VR3 BUH or VPM

silent running · 17th April 2008, 11:04

Quote: (Originally Posted by 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)

Thanks very much GM for posting this recap of how ZHL-16 was derived. It's a very clear explanation of how maned testing and models work together to give us a reasonable chance of predicting outcomes. -Andy

solocavediver · 17th April 2008, 12:29

Concerning how well tested VPM is, the GUE/wkpp guys use VPM based deco in their long dives around the 200'-300' region (60-90m). Of course they're also trying to sell you deco software so their statements should be taken with an automatic pinch of salt, but they do have a good record of not bending people too often. If you're a wkpp diver I suspect the difference between VPM and Buhlmann adds up over time to many days in the decompression habitat that you don't have to spend, so they definitely reckon it a good thing. For their kind of diving - 200-300', warm water, divers required to be fit, often several hours bottom time - I think you can regard VPM as pretty well tested. And I think it is really well established that deeper stops are a good thing (even in my limited experience, I know this to be true), so someone has to come up with some sort of a mathematical model for the process. In a few years' time, VPM will be uncontroversial I reckon - in the meanwhile, use best judgement....

Cheers,

Charles.

rossh · 17th April 2008, 12:57

Quote: (Originally Posted by Gasman)

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.

.
WTF is this?? At the recent DAN conference you told some of your peers, that you *did* pass these incidents onto me. So which is it Andrew.. you contacted me or you didn't?

People take hits using all models, and that includes the most conservative planning methods available. No tech diver should ever assume that they are protected from DCS! Read the warning on the bottom of a V-Planner dive plan.

Have you bothered to investigate the root cause of any of these DCS incidents? Any diver who takes a serious hit on a dive that the vast majority of other divers can accomplish without problems, then that diver has to take a good hard look at what they did wrong. Bad procedures, bad mixes, and a whole set of other well know causes can ruin any dive plan. And there is a 1-2% chance anyone will get hit at any time, on any dive, on any model!

Of course you still ignore the fact that all divers have long ago abandoned the very man tested dives your hoping to scare everyone back too. Many divers do dives shaped to look like a deep stop / bubble model, regardless of the planning tools used - the very thing your campaigning against.

PS. Your references have missed the additional work of Prof Yount on the VPM from 98 through to his death in 2000. That is where you will find the modern implementations of VPM used today.

**UWSojourner** · 17th April 2008, 19:55

Quote: (Originally Posted by Gasman)

... 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?

In a prior post you provided examples of dive teams experiencing up to 33% severe DCS hits. Can you provide some sort of context on why you think "the incidence of DCI will probabably be low..." in systematic trials of VPM?

"The plural of anecdote is not evidence” That's a great quote.

Quote: (Originally Posted by Gasman)

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 ...

If dives ending in DCS are not being reported, then its probably fair to say successful VPM dives are certainly not being reported.

We're left with both unknown numerator AND unknown denominator which makes all categorical statements suspect IMO. It would seem logical that those treating DCS tend to get a biased segment of the data? (i.e. divers coming in for treatment). Absent denominator data we're left with a pretty cloudy picture IMO. Great anecdotes on both sides, but no definitive studies.

Gasman · 17th April 2008, 23:17

[quote=rossh;181937].
WTF is this?? At the recent DAN conference you told some of your peers, that you *did* pass these incidents onto me. So which is it Andrew.. you contacted me or you didn't?

You know Ross, I am trying very hard to keep this proffessional and not personal. You know full well that I contacted you several years ago when we started seeing people getting bent on VPM and .... well lets say the dialogue was less than friendly and not all that productive. I did not state to anyone at the DAN conference that I had contacted you over the latest cases, nor have contacted you over the many I have treated inbetween... largely becasue of the response I received initially.When a group of divers all dive to gether and ascend together, supply the printout of their dive and it conforms to the plan... I tend to think that they did not do anything particulalrly wrong. You need to get off that one mate!
Looking at the cause of diving accidents is a big part of what I do. Im the medical advisor to the Australasian diving mortality study as well as advising divers that have received DCI hits. Ignoring the fact that there seems to be a fairly high incidence of DCI when conduction deep dives using certain bubble models will not make it go away no matter how often you blame the divers.
Andrew

01RMB · 18th April 2008, 01:42

I have watched this thread with interest for a while but said nothing because my knowledge and experience is limited compared to others that have made some great points here.

