NEDU Study

[Freewillow]

@Patoux. It is interesting indeed, thank you for the reference .

Please note that I do not dive with helium and I am 68 years old. So when they will have figured the He/N issue out, I will be most probably dead

 

[lv2dive]

I have been gradually increasing my GFLow from 20 to 45 over the past couple of years ... the only reason I haven't made it to 50 is I want to stay within 10 feet of my buddy on deco and 45 seems the magic number to support that. I typically run a GFHigh of 80 or 85. This is for dives in the 4-6 hour range, so my CNS is well over 100%.

I am 47, and could stand to lose a few pounds, and have had very good results (knock wood!) with GF40-45/80-85 on these long dives (CCR 10/60+). Just a bit of anecdotal data to add to the discussion.

 

[Basking Ridge Diver]

There are a number of problems associated with using information from people who were bent while doing dives outside of a formal study.

I found this interesting - it mentions that the Severity of the dive profile and the Effect of the Environment on the Dive Profile has a direct link to the cases of DCS which makes sense. NEDU testing at or beyond what is safe limits for DCS. He also says his correlation can not be made directly since these are different environments that are being compared (4 dive sites) - but it is an interesting look at DCS that I have not seen before.


Watch the entire clip but at about 39:48 through the end is the interesting part to me. It links tunnel workers and divers with DCS.

 

[UWSojourner]

I found this interesting - it mentions that the Severity of the dive profile and the Effect of the Environment on the Dive Profile has a direct link to the cases of DCS which makes sense. NEDU testing at or beyond what is safe limits for DCS. He also says his correlation can not be made directly since these are different environments that are being compared (4 dive sites) - but it is an interesting look at DCS that I have not seen before.


Watch the entire clip but at about 39:48 through the end is the interesting part to me. It links tunnel workers and divers with DCS.

Thanks for the link. Interesting presentation. The part that jumped out at me was around minute 38 when he talked about 1-g vs. u-g differences.

Based on the differences in DCS discussed, I'd think the strategy employed by VPM-B whereby you favor the fast compartments at depth and cause more deco stress in the slower compartments at the surface would be suspect. Reentry to a 1-g environment with more of a gas load seems like a losing proposition. That also aligns well with the NEDU test and the bubble count studies that showed more bubble formation from deep stop profiles.

 

[rossh]

Thanks for the link. Interesting presentation. The part that jumped out at me was around minute 38 when he talked about 1-g vs. u-g differences.

Based on the differences in DCS discussed, I'd think the strategy employed by VPM-B whereby you favor the fast compartments at depth and cause more deco stress in the slower compartments at the surface would be suspect. Reentry to a 1-g environment with more of a gas load seems like a losing proposition. That also aligns well with the NEDU test and the bubble count studies that showed more bubble formation from deep stop profiles.

The dive plan shown, is about a GF 70/x. But I really can't identify what it might be after that. Its most likely an OC dive. It kind of fits a plain air dive with no deco gas. Most likely its a navy table or a commercial one.

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The tiny difference that you mention in VPM-B plans, is moot. A 5 minute increase in dive bottom time, will cause far a greater change to surface stress levels, than the tiny difference you reference.

This fuss over VPM surface stress, is about the size of a storm in a tea cup.

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[UWSojourner]

The tiny difference that you mention in VPM-B plans, is moot ... This fuss over VPM surface stress, is about the size of a storm in a tea cup.

Divers will have to make their own risk decisions. But for the dive I showed earlier (CCR 270ft 20min), the difference doesn't seem "tiny".

For that dive, for the same runtime, I can exit the water at a GF of 82 by choosing GF50/82. Or I can exit the water at a GF of about 107 by choosing VPM-B+2. So the decision to use VPM-B+2 for that dive incurs a 30% increase in surfacing GF.

About the same thing is shown by the integral supersaturation chart. VPM-B+2's integral supersaturation at the surface is roughly 33% higher than GF50/82 for the same runtime.

Now, because the NEDU study demonstrated that "protecting the fast tissues" is not the defining characteristic of a safe profile (see this discussion), a logical question to ask is "What benefit is VPM-B+2 providing that justifies the increased supersaturation exposure???"

If you see these issues as "moot" or "tiny" then VPM-B may be for you. I doubt most divers see them that way.

 

[rossh]

Diver's will have to make their own risk decisions. But for the dive I showed earlier (CCR 270ft 20min), the difference doesn't seem "tiny".

For that dive, for the same runtime, I can exit the water at a GF of 82 by choosing GF50/82. Or I can exit the water at a GF of about 107 by choosing VPM-B+2. So the decision to use VPM-B+2 for that dive incurs a 30% increase in surfacing GF.

