Will http://www.ncbi.nlm.nih.gov/pubmed/25525213 change deco procedures?

[ajduplessis]

.........Clearly we need to stop, and there is a depth where, according to the truth in the universe, it would be optimal to make our first stop. That is the truth we seek. You assume it is prescribed by bubble models. Although we don't agree on that, I think we can agree that there is a sweet spot.........

Simon M

You dont agree, but agree that there is a sweet spot on something you dont agree on???

This along with all the fragmented information you leave in your wake and the ridiculously silly dive profiles is why many are skeptical, dear Dr.

 

[victorzamora]

You dont agree, but agree that there is a sweet spot on something you dont agree on???

This along with all the fragmented information you leave in your wake and the ridiculously silly dive profiles is why many are skeptical, dear Dr.

That's certainly not how I understood it. I understood him to mean that they disagree on where the "sweet spot" is for the first stop but there's clearly an optimal first stop location. There can't not be an optimal first stop location.

 

[tomfcrist]

Tom, what do you base this assumption on, because as far as I can see that is all it is: an assumption based on bubble model dogma. What evidence do you have that it is true?

Simon M

Simon, the evidence has been on your desk for a while now. Even the NEDU study showed obvious advantages of the deep stop theory in that it proved there is a huge protection from supersaturation at the beginning of the ascent. Now overall outcome was disadvantageous for the deep model because of the long ass run time where massive amounts of additional on gassing occurred, thus resulting in higher supersaturation figures upon exiting the water.

You really can't see where there may be a middle ground? I find that imrobable. The shallow stop model suffered some DCS too. Do you suggest it is improper to assume that if the enormous amount of supersaturation at the beginning of ascent had something to do with that? If you could eliminate that initial supersaturation by adding deport stops for a very short time, and the occurance of DCS plummeted, would that be evidence enough for you that deep stops have a purpose if done correctly?

You cannot honestly tell me y'all haven't thought of this....and if you discounted it as improbable without testing it.....well then you can understand my skepticism of the studies findings.

Merry Christmas



I apologize for saying You. I know you didn't run the study. You get my drift though.

 

[UWSojourner]

If he is saying that the longer the deco is, the lower the risk of DCS...I disagree. There IS such a thing as too much Deco.

ring…ring…ring

TOM Safe diving. This is Tom.

Bryan Hi Tom. This is Bryan. You taught my tech course last year.

TOM Hello Bryan. How's the diving?

Bryan Well, recently I've been diving to about 200ft surveying a wreck. But I've been having fairly consistent joint pain.

TOM Welcome to the tech community Bryan! You're a real tech diver now.

Bryan Ha! I guess so.

TOM But seriously. What kind of deco are you doing?

Bryan Initially VPM-B+3, but I upped that to VPM-B+4 for the last 15 or so dives,. But I'm still getting some joint pain more frequently than I'd like. I'm actually more concerned now. Do you think I should add some shallow time? Or find another model?

TOM Well, let's think about that. You tried VPM-B+3 and you have some signs that wasn't best. Then you went to VPM-B+4 and even though you added time you're still getting problems. You know Bryan, I think you might want to try VPM-B+1.

Bryan Uhhhhhhh … you mean VPM-B+5, right?

TOM No, you heard me correctly. I mean VPM-B+1. You tried longer deco and that didn't work. I think you might be doing too much deco.

Bryan Really!?? I always thought you'd need more deco if you were getting bent.

TOM Everyone seems to think that! Especially researchers…and Navy guys. But they don't do the kind of dives we do.

Bryan I can see why! I'm getting bent!

TOM (sarcastically)ha ha. Very funny Bryan. But that won't fix your issues

Bryan Ok. Sorry.

TOM Look Bryan. I'll let you in on a little secret --- there IS such a thing as too much deco!

Bryan Wow. I never knew that. Actually I've never even heard of that. Are you sure?

TOM Absolutely! Look, you had problems so you tried MORE deco. But that didn't fix it, did it?

Bryan No.

TOM Well. It's time to think outside the box. Give VPM-B+1 a try. And make sure you control your ascent rate.

Bryan Ok. I guess it's worth a try. I'll give it a shot. Thanks for taking the time Tom.

TOM No problem Bryan. Let me know how it goes. Safe diving!

--click--

TOM Heh … newbies!


… two weeks later … ring ring ….

TOM Safe diving. This is Tom.