I typically dive to 80m and have completed dives to 120m but after spending 2 ½ hours attempting to resuscitate a friend of mine who died with severe DCS after a 50m dive I have a deep interest in finding out more about the real risk profile of each of the discussed deco models. I would think that better visibility of the level of risk present when following a particular deco model would be needed or at least of interest to everyone diving beyond PADI tables.

We all know that the only way to avoid DCS is to not dive (or fly) but I get concerned with comments that say ‘follow this plan but add padding to be safe’!! What is the level of risk of actually following a dive plan produced by one of these models? How is the risk profile affected by the different ways people use to pad their plans?

Based on the information available what is the likelihood of DCS after following plans produced by each of the models without adding any additional padding? Is it really as bad as 30% mentioned by Andrew or even the 3% as mentioned by Ross and is this really acceptable? Wouldn’t 0.1% or 0.01% be more acceptable and what sort of model and settings need to be used to achieve these sort of results?

Given each person’s appetite for acceptable risk is different, I would still be a lot happier knowing that I had a plan that provided me with a better than 30% or even 3% chance of a trip to a chamber, especially when I am in a remote location.

For each of the deco models there are a bunch of data points used to qualify the use of the models. This thread has raised the question over the validity of some of the data being used to promote one of the models. Given that it has been shown that a number of the dives were not to the depths which could be construed as being dived, dives which were padded using some method and others where the deco model was not even used – what is the level of confidence I have that the plans produced are within my acceptable risk level?

There is little true verification of the deco models currently being used although each of the models has a different foundation and level of study being conducted – one being based on studies with divers and another based on a theoretical model. Both are adjustable and have had changes made since they were initially released. Great – I am glad that weaknesses have been identified and rectified.

I am no hyperbaric specialist but given the limited amount of verification I am interested in knowing more about the tools and the data being used to qualify and validate the deco models I use to plan and execute dives. To really resolve this problem we need to know what models are being used, the settings and what padding is being added to achieve what level of DCS incidents? If one model is demonstrated to show a higher level of DCS incidents than I am willing to accept I will either use more conservative settings or chose a different model.

Gene_Hobbs · 18th April 2008, 03:01

Quote: (Originally Posted by Gasman)

Gene may well have many of these as they are fairly well known references.

Sorry, wish I could say we had most of those but you list is heavy on Aviation Space and Environmental Medicine. We became a non-profit with the hope of landing some donations and grants. We have not had much luck with either so far but if we can get enough this year, we want to approach the AsMA about a license for their journal. (I know they are looking to recoup the money they laid out for the scanning so we have a goal.)

In fact, the only one we do have the permission for is the workshop:
Nashimoto I, Lanphier EH (eds). Decompression in Surface Based Diving. 36th Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 73(DEC)6-15-87. Bethesda: Undersea and Hyperbaric Medical Society; 1987; 151 pages. RRR ID: 6460
NOTE: This is a VERY large download.

I did recently make the references on the Wikipedia VPM page link to the sources if they were available. Some of you might enjoy those. (Thanks for the help Ross!)

Quote: (Originally Posted by 01RMB)

Given each person’s appetite for acceptable risk is different, I would still be a lot happier knowing that I had a plan that provided me with a better than 30% or even 3% chance of a trip to a chamber, especially when I am in a remote location.

