VR3 BUH or VPM

solocavediver

Hello all - I only just noticed this thread, which was relevant to me as I recently did my first dive on VPM based deco. I previously reckoned that the difference was not going to be much 'til I went deeper, so VPM versus Buhlmann became an issue when I decided to go into the Eagles nest sinkhiole in Florida (cave starts around 200'/60m). I reckon the mathematics is better with VPM (I can explain this but since I'm Prof. Read in Pure Mathematics, are you sure you want me to?) but Buhlmann is tried and tested; so I used VPM but with over-the-top safety factors. Still shorter than Buhlmann deco for a dive to 250' though.

Full preparation process for this dive is on <Lone Eagle in the Nest>.

Cheers,

Charles.

rossh

.
Do your own homework. Your not getting any detailed specs to look at though .. no body owes you an explanation.

Cedric Verdier on a Meg and VPM-B/E along with Ben Reymenants on OC, do a team dive to.....

The site does NOT say what Ben used for a deco model. I've heard you lot trying to swing ZPlanner into that role.... but I don't trust any report on this matter. Hence it will stay open.

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Regards, Ross Hemingway

www.v-planner.com

aainslie

Two things here:

1) EVERY model has been revised repetedly. THis has been said a hundred times in this thread, but one more time - EVERY MODEL HAS BEEN REVISED REPEATEDLY.

2) What evidence do you have that VPM B/E is "still grossly short of acceptable"?

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Andrew Ainslie

UWSojourner

Well, Ross, I certainly don't believe you've turned into Attila-the-Bend . This discussion might have been more interesting as a discussion. That's a bit much to ask given the players.

However, if you are gathering data Ross, maybe you could turn it into a true study when it becomes a large enough data set? I bet an independent person in academia would help in the analysis. Real data would be valuable to the discussion and to those who are actually using VPM. The shrillness of those attacking you might be a bit more muted if actual data could be presented.

Maybe that's one thing we can all agree on ... an actual study on the effectiveness of VPM would be a good thing.

Serge

Mike, I understand your point. Did you understand mine? I know the validation process - the plan, risk and impact assessments, user and functional requirement specs., functional and detailed design specs., qualification and reporting, traceability matrices, summaries, and defending my findings to the regulatory agencies. I hear the v-word loosely thrown around, but few actually know what it means. If you're referring to data collection, then - yes, there are substantial Buhlmann data collected; and there lies the flaw. The Buhlmann is completely reliant on hard data. The more you veer away from the test parameters, the more data become ambiguous. My point was how well these data approximate actual dive conditions, and more specifically in the modern world given the tools available at our disposal. And that was my only point.
See above.
I never said VPM is not guessing. What I said was it attempts to approximate, this is different. Exactly how deep was Buhlmann "validated" to, and how deep do you dive? Do you dive multi-level profiles, and was Buhlmann "validated" for the same profiles?
Of course! This makes perfect sense. The model confirms what we already know. Further it not only confirms the data, but the validity of the model. Is the model perfect? I don't think anyone is saying that. But if it works well, then it is no longer bound by the underlying data, but is free to be implemented in a wide range of applications.
That's a fair statement.

Look, I think it's great that you take the time from your busy schedule to debate this important topic. You have been very objective and analytical in your responses, and I appreciate that; which is more than I can say for your side-kick, who undoubtedly has a lot of deep diving experience, but tact of a bull in a china shop. - Serge

diverklondike

Couple items...

Item 1 is correct...

Item 2 is a pretty scary thing to have to ask since we know the origional vpm was... b was better... b/e not sure but closer... What's worse is we know for the most part that almost everyone has their own approach to pad things because we don't trust them. For the most part we all agree that deep stops are good things but we don't have a whole lot of confidence in any one approach to calc the entire dive.

M

scuba_phil

One note about revising models. I have had owned both a VR3 and the new X1 Liquidvision. On the X1, at least I can update the software - not true on the VR3 (you can but it is a major pain). Thanks Ross/Eric!, you delivered a product that work the way I want it to work!! VR3 promised it but never delivered!

Back to eating popcorn and watching this thread

Phil

Gasman

Thought it might be worth while clarifying a few points on this thread.
The first is that one really shouldn’t talk of “fast” and “slow” tissues with regards to models. When we do a big dive the slow ”tissues” of the model control the dive… yet the DCI symptoms are the same. In Haldane’s original paper, the are fast and slow compartments of the gas exchange model which was a mathematical description of one or more critical tissues (i.e. where the bends would occur first) and made allowance for the variations in gas uptake and elimination within that (those) tissues caused by variations in regional blood flow.

