NEDU Study

[UWSojourner]

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.

Perhaps those "careful readers" should listen to Dr. Doolette (NEDU) present the scientific and mathematical connection between the NEDU study and VPM-B in this presentation. See minute 34:30-38:50.

When Dr. Doolette talks about "adding together the area under these curves for the shallow and fast compartments" at minute 36:30-36:45 he is simply describing the calculation method of the ISS chart shown below. Clearly A2 and VPM-B are closely matched, especially in comparison to A1 (lower DCS risk) and GF.

Also, Dr. Neal Pollock has stated:

"The impact of deep stops is not that they target some different physical reality. It is actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving."

That statement describes in words what the heat map shown below shows pictorially. The extra time spent deep (see the low superstaturation colors early in the ascent for A2 and VPM-B) results in the higher degree of decompression stress at the surface (see the reddish colors upon surfacing for A2 and VPM-B).

In contrast, the higher supersaturation allowed early in ascent for A1 and GF allows surfacing with less decompression stress at the surface. The net result for the deeper stop profiles A2 and VPM-B is an overall higher level of decompression stress as shown by the ISS chart above.

 

[Dr Simon Mitchell]

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.

Ross,

Part of the reason why your credibility suffers is that you continue to make claims like this (and the ones below), with no referral to supporting data or references. In contrast, your claims can often be demonstrated to be overtly incorrect by drawing on supporting data or references from multiple sources.

Integral supersaturation is not "home made" and there is nothing wrong with what Kevin is doing with ISS. It is used as a basis for several US Navy probabilistic decompression schedules as clearly articulated here:

Deep stops debate (split from ascent rate thread) - Page 20

....and it is used for much the same purposes as Kevin puts it to in the NEDU study reported by Drs Doolette, Gerth, and Gault (see, for example, page 17 where they say)....

The DSS and sum (fast + slow compartments) integral supersaturation of the tested shallow stops and deep stops dive profiles are also indicated on Figure 7A

Bizarrely, given your claims, It is a central component of the way VPB-M works, as illustrated here:

Deep Stops (rebreather dive charts) - Page 8

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.

No, we are not allowed to "make stuff up" Ross. Which is why you cannot say that VPM-B+7 does not exist or that no one can make it. Plus 7 is clearly within the original model parameters (critical radii 0.7 - 1.2 microns) as illustrated here:

VPMechanics4.nb

...and the contextualization of a critical radius of 1.01 (which represents VPM-B +7) with the present debate is provided here:

Deep stops debate (split from ascent rate thread) - Page 62

And Kevin was not the first to use it... the original comparison with VPM-B + 7 and the NEDU results was made by Dr Doolette here:

Deep stops debate (split from ascent rate thread) - Page 20

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.

The heat map comparisons of supersaturation patterns are perfectly valid when used to compare decompression from dives with identical depths, bottom times and breathing gas; that is, where you start with identical gas loads and distributions in the various tissues. They are also useful for comparing patterns of tissue supersaturation during decompression.

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.

Addressed above. Integral supersaturation is what it is. Kevin has not made up his own methods. You just don't like the results.

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

The position that I am taking is well-supported by logic and the available data. Your position, in contrast, is supported by nothing.

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

The science to connect the NEDU study to VPM was first discussed in the NEDU study report where (using integral supersaturation) they compared their profiles to 500,000 other possible profiles, some of which inevitably emulated VPM. A more specific comparison with VPM was presented by Dr Doolette (the NEDU study lead author) at that link to RBW above. Finally, the connection between more typical tech dive profiles prescribed by VPM and alternative approaches has been promulgated by Kevin, using essentially the same integral supersaturation approach as Dr Doolette. All of these comparisons have concluded the same thing.

There is an obvious thread of scientific methodology and logic throughout this sequence and you can deny it as much as you like, but there certainly is science to connect the NEDU study and VPM.

