NEDU Study

[Dr Simon Mitchell]

The real world DCS rate has been in decline for the past 15 years, including tech diving

Ross, you keep making this claim about tech diving DCS rate and I keep asking you to cite the data that justifies the claim, but you never do. Once and for all, please cite the valid data that proves your point, or don't make the claim again.

This image made using proper scientific measures, and industry accepted formula

You keep using the terms "proper scientific measures" and "industry accepted formula" in a manner intended to give credence to your claims. These measures and formula are just the basic tools that all calculations of tissue gas pressures are based on. UWSojourner uses these same "proper scientific measures" and "industry accepted formula" in his calculations too.

The significant stress is from the dive portion. This is where the injury starts - the surface part adds fuel to the fire.

The most important lesson we have learned from the NEDU study is that the "significant stress" is probably supersaturation in the slower tissues late in the ascent and at the surface, and that protecting fast tissues from supersaturation early in the ascent is not as important as bubble modellers theorized it to be. Your comparison with raw ZHL-C shows that VPM protects the fast tissues early at the expense of greater slow tissue supersaturation later. I don't know what, exactly, you are trying to prove, but it is conceivable that if you ran a trial of these profiles that (based on what we currently know) the ZHL-C profile might carry less risk. Or it might be too far in the shallow stops direction, which is why we are cautiously favouring a gradient factors approach to de-emphasising deep stops.

The surface portion is declining across all cells. After an hour or two on the surface, the supersaturation has decayed to harmless amounts.

Yes, of course it is. It is called off-gassing. What is your point Ross?

ZHL has higher dive stress than VPM-B, for the first half of the dive.

Yes, and the NEDU shallow stops profile had higher stress than the bubble model profile in the first part of the ascent too, and yet it resulted in significantly less DCS.

Added: The above is part of the "profile stress" component of a DCS injury. This is the only part that the deco model has any control over. If the above profile and stress is too fast, too short, too shallow, too crazy, then an injury will likely follow. But with today's models and ascents, we are not usually threatened by "profile stress", because all models normally are slow and long enough to avoid the dangerous amounts.

How do you know this? Where is your database of precisely controlled dives of known outcome using "todays models and ascents" that tells you that this statement is correct?

Take a look at this diagram by Neil Pollock from his excellent decompression stress presentation. It shows 20 possible sources of stress. Note that deco model controls just 2 items (stops, time). Most injuries today are from one of the 18 other causes.

How would you know this? Some of the risk factors can be influential; there is no doubt about that. But I have heard Neal give this presentation many times and I can tell you he does not agree with your interpretation. He is now including a statement highlighting the pre-eminent importance of the dive profile specifically because of your habitual misrepresentation of his views.

ZHL-C + GF also suffers from compounding errors... its not proportionally consistent across the dive spectrum. The shallow time feeds off its own compounding, and jumps to the next cell and exaggerates further. In addition, its a linear adjustment applied to values that are exponential in design.

This is obfuscation. Gradient factor modifications to Buhlmann produce profiles that are able to be analysed and compared to any other profile in terms of tissue supersaturation levels and patterns. The effects of adjustments are transparent and measurable. You just don't like the GF profiles because the method allows divers to generate a profile that produces tissue supersaturation patterns most like the successful NEDU profile and least like the unsuccessful one whist avoiding radical departures from current practices. And they compare favourably in integral supersaturation analyses against profiles generated by your model as UWSojourner has demonstrated.

Parenthetically, if you want an example of a model that "is not proportionally consistent across the dive spectrum" look no further than your own for reasons UWSojourner has explained in the past. Your own insistence that it works on low conservatism but not high conservatism also does not give me much confidence in its "proportional consistency".

There is only one real ZHL-C model plan. All else is made up fiddle to fit some dive preference, or to suit some argument.

It is not to "suit some argument" Ross, it is an attempt to meaningfully apply our gradually evolving knowledge of optimal decompression. You just don't like it because evolving GF approaches are not the same as your favoured approach.

Simon M

 

[Diver0001]

You really have problems incorporating the idea of TIME into your thinking.

The two dives you show differ in runtime by about 12 minutes (roughly 20+% of the decompression). What is that supposed to show? That you can graph two dives?
.

He has been doing this since the very beginning. I'm tried to confront him before about presenting graphs printed at different time scales to make them look comparable when they were not. Scientists have been trying to get him to understand this and yet for some reason the coin will simply not drop. Since I do not think that Ross is unable to understand this, my conclusion is that he must be making a deliberate attempt to confuse people.

