Benefit of Nitrox?

[DevonDiver]

The only remaining question is why the divers felt better on Nitrox versus air. It certainly was not a placebo effect; it was a double-blind study and the divers had no idea if they were diving with Nitrox or air. The "why" of this is up for debate,....

It's been answered repeatedly.

Sub-Clinical DCS.

Nitrox (>ppO2 / <ppN2) is a more optimal ascent gas than air; reducing tissue tension across the surface of micro-bubbles, helping to maintain a negative pressure gradient that promotes more effective off-gassing and bubble elimination.

Decompression stress is the incidence of micro-bubbles.

Micro-bubbles are not sufficiently large to cause tangible DCS symptoms, but may be significant in number. Whilst not presenting definitive DCS symptoms, micro-bubbles are not without effect on the body. They might still provoke an immune-system 'foreign body' response (malaise anyone?) and could effect neuro-chemistry through altering serotonin levels (guess what... that controls somnolence, mood and other things). Serotonin is known as a primary cause of CNS Fatigue in endurance athletes...


"... "mild DCI" is harder to define. This is largely because bubbles form, and can be detected in the venous blood, following a significant proportion of dives that do not result in symptoms that would normally be labelled "DCI". It is therefore hardly surprising that there can be a poorly defined boundary between wellness and mild DCI following diving. [...] It is not infrequent for divers to report highly non-specific and vague symptoms of variable latency, such as mild evanescent aches and pains, fatigue, demotivation and headache".
MANAGEMENT OF MILD OR MARGINAL DECOMPRESSION ILLNESS IN REMOTE LOCATIONS: AN INTRODUCTION TO THE PROBLEM. S.J.Mitchell Ph.D, D. J. Doolette, Ph.D. DAN Remote Workshop Proceedings


"Inappropriate fatigue is a clear-cut symptom of subclinical decompression illness. I&#8217;m not a technical diver, Lord knows; but I see a lot of these guys. I send them out with decompression tables and they tell me what happens. They use their fatigue, their feeling of well-being &#8211; we called it constitution yesterday &#8211; as a major item in judging whether their decompression was adequate. The fact that they don&#8217;t have any joint pain or tingling or rash or anything is secondary. Their major thermometer as to whether they&#8217;ve been properly decompressed is how well they feel. And that has to do with the fatigue and inappropriate fatigue. So we have to keep this as a symptom, not as a side issue".
MANAGEMENT OF MILD OR MARGINAL DECOMPRESSION ILLNESS IN REMOTE LOCATIONS: AN INTRODUCTION TO THE PROBLEM. Bill Hamilton in discussion. DAN Remote Workshop Proceedings


"Doppler monitoring has revealed the presence of gas phase bubbles in divers ascending even from relatively shallow dives. We have also all experienced symptoms such as headache and fatigue in the immediate post-dive phase which we have put down to overexertion on exiting the water etc. In more recent years, we have been told that these symptoms are those of subclinical DCI and we have lived with these, perhaps naively, thinking that because they are not associated with overt symptoms of DCI, they are not causing any damage and are nothing to worry about. However, enter the iceberg principle. Nine tenths of the damage may be invisible and cummulative".
THE TROUBLE WITH BUBBLES. Richard Heads PhD. 9-90 Magazine: UK Diving in Depth

 

[Centrals]

Except me because I hit my turn around pressure before the NDL for 21%. Am I the only one with this situation?

---------- Post added September 7th, 2015 at 06:25 AM ----------

But if you bring a bigger tank or twin set then you will find EAN28 will give you slightly longer bottom time than AIR at 40m.
You have to decide whether the extra cost for EAN28 is justify to extend the bottom by few minutes over AIR.
It would be a complete waste of money and time if the under water conditions are poor!

 

[AfterDark]

But if you bring a bigger tank or twin set then you will find EAN28 will give you slightly longer bottom time than AIR at 40m.
You have to decide whether the extra cost for EAN28 is justify to extend the bottom by few minutes over AIR.
It would be a complete waste of money and time if the under water conditions are poor!

Absolutely agree. That's why I have 4 O2 cleaned tanks for 2 set's of ID's.

I think I've made my choice very clear.

The absolute best vis gets here in RI is 30' but that is so rare and unpredictable it's like hitting the lottery!