Simon M

 

[rossh]

Thanks for the reply @rossh

I've only been using MultiDeco for a little less than a year and have mostly used Buhlmann. The debate around the NEDU study has led me to look at VPM-B also. I assume you have included VPM-B +GFS so that divers using Shearwater computers can plan their dives on MultiDeco. Why do you think Shearwater invented this Haldanian add on to VPM-B that allows choosing a surfacing GF of 70-100? Do you think they believe that the surfacing GFs of native VPM-B are too aggressive? In my initial question, I referenced an example where the surfacing GF of a VPM-B +2 profile was 107.

Using the NEDU dive as an example, at +2, VPM-B, VPM-B/E, and VPM-B +GFS/100, all give the exact same decompression profile. Starting at +GFS/95, additional time at shallow stops is added, leading me to believe that native VPM-B has a surfacing GF in excess of 95, but below 100. At +GFS/80, there are 22 minutes of additional decompression, 20 minutes of it at 10 feet. I bring up this last point because the NEDU dive has essentially the same run times using VPM-B +2 and Buhlmann ZH-l16C 50/80.

Your answers to my questions will help me understand this complex and interesting topic.

Good diving, Craig

The Shearwater GFS was created at a time, when VPM-B/E was popular. The B/E is proprietary to me. So they wanted something to do the same job as B/E, and the GFS is what they made.

This fussing of GF end values and all that, only came later after this fuss over deep stop and the nedu test started.

The negative variation your concerned about, only starts after the high helium makes ZHL plans go really long. It was called the helium penalty 10 years ago and deemed to be unnecessary. It seems we are back here again today..

 

[Shearwater]

The Shearwater GFS was created at a time, when VPM-B/E was popular. The B/E is proprietary to me. So they wanted something to do the same job as B/E, and the GFS is what they made.

This fussing of GF end values and all that, only came later after this fuss over deep stop and the nedu test started.

The negative variation your concerned about, only starts after the high helium makes ZHL plans go really long. It was called the helium penalty 10 years ago and deemed to be unnecessary. It seems we are back here again today..

First there was VPM. After some early tests of the implementation, it was clear that as the dives got bigger, the algorithm was too agressive. VPM-B was the result. When it became clear that even VPM-B still wasn't conservative enough for "expedition level" dives, VPM-B/E was born. When we implemented VPM-B from Erik Baker's work, we had to provide the diver with a way of making the surfacing values more conservative. VPM-BE was Ross's work, but it was clear what needed to be done. GFS is our implementation of B/E. It has and had nothing to do with the helium penalty.

This was all discussed on the mailing lists, but I don't have an archive of the nwdesigns rebreatherlist mailing list. Maybe someone else can find the original discussions. Ross knew that the surfacing values of VPM-B were too aggressive on big dives a decade ago.

Bruce

 

[rossh]

First there was VPM. After some early tests of the implementation, it was clear that as the dives got bigger, the algorithm was too agressive. VPM-B was the result. When it became clear that even VPM-B still wasn't conservative enough for "expedition level" dives, VPM-B/E was born. When we implemented VPM-B from Erik Baker's work, we had to provide the diver with a way of making the surfacing values more conservative. VPM-BE was Ross's work, but it was clear what needed to be done. GFS is our implementation of B/E. It has and had nothing to do with the helium penalty.

This was all discussed on the mailing lists, but I don't have an archive of the nwdesigns rebreatherlist mailing list. Maybe someone else can find the original discussions. Ross knew that the surfacing values of VPM-B were too aggressive on big dives a decade ago.

Bruce

Bruce Partridge on the decolist, on original VPM....

"I have over a hundred dives on VPM. Ghassem Gheissary probably has more
dives, and certainly has more deep dives than I do. Its real. It works. I find the profiles to be intuitively satisfying. How many times have we discovered that major mathematical principles produced shapes that looked good. How's that for a stupid reason for diving VPM? It suggests that decompression should be a segement of a curve."

The deco list: RE: VPM Question from Bruce Partridge on 2001-05-22 (DecoList (2001))

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[RainPilot]

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A ScubaBoard Staff Message...

Several posts about software have been removed as they are not on the topic of the NEDU test. There are several threads addressing these issues, please use them. Again, for those in the cheap seats:

NO POSTS NOT DIRECTLY RELATED TO THE NEDU TEST WILL BE ENTERTAINED IN THIS THREAD.

Thanks for your cooperation.