I'm actually glad that someone else has clued in to the fact that this is what he's doing so that readers can see multiple people pointing this out.

Take a look at the attached graphic. I clipped that out of the video someone posted above. This is what the entire discussion is about. This graph is simplified but absolutely clear for the layman and it is not a manipulation. Read the studies. The science is good.

The complication for Ross, of course, is that you need to use higher and higher levels of "conservatism" in VPM in order to get the same run times. One would logically think that higher conservatism in a decompression model would lead to lower levels of DCS risk. In the case of VPM it's pretty clear that LOWER levels of conservatism leads to "safer" (let's put it that way) dives.

The HUGE disconnect in this, and the implications for VPM are substantial. With this paradoxical finding in mind, my conclusion is that there is something fundamentally broken about VPM. For myself I also draw the conclusion that other other models that are designed around bubble mechanics will suffer from the same "problem" and for the same reason (protecting the wrong tissues).

If you hammer the entire discussion into one broad statement it's this: The entire premise made by all bubble models that deeper decompression is more efficient is ... wrong.

Ross can dance around that elephant in the room all day, but the elephant is not going away.

 

[Patoux01]

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.

Please explain to us why taking 2 dives with the same amount of deco would necessarily favor shallow profiles?

@others, please don't answer this, we all know it doesn't...

 

[rossh]

Please explain to us why taking 2 dives with the same amount of deco would necessarily favor shallow profiles?

@others, please don't answer this, we all know it doesn't...

The discussion is about the stress measures that Kevin is trying to create / use to compare with. So far, his efforts have produced only ones that always make a bias result for the shallow version, or are invalid in the method.

The explanation of that is in each post above.

.

 

[Diver0001]

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.

Ugh.... so painful to watch presentations like this. Brings back painful memories of spending way too much time in university lectures listening to way too long presentations being presented way too slowly for me.

Nevertheless some interesting information. I knew about the warm/cold thing (highly relevant to me because I do a lot of warm/cold schedules) but what I didn't understand was what seemed like an outlier to me where the warm/warm schedule gave higher decompression rates with the lowest exposure time than the warm/cold schedule. Did I see that right?

Other than that, not too many surprises and once again showing what I think I've come to accept as a fact that schedules with a lot of deep stops are less efficient.

One thing that got me thinking was the discussion about the use of O2 and the statement "O2 is your friend". I've been doing most of my dives with up to about 30min of deco using 50% for logistical reasons but it made me wonder if I shouldn't be rethinking that choice. With that statement in the back of my mind and thinking about the warm/cold dives we do, I could potentially be a candidate for improving my procedures....

R..

 

[rossh]

He has been doing this since the very beginning. I'm tried to confront him before about presenting graphs printed at different time scales to make them look comparable when they were not. Scientists have been trying to get him to understand this and yet for some reason the coin will simply not drop. Since I do not think that Ross is unable to understand this, my conclusion is that he must be making a deliberate attempt to confuse people.

I'm actually glad that someone else has clued in to the fact that this is what he's doing so that readers can see multiple people pointing this out.

Take a look at the attached graphic. I clipped that out of the video someone posted above. This is what the entire discussion is about. This graph is simplified but absolutely clear for the layman and it is not a manipulation. Read the studies. The science is good.

The complication for Ross, of course, is that you need to use higher and higher levels of "conservatism" in VPM in order to get the same run times. One would logically think that higher conservatism in a decompression model would lead to lower levels of DCS risk. In the case of VPM it's pretty clear that LOWER levels of conservatism leads to "safer" (let's put it that way) dives.

The HUGE disconnect in this, and the implications for VPM are substantial. With this paradoxical finding in mind, my conclusion is that there is something fundamentally broken about VPM. For myself I also draw the conclusion that other other models that are designed around bubble mechanics will suffer from the same "problem" and for the same reason (protecting the wrong tissues).

If you hammer the entire discussion into one broad statement it's this: The entire premise made by all bubble models that deeper decompression is more efficient is ... wrong.

Ross can dance around that elephant in the room all day, but the elephant is not going away.

VPM does NOT make any claim about efficiency... that is the rubbish they teach elsewhere, or some silly assumption. Its also the stuff they teach for RD, and the fiddling they do to profiles, and how they undercut the ascent.


Please stop trying to blame VPM-B for other peoples bad ideas.


VPM theory: "The VPM aims to minimize the total volume of these growing (tissue) bubbles by keeping the external pressure large, and the inspired inert gas partial pressures low during decompression."


I can't possibly see how you would make such a distorted description of conservatism.

