"re-assessing deco profiles and deep stops", plus other bits..

[Igor P]

If you utter the view, which can be easily calculated and the result is contrary to the view.
It falls to comment or withdraw from wrong view.

Showed that the change in free tissue saturation of 10% gives you extra time by about 50% at the shallow stops, for speeding up calculations applied oxygen decompression.

greet rc

Sorry RC I do not understand what you are saying...

 

[rossh]

I suppose it suits you to trivialise the points I have made by calling it "tit for tat". But in this "tit for tat" I have demonstrated that you misrepresented the facts about bubbles and risk and of DCS, and about sequential analysis of comparative trials. It is also where I point out that the published consensus view of the diving scientific community is that you have no evidence to support your claim of superior efficacy of the decompression methods that you aggressively promote. I think that is a crucial point.

As to the debate about redistribution of decompression time between deep and shallow stops, I can go no further with that without encroaching on other people's unpublished work. Hopefully we will not have to wait long for it.

Finally, since these debates can give a false impression of total polarisation, I would like to restate my position that I am not saying that deep stop decompression methods are bad or that they don't work. What I am saying is that the best evidence currently available does not support Ross's contention that these methods are demonstrably superior. That view has the backing of the diving science community as expressed in the consensus statements published in the UHMS Deep Stops workshop proceedings.

Simon M

Simon, You want nit pick this whole thing the death - no thanks, we have seen enough. You will need to concede to a few obvious flaws in this USN test first. Just because the navy wrote it - does not make it true Simon.

I have watched the UHMS and its "decompression specialist" on a one sided trajectory on these issues for many years. The world has moved onto new things, and UHMS has not.

You travel the world Simon. Have you ever met a DIR diver, a CCR diver with a Shearwater, or any other tech diver who bought any new dive computer in the last 5 years? They all use deep stops. Anecdotal data - everywhere.

DCS chamber treatments are in decline (DAN statistics). Chambers close because they don't have enough customers to pay the bills. Tech diving continues to grow. Training and gas choices improve, and better ascent profile management are to thank for this.

As I wrote - none of its formally tested. But it does exist. Stop picking on me for this Simon. It was going to happen anyway.

....does not support Ross's contention that these methods are demonstrably superior.

I have not written or said anything like that Simon - kindly stop inventing fantasy phrases.

 

[Igor P]

H

If you utter the view, which can be easily calculated and the result is contrary to the view.
It falls to comment or withdraw from wrong view.

Showed that the change in free tissue saturation of 10% gives you extra time by about 50% at the shallow stops, for speeding up calculations applied oxygen decompression.

greet rc

Yes, RC it is like you suggest using clasic M values as limiting factor for decompression, but does not geave same result using boubble model calculations.

The problem is just in that some does not belive to boubble dinamics studyes on which VPM and RGBM are based.

Best

Igor P
Sent from my GT-I5800 using Tapatalk 2

 

[Igor P]

And here some more from TDS - BRW on the study and his toughts:
The Deco Stop

I made some comparisions between the BVM3 profile and VPM-B with nominal conservatism and get VPM-B requiering two deeper stops than BVM3, so can not for now make comparision that would compare both starting with stops at the same point. I belive the BVM3 profile is completerly unrealistic, and so irelevant for our diving same as the 26036-NEDU-Experiment.

Igor P

 

[rossh]

We see that the decompression controls oxygen decompression another range tissue 8, time increased from 20.654 min to 30.26 min.
This change in free tissue saturation of 10%, given the change in oxygen decompression time.
Yes, this approximate calculation.

Clearly shows that intuition leads to errors thick and lethal.
Just calculate, it is not difficult.

Ross did not you answer.

greet rc

Hi RC, That is interesting, Our problem here is to solve the MN78 and the unknown "Haldane style" profiles in the EAP tests. I don't have data on either of these models, and hence my simple assumption calculations. Its quite difficult to truly compare, because if each model uses a different design internally, then they only over lap by coincidence.


Rossh

 

[Bobjr]

.
I realize that Dr.'s have an etiquette to uphold, with regards to others published papers. But I don't and I can call BS at any time.:banana1:

rossh

That is the most stupid thing I ever read on a forum ... there is no etiquette between scientists who enjoy nothing better than disproving each other with evidence!

