Deep Stops Increases DCS

[emmbee]

Sorry Mathiew,

if YOU think paper is wrong, YOU need to do formal review and reject the paper.

Let me get this straight...

When somebody who says things you like goes up against multiple papers by multiple respected authorities in the field, "we have seen lot of times simple man solve the most complicated enigmas where scientists didnt have a clue".

But when somebody who does not has a problem with two lines of high school level mathematics in one paper, "[HE] need to do formal review and reject the paper".

Are you kidding me?

In any case I didn't ask for the paper to be rejected.

The paper was published in "Computers in Biology and Medicine", and the topical part, computers, is reasonable enough (I'd have a few things to say about that too, but that's not the point).

What I'm asking you is whether you:
- agree with the paper that Haldane models give credit for undersaturation against supersaturation later (or before), in which case you're wrong, and so's the paper, as far as decompression theory is concerned.
- disagree with the paper that Haldane models do that, in which case you agree that the paper is wrong, again as far as decompression theory is concerned.
- or disagree with the paper that Haldane models do that, but that the paper does not in fact reflect what was done, in which case you agree that the paper is bad.

Simple. So which is it?

Cheers,

Matthieu

 

[RyanT]

Sorry Mathiew,
if YOU think paper is wrong, YOU need to do formal review and reject the paper.

Huh? Do you know how science works? If you aren't an original reviewer of the manuscript, you can't reject a paper. You can write a rebuttal, but you can't single-handedly "reject" the paper.

 

[rossh]

Thanks. You could have added that this is nothing new: check out the references. It's nothing new in the diving world, either. If you got a copy of Tauchmedizin, look at the circulation diagram in section 5.1, the A-V shunt is right there (in 5th ed, 2002, it's on page 95).

That's not the real problem, tho, IMHO.

Let me try to put Ross's argument in a different context, to try to make it clearer: speeding.

The rate of road accident is low, 0.05%. Accidents due to speeding is "far less of a problem still", 0.02%.

Compare that to known speeding. We know 25% drive above the speed limit often. Half of us sometimes.

That's a huge gap between speeding and the accident rate, and trying to reduce speeding is not the answer.

This is not a problem for 99.97% of us, at all.

There's (at least) two problems with this:

1) It ignores the magnitude of the excess. You can't just reduce it to a binary situation, VGE/no VGE vs DCS/no DCS or speeding/no speeding vs accident/no accident. Speeding by 5 (km/h, mph, whatever) is not the same as speeding by 50. Likewise a small VGE grade is not the same as a high VGE grade. If there is a correlation between magnitude and rate of accident, that's a rather strong indication that the two are linked, or rather, in this case, that one causes the other. Such a correlation exists for VGE grades and DCS.

2) It ignores the context of the excess. Speeding on a highway is not at all the same as speeding on a small winding 1.5 lane wide country road with a hedge on both sides. Likewise a high VGE count on a no-deco dive with bubbles originating from the very fastest tissues lodging themselves in slightly less faster ones that won't be controlling because they already allow ascending to the surface is not really a problem. On the other hand bubbles from slow-ish tissues lodging themselves in highly loaded next controlling compartment slower ones, that's a problem.

Cheers,

Matthieu

Matthieu....

Yes magnitude is important in all aspects. But with such a vast difference between the artVGE condition and injury, its impossible to see any influence of magnitude.

The implied correlation of VGE to DCS is BUNK. More correctly, VGE has some relationship to the underlying tissue pressure (profile) stress, but not much. Simply put: faster profiles have higher tissue stress and off gas faster - making (only sometimes) co-incidentally more VGE . However, VGE is not correlated dive stress in any reliable or absolute sense. VGE is better correlated and dependent on gas type, individual diver variations, daily changes, dive condition changes and many other influences.



Also you might like to ask Simon how the they justify the onset of Inner Ear DCS. I believe they estimate only a tiny amount of artVGE is needed, therefore, it would imply up to 50% of divers should encounter IE DCS on a regular basis ?? Obviously that does not not happen.

****

So lets ask the flip side question - where do artVGE go to? How do they dissolve? Are they really harmful?

.
Commercial footnote: We make a program called MultiDeco. It has most of the current deco models and variations available for you to choose from. Your welcome to choose any model, and to do as much, or as little deco time as you want - its your choice.

 

[oya]

VGE is not correlated dive stress in any reliable or absolute sense.
...

So lets ask the flip side question - where do artVGE go to? How do they dissolve? Are they really harmful?
.
Commercial footnote: We make a program called MultiDeco. It has most of the current deco models and variations available for you to choose from. Your welcome to choose any model, and to do as much, or as little deco time as you want - its your choice.

Other things with no demonstrable correlation:

Amount of whiskey I drink and how drunk I get. Study after study shows that certain people hold their liquor really well.

Amount of Fritos I eat and my waistline. Some people have a really fast metabolism... there's just no proof!

Falling from high places and broken limbs. People are falling down all the time... Do you see everyone walking around with a cast? No. Therefore gravity isn't really that big a problem!

So isn't it a relief to us divers that we don't really have to worry about bubbles? They aren't really the thing causing DCS.

It's witches, I tell you!!

 

[Storker]

The implied correlation of VGE to DCS is BUNK.

It seems as if Drs. Doolette and Mitchell aren't the only qualified decompression scientists who disagree with that statement.

