Deep Stops Increases DCS

[lowviz]

OK, I spent years doing research support. Fabulous group, we all supported each other. An IT guy dropped by one day and said he found some really interesting software.

TableCurve2D. Brilliant sparse matrix software by Dr. Ron Brown. I think that he is in Atlanta now.

How? Child's play. Enter the depths and NDLs, choose "simple equations" then pick the fit you like. 222,222 is not the "best" number, but it is the easiest to remember. (well, mostly... )

 

[Dr Simon Mitchell]

However, from a purely deco schedule perspective, the decision has been made already - for 45 years we have all collectively ignored VGE in our deco planning, instead used math of tissue pressure stress.

Utter rubbish. For example, in the deveopment of the DCIEM tables (which you have praised in the past) VGE grades were explicitly measured after dive exposures to check the math, and profiles with greater than pre-selected VGE thresholds were rejected.

Simon M

 

[RainPilot]

I don't think thats an accurate thing to say. Frequency of a genetic illness isn't really the same thing as saying a dive profile has an x% chance of resulting in DCS.

What you get away with one day doesn't affect what you'll get away with on another day.

Poor example possibly. What I meant to address was NetDocs concerns over his students in NDL and the % risk of DCS for them. If you dive NDL with a 1000 people on the same profile some small percentage may have an issue but if you as an individual are fine today you'll probably be fine most of the time (identical dive profiles). Obviously aging and some other factors kick in but mainly trying to say that a 1% DCS risk on a given profile may not mean that if you dive it 100 times that you will get bent once, rather that 100 divers diving it, one may get bent.

Man its too early, never type before the coffee kicks in....

 

[rossh]

In Erik Baker's VPM code of 2001,
ftp://decompression.org/Baker/VPM%20Decompression%20Program%20in%20Fortran.pdf
you will find the parameters
Critical_Radius_N2_Microns, Crit_Volume_Parameter_Lambda, Surface_Tension_Gamma, Skin_Compression_GammaC, Regeneration_Time_Constant
to be the same as in Yount's 1986 paper.

When adding Boyle's law adjustment, Baker saw that the VPM-B algorithm became more conservative and suggested to reduce the critical radius and lambda. Great. Tune internal parameters so that the runtime looks OK to the unsuspecting user, but don't worry about parameter calibration by controlled experiments, DCS risk, efficiency or anything.

You got it backwards. The CR works in reverse. Bigger CR is more conservative. VPM-B needed lower CR settings, because the missing Boyle law component has larger effect on the overall attributes of the model output.

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[rossh]

Utter rubbish. For example, in the deveopment of the DCIEM tables (which you have praised in the past) VGE grades were explicitly measured after dive exposures to check the math, and profiles with greater than pre-selected VGE thresholds were rejected.

Simon M

No Simon. The DCIEM tables were derived from the KIdds-Stubbs dissolved gas model. What they did was adjust some parameters in the model to make the model more gentle, and then confirmed the changes with VGE checks.

So its still a tissue pressure stress measurements first as a primary measure, with VGE as a secondary check only.


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[rossh]

Let's draw an analogy. If you look at U.S. automobile fatalities, the rate has declined substantially since 1975. This is due in large part to better automobile safety technology. So if automobile fatalities are declining, then there is no need conduct additional research to make cars even safer. It's hard to imagine anyone would make that argument!

Your right - when there was a problem to solve it works.


But state the problem you are trying to solve now ??


It's NOT high DCS numbers.


The dcs we get today, all comes from issues we can mostly identify. An excess of model derived tissue pressure (profile) stress is not the issue. Tissue pressure (profile) stress is the ONLY thing a deco model can control. So obviously there is no point in trying to fiddle profile stress any more, because it won't solve any issues !


Here is a chart of all known causes of DCS. The deco model / program has control of just 2 items (stops/time) in there. Everything else is from some other influence or control of the diver.

