VR3 BUH or VPM

graham_hk

Interesting stuff - can you provide the citations?

rossh

Has this procedure tested the deep stop components of any deco model in tech diving use today? NO!

The Navy test appears to be looking a deeper version of the Navy's own (WAL18) models. No diver on this board here uses a WAL18 or a Workman profile. Every tech model or method in use today by tech divers, is not related to the test procedure shown here.

The other study results don't add up either. Killing animals as a measure of humans - humans don't normally die from DCS. Also, bubble scores via soundings are too subjective, and have been shown to be a poor measure of possible DCS.

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Does any tech diver today use a "man tested" dive plan today (and I mean real raw Bulhmann, Navy, DCIEM, not the padded up things in computers)? NO. No one uses these today.

Most divers have abandoned man tested models long ago. Todays tech diver will use a hybrid of some kind. They use a Gradient Factor, Pyle Stop, or other padding methods, or they use a simple math relational method of deep stops, or they use a bubble model that produces all these changes naturally. A heavily adjusted Bulhmann plan is not a man tested plan - it is a one-off experimental design.

The most popular computer is use by people here is the VR3. It has Pyle stops. The next computer is the Shearwater range. It uses GF, set at 20/85 or there abouts. I say again, no one uses man tested plans anymore, and they want to use plans with deep stops, and often a reduced shallow section - just like a bubble model.

The point is, deep stop models and variations are in wide spread use now.

The facts are that many divers are doing deep stops now, and are happy to be doing so. Many training agencies use deep stop models in their programs. No new diver will ever carry out man tested profiles ever again.

Therefore... the critisism that Bubble models are un-tested - so what, all the current alternatives are untested too.

When medical / hyberbaric staff criticize deep stop and bubble models, they seem to forget that the alternative "man tested original" model is not used anymore either. And the alternatives is use, are for the most part, just trying to emulate bubble models anyway.

***********

DCS treatment numbers... Andrew, How many treatments have you done on Haldane, Bulhmann patients - 500, 1000, more?

25% ... sounds like FUD Andrew.

The facts are that DCS treatment numbers have been holding steady or in decline since 2002. Tech diving has been increasing dramatically, but DCS treatments have not. Why is that? Could it be that deep stop models of all types are in wide spread use?

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Drmike

The basis of all the deco algos in computers and tables in common use is man tested models. This is a fact. Yes they have had various degrees of conservation added, they have been padded - but the basis of the algos is man tested and such padding adds safety and doesnt necessarily degrade the value of that man testing. The basis of vpm has not been man tested. Thats the difference.

Man tested model thats been tweaked 'V' non man tested model thats been tweaked.

It could be. It could also be due to:
1) better training
2) better equipment
3) greater usage of dive computers
4) better tables
5) more common use of O2 and He mixes
6) Increased usage of Nitrox

who knows.

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Wreck diving is a sport
Diving in general is a sport

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Drmike

Ill ask Matt when he finishes his dive if he has it.
Yes used sucessfully,although there was some light padding and rounding up of some stop times. Which although normal, in a way is a shame as It does make it a little bit harder to draw conclusions if profile isnt exactly followed (on deep dives they rarely are - people pad). Nice looking wreck though from what I can see from matts video. A dive made all the more impressive given they had to carry a shed loads of tanks with them

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

AM

Sorry to be late to the party.

I use VR3 Buh and wouldn't consider VPM incarnation (nor VPMBE) - they are still too short when compared with Buh over longer decos. For sure Buh algo is bend and mend but it is common sense that when it indicates ascent is possible through a large range, to pad some of this. Underlying in the algo is that on the deep stops, offgassing is happening from fast tissues but ongassing is occurring to slow tissues....hence the hang-around for ever at 6m to combat..

Everyone I know who has told the computer they are on air while continuing to ongas He, has ended up bent. He is a faster gas both in and out and needs to be accounted for. There are still some killer instructors teaching air flushing. Why on earth anyone would want to introduce a large N2 spike (especially near a deco ceiling) is beyond me.

Quality deco is what counts, not just quantity. Even with conservatism racked up on my VR3, I'd still rather tell the computer I am on 1.3 and flush O2 in the bags regularly to get inert gas out of the loop.

I care less about CNS being through the roof than performing poor quality deco. In fact I have deco'd at 2.0 bar without problems and felt clean after such dives. Having used GF and shaved up to 40 mins off the deco for the same dive on a VR3, I needed a sub-clinical snooze on the boat.

The VR3 is still a great computer. All this focus on cutting down deco time is not necessarily a positive. Poor deco leads to long term subtle manifestation of neuro damage, even with no obvious bend symptoms.