About the same thing is shown by the integral supersaturation chart. VPM-B+2's integral supersaturation at the surface is roughly 33% higher than GF50/82 for the same runtime.

Now, because the NEDU study demonstrated that "protecting the fast tissues" is not the defining characteristic of a safe profile (see this discussion), a logical question to ask is "What benefit is VPM-B+2 providing that justifies the increased supersaturation exposure???"

If you see these issues as "moot" or "tiny" then VPM-B may be for you. I doubt most divers see them that way.

You are not making a valid comparison. You have taken a ZHL plan, stretched and reshaped the thing like you want it. Then turn around and say... "look my stretched out and fiddled profile, fits my criteria, better than yours". The answer to that is a big fat so what.

You keep showing us how some vague, undefined, baseless fiddled GF profile. The GF keeps getting changed in every example.

The biggest stress is clearly the in water portion and ascent, where the injury starts and is seeded. But that part is drawn as a small number in you charts.

The surface stress, which you draw very large, is actually in rapid decline, and quickly falls to insignificant values. But your method has no ability to discern that, and instead it adds up loads harmless time, which outweighs the actual important parts.

Its a frivolous comparison. You are using a measure that has never been approved for this purpose, and your method has some clear violations of the basic model design criteria. i.e. ZHL cell data simply cannot be added up into one giant number like this.

This application of ISS, as done here, is not valid. The drawings are out of scale with the real stresses.
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[UWSojourner]

You are not making a valid comparison. You have taken a ZHL plan, stretched and reshaped the thing like you want it. Then turn around and say... "look my stretched out and fiddled profile, fits my criteria, better than yours".

The GF settings were chosen so that the dive runtimes match. VPM-B+2, GF20/90, GF30/88, and GF50/82 all surface at the same time. Therefore the dives only vary by the deco algorithm's stop recommendations.

VPM-B+2 causes the diver to surface at a GF of 107 vs. 82 for GF50/82 -- FOR THE SAME RUNTIME. I doubt most divers will fail to see the relevancy of the comparison or believe that the difference is "tiny".

 

[rossh]

There is no validation or test, that says or proves, that all dives are some how magically made equal, by having the run time the same. It's a fallacy... a convenience that is being exploited. It is an artificial limit, that always favors the shallow profiles. Real models are not constrained this way.

If you compare actual models.... VPM-B vs ZHL-C then VPM-B is much longer that your samples above. (ZHL-C=74min, VPM-B=93min).

Like I said... Your comparisons are biased for the result you want, and are using invalid measures and methods. You need to: a/ get the method validated, and b/ remove the inbuilt bias in the test.


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There is a database of real dives, using all these kinds of settings and depths.

data base - 270ft CCR examples

There are literally hundred of examples of dives with 20 mins on CCR at these typical depths. So maybe, your diagram is making a giant fuss, over nothing. The differences you are pointing at, don't seem to matter much in the real world.

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[Dr Simon Mitchell]

There is no validation or test, that says or proves, that all dives are some how magically made equal, by having the run time the same. It's a fallacy... a convenience that is being exploited. It is an artificial limit, that always favors the shallow profiles

No its not a fallacy Ross. Equivalent run times is a simple requirement, recognised by all experts in decompression, that must be adhered to if you want to answer the relevant question. That question is:

"If I have x amount of time to spend decompressing, what is the most effective way of distributing my decompression time among the various stop depths?"

If the run times of test profiles are different, you cannot answer that question.

Translated to a more specific situation, if a diver is a VPM user, the algorithm will prescribe a specific duration of decompression and a pattern of stops to complete. The question the diver might ask is: "is that pattern of stops suggested by VPM the most effective way of using the total period of decompression that VPM has prescribed?"

UW Sojourner is presenting us with evidence that there are more effective ways of using the total decompression time prescribed by VPM, by distributing the stops differently. The evidence is based on analysis of supersaturation patterns and total integral supersaturation. Contrary to your claims, these are not invalid or untested measures. Summed integral supersaturation is commonly used as a parameter in decompression algorithms and the supersaturation patterns produced by a shallower distribution of stops than prescribed by bubble models (like VPM) were shown to be more successful in the NEDU study.

There is a database of real dives, using all these kinds of settings and depths.

data base - 270ft CCR examples

There are literally hundred of examples of dives with 20 mins on CCR at these typical depths. So maybe, your diagram is making a giant fuss, over nothing. The differences you are pointing at, don't seem to matter much in the real world.

You don't have outcomes for these dives so the mere fact that they have been done is totally irrelevant.

Simon M