Doolette's Alert Diver Interview

[PfcAJ]

AJ: no, taking oxygen breaks does nothing to improve off gassing. It reduces damage from the production of reactive oxygen species generated in the high oxygen environment of the lungs, but it does not alter diffusion gas gradients.

If your lungs are damaged do you think that impacts gas exchange?

 

[Jack Hammer]

I'm gonna have to go with the guy here who routinely does dives in the 300'+ range with a half days deco...

(Hint: his name rhymes with Aay-Jay...)

 

[huwporter]

I would imagine that the pulmonary benefits from taking breaks helps with offgassing. Reduced total exposure to oxygen.

I would see that as, "the pulmonary benefits from taking breaks keeps off-gassing as efficient as possible" rather than the breaks make off gassing more efficient somehow. I would also agree that there is some level of off gassing (at least in some tissues) still while on back gas, but I would strongly suspect that as theory suggests it is at a much slower rate than while on oxygen.

I've no doubt that you can treat gas breaks as oxygen and get away with it (all you are doing is pushing your GFHi more aggressive - I'll run some numbers later) in most cases, particularly if you are fit etc.

As far as I can recall, the whole treating gas break time as oxygen time comes from one of Georges assertions that your body continues to behave as if it is still breathing oxygen during the break, and I wonder if there is any actual evidence behind this or is it another piece of voodoo like s-curves and the like?

 

[PfcAJ]

I would see that as, "the pulmonary benefits from taking breaks keeps off-gassing as efficient as possible" rather than the breaks make off gassing more efficient somehow. I would also agree that there is some level of off gassing (at least in some tissues) still while on back gas, but I would strongly suspect that as theory suggests it is at a much slower rate than while on oxygen.

I've no doubt that you can treat gas breaks as oxygen and get away with it (all you are doing is pushing your GFHi more aggressive - I'll run some numbers later) in most cases, particularly if you are fit etc.

As far as I can recall, the whole treating gas break time as oxygen time comes from one of Georges assertions that your body continues to behave as if it is still breathing oxygen during the break, and I wonder if there is any actual evidence behind this or is it another piece of voodoo like s-curves and the like?

I'm unaware of any real "evidence" one way or another other than anecdotal.

Counting it as "on-oxygen time" clearly has a good track record.

 

[RyanT]

If your lungs are damaged do you think that impacts gas exchange?

On a short-term basis, no, the lung damage you experience from the development of ROS is not likely to influence gas exchange. Gas exchange is a function of inert gas gradients across membranes, relative to the tissue diffusion gradient, which is largely a function of tissue thickness. In the short-term (e.g. on one particular dive), free radical damage to cells, will not have a large effect on diffusion rates. Free radical damage will have an effect on overall cellular function, but it won't appreciably alter the overall diffusion rate. Air breaks function largely to limit overall CNS oxygen toxicity effects and short-term ROS damage to lung tissues.

 

[PfcAJ]

On a short-term basis, no, the lung damage you experience from the development of ROS is not likely to influence gas exchange. Gas exchange is a function of inert gas gradients across membranes, relative to the tissue diffusion gradient, which is largely a function of tissue thickness. In the short-term (e.g. on one particular dive), free radical damage to cells, will not have a large effect on diffusion rates. Free radical damage will have an effect on overall cellular function, but it won't appreciably alter the overall diffusion rate. Air breaks function largely to limit overall CNS oxygen toxicity effects and short-term ROS damage to lung tissues.

your last sentece nails it. Short term lung tissue damage. But you think that doesn't have an effect on offgassing?

Yer lungs are purdy important fer dat.

[abstract] INHIBITION OF APOPTOSIS AND OXIDATIVE DAMAGE IN LUNGS BY INTERMITTENT EXPOSURE TO AIR.

 

[RyanT]

AJ: No, I don't think that short term damage has an effect on off gassing, at least in any appreciable way. The paper your cite discusses the role of hyperbaric oxygen on ROS damage and apoptosis (programmed cell death). There is no indication that these processes impede gas exchange in the short term. On a particular decompression dive, again, I'm not aware of any data showing an increased efficacy of off gassing from air breaks. They seem to function solely to limit overall oxygen toxicity effects. Of course I'm always open to new information, but after extensive searches of the literature, I'm just not aware of any evidence pointing to this right now.

Yer lungs are purdy important fer dat.

And as a Louisiana boy, I appreciate the vernacular more than you know!!!

 

[PfcAJ]

AJ: No, I don't think that short term damage has an effect on off gassing, at least in any appreciable way. The paper your cite discusses the role of hyperbaric oxygen on ROS damage and apoptosis (programmed cell death). There is no indication that these processes impede gas exchange in the short term. On a particular decompression dive, again, I'm not aware of any data showing an increased efficacy of off gassing from air breaks. They seem to function solely to limit overall oxygen toxicity effects. Of course I'm always open to new information, but after extensive searches of the literature, I'm just not aware of any evidence pointing to this right now.



And as a Louisiana boy, I appreciate the vernacular more than you know!!!

Glad you liked it

I cannot separate lung function from decompression efficiency. Any damage would almost certainly impede gas exchange.

In any case, tons of folks are not extending the oxygen time to account for gas breaks. The plural of anecdote isn't data, but if it ain't broke I don't see a reason to change anything. And this is working from 30min all the way to 120min+ oxygen stops.

 

[RyanT]

Oh yes, don't get me wrong... I'm not advocating for a re-evaluation of decompression theory on hyperbaric oxygen mixes. Not at all. My point is simply that air breaks are not "increasing" off gassing efficiency. They are merely mitigating physiological oxygen damage in the short term. The short-term cellular damage likely includes a reduction in cellular second-messaging functions as well as some slight edema between the walls of the capillaries and the respiratory membrane. Neither of these is likely to have any significant impact on diffusion rates.

 

[PfcAJ]

Oh yes, don't get me wrong... I'm not advocating for a re-evaluation of decompression theory on hyperbaric oxygen mixes. Not at all. My point is simply that air breaks are not "increasing" off gassing efficiency. They are merely mitigating physiological oxygen damage in the short term.

I'd argue that they are increasing efficiency relative to not doing them.

If oxygen damages lungs, and damaged lungs don't offgas as well as undamaged lungs, then doing gas breaks (which help prevent lung damage) keep you offgassing as efficiently as possible. Increasing efficiency relative to not doing the breaks.

That's all.