Sorry, I just edited my post above. "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".
Doolette's Alert Diver Interview
- Thread starter Michael Guerrero
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huzenhagen
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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.
Healthy lungs are pretty good at gas exchange. Decompression efficiency is largely driven by the delta partial pressure between the gas you are breathing and tissues so i don't think it'd have a significant effect during a dive
Sorry for the delay--I have been busy.
All I know about that specific dive and what he did is the results. The diver told us before the dive that he would follow the plan we had set up using Buhlmann with GFs of 40/80, he spent 20 minutes (by actual count) more than us, with most of that time on the final stops right below us, and when it was over, he explained that he could not bring himself to go that shallow that soon and had followed his previous training to do deep stops and then finished up on the computer.
So I went to multi-deco and took a look. I created a dive similar to the one we did. I then made another profile with one minute stops (including ascent time between stops) starting at 3/4 depth. That second profile did not add anything close to 20 minutes total deco time. Now that I have done that, I am completely mystified as to what he was doing down there that long.
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Sounds like he was paradigm trapped. I had cause to think about that today..... A lot of us start building ascent strategies that we "believe in" almost religiously, regardless of what the computer says.
Just today I made a dive with a buddy of mine that demonstrates this. We are accustomed to making somewhat "bigger" dives at the site we dove but we wanted to keep the dive today short because the water is getting colder :/ (God, I hate the winter)...... Nevertheless we made exactly the same ascent from 18m to the 6m stop as we would have done if the dive had involved double the bottom time and 3 or 4 (or maybe 5) times as much deco..... this, even though it was a tame dive (for us) and when leaving the bottom his computer was giving a ceiling of 7m and my computer even shallower than that (which my computer always does because it's an old Suunto that only gives me a ballpark estimation of TTS and zero information about how to actually shape the ascent).
Why? because for us this is our SOP. It's a paradigm, in part, built up over many dives to compensate for the fact that while he has a modern computer, I'm still "stone aging" it and sort of using my computer like it's a "back up" for the plan in my head...... This is something a lot of older or "low tech" tech divers might do.
Turns out that my computer cleared during the swim back despite the deep ascent line and his computer calculated another 7 minutes of deco time after the point at which we had estimated to leave the water. We were at 5m and I was ready to get out and he was saying "7min" ... so we did that. Whose computer was right, I'm not sure......but I *am* pretty sure that if we had ascended to much closer to the ceiling earlier in the dive we would have been out the water sooner.
R..
Just today I made a dive with a buddy of mine that demonstrates this. We are accustomed to making somewhat "bigger" dives at the site we dove but we wanted to keep the dive today short because the water is getting colder :/ (God, I hate the winter)...... Nevertheless we made exactly the same ascent from 18m to the 6m stop as we would have done if the dive had involved double the bottom time and 3 or 4 (or maybe 5) times as much deco..... this, even though it was a tame dive (for us) and when leaving the bottom his computer was giving a ceiling of 7m and my computer even shallower than that (which my computer always does because it's an old Suunto that only gives me a ballpark estimation of TTS and zero information about how to actually shape the ascent).
Why? because for us this is our SOP. It's a paradigm, in part, built up over many dives to compensate for the fact that while he has a modern computer, I'm still "stone aging" it and sort of using my computer like it's a "back up" for the plan in my head...... This is something a lot of older or "low tech" tech divers might do.
Turns out that my computer cleared during the swim back despite the deep ascent line and his computer calculated another 7 minutes of deco time after the point at which we had estimated to leave the water. We were at 5m and I was ready to get out and he was saying "7min" ... so we did that. Whose computer was right, I'm not sure......but I *am* pretty sure that if we had ascended to much closer to the ceiling earlier in the dive we would have been out the water sooner.
R..
What if he didn't reach his first stop until very shallow. Let's guess that was at 9m rather than 15m. Now he interpolating GF from 40 to 80 such that at 6 he will have a GF of about 53 whereas if the first stop was at 15 it could be 64. You can see it will take longer not only because of the extra exposure but because of the way the GF interpolation works.
I am assuming the computer does this by the first stop, it may not, for example subsurface uses the deepest ceiling.
OP
Michael Guerrero
Contributor
Even though all this is pretty far off topic, my understanding for air breaks on shorter dives is to limit vasoconstriction, not really for pulmonary damage. Once you start getting exposures similar to those experienced in hyperbaric medicine (both in duration and ppO2 levels) air breaks stave off the risk of pulmonary damage and the associated decreased vital capacity.