 

[rossh]

That is the most stupid thing I ever read on a forum ... there is no etiquette between scientists who enjoy nothing better than disproving each other with evidence!

OK... thanks.

 

[Hanssing]

OK... thanks.

Rossh, your products are world-class. And VPM-planner is second to none for PC-software in its usability.

That being said, arguing that increased spencer-grades have no risk correlation with DCS, just gave you "egg" in your face.

I agree that there is plenty of anecdotal evidience that VPM and other deep-stop algos produces divable ascend-profiles at least when used with proper caution. That in my view means deepstops when used from these algo's are not bad. But no where has it been demonstrated that they are optimum.

The question: Given a certain dive-profile, and a constraint of a certain TAT [total ascend time], which ascendprofile is optimal in regards to DSC risk, and severity.

If the optimal profile had been shown to be deep-stops, or not, we would not be having this debate. It has *not* been shown either way.
There are no *controlled* comparing constant TATs, using modern deep-stops or not. In this regard it has not been *shown*.

You know this, but you do not like to be reminded of it. I think VPM and GF is more right than wrong, but I am not sure we are not overdoing deepstops - you are however the only one in this debate, who makes a living from deepstop-use ie. the V-planner software. In this regard I can understand you coming up in arms, but it does not serve your credibility.
You have done theese debates before; Sometimes you just implement the algorithms, sometimes you are a decompression expert. But I would urge you to not be so final in your approach.

Hanssing

 

[anarchista]

Hi RC, That is interesting, Our problem here is to solve the MN78 and the unknown "Haldane style" profiles in the EAP tests. I don't have data on either of these models, and hence my simple assumption calculations. Its quite difficult to truly compare, because if each model uses a different design internally, then they only over lap by coincidence.

The assumption is mistaken for a model class Buhlmann, the calculation would be similar for other models with exponential off-gassing, multi tissue. Off-gassing level remains the same (in the model), off-gassing from a higher level and function is not linear (exponential). To calculate the time using logarithms.

8 P8 18.78 (0.5 ^ (t/77)) = 14.3 m t = 30.26

18.78-The inert gas pressure in the tissue.
14.3 m-Saturation pressure at the surface of the resulting model, the level of conservatism.

0.5 ^ (t/77) = 14.3/18.78
t/77 = log(0,5)[14.3/18.78]
t = 77*log(0,5)[14.3/18.78]

greet rc

 

[Simon Mitchell]

Ross,

Let's deal with your latest "black is actually white" statement first:

....does not support Ross's contention that these methods are demonstrably superior.

I have not written or said anything like that Simon - kindly stop inventing fantasy phrases.

What about this from your post number 89....

Deep stops profiles are ubiquitous and more successful than there predecessors

Moving on...

You will need to concede to a few obvious flaws in this USN test first. Just because the navy wrote it - does not make it true Simon.

All studies have flaws. From the the mainstream tech diver's point of view, the USN study's main flaw is its lack of obvious comparability to typical tech diving decompressions. Nevertheless, there are underlying principles that make it relevant. My objection is to your use of strongly stated but incorrect "facts" (as I have documented) to justify your critique of studies that don't agree with your contentions.

I have watched the UHMS and its "decompression specialist" on a one sided trajectory on these issues for many years. The world has moved onto new things, and UHMS has not.

There is no UHMS "specialist". It is you who is isolated on this Ross. In trying to claim that the case for deep stop decompressions is established you are effectively arguing against the diving science community which does not agree with you. I refer you to the consensus statements from the Deep Stops workshop. Please note: the workshop is not saying that Deep Stop approaches are wrong... just that the case is unproven. Why don't you just try to be a bit more objective about this Ross.

You travel the world Simon. Have you ever met a DIR diver, a CCR diver with a Shearwater, or any other tech diver who bought any new dive computer in the last 5 years? They all use deep stops. Anecdotal data - everywhere.

I'm sorry Ross, but I can't allow you to imply that this supports your claim of superior efficacy. This is not comparative data.

