profiles reduces post-dive fatigue. Proper multi-level profiles instead of square profiles, a good safety stop, ascending on a (dSMB) line instead of just corking from the SS or using nitrox, particularly on deep or repeated dives, all seem to reduce my post-dive fatigue. Since post-dive bubbles have been shown to be prolific even in DCS-asymptomatic divers, I'm pretty convinced that nitrogen loading induces a stress on the body, even if you don't exhibit DCS symptoms.

"What he said..."

Note the words I underlined this time...

 

[blue steal]

Speaking to the benefits of using Nitrox. Here is a scenario I frequently run into every year while vacation diving.
Never have the problem of running low on gas, always time with NDL.
2-tank dives each day running for 12 days with a day off every three days.
1st dive to max 90' total BT say 65 minutes. Not a square profile, but down to 90, then gradually up to 50-60' and further ascending as NDL closes in.
1 hour SI
2nd dive to 60', total BT say 65 minutes. Again not a square profile, but ascending as NDL closes in. And it does.
Which dive would give the best benefit of using Nitrox? 1st or 2nd?
Which FI02 .32 or .36? Those are the offerings.

I know some will say just use Nitrox on both dives, but if you were limited to using only one tank if Nitrox, then which dive 1 or 2?
Thanks...........

 

[scubadada]

There will never be the perfect clinical study(ies) to definitively answer the questions regarding nitrox. There is essentially no money to support quality scuba research. You can either accept the best scientific evidence or go with your own anecdotal experience. These discussions on SB always break down into those who prefer to accept the science vs. those who prefer to accept their own experience or others beliefs. Who cares? I doubt many of you would like to receive medical care based on the same criteria. Fortunately, beliefs regarding nitrox are unlikely to do any harm

 

[RJP]

The rate of DCS is less than .01% using air.

What does the 0.01% chance mean?

Don't confuse the "rate" at which an event is observed to occur with the concept that the occurrence of that event is due to "chance."

Dive conservatively and the likelihood that you will experience DCS during your lifetime is virtually zero. On the other hand, there's all kinds of things you can do to increase that likelihood to darn near 100% on any given dive. In neither case is the potential for getting hit due to chance.

---------- Post added September 6th, 2015 at 12:34 PM ----------

1st dive to max 90' total BT say 65 minutes. Not a square profile, but down to 90, then gradually up to 50-60' and further ascending as NDL closes in.
1 hour SI
2nd dive to 60', total BT say 65 minutes. Again not a square profile, but ascending as NDL closes in. And it does.
Which dive would give the best benefit of using Nitrox? 1st or 2nd?
Which FI02 .32 or .36? Those are the offerings.

Nitrox on the first dive... you have a greater likelihood of not doing the second dive (weather, conditions, don't feel like it, etc) than you do of not doing the second dive. Therefore the potential to gain "no benefit" from nitrox on the second dive is automatically higher if you don't use it on the first dive.

But here's another consideration: how much gas do you need to conduct a dive to 90ft max for 65min, gradually ascending as NDL closes in? Since you specified "vacation diving" I'll assume you're diving an AL80. Quick V-planner run suggests that descending to 90ft and then chasing NDL for 65 minutes on either 36% or 32% - including a 3min safety stop - requires 104cf of gas.

With pretty good air consumption, chasing NDL on an AL80 gives you about 43min of bottom time chasing NDL up from 90ft.

Going OOA at 35-40ft 43min into Dive #1 greatly reduces the likelihood of you doing a second dive, so there's another reason to use Nitrox on the first dive. And might be a good reason to go for the 36% instead of 32%.

:shocked2:

Let's assume you don't want to get a helicopter ride home, and decide to limit the first dive to a plausible 43min run time (on 36% or 32%) and took an hour surface interval. Your planned dive 2 - chasing NDL up from 60ft - requires about 86cf of gas.

So, long story short, diving nitrox will not meaningfully help you conduct either of the dives you have "planned" in terms of achieving your desired run times... since gas supply rather than NDL will be your rate limiting factor.