Seems to me that you would be happier getting away from deterministic or bubble models and turning to a probabilistic model. They might not be as fast but the risk is known. But that's just me...

rossh · 18th April 2008, 03:26

[quote=Gasman;182050]

Quote: (Originally Posted by rossh)

.
You know Ross, I am trying very hard to keep this proffessional and not personal. You know full well that I contacted you several years ago when we started seeing people getting bent on VPM and .... well lets say the dialogue was less than friendly and not all that productive.

Here is an exert of one the thirty(30) messages we exchanged in 2004. Back then I was happy to help. Lets see how the others interperut these.

Hello Andrew,
Thank you very much for passing this along.
................
Anyway, thanks for the feed back and I'd like to here more.
Regards

In 30 messages we discussed the VPM model in depth, other model systems, Brian Hill, one diver accident, your efforts to create a diffused model, I offered you programming help, personal details, and so on. But, this all stopped when I challenged your biased posts on the Dive-Oz forum.

So Andrew, why are you trying to mislead these readers here with more miss-information about me?

You made it personal though, as you have included my name and asserted things in the middle of a professional subject posts.

You are using your position for fear mongering and FUD, with biased information, unbalanced views, and embedded these into your professional activities. That's not good!

Quote: (Originally Posted by Gasman)

When a group of divers all dive to gether and ascend together, supply the printout of their dive and it conforms to the plan... I tend to think that they did not do anything particulalrly wrong. You need to get off that one mate! Looking at the cause of diving accidents is a big part of what I do. Im the medical advisor to the Australasian diving mortality study as well as advising divers that have received DCI hits. Ignoring the fact that there seems to be a fairly high incidence of DCI when conduction deep dives using certain bubble models will not make it go away no matter how often you blame the divers.
Andrew

Then kindly answer these questions:

1/ How does most of the world use bubble models, deep stops methods, ratio deco, to all depths and times, and have no significant problems. But your sample set is full of problems? Can you explain this difference?

2/ How is it that DCS treatment numbers the world over are in relative decline, except for your subset of presented data?

.

Gasman · 18th April 2008, 06:00

[quote=rossh;182091]

Quote: (Originally Posted by Gasman)

1/ How does most of the world use bubble models, deep stops methods, ratio deco, to all depths and times, and have no significant problems. But your sample set is full of problems? Can you explain this difference?

2/ How is it that DCS treatment numbers the world over are in relative decline, except for your subset of presented data?

.

Firstly Ross,The majority of the worlds divers do not use bubble models. Secondly, bubble models when used in the recreational range produce more conservative results and would be expected to further reduce DCI rates. Third, evidence from the Norwegian study would support the notion that for shallow (recreational type dives) the addition of deep stops reduces decompression stress as measured using venous gas emboli.
Because of the very successful marketing of bubble models the majority of the technical divers that we see have been using one or other of the VPM /RGBM family. As I have stated several times I cannot prove that those people would not have been bent if they had used Buhlmann, but that is not the point. The point is that they DID get bent using the bubble model...
As with the rest of the world our DCI overall numbers have declined over that last few years. However, we do keep a log of the depth, algorithm used etc.. Over the last few years (since we started keeping these records) the numbers of technical divers presenting has increased and is out of proportion to their representation in the diving community. In addition, this group contains the sickest divers we see with the exception of the CAGE patients.I do not have any cross to bare on this subject other than to help educate the divers of forums such as this as to the current best scientific information on the subject. I have tried to not inject too much of my "opinion" into this. This is why I have included references for the statements that I have made. I am not attacking you and yes we did also have some cordial correspondence as well.... however, I think it is grossly inappropriate to drag out parts of old e-mails and resubmit them in a public forum..... rather poor form mate! I really dont understand why you take so much offence to me stating that we have treated people for DCI who were using bubble models. That we have done so is a fact, nothing more.

Andrew</p>

lizardland · 24th April 2008, 22:48

Quote:

The VPM model revision work started in mid 2002, and was completed by years end. It was done by two of the principal authors of the VPM, and changes were based on reasons of math and physics. VPM-B was made available in Jan-Feb 2003.

