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”
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"
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”
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"
