Dive computers and DCS

[dmaziuk]

NDL is NDL.

NDL is based on nitrogen loading. The more nitrogen in the gas you are breathing the quicker the ongassing. So the significance of nitrox is not the added O2 (mod/oxtox is the limiting factor here) but in the lower percentage of nitrogen.

So if you lower the percentage of nitrogen in your breathing gas you can extend your NDL. But diving to the limit of NDL gives the same risk of DCS, air or nitrox.

Yeah, that's the part I don't quite buy: I'm pretty sure my metabolism won't burn more oxygen just because I breathe more in -- I wish my body worked that way and I could eat more and just metabolize it all away instead of it inflating my spare tire and ldl count. O2 I don't burn should act just like the "inert gasses" traditionally considered by the models. These guys, for instance: ARTICLES | Journal of Applied Physiology gave O2 up to 40% of the risk of N2 up to 1.3 PO2 a decade ago. That's a 60% reduction in the extra 10-15% of O2 in your EAN mix, which is great, but I wonder if it's enough to trump things like PFO or even a bad hangover with hypotermia and some arterial plaque on top..

 

[BRT]

Yeah, that's the part I don't quite buy: I'm pretty sure my metabolism won't burn more oxygen just because I breathe more in -- I wish my body worked that way and I could eat more and just metabolize it all away instead of it inflating my spare tire and ldl count. O2 I don't burn should act just like the "inert gasses" traditionally considered by the models. These guys, for instance: ARTICLES | Journal of Applied Physiology gave O2 up to 40% of the risk of N2 up to 1.3 PO2 a decade ago. That's a 60% reduction in the extra 10-15% of O2 in your EAN mix, which is great, but I wonder if it's enough to trump things like PFO or even a bad hangover with hypotermia and some arterial plaque on top..

You don't burn the extra O2. You exhale it.

 

[fmerkel]

In fact the O2 does dissolve into the plasma same as the N2. This is a critical issue in treatment of Carbon Monoxide poisoning where the hemoglobin is viciously tied up by the CO. The dissolved O2 in the plasma supports the tissues while the CO is being slowly blown off during hyperbarics.

The body doesn't ever use most of the O2. The brain, heart and kidneys DO, that's why they are so subject to O2 starvation so quickly. MOST of the O2 is bound up in the hemoglobin. That which does come out does not seem to become a bubble problem, at least I've never heard that it does. Probably just metabolized away.

 

[BRT]

Of course it raises the amount of O2 in the body. A higher PP of any gas does that. If it didn't we wouldn't get O2 seizures. It does not make you use more O2 and in the end it just raises the % of O2 you are exhaling.

 

[stuartv]

I think y'all may be missing the point. Imagine if you could stand breathing 100% O2 while spending an hour at 100' depth. If you came straight to the surface, I expect you would get bent ... because the tissue tension of O2 would exceed the O2 M-value (not that I'm saying anyone has ever researched it and actually figured out M-values for O2).

The point is, any dissolved gas is going to have some pressure gradient that will cause it to go from being dissolved to forming bubbles. I think, anyway. So, there is the potential (under other than ordinary circumstances) for Oxygen to give you the bends, just like any other gas dissolved in your body tissues.

I think the issue with O2 is that, one, we always limit our O2 partial pressure to 1.4 bar, or thereabouts. And since you can stay at 40' depth indefinitely without incurring a deco obligation, where the ppO2 for air is about .45 bar, I suspect that the reason we don't worry about getting bent by O2 is that the M-values for O2 are somewhere higher than the M-values for N2 or He. And we never experience especially high partial pressures of O2 as compared to the partial pressure that is always safe to just take straight to the surface (i.e. 0.45 bar).

I don't know. I could be totally off base on this. I freely admit to talkin' out my rear on this one.

 

[uncfnp]

Yeah, that's the part I don't quite buy: I'm pretty sure my metabolism won't burn more oxygen just because I breathe more in -- I wish my body worked that way and I could eat more and just metabolize it all away instead of it inflating my spare tire and ldl count. O2 I don't burn should act just like the "inert gasses" traditionally considered by the models. These guys, for instance: ARTICLES | Journal of Applied Physiology gave O2 up to 40% of the risk of N2 up to 1.3 PO2 a decade ago. That's a 60% reduction in the extra 10-15% of O2 in your EAN mix, which is great, but I wonder if it's enough to trump things like PFO or even a bad hangover with hypotermia and some arterial plaque on top..

Ok I think I get it now. Its before my time but I think you are talking about VooDoo gas.

My understanding is that dcs risk from O2 has not been substantiated. And part of the reason you didn't link anything more recent. Even some of Weathersby's prior research publications did not find a significant association.

But I am far from an authority on the subject and would be interested in any input from someone that is.

 

[BRT]

I've never heard of DCS from O2. You would die from the high PPO2 before you would get DCS from it.

 

[dmaziuk]

My understanding is that dcs risk from O2 has not been substantiated. And part of the reason you didn't link anything more recent. Even some of Weathersby's prior research publications did not find a significant association.

Actually I pulled it out of a 2002 review article: Kinetic and dynamic models of diving gases in decompression sickness prevention. - PubMed - NCBI (and it should've been "two decades ago", not "a decade ago"), but you are correct: there does not seem to be anything more recent. I too hope one of the gurus sees this thread and comments.

(And of course you'd die from CNS oxtox before you get DCS from O2: my point is that I can't see it reducing your risk of DCS by that much.)

 

[dmaziuk]

MOST of the O2 is bound up in the hemoglobin. That which does come out does not seem to become a bubble problem, at least I've never heard that it does. Probably just metabolized away.

No.

You'll need at least glucose to "just metabolize away" what your hemoglobin can carry (which also has a limit that doesn't "just" go up because you're breathing more oxygen). And of course an energy sink.

 

[scubadada]

@dmaziuk ,

Sorry, but you seem seriously deficient in your knowledge of human physiology. I delayed writing this post until you had posted a series of messages demonstrating your ignorance. My advice would be to stay out of discussions that are well over you head.

Good diving, Craig