DCS chamber treatments are in decline (DAN statistics). Chambers close because they don't have enough customers to pay the bills. Tech diving continues to grow. Training and gas choices improve, and better ascent profile management are to thank for this.

This is dangerously naive speculation, and it exemplifies why people like me feel the need to respond to you. Tech divers have always represented a small proportion of the total DCS cases. While that total is declining as you say, there is no evidence that it it declining because of a decrease in the incidence of tech diving cases. Indeed, I think you will find that those of us associated with hyperbaric units located in areas of tech diver activity would not have formed that impression. But there are no solid data on this.

Simon M

 

[Mark Chase]

I think it was Mark who, several pages ago asked about using a higher GF Lo setting such as 75 or thereabouts. Has anybody tried this? Is this practical or is it less safe than say a more accepted GF Lo such as 30 that most computers default to? Theoretically, this seems like a reasonable proposal. What would be the downside of this?

Getting bent,

I lack the courage of my convictions. I have read as much of the available information on deep stops as i could find and done my best to understand the findings.

My logical brain tells me 75/75 is probably a better profile than 20/90 but my problem is I have been fine on 20/90 so why take the risk?

In truth, whilst i have always been on the side of doing more deco than most of my fellow divers, I am looking for a way to stay safe but ultimately reduce in water time spent on deco.

Arnt we all

I am diving Friday and i am solo so maybe 75/75 will get a look in.


ATB

Mark

 

[Simon Mitchell]

Very interesting and thank you very much for posting. All these tests where done on Air. Is it possible that there might have been better results from deep stops if helium based mixes where used? Helium off gasses faster and a deco profiles might benefit more from deep stops using helium than when using air? Have any deep stop tests been done using helium based breathing gases ?

Hello Igor,

Sorry about the delay in replying.

There are very few data available in respect of the questions you have asked. The only actual comparison I am aware of is not published yet, but compared a deep stop approach with a more traditional approach and found more venous gas emboli with the deep stops. Hopefully this will get published soon.

There is another interesting paper in which divers performed "perfect" 65m trimix dives according to VPM-B (with deco on nitrox 50 shallower than 21m). This study found sustained high bubble grades (median grade = 3) after surfacing in the majority of dives, with arterialisation of these bubbles after 9 out of 21 dives and in 5 out of 7 subjects. The reference is:

Ljubkovic M, Marinovic J, Obad A, Breskovic T, Gaustad SE, Dujic Z. High incidence of venous and arterial gas emboli at rest after trimix diving without protocol violations. J Appl Physiol 2010;109:1670-4.

This paper is not a comparative study so we can draw no conclusions in respect of deep stop vs non-deep stop protocols, but it does at the very least show that use of VPM-B without protocol violations for trimix diving results in high bubble grades under the test conditions of the study. I suspect that the recent emergence of this study may be the reason Ross is enthusiastically downplaying the significance of venous bubble grades. I would be happy to send you a copy of the paper if you pm me.

Simon M

 

[Igor P]

Could you please fwd the papers to me too?

Igor P

Sent from my GT-I5800 using Tapatalk 2

 

[rossh]

Ross,
Tech divers have always represented a small proportion of the total DCS cases. While that total is declining as you say, there is no evidence that it it declining because of a decrease in the incidence of tech diving cases. Indeed, I think you will find that those of us associated with hyperbaric units located in areas of tech diver activity would not have formed that impression. But there are no solid data on this.

Then you are the one trying to manipulate opinion here. "Tech dive cases are declining" ... thank you. Are recreational cases not changed or increasing? We are not concerned about them here, because they don't do decompression.

You guys are sitting on the statistics, but you don't publish the reports anymore. Why is that?

All studies have flaws. From the the mainstream tech diver's point of view, the USN study's main flaw is its lack of obvious comparability to typical tech diving decompressions.

Thank you. Now if we could just stop the FUD around this report coming from various medical corners, that is implying the opposite view, and misleading the diving public.

You travel the world Simon. Have you ever met a DIR diver, a CCR diver with a Shearwater, or any other tech diver who bought any new dive computer in the last 5 years? They all use deep stops. Anecdotal data - everywhere.

