NEDU Study

[Kevrumbo]

So again what do you tell those who actually get bent on VPM-B, @rossh ?

Hypothermic Stress? Multi-day Fatigue? Some other "bad practice" oher than "innocent" VPM-B???

Or:
A finger should have been pointed directly at the problem above and to name where it comes from. These concerned scientists should be directing there attention on this RD and the source of these weak theories. But sadly, the current antagonists and friends have never once mentioned RD or DIR theory as the culprit. Instead the focus has been on innocent VPM-B and to use it as scape goat and to blame it for other peoples problems, and to tarnish VPM-B with other peoples model theories.

Or:
VPM-B (like ZHL) is a proper model, and it follows the proper formula for gas kinetics. These do not suffer the gas imbalance issues as the ad-hoc RD methods do. VPM-B, ZHL, follow the same basic gas kinetic formula as used in the successful nedu A1 profiles, and all these models are correctly orientated with the nedu test results.

Or:
The underlying message from the nedu test, was to keep following, the stick with the basic gas kinetic formula. ZHL and VPM-B already do this, and follow those same well tested and accepted formula. So... nothing is wrong, nothing to fix.

Or:
The nedu BVM(3) "bubble" model is a shallow stop design, a TDBM design. It has elongated shallow stops and includes a most irregular gas kinetic pattern, that are not present or representative of in any tech models.

Or:
Please do not get conned or further assist in this game of "guilt by word association" ... the words "bubble", "deep" are being used as a metaphor and substitution for actual science.
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The practical point and caveat of the NEDU Study is not that the decompression profiles tested experimentally in the study's object paradigm are non-representative of "real world" deco profiles as performed by civilian sport technical divers, but that the same disadvantageous pattern of Slow Tissue Supersaturation and potential increased risk of DCS is inherent to bubble models with prescribed deep stops profile distributions.

 

[Dr Simon Mitchell]

Nothing matches the failed A2 profile. The A2 does not follow conventional gas kinetic limits.

As has been pointed out to you many times, other profiles relevant to tech diving (including decompressions calculated using VPM-B +4) that place heavier emphasis on deep stops produce the same disadvantageous tissue supersaturation patterns as those produced by A2.

The underlying message from the nedu test, was to keep following, the stick with the basic gas kinetic formula. ZHL and VPM-B already do this, and follow those same well tested and accepted formula. So... nothing is wrong, nothing to fix.

Ross, this is like trying to claim that mathematicians with completely different beliefs on some construct actually agree with each other simply because they used the same brand of calculator.

Just so everyone is clear, constructing a decompression algorithm (broadly) involves two steps:

Step 1: Calculate gas supersaturation in different theoretical tissues as you ascend. Pretty much all decompression models use similar formulae for this purpose. These are what Ross is referring to as the "well tested and accepted formulae". They are indeed "accepted" though they are only estimates of reality and not particularly well tested.

Step 2: Apply some sort of rule about how much supersaturation (calculated using the "well tested and accepted formula" in step 1) is tolerable in the various tissues and allow ascent to proceed according to that rule. Once tolerable supersaturation is reached, you stop and off gas for a while, then resume the ascent. This is where models differ substantially and why they produce different ascent profiles. Ross's own diagrams earlier in this thread clearly demonstrate this. The gas loading in the tissues for all the models represented by those curves were calculated using the same "well tested and accepted formulae" mentioned in step 1, but the curves all look different because of different beliefs around how to apply step 2.

Of relevance, bubble models hold that limiting supersaturation earler in the ascent to try to prevent bubble nucleation is important so they impose deeper stops. Gas content models like Buhlmann have ascent rules based on other considerations with some empirical adjustment and typically allow greater supersaturation in the fast tissues early, and so longer ascents to the first stop.

With all of this in mind, to imply that different models are comparable simply on the basis that they use a similar approach to calculating gas supersaturation in tissues (step 1) is clearly ridiculous and I really cannot understand why Ross is attempting to do this. I cannot believe that he doesn't actually understand why this logic is flawed so I conclude it is a deliberate attempt to muddy the waters and create uncertainty.

Simon M

 

[rossh]

So again what do you tell those who actually get bent ...