Quote:

Ha, nice marketing spin - changes for maths and physics. I think not. Changes were made several times following reports of multiple DCIs and it became apparent that the model fell grossly short of an acceptable deco algorithm. Speak to any diver that has dived VPM to beyond 100m and done bottom time, not pissing about in mid-range diving, they won't be using VPM, I can guarantee you that! In fact, I'd like to hear from a diver that has done, say 20 minutes at 120m with no padding on VPM. They are probably too incapacitated to come and share it!

I've only just read through the thread after hearing about the above quote. I was one of those divers that reported DCI after the release of the Baker FORTRAN code. Erik Baker had sent me, along with quite a few others, an early release of the program. I reported my incident on the VPM list, IIRC I was one of the first to publicly report DCI incidence and I recall that quite a few people started openly reporting problems after that. Certainly people contacted me privately to say that they too had similar problems.

One of the common factors was how quickly/easily the DCI resolved, often on just O2, which may explain why there weren't a massive amount of VPM hits turning up at chambers. In fact, by the time I got to the NWHC after a good 3hrs on oxygen the hyperbaric doctor on call said the residual symptoms were remarkably minor.

Baker & Maiken revised the code in direct response to these incidents. That should be clearly apparent from the archives of the VPM list. Based on reasons of maths & physics? Well... duh... people getting bent because of numbers produced by a computer algorithm... it's a semantics question and, quite frankly as one of those people who did get bent, I find it a bit of a cynical statement.

I dived the same profile twice and got bent twice. The first was minor stuff that I wrote off to tiredness and injury but in retrospect I was bent -- 5hrs in a pot is an excellent vaccination against DCI denial for the future. The second wasn't, it was full blown PISS symptoms and it hurt like ****, no other way to put it. I don't remember the exact profile, sorry AnneMarie, it wasn't 120m for 20min, more like 90m for 15min. I don't recall the exact numbers, but yes it was unpadded. The first bent dive was on a scooter which I have always attributed as to why the symptoms stayed minor, the next time my scooter failed just as I got in the water so I was free-swimming. I also had a suit flood so I was cold too.

It was not my intention at the time to moan about it. It was my choice to dive an untested table. Looking back it wasn't a happy schedule but this was a time when decompression had become a competitive sport so short, aggressive tables were a la mode. At the time it seemed acceptable. Like I said, I didn't bitch about it in the reports because I wanted them to be as constructive as possible for Eric & Erik (and everyone else who was contributing to VPM uncredited in their own way). I'm not bitching about it now either. I do, however, find the above statement as to why VPM was re-written contentious to say the least. There can be no doubt VPM was re-written in response to DCI incidents.

I have no idea how VPM progressed after 'B', I lost interest in it partly because I'd never felt right on it deeper than 50m and mainly because at that time it was useless for cave profiles as the code shat a brick if you tried to do any multilevel stuff. I started diving Bill Hamilton's model after that with a bit of deep stop padding and it's worked for me since so I've paid little attention to VPM.