Regards

AnneMarie

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Mixaddict

AnneMarie,

Would you be so kind as to further explain this comment?

Thanks,
Randy

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Randy Thornton (MixAddict)
Inspiration, Evolution,Hammerhead & Sentinel
CCR Instructor

Serge

I think you hit the nail right on the head. Look, I'm about as much a newbie when it comes to closed circuit as they come. But, I do have a little experience with successfully carrying out semi-constant fO2 decompression on OC. While the Buhlmann approach is to treat the overall human body, the bubble models are more focused on individual bubble dynamics, i.e., bubbles don't just appear from nowhere. Each individual bubble has distinct physical characteristics and is therefore bound by certain physical criteria. It is the manipulation of those physical characteristics of bubbles and their origins that allows bubble models to achieve successful decompression schedules. Haldanian models have just too many variables unaccounted for, variables that can have unexpected, and sometimes completely counter-intuitive results. It is impossible to predict and "man-test" every dive condition. And this is exactly where I believe bubble models outshine traditional methods.

For example, what happens if you plan an air dive to 100' for 60 minutes? With a bubble model, you get approx 175 minutes run time. Now, let's say you do the same air dive to 100' for 60 min, but this time add 5 minutes at 170' at the beginning of the dive; you get approx 156 min run time. A deeper, longer dive reduces total run time by 10%? Why? This is a result of a completely counter-intuitive manipulation of physical bubble structure characteristics at the molecular level, which cannot be accounted for by empirical means.

UWSojourner

Quote: (Originally Posted by am)

Quality deco is what counts, not just quantity. Even with conservatism racked up on my VR3, I'd still rather tell the computer I am on 1.3 and flush O2 in the bags regularly to get inert gas out of the loop.

So 'quality deco' is tricking your computer into not bending you?

Here's my take on the VPM/Buhlmann debate (all my opinion only). The development of non-Buhlmann models didn't occur in a vacuum. Some divers were reporting feeling better after deeper stops (Pyle) and others were finding they could drastically cut hang time in the shallows following slower ascents (WKPP). There was some evidence that the strict Buhlmann profiles were not always optimal.

The major contribution of VPM (IMO) was that it was a theoretical model that provided an plausible explanation of some of the phenomenon being reported. Why might deeper stops be a good idea? Why might less shallow time be required? Why might reverse profiles be riskier? VPM provided a theoretical model with an explanation.

VPM, though, still has its problems. The original VPM was definitely range bound and not appropriate for deeper dives. Nothing in the theoretical model would predict this outcome a priori. VPM-B (IMO) was born of necessity, not theory.

Second, VPM (being a theoretical model) has a bit of a parameterization problem. Just what is the appropriate critical bubble radius? Prior to VPM-B the 'defaults' were 0.8/0.7 microns for nitrogen/helium. When the Boyles adjustment was implemented these were changed to 0.55/0.45 microns. Did we somehow realize that the appropriate critical radius for bubble distributions was actually quite a bit smaller than we thought? Or was our 'theoretical model' being tuned to our somewhat preconceived understanding of acceptable profiles? And might this new tuning also be inappropriate over portions of the dive spectrum?

Also, because the bubble radius directly translates into VPM's recommended dissolved gas supersaturation gradients, and because the bubble radius is a parameter, one could ask what the model is actually recommending? The same issue occurs in other models (e.g. gradient factor) where large changes in profiles occurs based on parameter values chosen by divers. If a study were initiated, just what would be studied? What bubble radii assumption, if studied and found wanting, would invalidate VPM?

Finally, from what I can tell most VPM divers are using something in excess of the default 0.55/0.45 bubble radius values. Is this solely an attempt at conservatism, or is some practical testing of VPM occurring that shows the defaults to be too aggressive?

BTW, I like VPM. But my feeling is that there is plenty of room for further research which we should welcome and not prejudge. It would surprise me if deep stops were invalidated for deep sport diving, but stranger things have happened. In the meantime, absent definitive data that I doubt will come soon, we should all be very deliberate in our reasoning about the risks we take. (Part of that deliberateness might include tempering the desire to be the first out of the water. ) All these models are experimental IMO, and the deeper you go the more you resemble a guinea pig.

nobody

Hi, could you shed some light as to what HKBM is? i've never heard of it and google didn't turn up anything. It looks like it deliberatly tries to stay at a depth for the longest possible time before additional loading occurs.

Cheers

EDIT: FOUND IT, WAS TYPING HKMB INSTEAD FOR HKBM!

schnappi

it is the Hamilton-Kenyon Bubble Model.

http://www.rebreatherworld.com/decom...on-kenyon.html

i am looking for a formal description of the model. if i find something, i'll let you know...


cheers
--bruno

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