Slow tissue on gas from stops

[rossh]

Hello Ross,

The only useful definition of efficient in a discussion about how to distribute your decompression stops across depths is "the least risk for a given amount of decompression time". You have been told this by true experts in the field time after time. Indeed, it was clearly stated by the author off the NEDU study right back in the early pages of the rebreather world deep stops thread:

Simon M

You (and David) are trying to re-define this term to suit your own end purpose. You don't get to just make stuff up Simon.

Ross, this particular line of argument sits alongside your recent insistence that it is tissue half times and not tissue perfusion that determines tissue gas kinetics, as unimpeachable evidence that you have very little knowledge of a field in which you portray yourself to be expert. It is all the more strange because you contradict yourself constantly on the subject. For example, in the very same post you say:Simon M

NO. I did not say or suggest that. You made up that false interpretation. You were loosing that topic of discussion too. Some of David's presentations confirmed what I really said. When cornered, is this your only defense? To make up rubbish about your your opponent to deflect... the typical 'academic' response?

Here we have two algorithms which by your own admission are legitimate models, which by your own admission use the "Haldane Schriener, equations, (as used in VPM-B and ZHL)", and which by your own admission give decompressions of different lengths for the same dive. It is very unlikely that the profiles are iso-risk.
Simon M

You don't know that (iso-risk). We don't have measures or risk levels in tech diving, and its not been tested.

Two same dive profiles by two different models will have different levels of supersaturation across the ascent. You would expect a different run time. And that is exactly what we see ...VPM-B is longer than ZHL-C plans (up to about 3 hours). So by that simple comparison, does that generally make VPM-B lower risk? Remember, DCS risk is proportional to in-dive supersaturation levels and times... not surface levels.

More importantly, as the last 16 years of lowered injury treatment rates suggests, current deco models and proper planning methods have more than enough extra deco time added to cater for risk. There is not much room for improvement in this area.
Today the risk is greatest from outside environmental and procedural influences, which is beyond the control of any model. That's a training issue and solution.

Parenthetically, it is also relevant to point out that you have very much changed your tune on this particular issue in comparison with years gone by when you used to trumpet VPM's superiority. How could it be superior in the context of your latest claims that use of the standard gas tracking formulae renders everything somehow equivalent?
Simon M

Your question is moot. The overwhelming tendency of the first 15 years of 2000's, has been to use and emulate a bubble model profile, and that includes with GF planning too.... therefore most diving planning was equivalent, regardless of the model name on the outside.


Your new approach today, has gone beyond decompression planning, and is now adding extra time, on top of safety, on top of conservatism, on top of minimum required deco. That's all fine and nice, and anyone who wants to adopt this low stress approach, then go right ahead. But please do not confuse this new approach with the essential limits of decompression - no one is on the bleeding edge of deco limits these days.

Ross, this is why it is so important to understand the concept of efficiency. The question is, if someone was prepared to do the same length of decompression
Simon M

This is a false limitation and false requirement. No one is choosing their deco based on shortest time, or any other form of falsely interpreted efficiency. People choose a model, or it attributes, or a basic GF setting, and accept the deco time it requires.

.

 

[Diver0001]

Yes I am.

But here is the problem. Simon .... snip....

.

The person asked you to post your credentials and you didn't answer the question.

R..

 

[Dr Simon Mitchell]

You (and David) are trying to re-define this term to suit your own end purpose. You don't get to just make stuff up Simon.

Ross, our definition is published in the peer reviewed diving medicine literature.[1] Let us know when you find another expert disagreeing with it, or when you publish yours.

___________________________________________________________________________________________

Ross, this particular line of argument sits alongside your recent insistence that it is tissue half times and not tissue perfusion that determines tissue gas kinetics, as unimpeachable evidence that you have very little knowledge of a field in which you portray yourself to be expert.

Your response....

NO. I did not say or suggest that. You made up that false interpretation. You were loosing that topic of discussion too. Some of David's presentations confirmed what I really said. When cornered, is this your only defense? To make up rubbish about your your opponent to deflect... the typical 'academic' response?

OK, here is one example of what you "said and suggested":

Models and the internal design are not designed as perfusion limited. The basic sequence of mono-exponential gas kinetic formula, uses the partial pressure of gas versus the tissue absorption rate. This rate is represented with a half time value.

So, not perfusion limited, but based on half time values. Sounds pretty much like what I said you said.

For those who may not get the point of this, perfusion is the most important determinant of tissue half time but it is clear from the quoted sentences above and many other comments in the thread that Ross simply did not understand this most basic aspect of decompression theory.

So, Ross, there is no point in denying it. It is in a thread on this site. Essentially you have left any credibility you may have had here, for two reasons:

1. The statement is so outrageously incorrect; and

2. You vehemently deny saying it when it is plain to see that you did. The things you say cannot be trusted.
________________________________________________________________________________________________

Two same dive profiles by two different models will have different levels of supersaturation ....etc

Your constant refrain is that VPM uses the standard gas tracking formulae to calculate inert gas pressures in tissues, and so that means that it must be just as valid as any other algorithm using the same formulae and that there cannot be "anything to fix". This claim is as ill-informed as the perfusion vs half time one. VPM may use those formulae to track gas pressures in tissues, but the supersaturation it allows in which tissues and when is very different to other models. Therefore, to simply assume that they are equivalent in risk and claim "there is nothing to fix" is completely invalid.

More importantly, as the last 16 years of lowered injury treatment rates suggests, current deco models and proper planning methods have more than enough extra deco time added to cater for risk.

Please show me the data describing lowered injury treatment rates. You clearly still do not understand what a rate is.

Your question is moot.