Bryan Hi Tom. This is Bryan. Hey, Tom, I just got out of the chamber. I need some more advice ….

 

[tomfcrist]

The first thing I would have told him is to quit using VPM. Also realize that the NEDU study relates to backgas deco on air...which is exactly when too much deco may not be a good thing. If someone is doing deco on say 50% from 70' and O2 from.20' to the surface, there is obvious benefit to doing a long deco....but that's not what is being discussed here.

 

[Diver0001]

Tom, what do you base this assumption on, because as far as I can see that is all it is: an assumption based on bubble model dogma. What evidence do you have that it is true?

The NEDU study suggests that it is wrong.

Actually, I see this as two assumptions. I'm not sure either of them is optimal.

On the one hand, clearly the history of deep stops has gone from "gut feeling" to "working theory" to "religious belief" and it's clear that more testing is necessary to see what it actually happening. In that sense a study similar to the NEDU study would be welcomed to verify models like RGBM beyond the promises of guys like Wienke that he knows for sure that he must be right (oh and he got rich -- or tried to -- by convincing people of this). So what Simon is saying really rings a bell with me. We can't simply assume that deep stops are good because we've been told over and over that this is the case by people with a vested interest in having us believe it.

On the other hand, I think the NEDU study should be seen as based on assumptions as well because it looks like the BVM3 model was forced by the research team into calculating the dive in a way it wasn't designed for (forcing it to calculate an ascent that gives exactly 174 minutes of ascent time from a dive that wouldn't ordinarily require it) and it gave a weird result that wasn't questioned again after that.... ergo, the study rests on a false premise, or would appear to, because the dive it calculated was actually a multi level dive, which is neither what they were trying to do, nor the way the other profile being tested was set up.

As it is, it would appear that when trying to extrapolate from the NEDU study to real world diving that the study serves to confuse the issue more than to clear it up. The way I'm looking at it, it's one data point in a discussion that needs a lot more research before we can draw any solid conclusions.

@Simon, do you know if the navy did any further studies after the one that we're talking about that tests different models if they are left to "free calculate" from default settings?

R..

 

[KenGordon]

@Simon, do you know if the navy did any further studies after the one that we're talking about that tests different models if they are left to "free calculate" from default settings?

R..

You imply that the deep profile was produced by some kind of fiddling. I think I noticed a similar assertion earlier. Reading David D's description quoted above from the RBW posts:

"you can specify a total decompression stop time, and an exhaustive combinations of stop depths and times (that add to the total) are tested to find the schedule that gives the minimum estimated risk."

says to me that the process was to calculate risk values for all possible profiles for that model and duration of deco and pick the lowest risk one. It searches the solution space for an optimal result.

This is a different approach to the 'classical' means of obtaining a profile by finding a ceiling from the some limiting physical measure (eg supersaturation, bubble size/number or whatever) and then creating a series of stops so as not to exceed the ceiling. That will come up with a single solution for a given set of parameters.

Each is a valid method, and given you wish to compare profiles of the same length there needs to be a scheme to ensure they match. I don't think that is fiddling.

 

[Diver0001]

You imply that the deep profile was produced by some kind of fiddling. I think I noticed a similar assertion earlier. Reading David D's description quoted above from the RBW posts:

I don't have any reason to believe that it was "fiddling" in the sense of doing something deliberately dishonest but if I understand correctly the model was forced to produce an ascent of exactly 174 minutes, which, judging from what it calculated as a result, it clearly wasn't designed to do (correctly). I think it was probably an unintentional side effect of forcing the model to calculate a dive to exactly the same runtime as the Thalmann model that caused it to calculate a multi level dive when actually the researchers would appear to have been attempting to get it to calculate a 174 minute bubble-wrapped bucket ascent.

I don't know if any of the researchers are actually technical divers but if they had been then it would have triggered alarm bells. This does not seem to have happened.

R..

 

[KenGordon]

The criticism seems to be that it ought to have come up with a profile which went shallow sooner so as to not on gas as much. If the "exhaustive combinations" included such profiles (a property of the model) then they must (by the chosen measure) have had a higher risk after 174 minutes than the chosen one. So the 'best' profile for that model, given whatever measure of risk used, must be the one they chose.

 

[tomfcrist]

I don't know if any of the researchers are actually technical divers but if they had been then it would have triggered alarm bells. This does not seem to have happened.

R..

From what I can tell, some of the researchers are very much tech divers.