VPM-B is slower / longer than real ZHL, for at least the first 3 hours.


The nedu did not test deep stops: They tested two kinds of low stress shallow stops, against high thermal stress.

The nedu result has been badly interpreted out here... When you get past all the made up explanations for the nedu result, it really comes down to this:

The difference in the nedu test is explained with gas kinetic rules - the same ones as used in ZHL and VPM-B. Models that followed the generic gas kinetics work (ZHL and VPM-B, A1), and the models that ignored the generic gas kinetic rules (BVM-3, A2) failed.

ZHL and VPM-B follow standard gas kinetic rules.... that was the successful A1 profile concept. Nothing matches the failed A2 profile - its a black sheep, that does not match any model we use out here.

Because VPM-B and ZHL follow the gas kinetic rules, they will have the correct balance of deep to shallow time. They don't need extra time patched on with GF or anything else.... if you can't agree, then you need to invalidate existing gas kinetic formula.


The problem you guys make for yourself, is that you then fiddle the ZHL with GF, putting a bias on it, and then thinking its a standard to compare to other plans.

.

 

[boulderjohn]

With that statement in the back of my mind and thinking about the warm/cold dives we do, I could potentially be a candidate for improving my procedures....

I am sure you will. All wise decompression divers constantly seek new information and rethink their procedures when they encounter clear evidence that what they have done in the past can be improved, if even ever so slightly. It is foolish to decide at some point that a certain procedure is ideal and therefore cannot be improved, thus locking yourself forever into that procedure.

 

[kensuf]

Ugh.... so painful to watch presentations like this. Brings back painful memories of spending way too much time in university lectures listening to way too long presentations being presented way too slowly for me.

Nevertheless some interesting information. I knew about the warm/cold thing (highly relevant to me because I do a lot of warm/cold schedules) but what I didn't understand was what seemed like an outlier to me where the warm/warm schedule gave higher decompression rates with the lowest exposure time than the warm/cold schedule. Did I see that right?

Other than that, not too many surprises and once again showing what I think I've come to accept as a fact that schedules with a lot of deep stops are less efficient.

One thing that got me thinking was the discussion about the use of O2 and the statement "O2 is your friend". I've been doing most of my dives with up to about 30min of deco using 50% for logistical reasons but it made me wonder if I shouldn't be rethinking that choice. With that statement in the back of my mind and thinking about the warm/cold dives we do, I could potentially be a candidate for improving my procedures....

R..

You can run the presentation back at 1.5x speed and shave some time off. It's sort of like VPM, but it actually works.

 

[fsardone]

Where is it written that GF is some universal and independent measure??? No where...

ZHL-C + GF also suffers from compounding errors... its not proportionally consistent across the dive spectrum. The shallow time feeds off its own compounding, and jumps to the next cell and exaggerates further. In addition, its a linear adjustment applied to values that are exponential in design.

Ross,
I tend to refrain from entering these threads, tends to be futile, but even if I am not a physiologist nor a decompression scholar, I understand math and physics.

GF=100% when refered to a tissue or a diver means that that person has one tissue or the leading tissue at the maximum allowable supersaturation.
Therefore surfacig with GF>100 is not good.

Also when we discuss efficiency, is how much bang for your buck. So how good is your decompression strategy compared to your cost (in water time).
This said, to see which strategy is more effiicent you decompress with equal run times. The profile with the lesser GF wins. Yours loose. But that is only on the clculations that you keep pushing to us as if the models were reality.

What the NEDU study did, was actually determine pDCS with a deeper and a shallower decompression strategy. The deeper strategy lost.

GF is a nice easy add-on patch, to give a longer "dial a profile". But its not a model, not consistent, and not an
independent standard.


There is only one real ZHL-C model plan. All else is made up fiddle to fit some dive preference, or to suit some argument. i.e. "my stretched out piece of GF chewing gum plan, is longer/fatter/taller than your real model plan".... so what! The comparison is not relevant.

Ross, as somebody else stated before me in this thread and myself in others, this hurts you more than you think.
GF actually do do not alter the model, but only what is the maximum allowable supersaturation in a linear way.

I'll say it again... I'd love to see a proper validated, unbiased, realistic cross-compare tool for profile performance and stress. We don't have one..

But you guy's are trying to fill in the gap, with half measures and things that fit your argument only .... sorry - no good enough.

.

Well anybody is free to asess who is actually doing that ...

 

[Diver0001]

You can run the presentation back at 1.5x speed and shave some time off. It's sort of like VPM, but it actually works.

Now you tell me...LOL

R..