Cheers,

Stuart

17th April 2008, 11:04	#161 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: VR3 BUH or VPM Quote: (Originally Posted by 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) Thanks very much GM for posting this recap of how ZHL-16 was derived. It's a very clear explanation of how maned testing and models work together to give us a reasonable chance of predicting outcomes. -Andy
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17th April 2008, 12:29	#162 (permalink)
solocavediver New Member Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Apr 2006 Location: Leeds UK Posts: 117	Re: VR3 BUH or VPM Concerning how well tested VPM is, the GUE/wkpp guys use VPM based deco in their long dives around the 200'-300' region (60-90m). Of course they're also trying to sell you deco software so their statements should be taken with an automatic pinch of salt, but they do have a good record of not bending people too often. If you're a wkpp diver I suspect the difference between VPM and Buhlmann adds up over time to many days in the decompression habitat that you don't have to spend, so they definitely reckon it a good thing. For their kind of diving - 200-300', warm water, divers required to be fit, often several hours bottom time - I think you can regard VPM as pretty well tested. And I think it is really well established that deeper stops are a good thing (even in my limited experience, I know this to be true), so someone has to come up with some sort of a mathematical model for the process. In a few years' time, VPM will be uncontroversial I reckon - in the meanwhile, use best judgement.... Cheers, Charles. Last edited by solocavediver : 17th April 2008 at 14:03.
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17th April 2008, 12:57	#163 (permalink)
rossh RBW Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Jul 2005 Location: Canada Posts: 118	Re: VR3 BUH or VPM Quote: (Originally Posted by Gasman) 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. . WTF is this?? At the recent DAN conference you told some of your peers, that you did pass these incidents onto me. So which is it Andrew.. you contacted me or you didn't? People take hits using all models, and that includes the most conservative planning methods available. No tech diver should ever assume that they are protected from DCS! Read the warning on the bottom of a V-Planner dive plan. Have you bothered to investigate the root cause of any of these DCS incidents? Any diver who takes a serious hit on a dive that the vast majority of other divers can accomplish without problems, then that diver has to take a good hard look at what they did wrong. Bad procedures, bad mixes, and a whole set of other well know causes can ruin any dive plan. And there is a 1-2% chance anyone will get hit at any time, on any dive, on any model! Of course you still ignore the fact that all divers have long ago abandoned the very man tested dives your hoping to scare everyone back too. Many divers do dives shaped to look like a deep stop / bubble model, regardless of the planning tools used - the very thing your campaigning against. PS. Your references have missed the additional work of Prof Yount on the VPM from 98 through to his death in 2000. That is where you will find the modern implementations of VPM used today. __________________ Regards, Ross Hemingway V-Planner Live for the X1 V-Planner VPM-B Nitrox Trimix CCR Deco planning for Technical Divers www.v-planner.com
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17th April 2008, 19:55	#164 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 558	Re: VR3 BUH or VPM Quote: (Originally Posted by Gasman) ... 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? In a prior post you provided examples of dive teams experiencing up to 33% severe DCS hits. Can you provide some sort of context on why you think "the incidence of DCI will probabably be low..." in systematic trials of VPM? "The plural of anecdote is not evidence” That's a great quote. Quote: (Originally Posted by Gasman) 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 ... If dives ending in DCS are not being reported, then its probably fair to say successful VPM dives are certainly not being reported. We're left with both unknown numerator AND unknown denominator which makes all categorical statements suspect IMO. It would seem logical that those treating DCS tend to get a biased segment of the data? (i.e. divers coming in for treatment). Absent denominator data we're left with a pretty cloudy picture IMO. Great anecdotes on both sides, but no definitive studies. Last edited by UWSojourner : 18th April 2008 at 02:47.
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17th April 2008, 23:17	#165 (permalink)
