Deep Stops Increases DCS

[Dr Simon Mitchell]

I suspect that is EXACTLY the hazarded 'guess' - an extrapolation of results not substantiated by the trial design.

Hello,

Your points about the hazards extrapolating the results of studies beyond the study parameters are, of course, well made and accurate. However, in this case the extrapolation is not quite in the realms of guesswork. It sounds as though you have read the original technical report. If not, please (I was going to say pm me and I will send it....

But I see you have read it.

So, you will have seen that there was quite a lot of thought given to the reasons for the result which was somewhat unexpected. There is quite a long section in the report dealing with the analysis of supersaturation patterns in fast and slow tissues, and analysis of the deep stops skew (similar to the integral supersaturation evaluations that have been discussed here). All of this is related to the heat map evaluations that uwsojourner has produced.

On the basis of these analyses, which applied well established physiological principles in both decompression physiology and decompression sickness pathophysiology, an extremely plausible (indeed, possibly the only plausible) explanation for the result was derived. The extrapolation that is occurring here is an extrapolation of that principled analysis to the broader range of deep stop decompressions (hence the comparisons of supersaturation patterns between VPM and GF undertaken by uwsojourner). The fact that the apparently detrimental patterns of supersaturation that almost certainly explained the result in the NEDU study can also be seen in the profiles that emphasise deep stops when compared to profiles with less emphasis on deep stops suggests that outcomes for the former would likely be worse than the latter. It is clearly not proof, but it is the best evidence we currently have to base our "opinions" on. And never lose sight of the fact that there is NO EVIDENCE whatsoever pointing in the other direction.

Simon M

 

[Colliam7]

It sounds as though you have read the original technical report.

Yes, I have.

And, one of my comments addressed the specific statement about hazarding a guess. I mean no criticism of the author of the statement. I am quite happy to 'hazard a guess' - or three - myself. But, if we want to be objective, let's be fair - to the data, as well as to those critical of the data. The very best outcome of a clinical trial is often a statement in the Discussion to the effect that, 'The results of this trial strongly encourage further study.' I have used that comment in more than a few publications myself.

 

[igor p]

Hi all,

I am reposting the comment BRW asked me to post once again with some
additions he wanted to make so that it is complete here in one post.
Same I am posting 4 papers that he asked to attach to his answer.

"Long time ago, I stopped worrying too much about the
ins and outs of deep stops vs shallow stops as ranted and raved
on blogs. The proof is in the pudding -- thousands of divers
employ deep stops and have used them safely without anything
but nominal DCS in the process for many years now. No probs.

No matter what model (USN, ZHL, VPM, RGBM) somebody
will always get hit, but the concern is how many and how often.
To date that number is very small by DCS incidences. As C&C
Dive Team Ldr, that is the bottom line for our operations. And
me personally.

You can argue deep stops vs shallow stops til you are
blue in the face. They both work, but for different reasons
is the simple fact. Here at LANL, we have dived both without
mishaps.

Deep stops are faster and get us out of the water quicker
so we use them. Period.

Just a couple of thoughts to pass on:

1) deep stop meters, tables and software have now been
around for 10s of years without reported problems with
DCS; and judging from the licenses we issue will enjoy
even more usage;

2) data is data no matter what generates it and for whatever
reason and LANL computer downloaded data is headed to
DAN as I have time to write translation software for 3000+
profiles;

3) both VPM and RGBM work well and have no reported
DCS spikes (unless misused) across meters, tables and
software renderings;

4) Balestra of DAN did a study of DCS rates in ZHL and RGBM
computers and found DCS incidence rates almost exactly
equal and small;

5) shallow stops vs deep stops are now for us mostly "religion"
questions;

6) the NEDU experiment suggested to us as operational divers
that if you don't do shallow stops and/or deep stops carefully
you can get hurt. Hats off though to all involved in that experiment
because it showed us what not to do. That is important information
but doesn't discredit deep nor shallow stops when looking at the
track record in the field -- where it counts. Both can be done safely
and that's good. End of story for us, training agencies, 1000s of
tec and rec divers, and growing numbers of same.

7) reading thru ScubaBoard a bit I would only say, without
names, folks who denigrate LANL Data Bank (3000+ computer
downloaded profiles in 10 sec intervals going to DAN) are
"uninformed" to put it politely. These profiles were discussed
a bunch at the Deep Stops Wkshp and published numerously in
followup papers -- some appended. Like I said, for some "deep
stops vs shallow stops" are more questions of religion than fact from
years and years of both shallow stop and deep stop safe diving.
Guess it depends on whether you have both mission and safety
concerns for real diving ops. Plus experience hopefully

Attached papers are some published work that was peer reviewed by
medical, physiological, engineering, computer and physical scientists -- all real divers too.

BTW, forgot to mention that commercial diving folks are now involved
in bubble model staging. We are working with them.

Regards and best,

Bruce Wienke, PhD
Program Manager Computational Physics
C&C Dive Team Ldr
Consultant EPA, DHS, ADA,DOE, US Military
Editor/Revviewer TTSP, CBM, PR, JQSRT, NSE, JCP
President SWE Consulting

PS The appended are all published in cited journals
or in progress for J Marine Science and Research, Bio Environmental Engineering, SIAM Statistics,etc.
Our focus is real world safe diving."