Last year on the last dive of the U853 I did the vis <1'

 

[DaleC]

They are not my studies and there are a lot of them, and they are not relating to the whole oxygen tent thing. Some focus on highly trained athletes but other studies deal with cardiac patients doing exercise (the other end of the spectrum). There was an increase in output/decrease in fatigue there too. There was a driving study that showed increased acuity and awareness. There appears to be at least two issues at play:

1. That a hyperoxic mix allows the circulation/respiratory system to work less to achieve the same result.

2. A reduced WOB may result in decreased fatigue, or be interpreted that way by the subject.

What would be curious would be to see is, at what rate weekend warrior/older divers may be working compared to high performance athletes. The exertion rates may be similar even though the output is less. It could be that for some, diving pushes one to the threshold of fatigue and a hyperoxic mix dials that threshold back one way or the other. It's what most of those studies (using O2 during exercise and not before or after) show.

Trying to relate studies specific to diving is a little crazy because there simply aren't that many good studies. It's like trying to determine the effect of alcohol consumption on unicycle riding. Hard to find a study but you can look at other studies in related fields and extrapolate some avenues of similarity.


I also subscribe to the subclinical DCS theory.

 

[beachbummer28]

It's been answered repeatedly.

Sub-Clinical DCS.

Nitrox (>ppO2 / <ppN2) is a more optimal ascent gas than air; reducing tissue tension across the surface of micro-bubbles, helping to maintain a negative pressure gradient that promotes more effective off-gassing and bubble elimination.

Decompression stress is the incidence of micro-bubbles.

Micro-bubbles are not sufficiently large to cause tangible DCS symptoms, but may be significant in number. Whilst not presenting definitive DCS symptoms, micro-bubbles are not without effect on the body. They might still provoke an immune-system 'foreign body' response (malaise anyone?) and could effect neuro-chemistry through altering serotonin levels (guess what... that controls somnolence, mood and other things). Serotonin is known as a primary cause of CNS Fatigue in endurance athletes...

Oh, I agree with you. When I said that the question of "why do divers feel better on Nitrox?" is still up for debate, I was being diplomatic. The answer seems pretty clear to me - especially since a double-blind study has proven that divers feel better after using Nitrox - but clearly there is still some dissension. Diplomacy never hurts and is free, so why not use it?

 

[RJP]

Thats not how I read it. It was very clear....It was nit picking and saying the same thing a different way, to have the last word.

How would one fix the problem? I doubt that doing jumping jacks each morning is a solution.

To be fair, from a clinical/scientific perspective "feeling less bad" is actually not the same as "feeling better." The former is a "reduction in the amount of decline from baseline" while the latter is actually "an improvement from baseline." I've had this discussion with med/reg/legal people several thousand times over the past 25 years.

Think about it like this:

There are 100 people in a room, who all then exit through a door that is only 5'8" tall. On the way out of the room 1/3rd of the people hit their head on the door frame, while the other 2/3rds either duck, or are shorter than 5'8" tall. We then ask them to tell us how their head feels, on a scale from 1 - 10.

A week later we gather the same people, in the same room, with the same door. But before they exit the room we have them all put football helmets on.

After exiting the room we ask each of them how they felt after exiting the room while wearing a helmet, as compared to the last time they exited the room without a helmet. When we tabulate the results, we will find that

• Most of the people who didn't hit their head would say they couldn't detect any benefit from wearing a helmet*
• Most of the people that did hit their head will report that they "feel better" when they exit the room while wearing a helmet

Two things become clear:

1. Wearing a helmet doesn't make anyone's head feel "good" - although it did provide some people the chance for their head to feel "less bad"
2. The problem of hitting your head on the way out the door can be avoided altogether by most people by simply ducking sufficiently... whether you're wearing a helmet or not.

*Interestingly, the group that didn't hit their heads will actually be comprise of three distinct sub-groups:

• Those who are shorter than 5'8" and will tell you that helmets are stupid, because they have no need for a helmet
• Those who are taller than 5'8" who will tell you that helmets are good, because helmets provide an additional margin of safety beyond ducking
• Those who are taller than 5'8" who will tell you that the helmets are stupid, because if you were trained properly you would know that all you have to do is duck!

 

[DevonDiver]

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.

