Will http://www.ncbi.nlm.nih.gov/pubmed/25525213 change deco procedures?

[PfcAJ]

More about pDCS increasing as length of dive increases:
[abstract]DECOMPRESSION RISK EVALUATION FOR TRIMIX DIVES DERIVED FROM COMMERCIALLY AVAILABLE DESKTOP DECOMPRESSION ALGORITHMS

 

[tursiops]

More about pDCS increasing as length of dive increases:
[abstract]DECOMPRESSION RISK EVALUATION FOR TRIMIX DIVES DERIVED FROM COMMERCIALLY AVAILABLE DESKTOP DECOMPRESSION ALGORITHMS

Was the full article ever published?

 

[rossh]

Ross, I'm not nearly as polite or patient as Doolette and Mitchell. All the questions you're asking me now have been answered by them over on ccrx.

1- No? Wtf do you get that idea out of what I wrote? Helium can (and does) cause DCS, I don't see where I suggested otherwise or where anyone has suggested that.... Adding extra deco just because of helium appears to not be warranted.

2- Its a problem with the 'big two' deco algorithms. None of them are calibrated to provide pDCS based ascent plans. You are unable to tell me what the pDCS is using vpm+2, just as I am unable to tell you the pDCS for a 20/85 ascent. Similarly, pDCS for a 20/85 ascent following a 20min@300ft dive is totally different (greater) than the pDCS for a 20min@150ft dive. Along the same lines, pDCS for a 20/85 ascent for a 20min@300ft does not equal pDCS for 80mins@300ft. Same same with VPM. It makes comparing apples to apples very difficult.

3- When I compare buhlmann (default 20/85) with vpm +2, the times are almost always shorter with VPM. Doing LESS deco (vpm) isn't going to help reduce your dcs rate.

1/ You misunderstood - not directed at you - sorry for giving that impression. It's a question for Doolette and Mitchell to answer (which they have avoided doing). They have proposed that helium is not what its seems, have said some vague things about why existing deco times might be incorrect in certain ways, but correct in others ways for different reasons, but have not explained the reasons behind that. All too vague I think. When pressed they skipped the answers.


2/ Well, no. pDCS is strictly a military planning tool and method, and you wont find it in commercial tools or models. But pDCS is a bigger measure and encompasses more details than gas pressure stresses and planning alone will provide. It works beyond the capabilities of a deco model.

Instead of pDCS, tech deco models have conservatism. It provides a scaled mechanism to reduce risk.

But the two paths do not usually cross, because the technical diving has experience with trimix. Most of the navies of the world are strictly full heliox, so its difficult to cross compare between the two. But each does use a different risk reduction mechanism.



3/ Where is it written that 20/85 is some standard of GF? It's not. GF can be / is a large extrapolation out of ZHL, but GF's simplistic nature does not make for a scaled outcome. The whole purpose of the split lo/hi GF was so you can decide what you want to have as a profile shape. You have huge power to make any shape you desire with GF, and very quickly it will abandon the underlying ZHL model principles. You say that when you try to emulate a VPM-B profile, that GF can't do it perfectly. To which the answer is - tough luck - that's a problem of using GF.

 

[PfcAJ]

1/ You misunderstood - not directed at you - sorry for giving that impression. It's a question for Doolette and Mitchell to answer (which they have avoided doing). They have proposed that helium is not what its seems, have said some vague things about why existing deco times might be incorrect in certain ways, but correct in others ways for different reasons, but have not explained the reasons behind that. All too vague I think. When pressed they skipped the answers.


2/ Well, no. pDCS is strictly a military planning tool and method, and you wont find it in commercial tools or models. But pDCS is a bigger measure and encompasses more details than gas pressure stresses and planning alone will provide. It works beyond the capabilities of a deco model.

Instead of pDCS, tech deco models have conservatism. It provides a scaled mechanism to reduce risk.

But the two paths do not usually cross, because the technical diving has experience with trimix. Most of the navies of the world are strictly full heliox, so its difficult to cross compare between the two. But each does use a different risk reduction mechanism.



3/ Where is it written that 20/85 is some standard of GF? It's not. GF is a large extrapolation out of ZHL, and GF's simplistic nature does not make a scaled outcome. The whole purpose of the split lo/hi GF was so you can decide what you want to have as a profile shape. You have huge power to make any shape you desire with GF, and very quickly it can abandon the underlying ZHL model principles. You say that when you try to emulate a VPM-B profile, GF can't do it perfectly. To which the answer is - tough luck - that's a problem of using GF.

Ross,
1. I think its fairly clear why existing deco times might be incorrect: The models are wrong. If your pDCS increases as the length of the dive increases (other variables held constant, like gases, GF/conservatism setting, etc), something isn't right. I think its safe to assume that everyone wants to keep their chances of getting bent to a minimum, and a deco program that doesn't keep that risk constant is broken. At present, all the popular models do no keep risk constant.

