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

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Nice summary of the arguments. This is the first post on the page for those not wanting to click on the link.

Deep Stops (rebreather dive charts) - Page 14






"Yes, it’s easy to lose the will to live when you debate someone over the course of months and 1300 posts only to have them repeat the same failed arguments all over again (as he has in his most recent post). I notice he is now dismissing that thread as meaningless because it was "ruined by a couple of puppets posting eye candy"! Well, like you, I cannot be bothered re-litigating it all again. Here is my summary of how the subject has evolved, and I will aim to avoid further debate on the matter.


It started with Ross initiating a two pronged attack on any evidence suggesting that deep stop approaches to decompression might not be ideal.


First he discounted the studies showing high numbers of VGE during use of deep stop profiles as meaningless because, he claimed, VGE have little (if any) pathophysiological significance. This was based on his fundamental lack of understanding that VGE could have poor positive predictive value for DCS, yet still be pathophysiologically significant. That debate took place in the first 10 pages of the "big thread" and is easy for anyone to find.


Ross simultaneously turned his attention to the NEDU deep stops study; a unique piece of work conducted by the only group of full time professional decompression modellers in the world, and amazingly, using DCS in humans as the primary outcome measure. In a comparison of shallow and deep stop profiles of identical duration, conducted in identical carefully controlled conditions, the deep stop profile was associated with a greater incidence of DCS. The most plausible explanation for this finding was that protection of fast tissues from supersaturation early in the ascent (by imposing deeper stops) resulted in greater supersaturation in slower tissues later in the ascent, and that this distribution (or “pattern&#8221:wink: of supersaturation is disadvantageous compared to the opposite one generated by a shallow stops profile.


Ross had no shortage of criticisms of the study and there were too many to enumerate them all here. Many, including Ross’s tiresome and repetitive references to the profiles being over-stretched, multi-level, and excessively conservative, were addressed in David Doolette’s excellent and comprehensive explanatory post which can be found here:


404 Not Found


Other criticisms have also received particular emphasis, not least of which was Ross’s attribution of all the injuries in the study to “thermal stress”. There have been many responses to this, but I would highlight one by David here:


404 Not Found


and a couple from me here:


404 Not Found
404 Not Found


Ross was particularly enthusiastic about the argument that the “thermal stress” in the NEDU study was far more severe than encountered in the real world. This was met by many posts by people who actually conduct technical dives assuring him that the thermal conditions in the NEDU study were not particularly unusual. One of the best of those can be found here:


http://www.rebreatherworld.com/444326-post910.html


Then there was the line of attack that had served Ross so well on other forums where no experts could be bothered posting a response; namely that the NEDU profiles bore no visual resemblance to “normal” technical diving profiles. In particular the NEDU deep stops profile looked different to a profile generated by VPM, and according to Ross, it had "no deep stops". Initially we tried simply pointing out the different appearances were largely irrelevant to the fact that the disadvantageous supersaturation pattern discussed above was likely in many deep stop profiles, including those generated by VPM-B. But that did not resonate with Ross, so then we observed that the NEDU deep stop profile was actually quite similar to a profile generated by VPM-B on a +7 conservatism setting. That similarity was first depicted by CYS here:


http://www.rebreatherworld.com/442682-post576.html


If there was a place in the debate where the wheels really began to fall off for Ross, I believe it was here. Despite having argued vociferously in the past that VPM was an internally consistent model that will prescribe correct decompression for the conservatism input, he claimed that VPM-B+7 was a ridiculously over-stretched iteration of the model and not relevant to the argument. Ross genuinely appeared to be arguing that his allegedly “internally consistent” model works on low conservatism but not high conservatism, which was somewhat confusing to say the least. But this only lasted as long as it took for CYS to point out that +7 was well within the model parameters published in the original literature:


http://www.rebreatherworld.com/444415-post943.html


With it widely accepted that the comparison between VPMB+7 and the NEDU profiles was legitimate, things then went from bad to worse for Ross when Kevin produced his heat map diagrams, first comparing the NEDU profiles with VPM-B+7 in respect of tissue outgassing gradients:


http://www.rebreatherworld.com/444115-post871.html


and then tissue supersaturation:


http://www.rebreatherworld.com/445956-post1251.html


These diagrams graphically illustrated that the potentially disadvantageous pattern of supersaturation that we had described earlier in the debate was common to both the NEDU deep stop profile and VPM-B+7. In the aftermath of this it was predictable that Ross would try to advance the argument that there were no true deep stops (and he keeps repeating this) and less protection of the fast tissues in the NEDU deep stops profile, alluding to the fact that the VPM-B+7 profile has a short series of deeper stops than the NEDU profile. These can be seen in the diagram I attribute to CYS above. The implication was that these very brief deeper stops and the associated protection of the fast tissues would somehow make the difference. However, Kevin's analysis of fast tissue supersaturation against time in VPM-B+7 and the two NEDU profiles allowed that argument to be effectively countered here:


http://www.rebreatherworld.com/446035-post1269.html


Indeed, it is possible to argue that those extra slightly deeper stops probably make the problem worse for VPM.


