Whats Wrong with VPM-B

[Blackwood]

GF is not a model. GF is only a mechanism to morph a model into something else.

I've always thought of GF as applied to buhlmann as not a way to morph the model, but rather a way to decrease the allowable extremes of exposure. If I don't want to see the full critical gradient as assumed in buhlmann, I'll use GF high to knock it down. If I want to slowly creep up on it, I'll use GF low (yes, deeper stops).

Out of curiosity, how are the various + conservatisms applied to VPM within Vplanner? Are they each discreetly coded algorithms? Or are they knockdown factors on the one algorithm?

 

[Shearwater]

Ross,

I guess I need to clarify the science part of my post.

Your position appears to be that VPM is the ONLY algorithm that works and that VPM is clearly SUPERIOR in some way.

That position has very little support in the scientific community.

My position is that BOTH algorithms produce plans that are usable in most cases. We plan to implement the algorithm to allow the diver to plan dives that don't violate either algorithm if they chose. It is also my position that the amount of exercise during bottom time and decomression and the temperature of the body during bottom time and decompression are both big factors in successful decompression.

I think I can say that my position is very much in line with the general beliefs of the scientific community.

Bruce

 

[rossh]

Out of curiosity, how are the various + conservatisms applied to VPM within Vplanner? Are they each discreetly coded algorithms? Or are they knockdown factors on the one algorithm?

In VPM the conservatism adjusts the Critical Radii in the core calculations of the model. VPM is unique in this way because this adjustment has a direct relation to the bubble loads that the model is calculating for the entire ascent.

Most other models just fudge conservatism by artificially inflating the depth or the bottom time or both, and then calculating this bigger (hidden) time / depth set. Other creative methods add a time bias to the off / on gassing calculations.

Now if GF comprised of just one uniform parameter, then you could call it conservatism. But instead GF uses a split system of Hi /Lo where the diver can pick and choose virtually any profile shape they like. When applying Lo numbers like 10 or 20, it will get you very deep stops, but the result is way beyond the base model. The deep stops are superfluous to ZHL model and the deeper stop results is a very different profile to the man tested original standard.

Regards

 

[rossh]

Ross,
I guess I need to clarify the science part of my post.
Your position appears to be that VPM is the ONLY algorithm that works and that VPM is clearly SUPERIOR in some way.
That position has very little support in the scientific community.
Bruce

You have misinterpreted the posts Bruce. One more time.....

There is only one profile shape or style used by vast majority of the diving community. It's the deep stop profile used in various proportions. Bubble models, RD, GF and others systems all create these. GF can create all shapes, but most people use GF exclusively to make deep stop profiles. This includes your products and customers too. Every training agency teaches deep stops. Deep stops are here to stay.

I find it hypocrisy for anyone to suggest that GF with its deep stop profiles, is still related to the man tested originals. You can't have it both ways Bruce - if your down at the deep end of the profile spectrum with the rest of us, then you have clearly abandoned the man tested origins, like the rest of us. Welcome to the untested world. Any criticism of VPM profiles, applies equally to GF profiles of today, and RD and all others too.

It's a fact - virtually no one dives or is trained in any of the man tested / published standards or profiles.

Now you keep harping on the medical aspects. Research is stuck in an awkward place. Very few researchers are working on this. For the last decade divers and training agencies have moved away from the man (lady) test standards in favor of anecdotal deeper stop methods. The transition has been much faster than the science can keep up. During the same period, training has vastly improved and a greater understanding of DCS factors is known - all anecdotal information of course.

Only the Navies of the world can fund new testing, but they have an invested history in their existing systems and methods. I don't expect them to produce any new testing that will cause them to change overnight.

 

[Blackwood]

In VPM the conservatism adjusts the Critical Radii in the core calculations of the model. VPM is unique in this way because this adjustment has a direct relation to the bubble loads that the model is calculating for the entire ascent.

Very cool. I've always wondered that. Thanks for participating!

 

[DiveNav]

......If you think we are just trying to support GF, we recently hired one of the mathematicians that was heavily involved in VPM in the early days, and we will be releasing the Shearwater take on VPMB in our products within the next few months. .....

I guess I will FINALLY have to add VPMB to our dive simulator then

I "almost" did it every month for the past year .... this time I have no more excuses.

Alberto (aka eDiver)

 

[rjack321]

When ZHL-16 has been sold in millions of dive computers and the press is not full of DCS or fatalities, it can't be that bad.

Except that most people don't dive the raw model (100% low/100% hi Buhlmann) without gradient factors. Even if they dive a gradient factor implementation they also may add some deep(er) stops or slower ascents on top of that. Why are they doing all these changes to the original Buhlmann model? Because native Buhlmann is really aggressive by today's standards.

Ironically gradient factors added to Buhlmann is a linear addition to a curve. Many other deep stop guesstimates (like those in Ratio deco and Pyle stops) are also linear additions to an otherwise curvilinear function.

 

[TSandM]

Well, my tech instructor told me that, on shallow staged decompression dives, as long as you do the total time, it probably matters very little WHERE you do it, at least in terms of full-blown DCS symptoms. My Cavern instructor is a tech instructor, and he does ALL his technical diving on a basic Buhlmann profile, using only 100% O2 for accelerated decompression. He's been doing it for years and teaching it for years, and he doesn't have any dysbaric osteonecrosis I know of

I think it's generally accepted that a slower curve is preferable, but I'm not at all sure that there are hard data to support that, and there are some data that show that the extremely deep stops that some folks are adding to their profiles actually result in higher bubble scores.

 

[rossh]

I think it's generally accepted that a slower curve is preferable, but I'm not at all sure that there are hard data to support that, and there are some data that show that the extremely deep stops that some folks are adding to their profiles actually result in higher bubble scores.

Except....... The only point of agreement amongst the researchers on bubble monitoring studies, at the UHMS Deep stops conference in 2008, was that they were not able to draw any conclusions between DCS and bubble score. The obvious assumption that more bubble score equals higher DCS, was found to be incorrect.

rossh

 

[TSandM]

Yes -- one of the big difficulties in evaluating decompression strategies is that we really don't have a good proxy for symptoms, and symptoms are actually fairly rare. And V-planner doesn't have the extremely deep stops I'm talking about, anyway, at least not in the depths where I have used it.