Gasman New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Jul 2005 Location: Australia Posts: 33	Re: VR3 BUH or VPM [quote=rossh;181937]. WTF is this?? At the recent DAN conference you told some of your peers, that you did pass these incidents onto me. So which is it Andrew.. you contacted me or you didn't? You know Ross, I am trying very hard to keep this proffessional and not personal. You know full well that I contacted you several years ago when we started seeing people getting bent on VPM and .... well lets say the dialogue was less than friendly and not all that productive. I did not state to anyone at the DAN conference that I had contacted you over the latest cases, nor have contacted you over the many I have treated inbetween... largely becasue of the response I received initially.When a group of divers all dive to gether and ascend together, supply the printout of their dive and it conforms to the plan... I tend to think that they did not do anything particulalrly wrong. You need to get off that one mate! Looking at the cause of diving accidents is a big part of what I do. Im the medical advisor to the Australasian diving mortality study as well as advising divers that have received DCI hits. Ignoring the fact that there seems to be a fairly high incidence of DCI when conduction deep dives using certain bubble models will not make it go away no matter how often you blame the divers. Andrew
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18th April 2008, 01:42	#166 (permalink)
01RMB Evolving Current Rebreather/s: Evolution Other Rebreather/s: Join Date: May 2005 Location: Brisbane, Australia Posts: 193	Re: VR3 BUH or VPM I have watched this thread with interest for a while but said nothing because my knowledge and experience is limited compared to others that have made some great points here. I typically dive to 80m and have completed dives to 120m but after spending 2 ½ hours attempting to resuscitate a friend of mine who died with severe DCS after a 50m dive I have a deep interest in finding out more about the real risk profile of each of the discussed deco models. I would think that better visibility of the level of risk present when following a particular deco model would be needed or at least of interest to everyone diving beyond PADI tables. We all know that the only way to avoid DCS is to not dive (or fly) but I get concerned with comments that say ‘follow this plan but add padding to be safe’!! What is the level of risk of actually following a dive plan produced by one of these models? How is the risk profile affected by the different ways people use to pad their plans? Based on the information available what is the likelihood of DCS after following plans produced by each of the models without adding any additional padding? Is it really as bad as 30% mentioned by Andrew or even the 3% as mentioned by Ross and is this really acceptable? Wouldn’t 0.1% or 0.01% be more acceptable and what sort of model and settings need to be used to achieve these sort of results? Given each person’s appetite for acceptable risk is different, I would still be a lot happier knowing that I had a plan that provided me with a better than 30% or even 3% chance of a trip to a chamber, especially when I am in a remote location. For each of the deco models there are a bunch of data points used to qualify the use of the models. This thread has raised the question over the validity of some of the data being used to promote one of the models. Given that it has been shown that a number of the dives were not to the depths which could be construed as being dived, dives which were padded using some method and others where the deco model was not even used – what is the level of confidence I have that the plans produced are within my acceptable risk level? There is little true verification of the deco models currently being used although each of the models has a different foundation and level of study being conducted – one being based on studies with divers and another based on a theoretical model. Both are adjustable and have had changes made since they were initially released. Great – I am glad that weaknesses have been identified and rectified. I am no hyperbaric specialist but given the limited amount of verification I am interested in knowing more about the tools and the data being used to qualify and validate the deco models I use to plan and execute dives. To really resolve this problem we need to know what models are being used, the settings and what padding is being added to achieve what level of DCS incidents? If one model is demonstrated to show a higher level of DCS incidents than I am willing to accept I will either use more conservative settings or chose a different model. __________________ Cheers Rod Last edited by 01RMB : 18th April 2008 at 02:25.
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18th April 2008, 03:01	#167 (permalink)
Gene_Hobbs Resident bibliophile Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Sep 2006 Location: Durham, NC, USA Posts: 133	Re: VR3 BUH or VPM Quote: (Originally Posted by Gasman) Gene may well have many of these as they are fairly well known references. Sorry, wish I could say we had most of those but you list is heavy on Aviation Space and Environmental Medicine. We became a non-profit with the hope of landing some donations and grants. We have not had much luck with either so far but if we can get enough this year, we want to approach the AsMA about a license for their journal. (I know they are looking to recoup the money they laid out for the scanning so we have a goal.) In fact, the only one we do have the permission for is the workshop: Nashimoto I, Lanphier EH (eds). Decompression in Surface Based Diving. 