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[fsardone]

Bruce Partridge on the decolist, on original VPM....

"I have over a hundred dives on VPM. Ghassem Gheissary probably has more
dives, and certainly has more deep dives than I do. Its real. It works. I find the profiles to be intuitively satisfying. How many times have we discovered that major mathematical principles produced shapes that looked good. How's that for a stupid reason for diving VPM? It suggests that decompression should be a segement of a curve."

The deco list: RE: VPM Question from Bruce Partridge on 2001-05-22 (DecoList (2001))

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Ross,
once again anecdotal evidence good for conversation at the pub while drinking beer, not in a scientific discussion against experiment in a controlled environment.
Basis of scientific method is independent repeatability to verify outcome.

Cheers

 

[Shearwater]

Bruce Partridge on the decolist, on original VPM....

"I have over a hundred dives on VPM. Ghassem Gheissary probably has more
dives, and certainly has more deep dives than I do. Its real. It works. I find the profiles to be intuitively satisfying. How many times have we discovered that major mathematical principles produced shapes that looked good. How's that for a stupid reason for diving VPM? It suggests that decompression should be a segement of a curve."

The deco list: RE: VPM Question from Bruce Partridge on 2001-05-22 (DecoList (2001))

.

That was 14 years ago, Ross.

Yes. Virtually all of the tech diving community thought this was the way forward. Others on this thread have said they were supporters. NEDU did the tests because they were considering changing to a bubble model. They would never have done the trial, which was expensive and could potentially harm their divers, if they didn't think that there was a strong possibility that distributing the decompression differently would create more efficient decompression.

It is your defense of deep stops in the face of strong new evidence that is baffling me.

Bruce

 

[rossh]

That was 14 years ago, Ross.

Yes. Virtually all of the tech diving community thought this was the way forward. Others on this thread have said they were supporters. NEDU did the tests because they were considering changing to a bubble model. They would never have done the trial, which was expensive and could potentially harm their divers, if they didn't think that there was a strong possibility that distributing the decompression differently would create more efficient decompression.

It is your defense of deep stops in the face of strong new evidence that is baffling me.

Bruce

Bruce, in the 17 years I have been making deco software, and watching all this, there is one underlying thing... the ever present creeping and exaggerations of deco times. Last years "standard" becomes this years bad practice. It continues today.

In 2001, you and some others were happy with VPM,
Then for another 12 years we were all happy with VPM-B, and B/E or GFS for the really big dives.
Today a small portion think its all bad and wants to exaggerate even further.

What these people seek today, is more than double what we did in 2001. Where is the justification?

Has human physiology changed? No.

Has there ever been an increasing trend shown or visible in the treatment numbers? No.

So why do they keep exaggerating for no apparent good reason? Its not needed or justified from a deco perspective, so I can only assume its for mundane reasons. Its more than double time now, so any reasons for deco profile stress has long since been left behind.

Where or when is all this unnecessary time creeping going to stop?

.

 

[fsardone]

Has human physiology changed? No.

Has there ever been an increasing trend shown or visible in the treatment numbers? No.

So why do they keep exaggerating for no apparent good reason? Its not needed or justified from a deco perspective, so I can only assume its for mundane reasons. Its more than double time now, so any reasons for deco profile stress has long since been left behind.

Where or when is all this unnecessary time creeping going to stop?

.

Ross,
you are mixing two things here.
Physiology has not changed, but our knowledge of it did.
Risk apetite of our society has changed and therefore acceptable risk level has gone down.

As a result times have gone up.
My father was diving an oxygen CCR at 15 meters in the 60s. He went dumb fat and happy at 2.5 bar PPO2, because the Italian Navy did it during the war. Even if he did not wash out all of the N2 and still had some to dilute the oxygen, woudn't you agree that is unsafe? And since he did it would you do it? I learned diving from him, should I do it?

Nowadays, we cannot accept bad outcomes, specially if those involve type II DCS. We have an aging divers population. What was demed safe then is not anymore today. The NEDU study showed where the risk is: extending the deeper portion of the deco profile.

That has been proved with scientific methods and no talking in the forums will reverse that. Only a repeatable experiment in controlled environment can have a chance.

Cheers