Benefit of Nitrox?

[Storker]

To confirm decompression stress reduction (sub-clinical DCS), you'd simply need to do a trial with 2-3 different dive profiles; which caused differing decompression stress/micro-bubbling scores, then compare post-dive fatigue between nitrox and air on those dives.

Sample size would need to be large enough to predict trend, accounting for individual pre-dispositions towards bubble formation etc.

To end, doppler test the participants to chart bubble score versus fatigue/vitality.

OR.... just investigate bubble scores versus post-dive vitality... knowing that nitrox reduced bubble score compared to air.

I don't think it's that straightforward.

Like I said in a previous post, I've attended a presentation of a project where post-dive bubbles were monitored by ultrasound. All the subjects were asymptomatic, but the amount of bubbles varied in the extreme. From none at all to levels where you were surprised the person wasn't bent. After exactly the same chamber dive. The only takeaway message was that the amount of post-dive bubbles was very dependent on the person. Unfortunately, the subjects weren't interviewed about post-dive lethargy, but I know a few of them. There were no remarks about feeling better or worse. Also, the (established) methodology for quantifying bubbles is too coarse to give any sensible data unless the study had been using several hundred subjects.

I've been searching a bit for a publication, but unfortunately I haven't found anything available. No surprise, really, since results without a takeaway message seldom get published. Here, the data was inconclusive.

My interpretation of those results is that it's very difficult to predict the outcome for a single person. Some divers have lots of asymptomatic bubbles, others have virtually none after the same type of dive. The physiological reaction to microbubbles may be just as unpredictable. Sure, lethargy may well be caused by unusual physical activity, psychological stress etc., but I think it's quite acknowledged that at least some divers react to subclinical bubbles with lethargy.

So either you bubble easily after a dive, or you don't, and it's unpredictable. Either your body reacts noticeably to micro-bubbles, or it doesn't. Either your zombie state in the evening is caused by sub-clinical DCS and microbubbles, or it's caused by (unfamiliar) physical and/or psychological stress from the diving itself. Either you feel better on nitrox, or you don't. And that can have physiological reasons, or it can be placebo. Or both. If someone feels better after a shallow, easy warm dive on nitrox compared to air I'll be prone to believe it's placebo. If someone feels better after one or more deep dives close to air NDLs, and/or under conditions that aren't ideal for offgassing, I'll assume that it's a real physiological effect, and that the reduced saturation and increased offgassing that nitrox provides has had an effect beyond placebo. That some divers don't experience any effect of nitrox doesn't mean that the effect isn't real for other divers, since people and physiologies are different.

To return to the anecdotes, my own experience that my post-dive lethargy is affected the same way by using nitrox as it is by doing shallow dives, diving in warm water, diving correct profiles and/or using correct ascent strategies makes me believe that I'm one of those who benefit physiologically from using nitrox, and that it isn't just placebo. And if it is placebo, it still works for me...

I don't believe using nitrox has any direct effect on gas consumption, though. I haven't seen one single plausible mechanism for that to happen.

 

[archer1960]

Nitrox doesn't help me one bit in an Al80, because I always run out of air before I run out of NDL time.

 

[Rhone Man]

The reality is that the sample size - and selection - would be enormous, and enormously complex. If you think of this as a clinical trial comparing two "treatments" and try to design it accordingly you'd have to do it as a

- prospective
- unbiased
- randomized
- double-blind
- cross-over design

You'd have to start prospectively with a large number of UNTRAINED, UNCERTIFIED prospective students... do complete battery of baseline tests... randomize them to either an "AIR" or a "NITROX" group... then train them the same and ensure that they have the same amount and type of dive experience over time BEFORE the study actually started. Then you'd need to have both groups do a large number of dives in each of multiple profiles and environments. Do all your measurements, data collection for each group, etc.

<snip>

It is a good post about research methodology, but if I wanted to seriously study this subject (I don't - nothing we discover or don't discover is likely to change my gas choices), I would start from the other side.

There is no point in dividing people into subject groups to test a hypothesis until we have a better understanding of the physiology of post-dive fatigue. At the moment our understanding levels on that are absolutely embryonic in medical terms.

One of the more influential non-scientific books that I ever read was Bill Bryson's A Brief History of Everything where the author describes (in his usual highly entertaining tone), basically the history of scientific discovery. One thing that comes out over and over and over again - in all different fields and across different centuries - is that people try to conduct experiments on the basis of a set hypothesis which they seek to confirm or refute. To no great astonishment in the vast majority of cases their studies are shown to support their initial hypothesis, which they then continue to reinforce. It is only long after the fact that people come to realise that they are "looking at the wrong thing" and the scientific endeavour takes its next step forward. There are far less entertaining papers that have been written which broadly point out the same thing - it is not so much inherent bias, as asking the wrong question (often because we simply don't know what the right question is yet).