(1) The gas models in both Buhlmann (and thus VPM) is the same… a series of mathematical exponentials which act together to produce an overall curve of projected gas uptake and elimination. Now, in the case of Buhlmann, the M lines which describe the decompression limits were initially derived by putting people into a recompression chamber and finding out when they developed symptoms. From these points, using real people, the series of M lines were mathematically drawn and the table derived. Most of the experiments were done in the air range, but there were some using heliox. If I remember it correctly, the deepest point used was 1000 ft.

(2) or there abouts. So, while there model is mathematically calculated, it is derived from manned experimentation. The mathematical model then extrapolates between the data points. This was then tested in a series of manned dives. Again, most of these dives were in the air diving range, and some were conducted at altitude. From there the M values were “tweaked” to make the model more conservative and correct for cases where it was seen to be wanting. Further field testing eventually resulted in the ZHL-16 series of models.

(3) There is no suggestion that the model is a mathematical model of the physiological processes in the body. However, as it is based on manned data there is a high probability that it will work. This is further bolstered by a large amount of supportive data from workers such as Hempleman which would suggest that this linear M value type relationship is valid to about 300ft.

(4)However, people like to have neat mathematical models … and a series of M line for each compartment is not very physiological. Yount et al using a mathematical model based on bubble behaviour, produced a comprehensive limiting value relationship which varied with both depth and time of the dive.

(5) This was melded with the Buhlmann gas kinetic model to produce the early versions of VPM.

(6) The output of this model in the air diving range is quite conservative when compared to Buhlmann with deeper initial stops and longer total decompression times.

(7) As such the model was greeted with much enthusiasm as here was a comprehensive descriptive model that did away with all those M lines and a and b values as replaced them with something based on bubble behaviour. However… the model is not an accurate physiological representation of what is going on the body….. things are far more complicated than the simplistic maths in this model. Of course…. That doesn’t mean that it will not work within certain boundaries…. The trick is to know the boundaries!Now people have repeatedly asked why there has not been manned testing of the new models. The reasons are reasonably straight forward. The incidence of DCI will probably be low, therefore the number of trial will need be high to detect the true rate, therefore the cost will be high. Who will pay? With saturation diving worked out, the money to develop tables to the depth that we are interested in dried up… hance no or little research. The problem of anecdotal evidence is, as my friend DT says, “the pleural of anecdote is not evidence”. Anecdote while interesting has too many biases (e.g. reporting bias) to be good enough to base opinion on. I know that few if any of the many people that I have treated for DCI and were using VPM have ever reported it to Ross. It is not therefore surprising that he and others would assume that VPM is fine. Additionally, some or indeed all of those people may have developed DCI if they had used Buhlmann…. I can’t definitely say one way or the other. All we can say is that they did develop DCI , in several cases very severe DCI.</p>

Andrew

1. Boycott D, Damant G, Haldane J. The Prevention of Compressed-air illness. J Hyg. 1908; (8): 342-443.
2. Keller H, Buehlmann A. Deep Diving and short decompression by breathing mixed gases. J Appl Physiol. 1965; 20(6): 1267-70.
3. Buhlmann AA. Decompression-Decompression Sickness. English ed. Berlin: Springer-Verlag; 1984.
4. Hempleman HV. Investigation into the decompression tables. In: RNPRC, editor.: MRC, London; 1952.
5. Yount DE. Application of a bubble formation model to decompression sickness in rats and humans. Aviat Space Environ Med. 1979 Jan; 50(1): 44-50.
6. Yount DE, Hoffman DC. On the use of a bubble formation model to calculate diving tables. Aviat Space Environ Med. 1986 Feb; 57(2): 149-56.
7. Yount DE. The Global Approach to table testing. In: I N, E.H. L, editors. Decompression in Surface-based Diving. Bethesda: Undersea and Hyperbaric Medical Society Inc; 1987. p. 122 - 9.
Gene may well have many of these as they are fairly well known references.

Gasman

PS Sorry about the above post... I can't seem to get it to format Andrew

Lancer4545

Thanks for the input Andrew.

Your posting makes a lot of sense......Specially the bit......

"The reasons are reasonably straight forward. The incidence of DCI will probably be low, therefore the number of trial will need be high to detect the true rate, therefore the cost will be high. Who will pay? With saturation diving worked out, the money to develop tables to the depth that we are interested in dried up… hance no or little research."

Regards,

Lance

(Can't get it to quote.....May have something to do with the size of the post)

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