Today most people already have a pretty good idea of what is the specific causes to their situation. Most often its a preparation or procedure or some event or trigger within the dive....

Fortunately most have moved past the "blame the model for everything" mentality, and realized there are many outside influences and causes. Neal Pollock puts on an excellent presentation on Decompression stresses, and includes this graphic of potential causes (here). Study it, keep it, and use it as a self-check list when ever trouble strikes.


*****


All deco model approaches in use today, have reasonable inbuilt margins and plenty of conservatism available, so few people are really pushing the envelope or getting injured directly from excessive profile stress. Only the really aggressive or old fast shallow model approaches can do that.


Deco treatment numbers have been in decline across the board, for the last 15 years, and that includes tech diving. Meanwhile during the same period, tech diving participation has grown exponentially. So the simple conclusion would be, we have all collectively improved our methods and lowered our risk. The reason are many - deeper stops with longer deco time all round. Better training, mixes, procedures, methods and improved understanding all round.

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..... but that the same disadvantageous pattern of Slow Tissue Supersaturation and potential increased risk of DCS is inherent to bubble models with prescribed deep stops profile distributions.

That is the lie that keeps being promoted - the excuse - the opinion, but its scientifically invalid.


The "fast tissue protection" difference argument simply does not exist in the nedu test. Both test profiles have about the same (lack of) "fast tissue protection".

And ..... ALL real profiles have much less of than both the nedu, including all your GF plans.

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Here is the full ascent supersaturation graphs. These are made using the same formula from the nedu test - the generic parallel, mono-exponential gas tracking cells. (These are also inside ZHL and VPM-B).

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This chart compares the alleged "...disadvantageous pattern of Slow Tissue Supersaturation.."

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OK, so from all this.

A/ the nedu test did not protect the fast tissues, in either profile,
C/ all real tech plans have more finishing supersaturation, than both nedu tests.
B/ all real tech profiles have much smaller slow tissue variance than the nedu test, including the preferred GF 40/75.


Kevin, these excuses and fallacy ideas used to justify and connect the nedu test to tech profiles, are just not there.... A whole lot of made up nonsense has been kicked around, without doing the proper homework to verify it.


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Footnote:

The above charts are made with MultiDeco. This is the only available tool that allows you to expose and draw both the supersaturation, and the tissue gradients. It also draws the surface surface supersaturation decay as well. You can also turn on drawing of individual cells, and watch the rise and fall those parts (not shown above).

The formula used are the industry standard mono-exponential gas kinetics (i.e 1/2 time cells). This are common to all parties concerned: the nedu test methods, VPM-B and ZHL-C, and provides a convenient way to cross compare all these.

The above shows the most prominent or leading cell, and draws this dynamically just as the divers experiences it (and as shown in the nedu test).



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[Dr Simon Mitchell]

Deco treatment numbers have been in decline across the board, for the last 15 years,

Numbers by themselves mean nothing. You need a numerator (numbers of cases) and a denominator (the number of divers or, even better, dives) to make any sense of changes in the numerator (numbers of cases). It is even possible for numbers of cases to decline even though the rate of cases has increased. We published a study 3 years ago showing that number of cases (all diving) had declined over the last 15 years, BUT numbers of new divers trained had declined at a similar rate. In other words, the decline in DCS cases could just be due to a decline in numbers of divers. This paper has been pointed out to you multiple times.....

HAAS RM, HANNAM JA, SAMES C, SCHMIDT R, TYSON A, FRANCOMBE M, RICHARDSON D, MITCHELL SJ. Decompression illness in divers treated in Auckland, New Zealand 1996-2013. Diving Hyperbaric Med, 44, 20-25, 2014

.....yet you still repeatedly talk about declining numbers of cases on these forums with no clarification or admission of the potential lack of relevance to any aspect of your argument. It is like deliberate, repeated, yet provable misinformation.

and that includes tech diving.

Can you please point out the data that demonstrates a declining number of cases of DCS among technical divers as a separate group?

Meanwhile during the same period, tech diving participation has grown exponentially.

Can you please point out the data that demonstrates that numbers of tech dives (or divers) have grown "exponentially".

The "fast tissue protection" difference argument simply does not exist in the nedu test. Both test profiles have about the same (lack of) "fast tissue protection".