36th Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 73(DEC)6-15-87. Bethesda: Undersea and Hyperbaric Medical Society; 1987; 151 pages. RRR ID: 6460 NOTE: This is a VERY large download. I did recently make the references on the Wikipedia VPM page link to the sources if they were available. Some of you might enjoy those. (Thanks for the help Ross!) Quote: (Originally Posted by 01RMB) Given each person’s appetite for acceptable risk is different, I would still be a lot happier knowing that I had a plan that provided me with a better than 30% or even 3% chance of a trip to a chamber, especially when I am in a remote location. Seems to me that you would be happier getting away from deterministic or bubble models and turning to a probabilistic model. They might not be as fast but the risk is known. But that's just me... __________________ http://rubicon-foundation.org/ Home of the Rubicon Research Repository. For help getting started with the Repository, please visit our FAQ page. PLEASE support our work. "Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991
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18th April 2008, 03:26	#168 (permalink)
rossh RBW Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Jul 2005 Location: Canada Posts: 118	Re: VR3 BUH or VPM [quote=Gasman;182050] Quote: (Originally Posted by rossh) . You know Ross, I am trying very hard to keep this proffessional and not personal. You know full well that I contacted you several years ago when we started seeing people getting bent on VPM and .... well lets say the dialogue was less than friendly and not all that productive. Here is an exert of one the thirty(30) messages we exchanged in 2004. Back then I was happy to help. Lets see how the others interperut these. Hello Andrew, Thank you very much for passing this along. ................ Anyway, thanks for the feed back and I'd like to here more. Regards In 30 messages we discussed the VPM model in depth, other model systems, Brian Hill, one diver accident, your efforts to create a diffused model, I offered you programming help, personal details, and so on. But, this all stopped when I challenged your biased posts on the Dive-Oz forum. So Andrew, why are you trying to mislead these readers here with more miss-information about me? You made it personal though, as you have included my name and asserted things in the middle of a professional subject posts. You are using your position for fear mongering and FUD, with biased information, unbalanced views, and embedded these into your professional activities. That's not good! Quote: (Originally Posted by Gasman) When a group of divers all dive to gether and ascend together, supply the printout of their dive and it conforms to the plan... I tend to think that they did not do anything particulalrly wrong. You need to get off that one mate! Looking at the cause of diving accidents is a big part of what I do. Im the medical advisor to the Australasian diving mortality study as well as advising divers that have received DCI hits. Ignoring the fact that there seems to be a fairly high incidence of DCI when conduction deep dives using certain bubble models will not make it go away no matter how often you blame the divers. Andrew Then kindly answer these questions: 1/ How does most of the world use bubble models, deep stops methods, ratio deco, to all depths and times, and have no significant problems. But your sample set is full of problems? Can you explain this difference? 2/ How is it that DCS treatment numbers the world over are in relative decline, except for your subset of presented data? . __________________ Regards, Ross Hemingway V-Planner Live for the X1 V-Planner VPM-B Nitrox Trimix CCR Deco planning for Technical Divers www.v-planner.com
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18th April 2008, 06:00	#169 (permalink)
Gasman New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Jul 2005 Location: Australia Posts: 33	Re: VR3 BUH or VPM [quote=rossh;182091] Quote: (Originally Posted by Gasman) 1/ How does most of the world use bubble models, deep stops methods, ratio deco, to all depths and times, and have no significant problems. But your sample set is full of problems? Can you explain this difference? 2/ How is it that DCS treatment numbers the world over are in relative decline, except for your subset of presented data? . Firstly Ross,The majority of the worlds divers do not use bubble models. Secondly, bubble models when used in the recreational range produce more conservative results and would be expected to further reduce DCI rates. Third, evidence from the Norwegian study would support the notion that for shallow (recreational type dives) the addition of deep stops reduces decompression stress as measured using venous gas emboli. Because of the very successful marketing of bubble models the majority of the technical divers that we see have been using one or other of the VPM /RGBM family. As I have stated several times I cannot prove that those people would not have been bent if they had used Buhlmann, but that is not the point. The point is that they DID get bent using the bubble model... As with the rest of the world our DCI overall numbers have declined over that last few years. However, we do keep a log of