Bubbles do not equal DCS. We do not treat bubbles. We look for bubbles. Bubbles are an indicator of decompression stress. If you actually make the measures with the right equipment, a skilled technician, and appropriate frequency and do not have bubbles, the data suggest that you can be 95% confident you are not going to develop symptoms of decompression sickness. The data are not exhaustive, but reasonable. If you have high grade bubbles, the best evidence we have is from the aviation decompression literature. And it suggests that you have at most a 40% probability of DCS. So, while bubbles do not equate to DCS, you also should not say they are unrelated.

(bolding mine)

Ref: Pollock, N.W. (2016): "Factors in Decompression Stress", In: Pollock NW, Sellers SH, Godfrey JM, eds. Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS June 16-19, 2015 Workshop. Durham, NC

 

[victorzamora]

@rossh, you sent me a PM regarding my post calling VPM-B/E out for not being scientific in any way.

GF is random changes that everyone makes... also without testing or reference to anything!

Right here, you're stating outright that VPM-B/E is without tesing or reference to anything. Correct?

Where I disagree with you (one of a growing list) is that GF is untested and without reference.

Facts:
Buhlmann ZHL-16 is man-tested scientifically.
Buhlmann ZHL-16 was developed from results of man-testing.
VPM was developed off of theory.
VPM was developed without man-testing.
VPM-B was an alteration of VPM to add conservatism.
VPM-B/E was altered without testing or scientific reason and without any reference.
Gradient Factors are a mathematical modelling trick to add varying conservatism to Buhlmann ZHL-16 base algorithm.

Back to opinions: GFs that you so frequently attack are based on Buhlmann (duh) and they're a conservatism setting. Each individual setting hasn't been tested, you're right, but it doesn't mean they're any more "made up" than Buhlmann proper. In fact, I'd posit that VPM (and variants) are far more "made up" in that it's based on unproven theory (that recent testing has started to seemingly disprove) and is just a theoretical mathematical model tailored to fit some dives some guys were doing. It was then re-fudged to add much needed conservatism (VPM-B). It was then re-fudged almost randomly to fit a profile one guy did once.

Your attacks on UWSojourner's charts and graphs as well as Gradient Factors as a concept for them being "made up" (and whatever other terms you've used) is honestly hurting your position. Every graph you've presented is using "made up" numbers in the same way that Kevin's are. It's not like you found your graphs in nature.

I'm not saying that Doolette, Mitchell, Pollock, or any other deco scientist has the right answer. I'm not saying Kevin's graphs are right. I'm not saying VPM is bad, or bubble models are bad, or deep stops are bad, or that GF models are perfect. What I know is I've moved my GFs to shallower settings (50/70 from 30/85) and I'm happy, and I've yet to see an argument that makes me want to re-consider VPM. If you're going to disagree, do so with cogent points...you can't hate on a chart because it's "made up." They all are. So are all algorithms. VPM+7 is valid and just as "real" as +0 or +5 because they're all "made up."

 

[scubadada]

@Storker
So you found the ONE other person who thinks that (whoever-the-hell this "Doctor" Pollock is. Probably some quack in the pocket of Big Bubble).

It's not like if you'd Google "VGE Decompression" your results would be hundreds of articles from various private and government studies supporting the correlation.

Neal Pollock: Neal W. Pollock - Wikipedia, the free encyclopedia

 

[UWSojourner]

I want to bring this back to what we do actually know.

We have a closely monitored NEDU study whose end point was DCS. The deep stop bubble model produced a DCS rate of 5%; the shallower model 1.6%.

Now, every way I've looked at this the deep stop profile "A2" is much closer to VPM and the shallower stop "A1" is much closer to GF. Prior to the NEDU trials Wienke called A2 "RGBM-like" (see here). I can see why he'd say that when you look at the analysis of RGBM/"LANL" with A2 (see here) ... they are VERY close.

You can equally see the relationship between A2 and VPM. All of this was discussed by Doolette in his "deep stop skew" analysis. He concluded that models that skew time toward deeper stops will suffer the same problem A2 suffered.

And what is that problem? I'll let Dr. Pollock describe it (numbers added and referenced on the heat map below),

"The impact of deep stops is ... actually quite simple; the extra time spent deep allows more inert gas uptake 1 in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress 2. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. " Dr. Pollock

The higher degree of decompression stress can be seen in the calculations of integral supersaturation (ISS). See below.

This pattern (i.e. extra time deep resulting in more deco stress) has been shown in other profiles we've looked at (see here, and here, and here).

I agree that we don't know everything. But we know a heck of a lot more than we did prior to the NEDU study, the VGE studies, and all the other research Doolette and Mitchell have been discussing. What we've learned is all based on observational science, not new theoretical ideas. And what we've learned all converges toward the idea that deep stops have been oversold to the diving community.

Dr. Pollock said it well, "it is time to respect the data."

 

[rossh]

Fact : there are NO deep stops in the nedu test.

The Nedu test results are NOT relevant to tech diving !

The nedu off gas patterns are NOT representative of VPM.

The nedu test did not protect fast tissues as claimed:

Heat maps are not supersaturation patterns. Heat maps do not predict risk. Heatmaps do not show absolute or realistic levels of risk or stress:

Beware of pretty graphs and other tricks... Only accept those with actual pressure and values shown. Heatmaps do NOT qualify.

ISS charts are bunk too. They add up numbers in ways that are not valid or proper. Do not accept those either. There is only one widely accepted measure of stress - Supersaturation.

.

 

[Storker]

There is only one widely accepted measure of stress - Supersaturation.

I may have asked this before - a couple of times, I believe, however at no avail - but how does one measure supersaturation?