Subsequently the debate went back to the real world relevance of these longer decompression profiles, and so Kevin performed some further tissue supersaturation analyses for VPM-B and gradient factor profiles where there can be no argument of their real world relevance. These appear in the current thread, and they show that the profiles with the heaviest emphasis on deep stops most strongly exhibit the potentially disadvantageous pattern of tissue supersaturation discussed earlier. The same pattern that David Doolette identified in the original NEDU study (and that we highlighted about 1000 posts ago).


I agree that the subject has been done to death, and I guess the poll thread result suggests that the effort has been worthwhile (sorry Ross, the poll says your arguments don't "stand up just fine"). However, the debate never needed to be as polarizing as it has been. For all the accusations of agenda, trickery, deception, and a "5 year campaign to rid the world of deep stops" (how ridiculous?)etc etc, my own message on the practical implications of the debate has been consistently moderate, and an example can be seen here:


http://www.rebreatherworld.com/439085-post132.html


David has been similarly moderate. As scientists we are merely following the evidence as it emerges. We have to be very careful in our appraisal of matters like this because it is our fellow divers’ health that is at stake. Ross should bear that in mind too.


I am already well in breach of the “Ainslie Principle” (that the value of a post is inversely proportional to its length) so I better sign off.


Simon M"
 
I would still like to see a legit comparison study where the deep stop model isn't calling for ridiculously extended stops in the "deep" end of the ascent. Limit those stops to 1-3 minutes dependent on depth(deepest stops being shorter) and keep the same times on the shallow zone stops. That would do two things...get out of the water faster than the shallow stop schedule, and limit the additional on gassing of the slower tissues during those deeper stops. I'd be willing to bet there would be a significant change in the NEDU studies findings.

I agree. I would like to see more actual dive trials too. Although, whatever models are being tested, they should all have the same runtime so that they vary only in the manner in which they allocate the decompression time.

In lieu of that, an analysis of a tech RB dive was done here for VPM-B+4, GF 66/66 and two others. If you compare the pattern of supersaturation in the heat map shown there to the heat map for the NEDU study I think you'll see similarities in how supersaturation is handled.

But notice the integral supersaturation (i.e. the time exposure to supersaturation). The VPM-B+4 profile endures about 30% more supersaturation exposure than the shallower GF 66/66 profile. If one profile, given the same dive, gases, and runtime, is requiring 30% more supersaturation exposure you have to at least question whether that's good. I guess I just don't have that level of faith in the VPM theory.

In making decisions with incomplete information, the NEDU study is clear enough (to me) to not be betting on the VPM-B+4 profile.
 
Are people looking for ways to go faster? Is anyone pushing the envelope? No. The opposite infact - looking for any reason to go slower and longer. So are we just making reasons to justify going slower??
I think so, yeah. I was told the main benefit of VPM is how much faster it gets you out of the water and especially while diving Helium, and this has certainly been repeated over a wide variety of Internet forums for quite a while. It seems to penalise for helium less than Buhlmann....yet you object to a study finding something potentially consistent with VPM, an algorithm you've publicly lauded. However, I think most divers would agree that their search for a deco model would end as soon as they had the fastest way to surface without injury. I can't speak for the entire community, but I don't enjoy deco. The least feasible deco without injury is exactly what I'm searching for.

Today we can dive just about any model or settings on the market and get away with just fine.

Then, after praising VPM and warning of Buhlmann you go to say that they're all "just fine" and have talked about assuming equivalent pDCS values to all algorithms and conservatism levels.
 
I would still like to see a legit comparison study where the deep stop model isn't calling for ridiculously extended stops in the "deep" end of the ascent. Limit those stops to 1-3 minutes dependent on depth(deepest stops being shorter) and keep the same times on the shallow zone stops. That would do two things...get out of the water faster than the shallow stop schedule, and limit the additional on gassing of the slower tissues during those deeper stops. I'd be willing to bet there would be a significant change in the NEDU studies findings.

Hi Tom,

You raise good points which represent the issues that are the hardest to get your head around in this debate. I think we have had a similar conversation before so I probably can't change your mind, but a couple of points.