Thus it will not shock me if in the future we all discover we have been looking at the wrong question on the issue of nitrox and fatigue. Scientific studies continue to say "Huh, it confirms what we thought - there is no link." Divers continue to say "I don't care what they say in a lab, I feel better afterwards." One day the dots will finally connect.

But I'm just going to keep diving nitrox to be on the safe side either way.

 

[DaleC]

To be fair, from a clinical/scientific perspective "feeling less bad" is actually not the same as "feeling better."...

I actually understand what you are saying in this post and agree with it, though it does not negate the positive effect that nitrox might have.

When I began diving I often felt excessively fatigued afterward. Shortly after OW I did EAN and dove with nitrox quite a bit. Over time I felt less fatigued. I might have chalked it up to the effects of EAN then but now I feel it had more to do with general anxiety (new to diving), repetitive dives and popping up too quickly at the end of dives.

These days I generally do one long dive, feel pretty relaxed throughout and have long shallow exits. I use air and do not feel fatigued. As you would say, I stopped hitting my head on the door frame.

 

[creamer]

There are prevailing myths that nitrox can:

- reduce air consumption

I was wondering about this recently. I understand that the same size nitrox tank with the same pressure has the same volume of gas. However, there have been studies shown in athletes of better performance with higher oxygenation of their breathing air. So I am wondering if the high oxygenation would reduce the breathing rate for an identical diver completing an identical dive on air and in turn reduce the SAC? Does any one have any evidence, experience or thoughts on this?

 

[MaxBottomtime]

Skeptical Scalpel: Why supplemental oxygen is not considered a performance-enhancing drug

 

[diverrex]

I was wondering about this recently. I understand that the same size nitrox tank with the same pressure has the same volume of gas. However, there have been studies shown in athletes of better performance with higher oxygenation of their breathing air. So I am wondering if the high oxygenation would reduce the breathing rate for an identical diver completing an identical dive on air and in turn reduce the SAC? Does any one have any evidence, experience or thoughts on this?

I have no evidence but do have some thoughts. You are way overthinking this. Nitrox is not much different than air. It just has more oxygen, not to provide more oxygen but to have less nitrogen which reduces nitrogen accumulation which is a benefit, but other than that I just don't see it reducing consumption at all. Breathing is breathing.

Another thought, most everyone posting on this thread including me has way too much time on their hands posting about nothing.

For the record I will use Nitrox on deeper dives, doing many dives over a week or when free or minimal cost. I don't feel any different during or after the dive but do notice increased bottom times at depth.

 

[dmaziuk]

I was wondering about this recently. I understand that the same size nitrox tank with the same pressure has the same volume of gas. However, there have been studies shown in athletes of better performance with higher oxygenation of their breathing air. So I am wondering if the high oxygenation would reduce the breathing rate for an identical diver completing an identical dive on air and in turn reduce the SAC? Does any one have any evidence, experience or thoughts on this?

No because it's not the oxygen that makes you want to breathe, it's CO2. You're not going to generate less CO2 just because there's more O2 in the air.

 

[EFX]

I don't think it's that straightforward.

So either you bubble easily after a dive, or you don't, and it's unpredictable. Either your body reacts noticeably to micro-bubbles, or it doesn't. Either your zombie state in the evening is caused by sub-clinical DCS and microbubbles, or it's caused by (unfamiliar) physical and/or psychological stress from the diving itself. Either you feel better on nitrox, or you don't. And that can have physiological reasons, or it can be placebo. Or both. If someone feels better after a shallow, easy warm dive on nitrox compared to air I'll be prone to believe it's placebo. If someone feels better after one or more deep dives close to air NDLs, and/or under conditions that aren't ideal for offgassing, I'll assume that it's a real physiological effect, and that the reduced saturation and increased offgassing that nitrox provides has had an effect beyond placebo. That some divers don't experience any effect of nitrox doesn't mean that the effect isn't real for other divers, since people and physiologies are different.

I agree. The problem with any study that compares air to Nitrox and its effects on post-dive fatigue is that physiological effects, i.e., bubbles, immune reactions, enzymes, etc. can be measured while fatigue is subjective. My post-dive fatigue may be someone else's tired.

 

[jbomb001]

There are prevailing myths that nitrox can:

- reduce air consumption
- make you feel better after a Dive with the same profile vs air

I always say that there are no data to prove any of these claims. Or are there studies to the contrary?

I personally dive Nitrox 97 % of the time and there for never noticed feeling better then I do on air because I don't dive air often enough to say so.
I find it interesting that I read all the time about this statement of " there are no studies or proof that Nitrox makes anyone feel better ". At what point does the huge number of people who claim they feel better become evidence that indeed it does make you less fatigued or "better"?
I mean seriously I bet I have personally read 2000 posts of people who say it makes them feel better. And yes I know better is a relative term and is inconsequential as far as a true scientific studie is concerned.

Sent from my galaxy S5 Active.