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

[Dr Simon Mitchell]

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.

Hello,

I think you might have misinterpreted the nature of the debates that have been partially (and incompletely) represented on this thread. Both debates arise from research work published by the US Navy Experimental Diving Unit where David Doolette is one of the scientists.

The first relates to their publication (in 2011) of a study that compared (using very generic language here) a deep stop vs shallow stop approach to decompression from the same dive, and showed the deep stop approach resulted in more decompression sickness (actual cases in human subjects). Because bubble models such as VPM-B emphasise a deep stop approach, their advocates (in particular Ross) did not like this study, and have expended considerable energy trying to discredit it. The major debate took place on the RBW thread that has been mentioned multiple times here.

The second relates to their publication this year of a study that compared identical decompressions from a trimix and heliox decompressions from the same dive and found to a predetermined level of confidence that decompression from the heliox dive was not associated with worse outcomes (once again, DCS in human subjects). Combined with some animal gas kinetic work also published this year, the implication of this was that the decompression penalty often imposed for use of higher fractions of helium by many decompression models is unnecessary. Having said that, we are not convinced that this means we can be doing shorter decompressions from deep helium dives because it may be that the assumption of a "helium penalty" has resulted in us serendipitously doing the right amount of deco from deep dives where helium is typically used. Anyway, probably because the gas tracking algorithm underpinning his decompression products assumes a helium penalty, Ross does not like these studies either and has once again expended considerable energy trying to discredit them. The main debate about this took place on the CCR Explorers site that has been mentioned a few times in this thread.

Those are the topics of the debates. It has never been about deterministic vs probabilistic models though the narrative has drifted into that area once or twice in relation to a few of Ross's claims.

I hope this helps.

Simon M

---------- Post added December 24th, 2015 at 10:48 AM ----------

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.

Hello Tom,

No one has done the study to measure DCS, but in respect of supersaturation UWSojourner has more or less done what you said with his comparison of a VPM-B+4 and a GF 40:74 CCR decompression (using real world gases and set point parameters) over on the RBW threads. The slow tissue supersaturations are still greater in the VPM-B+4 profile as a result of its greater emphasis on deep stops early in the decompression. I am perfectly happy to admit that if you ran a study with the NEDU trial subject numbers on those two profiles you might not find a difference in outcomes. However, I struggle to believe that the result would be reversed for some reason.

Anyway, Merry Christmas.

Simon M

---------- Post added December 24th, 2015 at 11:17 AM ----------

Ross, it is a matter of public record on this thread that you have raised an allegation that there were "paid trolls" operating on the RBW thread. Since the focus of the debate has been with me, I think any reasonable person would agree that I have grounds for concern that your allegation reflects badly on me (as the person who might have paid the alleged trolls). Not surprisingly, therefore, I have asked you to back that claim up with evidence.

Your response...

You invented the fake insinuation. You invented the phony allegation.

....is neither rational (because you clearly made the allegation) nor adequate. I will keep raising this in any debate with you until you admit there is no evidence (which there cannot be because it did not happen). So you might as well get it over with now.

You are deliberately deceiving people with this stretched out fallacy justification, and you know it. deception, fallacy justification, assumption and supposition

What I know is that VPM pioneers like Baker and Maiken frequently referred to a range of micro-bubble radii (which equates with a range of conservatism settings for the model) which embraced the radius defining +7 conservatism (around 1.02 micron). An example can be found here:
http://www.decompression.org/maiken/VPM/RDPW/VPMech4/VPMech4.htm
The fact that you did not include +7 in your software package was an entirely arbitrary decision on your part (which I acknowledge you were perfectly entitled to make). But I think trying to pass it off as an invalid profile just because it looks uncomfortably like the US Navy deep stops profile is, to borrow your words, is where the "deception, fallacy justification, assumption and supposition" is occurring here.

Simon M

 

[UWSojourner]

What I know is that VPM pioneers like Baker and Maiken frequently referred to a range of micro-bubble radii (which equates with a range of conservatism settings for the model) which embraced the radius defining +7 conservatism (around 1.02 micron). An example can be found here:
http://www.decompression.org/maiken/VPM/RDPW/VPMech4/VPMech4.htm

For completeness regarding the VPM-B+7 issue ...

This fortran code is from the public VPM-B algorithm Baker released and clearly allows the N2 critical radius to be in the range [0.2,1.35]:













The chart below shows where VPM-B+7 falls relative to +0 thru +5. It's clearly within the range [0.2, 1.35].

 

[rossh]

The Critical Radii ranges are too wide for diving purposes. The 0.2 to 1.35 is not usable in a dive application.