But given that your plan of chasing NDL up from depth offers a pretty good potential for going OOA on BOTH dives... nitrox might be a good idea.

 

[BRT]

I get a kick out of those who say you can get longer NDL's OR less chance of DCS but not both. The fact is you can stay down longer than with air and come up with more bottom time remaining. You can get both and for this I really like nitrox. Plus I feel better when I dive it. If the placebo works, use it!

 

[RJP]

I get a kick out of those who say you can get longer NDL's OR less chance of DCS but not both. The fact is you can stay down longer than with air and come up with more bottom time remaining.

I think you're confusing things a bit with a self-limiting proposition. By definition, if you come up "with bottom time remaining" you have a statistically lower likelihood of DCS than if you maxed out NDL. This is true whether you're diving air or EANx.

The people who say that you can have one or the other (but not both) typically mean that if you max out NDL with either AIR or EANx your nitrogen exposure is the same. With a maxed out NDL on Nitrox you've been exposed to less nitrogen per minute, but for more minutes.

While it is mathematically possible to "stay longer" and still have "more bottom time" remaining, in practicality the bigger question is whether NDL or gas supply is your limiting factor.

Consider a dive to 55ft. On air I'd have a rough bottom time of 60min based on NDL. With 32% you'd have a rough NDL time of nearly 80min.

However, in both cases, an AL80 only gives you and I enough gas for about a 50min dive... assuming we breathed it to ZERO. Accordingly, nitrox would lower your nitrogen exposure, but it would not extend your bottom time. (ie practically speaking "you can't have both")

Switch it up and assume we're both diving doubles and have plenty of gas. On Air I come up after 60min and you stay for 80min. Yes, EANx has extended your bottom time; but since we've both maxed out NDL... we both have the same nitrogen loading and therefor (statistically speaking) the same DCS risk. (ie practically speaking "you can't have both")

Where it gets grey is the in-between zones. Sure, if you dive EANx and opt to come up at some time after 60min but before 80min you will have extended your bottom time AND reduced your DCS risk. But that requires specific planning, which isn't a bad thing. However, for most divers that only happens "automatically" in the situation where their gas consumption is low enough to still have gas remaining when they've exceeded the NDL for 21%... but high enough that they don't have enough gas remaining to reach the NDL for 32%.

Ultimately, I think that what people mean is... "For the most part nitrox offers divers the choice of either longer bottom times or lower DCS risk."

I, for one, like to ensure that my students don't walk away from an EANx course believing that diving nitrox magically offers both at all times.

 

[Bob DBF]

There will never be the perfect clinical study(ies) to definitively answer the questions regarding nitrox. There is essentially no money to support quality scuba research. You can either accept the best scientific evidence or go with your own anecdotal experience. These discussions on SB always break down into those who prefer to accept the science vs. those who prefer to accept their own experience or others beliefs. Who cares? I doubt many of you would like to receive medical care based on the same criteria. Fortunately, beliefs regarding nitrox are unlikely to do any harm

As I discussed in my previous post, the study did not say that divers did not feel better after using nitrox, in fact they noted that on one of the tests the nitrox divers felt better, but they were studying fatigue.

Say I'm looking into a pen with 15 animals and I ask a scientist doing a study how many animals are in the pen. The scientist says 10 cows. I ask what about the 5 ducks? He answers that they are there but I'm only studying cows.

The point is that the study is about a very specific meaning of fatigue, not what I would necessarily mean when saying fatigued or tired. They did note in the study, that the divers on nitrox felt better on one of the tests after the dive, over divers on air. The conclusion was kind of like the ducks, it is there but we are studying fatigue, not what might be stress caused by nitrogen off gassing.

I'm with you about the chances of a broader study being done, not likely but the study's author would like another crack at it, and maybe study more about the "decompression stress" as well.


Bob

 

[Aotus]

Check out the book/audiobook "scuba confidential"

He makes a very good case that air is not a good gas for diving, period. Nitrox or mix, that's it.