Why Nitrox

[Scubagolf]

 

[Walter]

I don't expect that, but whatever it shows, it shows. I've been wrong before, I'll be wrong again. There's a very remote chance I'm wrong here. I'd love to find out. Let the chips fall where they may.

 

[espenskogen]

Perhaps you should follow the link I provided and read the material there.

I've read that post, and there are a number of problems with that study when applying it to real world diving.

Firstly, being done in a dry chamber, the ascent is slow and controlled - 15 minutes from 60' is 4' a minute. Most computers operate with 33'/minute. At 4' a minute, you achieve sufficient off-gassing to avoid any doppler effect. At 33'/minute you may not. Certainly, for new divers, maintaining a slow calm ascent may be difficult and they may be experiencing far faster ascent rates.

If you've read my previous posts, I've maintained that the fatigue experienced by some may be caused by subclinical dcs. Diving Nitrox may help eliminate the doppler effect even at higher ascent rates, because the N2 gradient remain lower. Eliminating microbubbles may stop the body initiating an immune response (As explained in my earlier posts) and subsequently avoid the flu like feeling some divers experience after dives.

Secondly, to be able to prove a study like the australian one, you will need a reference person who actually feel fatigued diving on air in the first place. If such a reference person feels fatigued because he consistently 'blows' his deco, then doing a chamber dive with a supercontrolled ascent is going to make him feel less fatigued, even if he's on air.

I have no doubt that if you decompress sufficiently, there will be no difference in the way you feel on air compared to nitrox - But the fact of the matter is that most recreational divers do not.

I was diving this weekend, and did a dive to 106', for 6 minutes. According to the Padi tables, I could do a controlled 18m/min ascent, a 3 minute safety stop and that's the dive for you.

According to V-planner, it would require a 1 minute stop at 6 meters, and 4 minutes at 3.

Now, I came out of this dive feeling great - No fatigue, nothing suggesting I'd just done a quite deep dive, but I am convinced if you did the same dive according to the RDP, you'd feel a bit rough.

Now, this is where the 'feelgood' factor of nitrox comes in. By diving on a higher mix, you effectively dive 'shallower' in terms of N2 loading, and so the dive is more conservative. Chances are you'll have less microbubbles following the dive, and you won't feel quite so fatigued.

But I agree that if you dive well within the NDL, then it makes no difference if you do the dive on Nitrox or Air.

So in conclusion, it is not the higher Oxygen levels that makes you feel less fatigued - Nor is it the lower nitrogen load. But instead, the reduced bubbles. If you do your deco to eliminate bubble formation in the first place, then it's not an issue.

We could get into a discussion on decompression models here, but I'll leave it at this - Nitrox is a benefit because it is safer -If the diver blows his deco schedule, or if the tables are insufficient - Or maybe the diver is a bit dehydrated - Nitrox will add greater conservatism. By decoing sufficently, you reduce fatigue post-dive. Nitrox helps decoing sufficiently. Simple as that.

 

[Walter]

If you've read my previous posts, I've maintained that the fatigue experienced by some may be caused by subclinical dcs.

I have read them, and I do understand your belief that fatigue is caused by subclinical DCS. I once thought that might be a logical explanation as well. It would explain the differences in how some people feel depending on their gas and also why I feel no difference. The problem with that concept is the lack of evidence that subclinical DCS actually causes fatigue.

I think we can all agree we'd like to see more double blind studies to answer additional questions on this topic.

 

[wedivebc]

At 4' a minute, you achieve sufficient off-gassing to avoid any doppler effect. .

This sentence confuses me. What is a doppler effect in this context?

 

[Walter]

I took that to mean there are no bubbles that can be detected using doppler testing.

 

[Pook-60]

I have read them, and I do understand your belief that fatigue is caused by subclinical DCS. I once thought that might be a logical explanation as well. It would explain the differences in how some people feel depending on their gas and also why I feel no difference. The problem with that concept is the lack of evidence that subclinical DCS actually causes fatigue.

I think we can all agree we'd like to see more double blind studies to answer additional questions on this topic.

Gents

A very well articulated discussion. Thank you for taking the time to put it on these posts. Very informative.

Pook

 

[Pyrofish]

There is another aspect of higher O2%'s that might make us feel better, and that's an increased metabolic rate. Although the increase is short term, we are only talking about a short term symptom. Perhaps, people with an already high metabolism aren't as affected by the higher O2%'s as much as people with "slow" metabolisms. Usually, the larger you are, the slower your metabolism is. Your metabolism also slows down with age. Small, skinny people, tend to have a higher metabolism.

So how about an informal survey:
Do you consider yourself larger, or older, and do you feel better after diving Nitrox?

If you don't feel better, are you small, or average size, and between 20 and say 40?

I fall into the first category, and so does my buddy who says it makes him feel like a new man. Just a thought, could be way off.
Jason

 

[Walter]

Define average size. I'm about 180 lbs and 49 years old. I feel no difference.

 

[espenskogen]

There is another aspect of higher O2%'s that might make us feel better, and that's an increased metabolic rate. Although the increase is short term, we are only talking about a short term symptom. Perhaps, people with an already high metabolism aren't as affected by the higher O2%'s as much as people with "slow" metabolisms. Usually, the larger you are, the slower your metabolism is. Your metabolism also slows down with age. Small, skinny people, tend to have a higher metabolism.

So how about an informal survey:
Do you consider yourself larger, or older, and do you feel better after diving Nitrox?

If you don't feel better, are you small, or average size, and between 20 and say 40?

I fall into the first category, and so does my buddy who says it makes him feel like a new man. Just a thought, could be way off.
Jason

I don't believe that would explain it. At a PPO2 of .21 bar (ie O2 Exposure on the surface) the haemaglobine is typically saturated 99% with O2. Increasing the partial pressure would account for a very small increase in O2 saturation in the blood plasma itself (Which is mainly water), but because O2 doesn't dissolve in water very easily, the increased oxygen uptake in the body is relatively insignificant.

The increase in PPO2 is mainly to reduce the PPN2, by replacing nitrogen with a gas which we metabolise hence during off-gassing it doesn't cause bubble trouble.

E