As a data point, NAUI says do not count the air break in your deco time and to take one every 20 minutes when on pure O2.
The Navy's manual (v6) says "a 12-hour exposure to a partial pressure of 1 ata will produce mild symptoms and measurable decreases in lung function. The same effect will occur with a 4-hour exposure at a partial pressure of 2 ata." They do air breaks if deco on pure O2 is longer than 35 min, otherwise not, and use a 6:1 ratio (30 min on, 5 off).
"9-8.2.2. ...The air breaks do not count toward required decompression time."
"3-9.2.1. ...The only way to avoid pulmonary oxygen toxicity completely is to avoid the long exposures to moderately elevated oxygen partial pressures that produce it. However, there is a way of extending tolerance. If the oxygen exposure is periodically interrupted by a short period of time at low oxygen partial pressure, the total exposure time needed to produce a given level of toxicity can be increased significantly. This is the basis for the “air breaks” commonly seen in both decompression and recompression treatment tables."
My view is air breaks aren't going to hurt, probably shouldn't be counted as deco time for short exposures unless the effects of vasodilation substantially offset the loss of inert gas gradient, and probably aren't that big a deal either way based on how much conservatism is already built into dive planning. For longer exposures (several hours or more of deco at high ppO2s), air breaks are probably recommended, and shorter on/off windows (12 on, 6 off or 20 on, 5 off) in a ratio somewhere between 2:1 and 4:1 appear more effective than long ones (e.g., 60 on, 15off).
As a data point, NAUI says do not count the air break in your deco time and to take one every 20 minutes when on pure O2.
The Navy's manual (v6) says "a 12-hour exposure to a partial pressure of 1 ata will produce mild symptoms and measurable decreases in lung function. The same effect will occur with a 4-hour exposure at a partial pressure of 2 ata." They do air breaks if deco on pure O2 is longer than 35 min, otherwise not, and use a 6:1 ratio (30 min on, 5 off).
"9-8.2.2. ...The air breaks do not count toward required decompression time."
"3-9.2.1. ...The only way to avoid pulmonary oxygen toxicity completely is to avoid the long exposures to moderately elevated oxygen partial pressures that produce it. However, there is a way of extending tolerance. If the oxygen exposure is periodically interrupted by a short period of time at low oxygen partial pressure, the total exposure time needed to produce a given level of toxicity can be increased significantly. This is the basis for the “air breaks” commonly seen in both decompression and recompression treatment tables."
My view is air breaks aren't going to hurt, probably shouldn't be counted as deco time for short exposures unless the effects of vasodilation substantially offset the loss of inert gas gradient, and probably aren't that big a deal either way based on how much conservatism is already built into dive planning. For longer exposures (several hours or more of deco at high ppO2s), air breaks are probably recommended, and shorter on/off windows (12 on, 6 off or 20 on, 5 off) in a ratio somewhere between 2:1 and 4:1 appear more effective than long ones (e.g., 60 on, 15off).
PfcAJ
Contributor
I wonder if he didn't switch deco gases on his computer? I have no idea. Mysterious.
Jack Hammer
Contributor
Maybe he also decided to run GF 20/85 instead of the plan??
OP
Michael Guerrero
Contributor
I thought this thread was about Pyle stops and an article in Alert Diver 
I find it interesting that we have a few threads on SB over a hundred pages long about the NEDU study and deep vs shallow stops and the correct distribution of each. We have people that feel strong one way or the other. We have people that say they do deep but then add on extra shallow time.
My question is, if our current bubble models with deep stops do not add on adequate shallow time and we are manually adding on more, and our buhlmann models with GF potentially are lacking the advantages of the deep stops, do we need a new model that does both? It would be more conservative and require longer deco obviously but would incorporate both the deep stop and the complimentary extra shallow stop time rather than people having to add it on/make it up themsevles in the shallows. Is the DCS rate for our bubble models and buhlmann GF models currently unacceptable to warrant a new model?
My question is, if our current bubble models with deep stops do not add on adequate shallow time and we are manually adding on more, and our buhlmann models with GF potentially are lacking the advantages of the deep stops, do we need a new model that does both? It would be more conservative and require longer deco obviously but would incorporate both the deep stop and the complimentary extra shallow stop time rather than people having to add it on/make it up themsevles in the shallows. Is the DCS rate for our bubble models and buhlmann GF models currently unacceptable to warrant a new model?
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