the depth, algorithm used etc.. Over the last few years (since we started keeping these records) the numbers of technical divers presenting has increased and is out of proportion to their representation in the diving community. In addition, this group contains the sickest divers we see with the exception of the CAGE patients.I do not have any cross to bare on this subject other than to help educate the divers of forums such as this as to the current best scientific information on the subject. I have tried to not inject too much of my "opinion" into this. This is why I have included references for the statements that I have made. I am not attacking you and yes we did also have some cordial correspondence as well.... however, I think it is grossly inappropriate to drag out parts of old e-mails and resubmit them in a public forum..... rather poor form mate! I really dont understand why you take so much offence to me stating that we have treated people for DCI who were using bubble models. That we have done so is a fact, nothing more. Andrew</p>
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24th April 2008, 22:48	#170 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,387	Re: VR3 BUH or VPM Quote: The VPM model revision work started in mid 2002, and was completed by years end. It was done by two of the principal authors of the VPM, and changes were based on reasons of math and physics. VPM-B was made available in Jan-Feb 2003. Quote: Ha, nice marketing spin - changes for maths and physics. I think not. Changes were made several times following reports of multiple DCIs and it became apparent that the model fell grossly short of an acceptable deco algorithm. Speak to any diver that has dived VPM to beyond 100m and done bottom time, not pissing about in mid-range diving, they won't be using VPM, I can guarantee you that! In fact, I'd like to hear from a diver that has done, say 20 minutes at 120m with no padding on VPM. They are probably too incapacitated to come and share it! I've only just read through the thread after hearing about the above quote. I was one of those divers that reported DCI after the release of the Baker FORTRAN code. Erik Baker had sent me, along with quite a few others, an early release of the program. I reported my incident on the VPM list, IIRC I was one of the first to publicly report DCI incidence and I recall that quite a few people started openly reporting problems after that. Certainly people contacted me privately to say that they too had similar problems. One of the common factors was how quickly/easily the DCI resolved, often on just O2, which may explain why there weren't a massive amount of VPM hits turning up at chambers. In fact, by the time I got to the NWHC after a good 3hrs on oxygen the hyperbaric doctor on call said the residual symptoms were remarkably minor. Baker & Maiken revised the code in direct response to these incidents. That should be clearly apparent from the archives of the VPM list. Based on reasons of maths & physics? Well... duh... people getting bent because of numbers produced by a computer algorithm... it's a semantics question and, quite frankly as one of those people who did get bent, I find it a bit of a cynical statement. I dived the same profile twice and got bent twice. The first was minor stuff that I wrote off to tiredness and injury but in retrospect I was bent -- 5hrs in a pot is an excellent vaccination against DCI denial for the future. The second wasn't, it was full blown PISS symptoms and it hurt like **, no other way to put it. I don't remember the exact profile, sorry AnneMarie, it wasn't 120m for 20min, more like 90m for 15min. I don't recall the exact numbers, but yes it was unpadded. The first bent dive was on a scooter which I have always attributed as to why the symptoms stayed minor, the next time my scooter failed just as I got in the water so I was free-swimming. I also had a suit flood so I was cold too. It was not my intention at the time to moan about it. It was my choice to dive an untested table. Looking back it wasn't a happy schedule but this was a time when decompression had become a competitive sport so short, aggressive tables were a la mode. At the time it seemed acceptable. Like I said, I didn't bitch about it in the reports because I wanted them to be as constructive as possible for Eric & Erik (and everyone else who was contributing to VPM uncredited in their own way). I'm not bitching about it now either. I do, however, find the above statement as to why VPM was re-written contentious to say the least. There can be no doubt VPM was re-written in response to DCI incidents. I have no idea how VPM progressed after 'B', I lost interest in it partly because I'd never felt right on it deeper than 50m and mainly because at that time it was useless for cave profiles as the code shat a brick if you tried to do any multilevel stuff. I started diving Bill Hamilton's model after that with a bit of deep stop padding and it's worked for me since so I've paid little attention to VPM. Cheers, Stuart __________________ Can you imagine drifting along in the sea with your mouth open and a load of f*ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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