The attachements were not accepted so they are posted in separate comments.
Igor P

 

[igor p]

Here are the attachments that should be together with previous post. Seem forum would not let me post all together so posting in parts.

 

[igor p]

And here are the last two. In last moment got another one. It is the Balestra paper....VDC which is an important one.

 

[UWSojourner]

And here are the last two. In last moment got another one. It is the Balestra paper....VDC which is an important one.

For the topic of this thread, why is the Balestra paper applicable? Is it not mostly dealing with recreational diving, although a good read?

One part of the paper that did catch my eye (as it relates to our discussion) was:

"PHYSIOLOGICAL MEASUREMENTS: VENOUS GAS EMBOLI (VGE)

Although VGE may be detected in divers in the absence of DCS, it is established that the higher the venous bubble load in the body, the more likely DCS is to occur (Francis and Mitchell, 2003). Therefore, measurement of VGE can be used in place of DCS as endpoint to aid in validation of decompression safety."

In the context of our discussion Ross has expended considerable energy trying to say the high VGE bubble grades seen in studies of divers using bubble models don't matter. His position doesn't appear to be supported by this paper (nor any other researcher that I'm aware of). Besides irresponsible, its also a bit comical that the bubble-model-marketer has to maintain that bubbles don't matter in order to avoid the rather obvious conclusion that a model that regularly produces grade 4 bubbles is not a model that is controlling them.

 

[UWSojourner]

Straight back to fantasy land I see.

Yes - they do show exact supersaturation values... In any pressure units you choose to select.

Ok. Then you can probably break those down into the N2 tissue compartment pressure and the surface pressure, right?

The points I see in the chart below as best as I can determine are:

surface ~38 kPa -- what is N2 tissue pressure for this one? And which compartment does it represent?
10ft ~ 42 kPa -- what is N2 tissue pressure for this one? And which compartment does it represent?
20ft ~ 28 kPa?? -- what is N2 tissue pressure for this one? And which compartment does it represent?

Feel free to correct my estimates. I had to eyeball them on the chart.

 

[rossh]

Ok. Then you can probably break those down into the N2 tissue compartment pressure and the surface pressure, right?

The points I see in the chart below as best as I can determine are:

surface ~38 kPa -- what is N2 tissue pressure for this one? And which compartment does it represent?
10ft ~ 42 kPa -- what is N2 tissue pressure for this one? And which compartment does it represent?
20ft ~ 28 kPa?? -- what is N2 tissue pressure for this one? And which compartment does it represent?

Feel free to correct my estimates. I had to eyeball them on the chart.

Yes, those numbers look about right. But I'm not going to provide you with the other details requested. I'm not interested starting a squabble over 1 pascal. You should use your own tools to verify it with. Just put it in a heat map


I'm guess others would like to verify... so here we go:

The minor line shows cell #10. This has almost the same half time as the 'slow' cell in the A2. 146 v 160 min. You can see the same details how the A2 slow cell line and the #10 tissue gradient line, align closely.

Can you spot the 2 errors in the TR11-06 Figure 5C graph?

.

 

[igor p]

For the topic of this thread, why is the Balestra paper applicable? Is it not mostly dealing with recreational diving, although a good read?

One part of the paper that did catch my eye (as it relates to our discussion) was:

"PHYSIOLOGICAL MEASUREMENTS: VENOUS GAS EMBOLI (VGE)

Although VGE may be detected in divers in the absence of DCS, it is established that the higher the venous bubble load in the body, the more likely DCS is to occur (Francis and Mitchell, 2003). Therefore, measurement of VGE can be used in place of DCS as endpoint to aid in validation of decompression safety."

In the context of our discussion Ross has expended considerable energy trying to say the high VGE bubble grades seen in studies of divers using bubble models don't matter. His position doesn't appear to be supported by this paper (nor any other researcher that I'm aware of). Besides irresponsible, its also a bit comical that the bubble-model-marketer has to maintain that bubbles don't matter in order to avoid the rather obvious conclusion that a model that regularly produces grade 4 bubbles is not a model that is controlling them.

Reread the paper. Yes It deals with recreational diving. DAN sums all diving that is not profesional saturation diving in recreational diving. That incorporates technical diving too. If you read carefuly you can read in the cited part dives from 5 to 192m were observed for VGE and Doppler bubble scores show low occurence of high bbuble grade. Not in ranges you say.

Whole paper is important as it deals with records of just ZH-L16 and RGBM algorithms used in the dives for directing the profile of the dive. Incidence was equaly distributed between. Neither one or the other had significently higher rate of incidence.The difference was marginal.

 

[UWSojourner]

Reread the paper. Yes It deals with recreational diving. DAN sums all diving that is not profesional saturation diving in recreational diving. That incorporates technical diving too. If you read carefuly you can read in the cited part dives from 5 to 192m were observed for VGE and Doppler bubble scores show low occurence of high bbuble grade. Not in ranges you say..

What I said was "mostly recreational". Although you cite the range [5,192m], you didn't show the average of 28.5m. If the midpoint of the range is 98.5, but the mean is still 28.5, doesn't that say that the distribution is skewed pretty heavily toward to low end of the range you cite? So I said "mostly" recreational. I guess I could have said "heavily weighted toward dive regions and times that might not draw out the issues we're discussing."
This is not a criticism of the article, just a question about how it intersects with this discussion.