I'm sorry Ross, but I can't allow you to imply that this supports your claim of superior efficacy. This is not comparative data.

Now your just being argumentative Andrew - Semantics - this in not a medical forum.

I challenge you to a simple field test; Go to your nearest tech dive charter boat location or a cave, and survey the first twenty tech divers, that are not your friends, and who you have never met before. What deco planning methods or tools will they be using? A deep stop one perhaps?

There is no UHMS "specialist". It is you who is isolated on this Ross.

For many years on your web site (maybe 5 or more), there was one Dr. with a position of decompression adviser, or a term like that. I see its been removed now. Yeah.


Thanks for the chat.

 

[rossh]

Rossh, your products are world-class. And VPM-planner is second to none for PC-software in its usability.

That being said, arguing that increased spencer-grades have no risk correlation with DCS, just gave you "egg" in your face.

I agree that there is plenty of anecdotal evidience that VPM and other deep-stop algos produces divable ascend-profiles at least when used with proper caution. That in my view means deepstops when used from these algo's are not bad. But no where has it been demonstrated that they are optimum.

The question: Given a certain dive-profile, and a constraint of a certain TAT [total ascend time], which ascendprofile is optimal in regards to DSC risk, and severity.

If the optimal profile had been shown to be deep-stops, or not, we would not be having this debate. It has *not* been shown either way.
There are no *controlled* comparing constant TATs, using modern deep-stops or not. In this regard it has not been *shown*.

You know this, but you do not like to be reminded of it. I think VPM and GF is more right than wrong, but I am not sure we are not overdoing deepstops - you are however the only one in this debate, who makes a living from deepstop-use ie. the V-planner software. In this regard I can understand you coming up in arms, but it does not serve your credibility.
You have done theese debates before; Sometimes you just implement the algorithms, sometimes you are a decompression expert. But I would urge you to not be so final in your approach.

Hanssing

Hi, thanks for your comments and compliments.

That being said, arguing that increased spencer-grades have no risk correlation with DCS, just gave you "egg" in your face.

Let me expand on that. (Its true, you can increase Grade number and no DCS occurs).

If you have a DCS event in progress, then the literature says you will likely have microbubbles associated. A few DCS events have no bubbles too. However, the presence of microbubbles on their own, does not imply an impending DCS...

It is an important distinction. The presence of Microbubbles does not mean a DCS will occur. Its also what Dr. Neal Pollock wrote in his presentation to the UHMS.

However, in the public arena, the information of recent testing is being construed into a negative form. Various people suggested that the presence of microbubbles are bad.

As for comparing DeepStop vs non DeepStop. The difficult problem is that its trying to compare two successful ascent approaches - both work just fine, without incident. But how measure success vs success? A great deal of the medical literature in written around ascent failure. Some of the methods and tools used to measure past failures, may not be the correct tools to measuring a success vs success problem.

 

[anarchista]

this in not a medical forum.

I'm losing confidence in what you pass.
You have no sense of what will be the effect of increasing tissue saturation of 10%.
Do not give numbers and sources proving your thesis.

greet rc

 

[rossh]

I'm losing confidence in what you pass.
You have no sense of what will be the effect of increasing tissue saturation of 10%.
Do not give numbers and sources proving your thesis.

greet rc

Sorry RC. The 10% was just a guestimation, and not a hard number. As you show, it needs much less to to fit the actual profiles in use. That would suggest that the real difference in gas volumes between the two profiles is lower still. Sorry, I don't have time to run a full calculation.

 

[Simon Mitchell]

Then you are the one trying to manipulate opinion here. "Tech dive cases are declining" ... thank you. Are recreational cases not changed or increasing? We are not concerned about them here, because they don't do decompression.

No, you have misinterpreted my post. I said that the total of all DCS cases was declining, not the tech cases. There is no definitive data on this, but my impression is that it is the rec cases that are declining; not the tech ones. Ross, I go on major diving expeditions as expedition doctor at least twice a year, and it is unusual not to see DCS in some form or another. DCS symptoms (usually mild ones) are common in tech diving. Many are ignored, or self treated, and never reported.

You guys are sitting on the statistics, but you don't publish the reports anymore. Why is that?