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[rossh]

That is not a tautology. That is saying the same thing twice in a different way.

Don't be silly Ross, "one thing leads to another" is a link by anyone's definition.

Yes, arterial blood arrives in a tissue un-supersaturated. If the tissue it enters is supersaturated then the tissue off-gases into the blood making it supersaturated too. In fact, you could think of it like this if it helps.... at any snapshot in time the blood contained in tissue capillaries is effectively part of that tissue, and its gas supersaturation will reflect that of the extravascular compartment of the tissue. That is why you cannot claim that VPM protects or models (or whatever you want to call it) the extravascular compartment only, while the blood is something separate and somehow unlinked.

You may remember this diagram which helps illustrate these things:

This is the best diagram that 45 years of medical study can come up with? You made that on your computer last night. Its terrible. And it has an impossibility drawn in the middle of it.


Do Doctors seeking a hyperbaric specialty use this in their training notes? Is that approved CHT/CHRN/DMT training materials?

You have written dozens of pathophysiological pieces, lectured and lots more. Please show use some real medical information, with actual research to back up the bubble formations you have drawn and claimed exist.


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[Dr Simon Mitchell]

Ross, You are starting to make a habit of telling me I am wrong, then agreeing with what I said.

You originally stated:

However, from a purely deco schedule perspective, the decision has been made already - for 45 years we have all collectively ignored VGE in our deco planning, instead used math of tissue pressure stress.

To which I replied:

In the development of the DCIEM tables (which you have praised in the past) VGE grades were explicitly measured after dive exposures to check the math, and profiles with greater than pre-selected VGE thresholds were rejected.

In that post I have acknowledged that gas modelling (the math) came first, followed by actual dive testing in which the outcome measure determining acceptance (or not) of profiles was VGE grade. Clearly, this renders your claim that we have collectively ignored VGE in our deco planning to be completely false.

Then you come back with....

No Simon. The DCIEM tables were derived from the KIdds-Stubbs dissolved gas model. What they did was adjust some parameters in the model to make the model more gentle, and then confirmed the changes with VGE checks.

Other than your attempt to make the "VGE checks" (upon which the entire test program was based) sound unimportant, isn't that essentially what I just said?

So its still a tissue pressure stress measurements first as a primary measure, with VGE as a secondary check only

"VGE as a secondary check" in the formal test program of this iconic algorithm is NOT the same as "we have all collectively ignored VGE in our deco planning". You are contradicting yourself.

Simon M

 

[Dr Simon Mitchell]

This is the best diagram that 45 years of medical study can come up with? You made that on your computer last night. Its terrible. And it has an impossibility drawn in the middle of it.

The diagram illustrates some basic principles that have been discussed in this thread. If you believe it is incorrect please articulate the exact reason why.

Simon M

 

[rossh]

Ross, You are starting to make a habit of telling me I am wrong, then agreeing with what I said.

You originally stated:

To which I replied:

In that post I have acknowledged that gas modelling (the math) came first, followed by actual dive testing in which the outcome measure determining acceptance (or not) of profiles was VGE grade. Clearly, this renders your claim that we have collectively ignored VGE in our deco planning to be completely false.
Then you come back with....
Other than your attempt to make the "VGE checks" (upon which the entire test program was based) sound unimportant, isn't that essentially what I just said?

"VGE as a secondary check" in the formal test program of this iconic algorithm is NOT the same as "we have all collectively ignored VGE in our deco planning". You are contradicting yourself.

Simon M

The DCIEM tables are approved and used by numerous government, science, commercial bodies. They are known to be slow and safer than other mil type tables.

DCIEM tables are designed with the full knowledge that VGE exist, that VGE are part of everyday diving, and that VGE are not harmful on their own. Therefore the VGE have been ignored as a cause for concern - officially.


We have all collectively ignored VGE in our deco planning, as a cause of concern.. either in total, or with the knowledge that VGE are not harmful.

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