My Journey into UTD Ratio Deco

[Storker]

if we assume a scenario where slow tissue on-gassing is less of an issue than what we saw in the NEDU-study (using actual gas and not freezing)

In the flooded suit-scenario, I'm preoccupied with fractions of inert gas.
Spending as much time as I can tolerate on O2 prior to ascend would be my goal.

So, what you're saying is that a study where the divers decompressed on air was stacked to favor shallow stops disproportionately, because if the diver is cold they'd better get shallow enough to switch to 100% O2.

This just doesn't make sense.

 

[Dan_P]

So, what you're saying is that a study where the divers decompressed on air was stacked to favor shallow stops disproportionately, because if the diver is cold they'd better get shallow enough to switch to 100% O2.

This just doesn't make sense.

I wouldn't say stacked. And I wouldn't imply that it was done to bring about a disadvantage to deep stop procedures. I don't think that's the case.
I think cold/hypothermia was introduced to aggregate results, to get a clearer picture (otherwise, presumably, the study would need a much bigger pool of divers, results may not be significant, etc.) - it made sense to introduce hypothermia in the NEDU-study.

But the point is, when hypothermia - assumably - reaches some "critical level", whichever it may be, one diver is shallower and one is deeper.
If for nothing but pure diffusion reasons, hypothermia, in my opinion, clearly has potential to skewer results in advantage of shallow stops.
This tells us that if the suit floods, we should probably seek shallow.

It is a bynote on my own accord that I think the value of switching to a gas with zero intert gas, and spending as much time as I can has a disproportionately positive impact on the decompression process in that specific case.

 

[Storker]

I wouldn't say stacked.

But that's what you said.

"I think"...

 

[Dan_P]

But that's what you said.

"I think"...

I'm fairly sure I didn't.
It's not that I think NEDU isn't valid, or there were some cloak-and-dagger maneuvers at play to discredit deep stops - it's just that slow tissue on-gassing would probably have a lessor impact relatively compared to inflammation levels, without an element of hypothermia or extended air decompression to aggregate.

With inflammation levels (CCL5) to a large extent genetically dispositioned, that would make reason behind hypothesizing that there may be "deep stoppers" and "shallow stoppers", as it relates to possibly explaining the GI3/AG-avenue touched on prior.

That, and I really wouldn't be surprised to learn that placebo could work.

 

[Michael Guerrero]

GFlow of 100 is perhaps swinging the pendulum a bit too far the other way, but its hard to know since again we have no real evidence for that aggressive of an initial ascent.

I think the evidence would be the manned trials that Buhlmann used to derive his M values. Those were empirical studies that derived an M value for various theoretical tissue groupings with different half times, that would result in an "acceptable" likelihood of causing DCS (if memory serves it was something like 2.5%). Of course, what isn't clear is whether the DCS outcomes were because the test subjects were riding the 100% line all the way up (across the fast, medium, and slow tissues), or if there was some specific set of tissues (e.g., the slow tissues) predominantly responsible for the DCS outcomes. We know lipid tissues store a lot more inert gas than aqueous tissues, and that the aqueous tissues are the faster tissues. We also suspect that DCS is partly the result of showers of bubbles coming through the body and shunting the heart/lung exchange in some way, rather than forming in situ in the brain/nervous system. So it could be that the DCS incidence encountered in his trials were due to the medium and slower tissues producing many more bubbles for longer. If that's the case, then getting shallower sooner, to off-gas the fast tissues closer to their M value while minimizing gas uptake in the slow tissues, and then progressively stepping back to give the slow tissues more time to off-gas their larger, slower load might be a reasonable approach.

This is speculation on my part though.

 

[Michael Guerrero]

...even before Navy studies were done, we already did that pure Buhlmann shallow stop which is being propagated now and we have gotten skin bends so no thanks.

If you're GF Hi is lower than 100 you're not doing Buhlmann anymore. Do you know if these profiles produced a surfacing tissue tension in the leading compartment that looked more like an 85% or 70% of the M value? Would be interesting to know what surfacing GF likely was.

...I am wondering if Helium could be a factor?

Helium obligations being different in some tissues could play a part. The Spisni study does talk about the ameliorative affects of Helium on the vascular system though. Good thing this stuff isn't complicated.

 

[rjack321]

I think the evidence would be the manned trials that Buhlmann used to derive his M values. Those were empirical studies that derived an M value for various tissue groupings with different half times, that would result in an "acceptable" likelihood of causing DCS (if memory serves it was something like 2.5%). Of course, what isn't clear is whether the DCS outcomes were because the test subjects were riding the 100% line all the way up (across the fast, medium, and slow tissues), or if there was some specific set of tissues (e.g., the slow tissues) predominantly responsible for the DCS outcomes. We know lipid tissues store a lot more inert gas than aqueous tissues, and that the aqueous tissues are the faster tissues. We also suspect that DCS is partly the result of showers of bubbles coming through the body and shunting the heart/lung exchange in some way, rather than forming in situ in the brain/nervous system. So it could be that the DCS incidence encountered in his trials were due to the medium and slower tissues producing many more bubbles for longer. If that's the case, then getting shallower sooner, to off-gas the fast tissues closer to their M value while minimizing gas uptake in the slow tissues, and then progressively stepping back to give the slow tissues more time to off-gas their larger, slower load might be a reasonable approach.

This is speculation on my part though.

People still get bent, in the water, at less than 100gf low. So knock yourself out if you want to try it. On baby deco dives (20min obligation) its probably irrelevant. On big dives its a good way to end up in diapers learning how to pee again lol

 

[Michael Guerrero]

People still get bent, in the water, at less than 100gf low. So knock yourself out if you want to try it. On baby deco dives (20min obligation) its probably irrelevant. On big dives its a good way to end up in diapers learning how to pee again lol

I'm going to need you to cite your sources buddy . Otherwise, it's just hyperbole and FUD.

@Dr Simon Mitchell had a good post for @huwporter from last year relating to this. Simon said (that never gets old) that had HUWp not been indoctrinated into thinking that a 93/44 profile was more dangerous than a 20/65 profile (might be getting these numbers slightly wrong) that he might not consider it a problem at all. Is our fear of ratcheting up the GF lo really just a result of our conditioning through training? If the NEDU study did a GF 100/44 profile to 170 ft on air, with air deco, with divers cold at the end of the dive and thus off-gassing inefficiently, who had done a decent amount of work on the bottom (a deliberately highly provocative dive), and still only had a DCS incidence of 1.5%, what's all the hysteria about?

Something to think about.

 

[rjack321]

For a recent report, check with dsix on RBW and CCRx. Bent badly very very badly in-water. Sure it was a 600ft dive, but he isnt the first or the last to have in water symptoms.
I was bent in-water roughly 10 yrs ago, I knew it at the 30ft stop. Unfortunately I was freezing cold and had only a limited supply of 50% left. I got out, warmed up a bit, got o2 from the truck, and did IWR about an hour later with 50% and O2.
It happens, and its usually type II symptoms that are noticed when you're in water. Reality is that if you haven't had some symptoms at some point you probably haven't been deco diving very long. 1.5% is about right and when its you that has a permanent deficit, has to cancel and upcoming trip, cant fly home, possibly cant dive again, it sucks. 1.5% might be reality but pushing up to 100% gf low achieves what?

 

[Michael Guerrero]

Moving the GF lo up closer to the M values may result in better outcomes and safer dives. The NEDU guys did something like 170 minutes of cold deco on air. What if they had done it warmer and on O2? How far down would the DCS incidence percentage be then?