Ross, your diagrams are uninterpretable because they are not properly labelled and they do not identify the tissues being examined. Moreover, they appear to suggest a lack of understanding of how evaluation of "supersaturation" needs to be applied in comparison of the decompression stress in tissues.

Supersaturation at a particular point in time is tissue gas pressure minus ambient pressure. Your evaluation of "fast tissue protection" appears to be derived from a subtraction of the peak supersaturation in the fastest tissue(s)? from the supersaturation in ??other tissues 30 minutes later. Supersaturation in a tissue is calculated from a baseline of ambient pressure - not tissue gas pressure in another tissue. Moreover, to appreciate the drive to form bubbles resulting from supersaturation you must also account for the duration of supersaturation. Thus, the correct way to appreciate protection of tissues from a tendency to form bubbles (or not) is to consider an integral of supersaturation and time specifically in the tissue(s) of interest as UWSojourner did in this diagram for the 3 fasted Buhlmann tissues:

Deep stops debate (split from ascent rate thread) - Page 108

This clearly shows that the NEDU deep stops profile did protect the fast tissues from supersaturation in comparison to their shallow stops profile as any profile that imposes deeper initial stops inevitably will. In addition, the diagram shows that the NEDU deep stops profile provided very similar fast tissue protection to VPM-B on high conservatism.

Simon M

 

[UWSojourner]

Neal Pollock puts on an excellent presentation on Decompression stresses, and includes this graphic of potential causes. Study it, keep it, and use it as a self-check list when ever trouble strikes.

Dr. Pollock also had some very good things to say regarding your interpretation of science. See this post.

The "fast tissue protection" difference argument simply does not exist in the nedu test. Both test profiles have about the same (lack of) "fast tissue protection".

This is just simply not true. Your argument regarding this, and other ideas, always disregards the TIME you're exposed to supersaturation. Given that VPM-B's methodology essentially does the same (see this post and related links), it's not that surprising that you'd make the same mistake.

When the time-exposure to supersaturation is considered, then NEDU's deep stop profile (A2) and VPM-B+7 are virtually identical in "protecting the fast tissues". But as Dr. Mitchell pointed our here, protecting the fast tissues does not seem to be that helpful in reducing DCS risk. NEDU's shallow-stop profile (A1) had much lower risk than A2 even though it is far less concerned with "protecting the fast tissues" than was VPM & A2.

 

[rjack321]

I can't believe we have to rehash this all over AGAIN. As if hundreds of pages on 4 or 5 different forums is somehow inadequate.

 

[rossh]

I can't believe we have to rehash this all over AGAIN. As if hundreds of pages on 4 or 5 different forums is somehow inadequate.

Well, lets see.... Some people here are still trying to dodge the truth, and still trying to prop up the argument with the invalid graphs and made up measures, quoting phony model designations, manipulation and playing guilt through word association games, and on it goes. The marketing effort is alive and well.


Do you want your deco to be based on dimensions derived from vivid imaginations, or actual valid science and proper modelling techniques?

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[Diver0001]

Do you want your deco to be based on propaganda and dimensions derived from vivid imaginations....

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Of course not. This is why people are listening to the NEDU study and why we are so happy that Simon and David have taken the time to explain their findings.

Ross, In all of these discussions we either have to believe that you honestly do not understand how important the NEDU study is for clarifying the reality of the bubble paradigm or you have some agenda to try confusing people.

R..

 

[rossh]

Of course not. This is why people are listening to the NEDU study and why we are so happy that Simon and David have taken the time to explain their findings.

Ross, In all of these discussions we either have to believe that you honestly do not understand how important the NEDU study is for clarifying the reality of the bubble paradigm or you have some agenda to try confusing people.

R..

Do you see the charts above... you see how their position and criticism of VPM-B is not valid? Their own description of the nedu test internals is not right, and the implied connections they make from that, do not exist. They did not do their homework.

The science is on my side here.... I insist on the truth prevailing.... because I have to make the software that produces these deco programs, and there is no room for vague math and vivid imaginations in that.

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[mmadiver]

Ross, want to win this debate? Write up your findings, get it peer reviewed, and publish it. It would be a hell of a lot quicker than debating this over and over for YEARS....