First, the deep stops in the NEDU study may look "ridiculously extended" in comparison with what you are used to doing, but they were very similar to those prescribed by VPM on a conservatism setting that is well within the originally published model parameters. Ross didn't include this level of conservatism in his commercially marketed version of the model, but that was an arbitrary decision (I don't mean that in a negative way - you have to draw the line somewhere). But Ross has assured us that the model is internally consistent, so a conservative application should work just as well (actually better) than a less conservative application.

Second, if you chose a deep stop test dive with shorter overall decompression (acheived by shortening the deep stops as you suggest), you would need to compare the outcomes from that dive to an alternative dive of the same length in which the stop time is distributed shallower. The dives must be of the same length in order to isolate the effect of stop depth distribution on outcome. In designing this experiment you would inevitably be left with a deep stop profile that protects faster tissues from supersaturation (I refer to an integral of supersaturation and time here) early at the expense of greater slow tissue supersaturation late. This is a physical inevitability and is the same pattern that was found to be disadvantageous in the NEDU study. Now here is the key question. Although you might expect the magnitude of the supersaturation differences between fast and slow tissues to be reduced in a shorter profile, the relative fast and slower tissue supersaturation pattern would still be as described above. Why then, would we expect a reversal of the result obtained in the NEDU study? The difference in outcome between the two groups might be smaller, and perhaps so small that you would not detect it in a study of practical size, but it is unlikely the "truth in the universe" would actually be different.

Simon M
 


A ScubaBoard Staff Message...

A few off-topic posts were edited/removed.
 
Last edited:


You post a clear insinuation that I (or someone related to my side of the debate) paid trolls to participate in the RBW thread.

I challenged you to back up that accusation, and your response was to claim:

1. That I agree there were trolls posting lies, fabrication etc; and,

2. That I have accused myself of paying them.

People can judge your rationality for themselves, but basically I rest my case.

Simon M








You invented the fake insinuation. You invented the phony allegation. You made up the stupid idea that you are paying your self to employ trolls to argue against yourself.

You fully approve and encourage trolls who work for free, and actively promote them to push fake data, junk science, insults, lies, fabrications, and endless amounts of other rubbish.


You ..you.... you ... fake, phony, trolls, All these things seem to go together.


As my favorite Pigin English phrase says " problem bilong yu" Simon.

Why don't you schedule a meeting with yourself, to discuss how yourself has made these allegations about you, or yourself, and then apologize to yourself and you, me, and everyone else here for making up this rubbish.



*****************


(or someone related to my side of the debate)


You mean there a gossip channel about me behind the scenes - gee what a shocker. You have a fan boiz club, all huddled around and co-ordinatined with the same bullet list of talking points against me. So you are an organized group after all.










---------- Post added December 23rd, 2015 at 03:02 AM ----------

I think so, yeah. I was told the main benefit of VPM is how much faster it gets you out of the water and especially while diving Helium, and this has certainly been repeated over a wide variety of Internet forums for quite a while. It seems to penalise for helium less than Buhlmann....yet you object to a study finding something potentially consistent with VPM, an algorithm you've publicly lauded. However, I think most divers would agree that their search for a deco model would end as soon as they had the fastest way to surface without injury. I can't speak for the entire community, but I don't enjoy deco. The least feasible deco without injury is exactly what I'm searching for.

Then, after praising VPM and warning of Buhlmann you go to say that they're all "just fine" and have talked about assuming equivalent pDCS values to all algorithms and conservatism levels.


No. The fast thing has never been said or suggested in VPM-B circles. You are listening to too much internet gossip, and innuendo. VPM-B is LONGER than real ZHL up to about 3 or 4 hours. Then ZHL takes off for the stars.

The study is not consistent with VPM or ZHL. The helium test is way of the end of scale. We showed that here: comparing VPM-B / ZHL-C+GF / helium test

The helium test is in fact much closer to all of Simons new deco methods and ideas. That is: Shallow stop model, long extended last stop times, and (guessing) expected low VGE numbers. But still it failed twice on the same day at the same time. Maybe Simon can explain why his preferred and recommended deco methods failed.

I work with both models. I prefer VPM-B of course, because its a nicer design and more dynamic and capable. But all these model "work", and you can use almost any of them.


pDCS - David can tell you all about this. But deterministic decompression models (VPM-B, ZHL, etc) cannot produce a pDCS number. pDCS is bigger than the deco model and takes in more data points. So your concern about non iso-risk (or any risk number) from models we use, will never be satisfied.

Here is a description of pDCS and its workings: ADA320268 Trends in deco, Statisicital pDCS - DCIEM, or here too









---------- Post added December 23rd, 2015 at 03:27 AM ----------

First, the deep stops in the NEDU study may look "ridiculously extended" in comparison with what you are used to doing, but they were very similar to those prescribed by VPM.
Simon M

RUBBISH !

