Son of Deep Stops *or* Waiting to be merged with the mother thread...

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Below is a comparison of VPM-B run times and surfacing gradient factors for short bottom time dives from 150 to 500ft. All dives are CCR.

VPM-BE+4 sure does seem fond of it's cousin VPM-B+7. Their run times are a near match after about 275ft. BE+4's better surfacing GFs are mostly due to more quickly getting to the higher O2 fractions on the CCR.

Gradient factors shown are based on ZH-L16C.
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Well, that's the problem , isn't it? What is this "DCS stress" you speak of?

Although the occurrence of VGE might be a relatively poor predictor of DCS,
the absence of VGE is a good indicator of decompression safety, and can be used to estimate
a level of decompression stress


Clearly it's not DCS, VGE being a "poor predictor" of that. Best I can figure from the above is it's some kind of "decompression unsafety".

"a close relationship between the number or load of VGE present and DCS cannot be derived"
I believe in these last few posts you are mixing up two possible ways in which VGE might be used. In an earlier posts you mentioned predictive power and specificity.These are measures of the utility of a binary classification test, for instance a diagnosis of DCS in an individual based on VGE. VGE are very poor for this purpose. This is the "1:1" relationship that Ross knows is poor, and therefore wants to use to discredit the real utility of VGE. But no one else on any of these threads is talking about using VGE to diagnose DCS. The real utility of VGE is that in a large enough sample of repetitions of a dive profile, the median (for instance) VGE grades are indicative of the decompression stress or probability of DCS.

Copied from the other thread:

As some background, VGE are graded using ordinal scales typically ranging from 0 to IV, that correspond to the number of bubbles heard in Doppler blood flow signals in large veins or seen in 2-D echocardiographic images of the heart chambers. These VGE grades have a general correlation with the incidence of DCS in large compilations of data. The biggest of these compilations is from the development of the Canadian Forces decompression tables and some of these data have appeared in several places, including Bennett and Elliott’s Physiology of Medicine and Diving, and were analyzed by David Sawatzky in his M.Sc thesis. If you separate the dives into those in which the maximum grade detected following diving was 0 or I or II etc, there is an increasing incidence of decompression sickness (DCS) in the successive higher VGE grades. For instance in air diving: grade 0 (0 DCS/ 819 dives); grades I (3 DCS/287 dives); grade II (2 DCS/183 dives; grades III (27 DCS/365 dives); and grade IV (9 DCS/72 dives). I do not have heliox and trimix data in front of me, but it contains the same correlation. This correlation arises in part because VGE can cause some manifestations of DCS, but also, because VGE form in response to the same stresses that form bubbles elsewhere in the body, VGE are probably correlated with an increase risk of bubble formation at other (extravascular) DCS site.

So, on to the possible uses of VGE.

1) Can you use the VGE grade in an individual diver to diagnose DCS or predict if they will develop DCS? No, the relationship is not strong enough. This is use for which the poor “positive predictive power” of VGE, which has been mentioned, is relevant. To illustrate this, let us suppose that we decided to diagnose DCS in divers on the basis of a VGE score of IV, i.e. any diver who shows a score VGE grade of IV gets tossed in the chamber and treated whether they have symptoms or not. The data above suggests that we would be correct about 13% of the time and wrong about 87% of the time. These latter 87% ‘false positives’, without going into details of the calculations, are the essence of poor positive predictive power.

2) Do the VGE grades measured in a group of divers, all who have performed the same dive profile, provide an estimate of risk of DCS of that decompression schedule? Yes. To illustrate, instead of an individual diver, imagine 50 divers conducted an identical dive profile (dive profile 1) and all 50 divers manifest VGE grade I and another 50 divers conducted dive profile 2 and all 50 divers had VGE grade III. We still would not know if any particular diver would go on to develop DCS, but we could estimate, with considerable confidence based on the data above, that profile 2 had a greater risk of DCS than profile 1, and even (with less confidence), that dive profiles 1 and 2 had risks of DCS of about 1% and 7%. This is an oversimplification, but again this is the essence of the use of VGE to estimate the risk of DCS.

2a) Are VGE used to validate decompression schedules? Yes. The gold standard for validating decompression schedules – and the method still used by the U.S. Navy - is the incidence of DCS, i.e. you test a schedule and accept it if it results in a low incidence of DCS and reject it if it results in a high incidence of DCS. However, many other navies now use VGE as well as, or instead of, DCS. The best example is the validation of the Canadian Forces (DCIEM) decompression tables, which produced the data mentioned above. In this approach, the maximum VGE measured after diving is considered a measure of “decompression stress”, and a schedule is accepted if it consistently produces low VGE grades and rejected if it consistently produces high VGE grades. The DCIEM criteria for heliox schedules is to reject a schedule if in 20 dives the median VGE grade is III or higher.

David
 
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not really, even with very conservative profiles among recreational divers there are ALWAYS divers who end up with DCS. It may be a PFO or an uncontrolled assent or something else. The question becomes if there was not any in 200,000 dives how that was possible? Was every case of DCS excluded thru a process of finding out the underlying "cause" of the DCS or was there simply an assumption made that any diver who got DCS while diving RGBM was somehow "at fault" and the record protected.