2. Tech deco models do have 'conservatism', but that conservatism isn't quantified. VPMs conservatism is easy to discuss as its numbered. How much less likely are you to experience DCS by selecting "+2" vs "+1" for a given dive?

3. 20/85 is at least the default condition in DecoPlanner, and I think its the default setting from Shearwater and iDeco. In my mind, the power of GF is that it allows you to modify a broken model (they're all broken, after all) to something that reflects the current understanding of decompression. I know you don't think its valid, but I've been able to move away from deeper stops and lengthen shallow times by manipulating GF settings.

 

[rossh]

Ross,
1. I think its fairly clear why existing deco times might be incorrect: The models are wrong. If your pDCS increases as the length of the dive increases (other variables held constant, like gases, GF/conservatism setting, etc), something isn't right. I think its safe to assume that everyone wants to keep their chances of getting bent to a minimum, and a deco program that doesn't keep that risk constant is broken. At present, all the popular models do no keep risk constant.

2. Tech deco models do have 'conservatism', but that conservatism isn't quantified. VPMs conservatism is easy to discuss as its numbered. How much less likely are you to experience DCS by selecting "+2" vs "+1" for a given dive?

3. 20/85 is at least the default condition in DecoPlanner, and I think its the default setting from Shearwater and iDeco. In my mind, the power of GF is that it allows you to modify a broken model (they're all broken, after all) to something that reflects the current understanding of decompression. I know you don't think its valid, but I've been able to move away from deeper stops and lengthen shallow times by manipulating GF settings.

Hi,

1/ Yes, and no. There are differences in people. Some can dive with no conservatism, and some cannot dive with all the conservatism they can possibly muster. Where do we draw the line? Does the slowest 0.001% set the standard for everyone else? Or do we make the 0.001% face up to the reality?

You say the models are wrong? Really - by how much? When Dr. Buhlmann published, he had testing with it. I'm confident his work was good, and his calibrations valid. But no one much wants to do real ZHL Buhlmann dives profiles anymore.


What about aging factors? We do absolutely nothing about this formally in dive planning. It's completely ignored by the aging re-breather population, who are the main complainers and source of these issues of late. Yet, I have here in front of me, a new book by Mitchell and 3 of his colleagues on Diving and Sub-aquatic Medicine 5th ed. In this they make is clear the effects of aging and how it requires more deco time to compensate. The cutoff point they suggest to slow down is 4th decade.


2/ Are you familiar with the expression, "if some is good, then more must be better" ? I think it applies to deco too. The VPM-B model has the conservatism changes made integral to the model core calculations - conservatism is baked into the computed result. Meanwhile, the other models have no conservatism mechanism at all. In ZHL and other Haldane designs, your options are to recompute the plan with added fake depth, or added fake time. Or use GF to stretch out the result. The VPM-B conservatism is based on science and parameter changes, while the ZHL conservatism is based on fudged extra time. Enough said.


3/ The 20/85 setting is yesterday's "standard GF". Today's "standard GF" is 40/70. And tomorrow it will be something else again. And so it goes on, because new people find new favorite settings, that fit to the narrow scope of dive ranges they choose. The standard GF numbers is vague and roams around, because GF is not a model or a baseline - it's extra time padded onto the end of a ZHL model result.

 

[PfcAJ]

Hi,

1/ Yes, and no. There are differences in people. Some can dive with no conservatism, and some cannot dive with all the conservatism they can possibly muster. Where do we draw the line? Does the slowest 0.001% set the standard for everyone else? Or do we make the 0.001% face up to the reality?

You say the models are wrong? Really - by how much? When Dr. Buhlmann published, he had testing with it. I'm confident his work was good, and his calibrations valid. But no one much wants to do real ZHL Buhlmann dives profiles anymore.


What about aging factors? We do absolutely nothing about this formally in dive planning. It's completely ignored by the aging re-breather population, who are the main complainers and source of these issues of late. Yet, I have here in front of me, a new book by Mitchell and 3 of his colleagues on Diving and Sub-aquatic Medicine 5th ed. In this they make is clear the effects of aging and how it requires more deco time to compensate. The cutoff point they suggest to slow down is 4th decade.


2/ Are you familiar with the expression, "if some is good, then more must be better" ? I think it applies to deco too. The VPM-B model has the conservatism changes made integral to the model core calculations - conservatism is baked into the computed result. Meanwhile, the other models have no conservatism mechanism at all. In ZHL and other Haldane designs, your options are to recompute the plan with added fake depth, or added fake time. Or use GF to stretch out the result. The VPM-B conservatism is based on science and parameter changes, while the ZHL is based fudged on extra time. Enough said.