You are deliberately deceiving people with this stretched out fallacy justification, and you know it. Then you assume the complete absence of deep stops in the nedu test, can be replaced with shallow stops. They cannot - simple math shows that. post #82

deception, fallacy justification, assumption and supposition.....
 
Last edited:
I would still like to see a legit comparison study where the deep stop model isn't calling for ridiculously extended stops in the "deep" end of the ascent. Limit those stops to 1-3 minutes dependent on depth(deepest stops being shorter) and keep the same times on the shallow zone stops. That would do two things...get out of the water faster than the shallow stop schedule, and limit the additional on gassing of the slower tissues during those deeper stops. I'd be willing to bet there would be a significant change in the NEDU studies findings.
If the difference between the profiles is very small - as is likely if you limit the deep stops to 1-3 minutes in a (e.g.) 120 minute (inkluding all deco) dive - you would need a very high number of dives to observe a significant difference in outcome.
 
Just a sidebar question here. I don't want to get in the way of the debate about theory (or the entertainment of the ego clash) but I've read through this thread and can't quite get a grasp on what is being said about the practical application of current models.

I think it was Simon saying "they're all broken" and Ross saying "40 years of empirical evidence can't be wrong" (or something to that effect). These two comments seem to basically define the trenches.

I'm happy to leave the science to the scientists but what is really being said about the common models in circulation now? It doesn't sound like what has been "discovered" is very surprising, but does this suddenly mean that we should start doubting the procedures that have been working for X amount of time?

I'm sure we can all stop diving these profiles and wait for a new model but based on what I'm reading here, i'm beginning to get the impression that any differences will, in a practical sense, amount to a slight adjustment to the "black line through the grey area".

Thoughts?
 
Hi Tom,

You raise good points which represent the issues that are the hardest to get your head around in this debate. I think we have had a similar conversation before so I probably can't change your mind, but a couple of points.

Yep, we surely had this discussion before.

First, the deep stops in the NEDU study may look "ridiculously extended" in comparison with what you are used to doing, but they were very similar to those prescribed by VPM on a conservatism setting that is well within the originally published model parameters. Ross didn't include this level of conservatism in his commercially marketed version of the model, but that was an arbitrary decision (I don't mean that in a negative way - you have to draw the line somewhere). But Ross has assured us that the model is internally consistent, so a conservative application should work just as well (actually better) than a less conservative application.

I totally get what you are saying. However, one has to question how much "Conservatism" is too much...especially when you start doing stops at those depths. If by adding conservatism to a model you increase the time spent deep to a point that you are doing more harm than good....does it really work just as well?


Second, if you chose a deep stop test dive with shorter overall decompression (acheived by shortening the deep stops as you suggest), you would need to compare the outcomes from that dive to an alternative dive of the same length in which the stop time is distributed shallower.

Great idea! Lets do that.

In designing this experiment you would inevitably be left with a deep stop profile that protects faster tissues from supersaturation (I refer to an integral of supersaturation and time here) early at the expense of greater slow tissue supersaturation late. This is a physical inevitability and is the same pattern that was found to be disadvantageous in the NEDU study.

Now here is the key question. Although you might expect the magnitude of the supersaturation differences between fast and slow tissues to be reduced in a shorter profile, the relative fast and slower tissue supersaturation pattern would still be as described above.

If you are running a linear model you are correct. If you merely limit the length of the deep stops to avoid the huge amount of additional on gassing of the slower tissues that was problematic in the NEDU study, the pattern would have to change. Realize that I'm not talking about changing the deco curve evenly across the board.


I would expect with a shorter deco time overall on the deep stop profile (limiting the deep stops as I suggested before) and the same curve in the shallow end, you would have fewer incidents of DCS and less super saturation overall. I would also expect the opposite to be true for the Shallow profile, where if you were to adjust it to match the runtime of the deep stop profile, you would find MORE super saturation and an increase in incidence of DCS.
 
...//... I’ve been trying very hard to follow this thread for insights. ... What I haven’t been able to do is to put the whole thing into some sort of “competing dogmas” framework that makes sense to me. I am lacking a general idea of how the two competing camps are coming at this problem. ...//...

...//... I've read through this thread and can't quite get a grasp on what is being said about the practical application of current models.

I think it was Simon saying "they're all broken" and Ross saying "40 years of empirical evidence can't be wrong" (or something to that effect). These two comments seem to basically define the trenches. ...//...
So, I'm not the only one with fundamental concerns as to the nature of this dispute.



Guys, Please. Rate your approaches to decompression modeling in two categories on a 1 to 10 scale:

Deterministic vs. Probabilistic

Theoretical vs. Physical

If that doesn't work for you, please rate the other camp's approach.

Thx.
 
http://cavediveflorida.com/Rum_House.htm

Back
Top Bottom