A 0.2 setting is a -13 and a 1.35 is a +11. That has a time range of just 9 mins to 234 mins to deco time range. None of those are realistic and so extended CR beyond the 0 to +4, is going beyond the realistic range.

Anyone can pretend that a +7 is useful for argumentative purposes, but it is a weak and stretch out fallacy.

http://www.hhssoftware.com/images/nedu_vpm_cr-ranges.png

 

[Dr Simon Mitchell]

Anyone can pretend that a +7 is useful for argumentative purposes, but the intelligent people see that its a weak and stretch out fallacy.

Actually Ross, looking at your own diagram I would say any intelligent person can see that +7 is just another step or two up the scale of conservatism. Are you really saying that VPM-B works on lower conservatism but not higher conservatism? Your characterisation of the zone above +5 as out of the diving range is entirely your own arbitrary judgement, and is inconsistent with source documents describing the model (see UWSojourners post above).

Also, can you please provide the evidence that there were paid trolls operating on the RBW thread.

Thanks,

Simon M

 

[rossh]

So, I'm not the only one with fundamental concerns as to the nature of this dispute.

Thx.

Deterministic vs. Probabilistic

These are very different models. VPM / ZHL, etc, are all deterministic models. These function on setting limits from physical properties, or with pre set arbitrary dimensions from testing. Deterministic models simply cannot make a risk number, because they have no information to make that from.


Probabilistic models are exclusively with the navy model designs. It needs a large data base of known results to function. They are survey based predictions, and don't always follow rules of physics. A probabilistic model is one that is waiting to be better defined by physics and physiology. David can explain this better.

Theoretical vs. Physical

The both work together hand in hand, to come to a result.

2 recent nedu tests

1/ The 2006 (no) deep stop test, was for the nedu's internal use. They had a decision between two SHALLOW nedu model designs: BVM-3 and VVAL-18. Now as it turns out, neither one actually made it into USN dive manual, and they went with a heavily modified version instead.


Then the problems started - how to adopt that test onto tech diving, or does it even fit? The answer is no, but with a lot of imagination, Simon and friends try to stretch it out and apply a lot of made up rubbish connections. For a man of science he sure does have loose morals and integrity. More on this below.


2/ The 2014 trimix test.

Don't really have much to say - its so far away from tech diving, it would take a stretch of imagination to connect it back to tech diving.


*********

I think both these tests are OK from a science method point of view. The reports conclusions are both OK with me (but read them properly).


The issue is how the result is interpreted onto tech diving practices, and how much science needs to be stretched out, and rubbish fudged up to bridge that gap.

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

The problem we have, is someone (Simon usually) occasionally keeps trying to stretch out the meaning and context of the science work that is being done. They try to read in too much significance, or try to connect pieces that do not match up. They cherry pick small parts without taking the big picture into considerations. In short, they don't do their homework. That is the basis of these arguments that keep coming up.

This little niche activity of ours is a neglected area of science. But, no matter how well intentioned, it is not an excuse to allow the over ambitious exaggerations of one, to overrule to the exclusion of all existing works. We are being pressured with sensationalized and exaggerated explanations of these new studies. Don't let him ruin it for everyone.


Look at the example of this deep stop argument. This is the chain of supposition that they hope we can't see.


nedu test 2 (shallow) internal models : in isolation to tech diving,

How to morph that into tech diving circles?

Stretch out tech diving models to pretend it matches: fabrication
Invent excuses using off scale data point to justify above: fallacy
Make up meaningless measures to compare and show: fabrication, fallacy, junk science
Show meaningless tissue pressure graphs with no actual data: advertising style, junk science
Launch viscous attacks on non-believers: argumentum ad hominem
Use trolls and friends with preset talking points to bully the issue: disgusting
Ignore any real science or measure that disproves the above: no moral or integrity
Ignore the differences in profiles: denial

Repeat as needed.



Where is the science in the connection? There is none, because there is no connection - just a stretched out fallacy, backed by trolls, marketing, and a trail of fantasy and fabrication.


Not for me thanks - I prefer real science and real connections.





---------- Post added December 24th, 2015 at 02:14 AM ----------

Actually Ross, looking at your own diagram I would say any intelligent person can see that +7 is just another step or two up the scale of conservatism. Are you really saying that VPM-B works on lower conservatism but not higher conservatism? Your characterisation of the zone above +5 as out of the diving range is entirely your own arbitrary judgement, and is inconsistent with source documents describing the model (see UWSojourners post above).

Also, can you please provide the evidence that there were paid trolls operating on the RBW thread.

Thanks,

Simon M

At some point, you actually have to drop the sham excuses, and start using your brains. You have a chain of supposition that connects the nedu test to tech diving, and nothing else.