3/ The 20/85 setting is yesterday's "standard GF". Today's "standard GF" is 40/70. And tomorrow it will be something else again. And so it goes on, because new people find new favorite settings, that fit to the narrow scope of dive ranges they choose. The standard GF numbers is vague and roams around, because GF is not a model or a baseline - it's extra time padded onto the end of ZHL model result.

We're approaching the patience threshold I wrote about earlier.

1. I refer you to the abstract I posted above. That's a serious problem with today's deco algorithms and ignoring it doesn't help anyone make informed decisions. If pDCS is 1% for one ascent schedule but 10% with another ascent schedule generated by the same algorithm with the same settings just by virtue of the dive being longer, something is up. The answer won't be found by sticking your head in the sand.

2. Its not enough said. You didn't really 'say' anything. You have no idea how much reduction in risk you get from moving to +1 to +2. That's fine, but just say "I don't really know, it hasn't been tested" and get on with your life.

3. You're using 'standard', I'm using default. Its for comparative purposes. Like I said, you can adjust the GFs however you choose based on what you're doing and what you know (or think you know).

 

[rossh]

We're approaching the patience threshold I wrote about earlier.

1. I refer you to the abstract I posted above. That's a serious problem with today's deco algorithms and ignoring it doesn't help anyone make informed decisions. If pDCS is 1% for one ascent schedule but 10% with another ascent schedule generated by the same algorithm with the same settings just by virtue of the dive being longer, something is up. The answer won't be found by sticking your head in the sand.

2. Its not enough said. You didn't really 'say' anything. You have no idea how much reduction in risk you get from moving to +1 to +2. That's fine, but just say "I don't really know, it hasn't been tested" and get on with your life.

3. You're using 'standard', I'm using default. Its for comparative purposes. Like I said, you can adjust the GFs however you choose based on what you're doing and what you know (or think you know).

Why the sudden urgency to adopt pDCS? There is no data base of results from trimix and deep (deeper) stops profile, to compile pDCS numbers from. The nedu and USN does not do tech diving practices.



We don't know the precise amount of risk reductions per each step of conservatism - never will. Same as we do not know how much a 5% change GF hi is worth "I don't really know, it hasn't been tested" That is correct.

But, using one's brain a little, its fair to think that extending deco time by x%, is going to provide a reduction in risk of y%. Do you need to know the precise amounts of x and y? No. What one needs to know is where one fits into the scheme and adopt that level across the range of dives.

 

[PfcAJ]

Why the sudden urgency to adopt pDCS? There is no data base of results from trimix and deep (deeper) stops profile, to compile pDCS numbers from. The nedu and USN does not do tech diving practices.



We don't know the precise amount of risk reductions per each step of conservatism - never will. Same as we do not know how much a 5% change GF hi is worth "I don't really know, it hasn't been tested" That is correct.

But, using one's brain a little, its fair to think that extending deco time by x%, is going to provide a reduction in risk of y%. Do you need to know the precise amounts of x and y? No. What one needs to know is where one fits into the scheme and adopt that level across the range of dives.

Probably because I want to maintain a low risk of getting bent? Call me crazy...

You're correct, we don't know the pDCS change by manipulating gradient factors. I never suggested that we do.

Using my brain a little, that answer isn't good enough. If a simple 10min extension of deco time dramatically reduces DCS risk, then its a good thing to do. If a 10min extension doesn't really reduce the DSK risk in a meaningful way, why bother? Those x and y values are important, and at present we don't know them.

 

[rossh]

Probably because I want to maintain a low risk of getting bent? Call me crazy...

You're correct, we don't know the pDCS change by manipulating gradient factors. I never suggested that we do.

Using my brain a little, that answer isn't good enough. If a simple 10min extension of deco time dramatically reduces DCS risk, then its a good thing to do. If a 10min extension doesn't really reduce the DSK risk in a meaningful way, why bother? Those x and y values are important, and at present we don't know them.

You are asking for levels of precision, that are not known, or likely to be achieved. All diving has risk, including simple shallow NDL dives. You cannot create or dive with a 0% pDCS risk.

You are welcome to do all the deco you want or feel you need. But, please do not insist that everyone else has to do your level as well. Public dive models have to serve a wide audience, ages and dive styles.

 

[PfcAJ]

You are asking for levels of precision, that are not known, or likely to be achieved. All diving has risk, including simple shallow NDL dives. You cannot create or dive with a 0% pDCS risk.

You are welcome to do all the deco you want or feel you need. But, please do not insist that everyone else has to do your level as well. Public dive models have to serve a wide audience, ages and dive styles.

I don't want or expect 0%. That's unattainable. Never suggested otherwise.

I also don't really care what you (or anyone, sorry guys) does for deco. If you're happy to accept a high level of risk, go nuts. If you want to minimize your risk, enjoy. However, I would like for people to know about their deco and make decisions accordingly. That can only be done through presentation of information which is all I'm trying to do.