 

[BRT]

To be fair, from a clinical/scientific perspective "feeling less bad" is actually not the same as "feeling better." The former is a "reduction in the amount of decline from baseline" while the latter is actually "an improvement from baseline." I've had this discussion with med/reg/legal people several thousand times over the past 25 years.

Think about it like this:

There are 100 people in a room, who all then exit through a door that is only 5'8" tall. On the way out of the room 1/3rd of the people hit their head on the door frame, while the other 2/3rds either duck, or are shorter than 5'8" tall. We then ask them to tell us how their head feels, on a scale from 1 - 10.

A week later we gather the same people, in the same room, with the same door. But before they exit the room we have them all put football helmets on.

After exiting the room we ask each of them how they felt after exiting the room while wearing a helmet, as compared to the last time they exited the room without a helmet. When we tabulate the results, we will find that

• Most of the people who didn't hit their head would say they couldn't detect any benefit from wearing a helmet*
• Most of the people that did hit their head will report that they "feel better" when they exit the room while wearing a helmet

Two things become clear:

1. Wearing a helmet doesn't make anyone's head feel "good" - although it did provide some people the chance for their head to feel "less bad"
2. The problem of hitting your head on the way out the door can be avoided altogether by most people by simply ducking sufficiently... whether you're wearing a helmet or not.

*Interestingly, the group that didn't hit their heads will actually be comprise of three distinct sub-groups:

• Those who are shorter than 5'8" and will tell you that helmets are stupid, because they have no need for a helmet
• Those who are taller than 5'8" who will tell you that helmets are good, because helmets provide an additional margin of safety beyond ducking
• Those who are taller than 5'8" who will tell you that the helmets are stupid, because if you were trained properly you would know that all you have to do is duck!

Problem with this example is that DCS fatigue may set in when we don't "hit our heads". We may feel somewhat bad when our heads get close to the top of the door.

 

[NAM001]

do you feel better or feel less worse,,,,,,,,,,,are you drunk or less sobe,,,,,,,,rin a 2 man race are you the fastest or not the slowest,,,,,,,,are you taller (not tall) or not shorter,,,,,,,,,do you have a surplus or a negative debt,,,,,,,,, that's all together different from educated or aint got no lernin.................I think most people in normal conversation understands the meaning of sentences. Most people so not use double negatives in conversation I feel better (positive)'''''''''' I feel less (negative) worse(negative).

 

[RJP]

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

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.

Then...

You cross them all over to the OTHER gas and do it all over again...

So, you're looking at doing tests on hundreds of divers, doing dozens of dives, in multiple environments... TWICE.

And because this is a PROSPECTIVE study to really ensure that the study is clean you'd have to factor in the typical dropout rate of new divers. So, just to make the math easy, if we assume that we need 100 divers in each group - but 50-70% of new divers leave the sport soon after training - we'd need to start with 200-400 divers in each group. (You need to do this because people who get easily fatigued, and certainly those who develop DCS symptoms, will probably have a greater likelihood of dropping out of the sport.)

So now we're starting with 800 divers.

Oh yeah... and they'll all need to have a transesophageal echocardiogram to screen out people with a PFO. (It would be unethical to include them in the study.) So, given the estimated incidence of PFO, you'd need to screen ~1,150 prospective divers for PFO in order to get ~800 that didn't have one.

But wait... by screening out people WITH a PFO you've just made it much, much harder to detect a difference in bubbles/DCS/symptoms. (Because you've removed a large pool of people where they'd be easily detected from your study, leaving you with a group less likely to bubble.) You know what that means, right? Yup... you need to increase the sample size. Probably 4-fold. And you'd probably need to do twice as many dives. So now you're starting - before a single dive happens - by doing a $2,000 TEE on 3,000-4,000 prospective divers.

So you're at least $6,000,000 in the hole on day 1.

When I used to work for a drug company we would get lots of kudos for doing clinical trials on cholesterol drugs with tens of thousands of high-risk patients. Were we that dedicated to helping the patients at highest risk? Um... sure. Of course the dirty little secret was that, if you want to be sure your trial results will help sell the product... you need to make sure that enough patients die in both groups, and the sooner the better, so you can count them. Do a study with "normal healthies" and you'll never detect treatment effect.

But I digress...

:cool2: