NEDU Study

[Diver0001]

We don't need to be overly concerned with the nedu test. No real deeps were tested, only exaggerated shallow stops. The test was one of thermal stress against shallow stops.

It should be noted that the NEDU study is one of the most widely accepted and definitive comparative studies ever done between the workings of bubble models as compared to the workings of Buhlmann. Aside from Bruce Wienke who sees his life's work going to hell because of this study, not a single decompression scientist on the planet didn't welcome the results of that study. I would say that's a good sign of solid research.

What explanation can you offer for the fact that all of these scientists agree that this was outstanding and important work?

Can you cite one peer review criticizing this study?

What explanation do you have for the fact that you are alone in your opinion that there something wrong with that study?

R..

 

[rossh]

Unlike others, I won't claim any expertise in decompression science, but I do believe I have a pretty decent grasp of chemistry and physics. Based on that, I have a hard time understanding what "gas kinetic formula" means. Last time I checked, the only thing all decompression models had in common was equilibrium phenomena like dissolved gas content. Which kinetic parameters are actually determined and used in the different deco models?

Since you - based on your own statements - are more qualified than internationally recognized decompression scientists with multiple peer-reviewed publications (such as Drs Mitchell, Doolette, Pollock and Møllerløkken to name a few), I expect that you can enlighten me.

In answer to your question:

From David Doolette, here on SB

"There is broad (universal?) agreement that modelling tissue gas uptake with a range of exchange rates - as we do for instance with a collection of compartments with mono-exponential gas exchange - captures the essential processes, at least crudely. "

This is the 16 cells of ZHL, VPM-B, the 2 test cells in the nedu test validations, and just about any other Haldane based dissolved gas tracking model: mono-expotential, gas kinetic formula. i.e. 1/2 time cells.

These are the basis for supersaturation calculations, and the basis of how models create their ascent limits. If your a GF fan, then those Hi/Lo numbers are also based and created on these values.

 

[Storker]

gas kinetic formula

Can you provide this formula?

 

[Dr Simon Mitchell]

Did you know, that both VPM-B and ZHL follows the same standard gas kinetic formula, and that those formula are typical of the A1 successful profile gas kinetics too.

Did you know that if you plan a dive in ZHL or VPM-B, and force more deep time into it, that will automatically adds extra shallow time? Also, if you force those nedu profiles into ZHL or VPM-B plan, then both will give longer deco time for A2.

Did you know that all dive computers follow those same gas kinetic formula as well, meaning we fully trust theses formula now, to do any kind of ascent.

Ross,

This nonsense about "standard gas kinetic formula" has to stop. This is deliberate misinformation and it has no place on a board like this where divers are participating in order to be educated.

YES, all models use "standard gas kinetic formulae" to track inert gas supersaturation in tissues. But the decompression profile prescribed by individual models depends entirely on how each model interprets how much supersaturation is tolerable, in which tissues, and when. Bubble models and gas content models have substantial differences in this regard. That is why VPM prescribes very different looking decompressions to ZHL-C or some GF approaches. You know this, yet you repeatedly try to deflect debate about the significance of these differences by stating that they all use "standard gas kinetic formulae" as though this somehow (magically?) makes the differences less meaningful.

It is like trying to claim that Barack Obama and Donald Trump (the models) will always react to pieces of information in exactly the same way so long as they read it in the same book (the standard gas kinetic formula).

Put simply, the fact that all models use common formulae to track in-gassing, out-gassing and tissue supersaturation has no relevance whatsoever to a debate about which model prescribes the safest decompression because the models treat supersaturation differently.

In answer to your question:

From David Doolette, here on SB

"There is broad (universal?) agreement that modelling tissue gas uptake with a range of exchange rates - as we do for instance with a collection of compartments with mono-exponential gas exchange - captures the essential processes, at least crudely. "

All David is saying here is that the commonly used gas kinetic formula seem to work well enough for use in decompression models (a point on which we all agree).

To cite it here as though it in some way supports your views is a shameful misrepresentation of the statement.

If you wish to educate yourself further on the reasons why you are misrepresenting the truth on this matter then feel free to read:

DOOLETTE DJ, MITCHELL SJ. The physiological kinetics of nitrogen and the prevention of decompression sickness. Clin Pharmacokinetics 40, 1-14, 2001

DOOLETTE DJ, MITCHELL SJ. Hyperbaric conditions. Comprehensive Physiol 1, 163-201, 2011

This more recent publication is a chapter in the American Physiological Society Handbook of Physiology, and was peer reviewed by Richard Moon and Richard Vann.

Simon M

 

[UWSojourner]

.... the A2 profile ... does not follow the natural gas kinetic rules. It does not follow normal supersaturation patterns. It does not follow a natural curve like that of other models. The A2 represents nothing from our tech world.

And yet A2 (DCS~5%) looks very similar to VPM-B (as you would expect two deep stop profiles to look). Also A1 (DCS~1.6%) and GF are more similar.

For review,

1. Supersaturation Heatmap -- The heat map supersaturation similarities between A2 and VPM-B are self-evident.

2. Total Integral Supersaturation. Clearly A2 (DCS~5%) and VPM-B are closer. And A1 (DCS~1.6%) and GF are closer as well. The ISS of A2 is about 25% higher than A1, VPM is about 19% higher, and GF is about 5% higher than A1. The difference in ISS between A2 and A1 is the best explanation of the difference in observed DCS according to the NEDU scientists.

3. Supersaturation Exposure by Tissue Compartment. It's clear that both A2 and VPM-B protect compartments 1-3 similarly, especially compared to A1 and GF. The cost of this "protection" is the ballooning up of the exposure in the slower tissue compartments 9-12. Clearly A2 and VPM-B would be expected to perform more alike than A1 and GF.