Well, if they removed the ones they identified the underlying cause as "an expansion of inert gas" that would drastically reduce the number of cases.

0 incidences in 200,000 dives is truly doubtful.

FWIW, I can not count the number of times I've been bent on all of my fingers and toes, and I truly do not know how many times I have been bent. Some of those hits were due to playing with ratio deco and "deep stops while shortening my shallow stops" in the 90s. Some of those hits were because a PFO I had managed to become a problem once I was in my mid-40s.

And I've been bend free since having my hole plugged in September 2014.
 
Well, if they removed the ones they identified the underlying cause as "an expansion of inert gas" that would drastically reduce the number of cases.

.
that may be it...LOL :)
 
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DCS is correlated with high grade VGE, but not the other way around. I can't in all fairness fault Ross for wanting to scream at the top of his lungs here.

David has beaten me to it with a much more comprehensive account. We keep telling Ross that everyone agrees we cannot use VGE to diagnose DCS in an individual diver, but he keeps raising quotes from the literature which make that point because it is easy to disguise them as suggesting that VGE are not useful in decompression research. This serves his narrative because the comparative studies have suggested that bubble models produce more VGE than gas content model decompressions. The latter scenario is exactly where the diving science community is in agreement; that is, that VGE are useful in evaluating the relative risk of approaches to decompression. Ross can scream at the top of his lungs all he wants, but he is completely at odds with the scientific community, including (ironically) all of those he quotes as if they support his position.

Simon M
 
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rossh:
SIMON ASKED: "....by way of a reminder, could you explain how VPM B/E+5 is sanctioned whilst VPM B+7 is considered "fake" even though....."

Answer:

VPM-B/E is published and used widely since 2004: info (Note: it won't make a Nedu A2 profile either).

+7 is not available, or used anywhere. It was entirely made up by ... and ..., to fabricate an non-existent data point, to make invalid comparisons with, for the sole purpose of inventing a connection between VPM-B and the shallow Nedu trail profiles. It's a clear attempt to deceive the public, and an attribution that does not exist. As a science person trying to make valid argument, I would think you would be ashamed of any association to such underhanded tactics.

You are completely missing the point Ross. The point is that there is a version of VPM (VPM-B/E+5) which you sanction, which does indeed produce profiles of a length approaching the NEDU deep stops profile (A2). It does not really matter what you think of VPM-B+7 any more. UWSojourner has produced comparisons. People can judge for themselves how similar they are.

Simon M
 
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You are completely missing the point Ross. The point is that there is a version of VPM (VPM-B/E+5) which you sanction, which does indeed produce profiles quite similar to the NEDU deep stops profile (A2) (which produced more DCS). It does not really matter what you think of VPM-B+7 any more. UWSojourner has produced comparisons. People can judge for themselves how similar they are.

Simon M

VPM-B/E cannot and does NOT make a Nedu A2 profile.

VPM-B/E makes a normal plan VPM-B plan for about 100 mins or so, and then morphs towards a combined VPM-B and ZHL plan after that. VPM-B/E was released in 2004, to satisfy the need for extra added safety and extreme / longer dive plans than exploration divers wanted at the time.

Nothing can make a Nedu A2 plan, because the Nedu plans are not real - they are stretched out, double time, test profiles. That is why you had to "invent" and non-existent +7 idea, so you could match up two unrealistic things.

****


VPM-B +7 does not exist - never will. It's a useless stretched out nonsense idea, that has gone beyond the context of the problem. Just like the Nedu profiles, the +7 has no use or purpose in the real world.

We cannot buy or make a VPM-B +7 plan. It does not exist. Kevin Watts is the only person who has it.

The only purpose of a fabricated +7 plan, is to compare to other non-realistic profiles. The whole thing is a fantasy - a fallacy - a figment of the imagination - wishful thinking. The basis of these/your attacks on VPM-B, is a non-sequitur comparison.

***

Stop it please Simon. If you think you can win this argument, by tricking a deceiving the public, then I think you have some serious integrity issues to be resolved. You are only fooling yourself in the end.

.
 
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VPM-B/E cannot and does NOT make a Nedu A2 profile.

....except that it's darned close. Also, VPM-B +7 fits within Eric Baker's parameters (having started going through the code myself, I don't see how it could possibly be considered invalid).

As for Nedu A2 profile being "not real"......I remind you that none of these are "real." It's also incredibly contradictory (like many of your statements) that the NEDU profiles are "fake" because they're "stretched out too long"....yet they have high DCS incidences. Clearly they're not overly long or the DCS rate would've been statistically zero, right? Imagine adding conservatism to a profile and getting an increase in DCS.
 
....except that it's darned close. Also, VPM-B +7 fits within Eric Baker's parameters (having started going through the code myself, I don't see how it could possibly be considered invalid).
+7 is perfectly valid. Increasing the critical radius should simply make the model more conservative. It is only considered invalid (by Ross) because it completely kills his argument about the relevance of the NEDU study to the sort of profiles prescribed by his model.

Simon M
 
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