No its not. Maybe you didn't understand it. You have claimed in the past that VPM is superior to other algorithms (that use the same gas tracking formula). But now you are continuously claiming that the use of those formulae makes models equivalent. You can't have it both ways.

Your new approach today, has gone beyond decompression planning, and is now adding extra time, on top of safety, on top of conservatism, on top of minimum required deco. That's all fine and nice, and anyone who wants to adopt this low stress approach, then go right ahead. But please do not confuse this new approach with the essential limits of decompression - no one is on the bleeding edge of deco limits these days.

There is no such thing as the "bleeding edge of deco limits". There is only risk, and perceptions of acceptable risk.

This is a false limitation and false requirement. No one is choosing their deco based on shortest time, or any other form of falsely interpreted efficiency. People choose a model, or it attributes, or a basic GF setting, and accept the deco time it requires.

You still don't get it. Once you accept the deco time it requires, then it is a very legitimate question to consider whether the distribution of stops prescribed within that time represents the safest approach, because if not, then it is not the most efficient approach to decompression.

Simon M

1. DOOLETTE DJ, MITCHELL SJ. Recreational technical diving part 2. Decompression from deep technical dives. Diving Hyperb Med 43, 96-104, 2013

 

[Storker]

here is the problem. Simon is out here pushing new ideas and new interpretations of existing science and deco theory. We get severed his opinion mostly. He does this change in the public arena - the internet... and not in the traditional peer review process of science. As a result, he gets the changes through, without the proper scientific backing.

As @UWSojourner points out, this is at best a gross misrepresentation of the facts.

If scientists were to only disseminate science from those articles which have been through the peer review grind, we (the ordinary public) would be at a great disadvantage since:

• Publishing proper peer reviewed articles often takes time. When the article finally is published, it has been through an extremely rigorous QC process, and the research front will often have progressed. Sometimes rather significantly.
• Minor results and additional insights don't necessarily get published in peer review journals because the results and insights aren't deemed big enough to merit a full journal publication. Or they may be obtained in an organization which doesn't emphasize peer review journal articles as an important communication channel for their employees. Which brings me to the third point:
• Not all science is disseminated via peer reviewed articles. Some is disseminated through reports like the NEDU study report, some through conference proceedings, some through conference presentations without proceedings, some through workshop discussions. If a researcher wants to stay current in the field, it often isn't enough to just read the peer reviewed literature.

The diving community should - and, for most who have an interest in this, is - very grateful for @Dr Simon Mitchell 's work at bringing hyperbaric medical science from the close-knit world of specialized scientists and out into the general public. Because in practice, that task isn't in a scientist's practical job description. Generally, that kind of activity doesn't give much - if any - credit in the academic community.

If you (general 'you') are a specialist speaking to a lay audience, you can't just quote published articles, you must also give your interpretations and your understanding, and you must explain the stuff in somewhat smaller words that what is used in the journal articles. Because most people, as you yourself have illustrated on several occasions, have serious issues understanding properly what those journal articles really are about. That requires skills that generally aren't taught before the university level.

You demonstrate once again that you have absolutely no understanding of science and how it is conducted. Those who have done science, and published proper journal articles in well-standing scientific journals, won't have any problems understanding this.

 

[RayfromTX]

---

---

A ScubaBoard Staff Message...

Due to past warnings and behaviors Ross is on a zero tolerance status for name calling. He has now been banned from this thread for calling other members trolls. He will no longer be able to respond to messages that are posted here. Please keep future posts in this thread respectful and on topic. We already had to delete other posts for name calling. There is no reason for that and it accomplishes nothing. We can address disagreements about the topic without accusing others of obfuscation, fabrication or nefarious motives. Carry on.

---

 

[DavidFL]

This thread and its predecessors, originating as far as I can tell from the NEDU study, have been both educational and, I have to admit, entertaining for me as a lay reader. But it is tedious to be drawn back into detailed graphs and charts "re-litigating" arguments that have been previously made and either not refuted or not refuted successfully. Most of the peers in this area of science, I suspect, don't choose to spend the time and effort on internet forums. I'm grateful to Dr. Mitchell and Dr. Doolette and others who have invested the time.

I don't believe any amount of evidence or effort will change Ross' mind.

I am curious, however, about some of the published authors in the peer reviewed literature who developed and supported VPM, RGBM, and the general theories of bubble models. Have Yount, Weinke, and others who published prolifically about the potential benefits of bubble models been convinced by the NEDU study and nearly 20 years of subsequent work and published anything recently about the distribution of decompression stops between "deeper" and "not deeper" and/or the efficiency of any particular distribution based on revision of their previous work?

 

[ajduplessis]

it really is not rocket science that a longer and deeper profile will produce higher dcs risk than a shallower profile.

 

[UWSojourner]

it really is not rocket science that a longer and deeper profile will produce higher dcs risk than a shallower profile.

That's generally true, but not what is being discussed.

The question is whether, for identical dives and identical time to surface, the stops recommended by bubble models or the stops recommended by a shallower-stop model (e.g. GF) are more efficient (i.e. result in a lower DCS rate).

The current evidence suggests that getting away from the deep stops recommended by common models like VPM, RGBM, RD will result in lower DCS risk. By how much the risk is reduced, and exactly where the dividing lines are between shallow enough and too shallow, is not known. What does seem clear is that the "protecting the fast tissues" obsession was way overblown and counterproductive to safety.

 

[dmaziuk]

So.. would you say that Haldane's half-pressure stops are on the "shallow enough" side of the debate?

 

[UWSojourner]

So.. would you say that Haldane's half-pressure stops are on the "shallow enough" side of the debate?

I'm not familiar with how schedules would look using "Haldane half-pressure stops". The generalized soft recommendation coming out of the earlier threads was something like GF40/70. I'm sure divers are moving that around to suit their needs.