There are other similarities that have been posted. But I think this clearly establishes A2 and VPM-B as similar. About the same thing was said by Dr. Doolette in this presentation -- see minute 34 to 38.

 

[scubadada]

Hi @rossh

Why then, in MultiDeco, is the surfacing for VPM-B, limited to the more conservative of VPM-B or Buhlmann ZH-L16C? One has the option of choosing a GF as high as 100, or as low as 70. I have seen examples of native VPM-B resulting in surfacing with a GF in excess of 100. @UWSojourner had an example, earlier in this thread, with a VPM-B+2 profile surfacing with a GF of 107.

View attachment 400807

@rossh

I would appreciate an answer to my question. Isn't GFS an attempt to fix VPM-B?

Thanks much, Craig

 

[rossh]

@rossh

I would appreciate an answer to my question. Isn't GFS an attempt to fix VPM-B?

Thanks much, Craig

Hi,

The VPM-GFS was an invention by Shearwater. It runs two calculations and picks the longest of the two. The GF one is a 70/70, or 80/80 kind of thing. That caused the GF part to become effective on longer dives only. For dive of 2.5 to 3 hours or longer, the dive shallow end is GF limited. For lesser dives, it was a plain VPM-B dive. This GFS was very much like the VPM-B/E idea.


Added:

If one takes a step back, and thinks about this GFS in the light of the "helium penalty". The dives under 2.5 hours, usually air or small helium amounts, are limited by VPM-B. Dives over 2.5 hours will likely use high helium content, but now its thought they are too long. ie. too much ZHL based helium penalty in there making them too long. So is VPM-B right all along?

.

 

[rossh]

And yet A2 (DCS~5%) looks very similar to VPM-B (as you would expect two deep stop profiles to look). Also A1 (DCS~1.6%) and GF are more similar.

For review,

1. Supersaturation Heatmap -- The heat map supersaturation similarities between A2 and VPM-B are self-evident.

View attachment 400814

2. Total Integral Supersaturation. Clearly A2 (DCS~5%) and VPM-B are closer. And A1 (DCS~1.6%) and GF are closer as well. The ISS of A2 is about 25% higher than A1, VPM is about 19% higher, and GF is about 5% higher than A1. The difference in ISS between A2 and A1 is the best explanation of the difference in observed DCS according to the NEDU scientists.

View attachment 400815

3. Supersaturation Exposure by Tissue Compartment. It's clear that both A2 and VPM-B protect compartments 1-3 similarly, especially compared to A1 and GF. The cost of this "protection" is the ballooning up of the exposure in the slower tissue compartments 9-12. Clearly A2 and VPM-B would be expected to perform more alike than A1 and GF.

View attachment 400817

There are other similarities that have been posted. But I think this clearly establishes A2 and VPM-B as similar. About the same thing was said by Dr. Doolette in this presentation -- see minute 34 to 38.

I wrote above in post #212.. "..., it's your home made and invalid measuring / comparison methods and graphs at the center of this problem. These have been used to widely promote a fallacy position."

I was referring to the diagrams Kevin created in the post quoted above. Those are the basis of a great deal of invalid assumptions.


1/ The VPM-B+7 that is used in the diagrams above, does not exist, no one can make it, you cannot buy it. It's something that was created by Kevin for this purpose only. It's a stretched out exaggeration, and used to make a non-existent comparison. We are not allowed to just make stuff up.


2/ The use of heatmaps are a relative measure but not an absolute measure. These maps have no dimensions, and its easy to be selective to cause them to show what ever you like. We must keep to standard comparison methods, using standard dimensions and baselines.


3/ Kevin's has created his own ISS methods: see post #167. His ISS method has not been tested, proven, or shown to be valid or fit for this purpose.... We are not allowed to just make up measures.


The above invalid information and methods, is assisting in the promotion of a fallacy position.


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


This is what happens when we use real science measures, real plans, and valid comparison methods:

A look at the similarity of supersaturation patterns.

It can be seen above, that the A2 and tech profiles are not related. The 40/75 approach and VPM-B +3 are quite similar.

Careful readers may notice that the scientist's involved have not offered, shown or presented a scientific or mathematical connection from nedu test to VPM-B, or to any other tech profiles. Instead there are only numerous opinion based explanations and theories made. I have shown and discussed those in post #116

.

 

[Patoux01]

1/ The VPM-B+7 that is used in the diagrams above, does not exist, no one can make it, you cannot buy it. It's something that was created by Kevin for this purpose only. It's a stretched out exaggeration, and used to make a non-existent comparison. We are not allowed to just make stuff up.

Limits on the parameters of VPM ?

That's been discussed rapidly there, I did not succeed in running the original fortran code as it broke my IDE at the time and could not deal with that at that time. I might look further into it someday... Surely one could plug in the right parameters in one of the various C implementations of VPM.

 

[Diver0001]

I wrote above in post #212.. "..., it's your home made and invalid measuring / comparison methods and graphs at the center of this problem. These have been used to widely promote a fallacy position."

This is indeed what you wrote. Can you explain why not a single decompression scientist in the world is saying the same thing?

As I said above, the NEDU study is one of the most widely accepted and definitive comparative studies ever done between the workings of bubble models as compared to the workings of Buhlmann.

Can you explain why you are alone in your belief that this is not the case?

I am interpreting your choice to refuse to answer these questions (they have been asked several times) as a tacit admission that you have no grounds upon which to argue your stance. Is this the case?

R..