That is a good question, and I don't know the answer for sure. I think DAN stopped publishing their annual report was for financial reasons.

I challenge you to a simple field test; Go to your nearest tech dive charter boat location or a cave, and survey the first twenty tech divers, that are not your friends, and who you have never met before. What deco planning methods or tools will they be using? A deep stop one perhaps?

What does this prove Ross? Yes, lots of tech divers use deep stop models. So what? I see DCS in tech divers on a regular basis. But you don't hear me going around claiming that this means the deep stop models are no good, because I have nothing to compare these outcomes against. You need to get it through your head that the mere prevalence of deep stop decompression in the community (and the proportion of dives which result in DCS) tells us nothing of the relative efficacy of different approaches.

My objection is to your claim of superiorityfor deep stop algorithms, which is baseless. You don't know and you should stop claiming it. This was the conclusion reached by the deep stops workshop representing the diving science community.

I'm not saying deep stop algorithms don't work, and I'm not even saying they aren't superior (though recent evidence suggests not). Nobody knows for sure. Nor am I suggesting that people should change what they do. I have stopped using VPM but I still use a GF algorithm, albeit tuned to de-emphasise the deep stops. I have based that decision on the emerging evidence. The rest of the diving community deserves to understand that evidence so that they can make decisions for themselves, and your representation of it is selective, inaccurate and biased.

Simon M

 

[rossh]

Hello Igor,

Sorry about the delay in replying.

There are very few data available in respect of the questions you have asked. The only actual comparison I am aware of is not published yet, but compared a deep stop approach with a more traditional approach and found more venous gas emboli with the deep stops. Hopefully this will get published soon.

There is another interesting paper in which divers performed "perfect" 65m trimix dives according to VPM-B (with deco on nitrox 50 shallower than 21m). This study found sustained high bubble grades (median grade = 3) after surfacing in the majority of dives, with arterialisation of these bubbles after 9 out of 21 dives and in 5 out of 7 subjects. The reference is:

Ljubkovic M, Marinovic J, Obad A, Breskovic T, Gaustad SE, Dujic Z. High incidence of venous and arterial gas emboli at rest after trimix diving without protocol violations. J Appl Physiol 2010;109:1670-4.

This paper is not a comparative study so we can draw no conclusions in respect of deep stop vs non-deep stop protocols, but it does at the very least show that use of VPM-B without protocol violations for trimix diving results in high bubble grades under the test conditions of the study. I suspect that the recent emergence of this study may be the reason Ross is enthusiastically downplaying the significance of venous bubble grades. I would be happy to send you a copy of the paper if you pm me.

Simon M

Link to the paper here: http://jap.physiology.org/content/early/2010/09/02/japplphysiol.01369.2009.full.pdf


I'm not afraid of that paper Simon. In fact its quite complimentary the to successful calibration and use of VPM-B. It's good to see.

There is no DCS, despite the high bubble count. "All seven divers successfully completed the diving protocols and no signs or symptoms of DCS were observed or reported." Like I have been saying, bubble count does not imply DCS. Microbubbles are an integral part of decompression.

This test was done with conservatism of 0 (nominal), and the results show the divers were "on the edge". Perfect! This confirms that the calibrations of VPM-B seems to accurate. For normal divers, the recommended conservatism setting is + 2 or more.

But like all tests, it has flaws. The diagram of the dive profile is all screwed up. The bottom segment should be drawn to 20mins - they drew it to 14 min - which is actually the time on bottom - not run time. With that corrected, the non existent stop at 43m will vanish and the ascents will look proper.

**********

Added profile information;

The best I can determine, these profiles used the planning below. Note that the supplied diagram has some drawing errors.

#1 63, 20, 16/45
#2 66, 20, 17/47
#3 64, 19, 17/49

All with deco 50% EAN

With these extra config items applied: last stop 6m. Extended stop mix swap of minimum 2 minutes.

 

[Simon Mitchell]

There is no DCS, despite the high bubble count. "All seven divers successfully completed the diving protocols and no signs or symptoms of DCS were observed or reported."

Ross, you need to go and do a course in statistics before arguing these matters.

Simon M