Key words: sham excuses .... suppositions....

Also, can you please provide the evidence that there were paid trolls operating on the RBW thread.

What ? You are saying there were PAID trolls in the RBW thread? Oh my God.. YOU (Simon Mitchell) said: quote - "that there were paid trolls operating on the RBW thread" - unquote.

That's terrible Simon. The trolls should work for free! Right?

Because you were perfectly happy using free trolls to promote fallacy, attacks ad hominem, fabrication, junk science, marketing garbage - you actively approved the lot. Where are your morals Simon - gone missing obviously!


Key words: Simon... trolls.... fallacy... junk science... attacks ad hominem... no morals.

 

[Centrals]

Repeat as needed.



Where is the science in the connection? There is none, because there is no connection - just a stretched out fallacy, backed by trolls, marketing, and a trail of fantasy and fabrication.

Not for me thanks - I prefer real science and real connections.

Talking about REAL science!
You kept repeating the same accusation but yet to produce any evidence to substantiate it! Don't you think it is about time that you put money where your mouth is?

 

[Diver0001]

Since we're repeating things then I'll repeat my question as well.. Does this new research mean that we should be doubting the utility of current decompression models?

R..

 

[lowviz]

Deterministic vs. Probabilistic:

These are very different models. VPM / ZHL, etc, are all deterministic models. These function on setting limits from physical properties, or with pre set arbitrary dimensions from testing. Deterministic models simply cannot make a risk number, because they have no information to make that from.


Probabilistic models are exclusively with the navy model designs. It needs a large data base of known results to function. They are survey based predictions, and don't always follow rules of physics. A probabilistic model is one that is waiting to be better defined by physics and physiology. David can explain this better. ...//...

Thank you for that.


Theoretical vs. Physical:

...//... The both work together hand in hand, to come to a result. ...//...

I agree in principle, but see this in a different light.

"Theoretical" is one end of a spectrum that extends to purely physiological observations as the other end. In-vitro would be nearer the theoretical end while in-vivo would be nearer the physical/physiological end. I feel that "Theoretical vs. Physical" also has a deterministic vs. probabilistic flavor to it.

I've thanked your post for these insights, or maybe more properly, for explaining your position towards your research.

I've now thanked both you and Simon for posts that put this contentious back-and-forth scientific discussion into focus for me. There is no lack of contention in science, I come from that world. Nothing said or done in this thread does anything other than inform or amuse me. There is good science in here on both sides. All models will always have flaws. Picking away at those flaws is called progress. Just like in repair, the hard part is finding out exactly what is wrong and why. Fixing that is usually straightforward.


Cheers, both of you.

 

[Storker]

Getting back to the models and the data, I'd like to ask a (perhaps very stupid) question.

Let us assume that there is a long/deep dive penalty that previously has been understood as a He penalty. Could this phenomenon be modeled by modifying the basic Haldanean multi-compartment model? AFAIU one of the concepts behind the Haldanean model is that the rate of on- and offgassing is equal, i.e. a simple equilibrium. Now it's well known that some absorption / desorption processes don't have equal rates in both directions, so this shouldn't be a very radical idea. If the offgassing, particularly from the slower tissues, has a lower rate than the ongassing I would think it could be quite feasible to model the long/deep penalty regardless of whether one believes that supersaturation or bubble growth is determining the pDCS.

As I said, this may well be a really stupid question, so if anyone cares to answer please leave the torches and pitchforks in the shed...

 

[Redshift]

I would also like to see a study where a series of shorter deep stops are applied. It would help evaluating deep stops as a concept. Could be generated by applying GF or a different conservatism to VPM-B (some experiments were apparently done with VPM-B +4 that also showed more bubbles?). And could be done comparing prescribed deco, meaning it could have a different total time. This includes another variable, but addresses the effectiveness of a certain deco strategy. Or deco time could be matched, by extending shallow stops and not the deep ones.

About VPM-B in particular, the fact that it can generate a "more conservative" profile that is worse, shows that there is something wrong with the model. Maybe it does work better with smaller conservatism levels, but it can't be argued that one can't use +7 "just because".

The original subject of this current threat is very interesting. (And seemed very simple to understand, so it was surprising to see Ross's initial comments, either personal attacks or incomprehension of something simple, that should be understood by someone developing deco programs. Either way, not good.)
And like Storker, I'd like then to see the "helium penalty" being removed from the helium and incorporated in the underlying decompression models, so that they cope better with deeper / more extended dives.
As it is, two dives of same depth and time, with different mixes, will have different decompression profiles, which should not happen. And maybe some gas mixtures will have a "helium penalty" that actually comes closer to the needed extra deco time, than others.