Deep Stops Increases DCS

[rossh]

WARNING.

Ignore all references to VPM-B +7. It is FAKE !

They could not make any real connection or faults to VPM-B, so they just made up a FAKE profile.

Pathetic! A deliberate deception. Do not let them trick you.

 

[boulderjohn]

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A ScubaBoard Staff Message...

Once again, we mods have started to be more aggressive with the comments in these posts. I would like to suggest that a problem that is occurring here is that there is a lot of information being withheld from these posts because they have been said in the past and the posters don't feel like repeating the details. In past disagreements of my own on ScubaBoard, I have often felt frustrated when I have to repeat details of past arguments when I feel someone with whom I have argued in the past is repeating misinformation. You have to do it, though! You have to remember that you are writing for a current audience that has not followed these details over time. To all sides--please be patient, avoid hurling insults, and make your points with your audience in mind.

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[shoredivr]

In that case, here is the Deep Stops thread from RebreatherWorld.

Deep stops debate (split from ascent rate thread)


All the arguements are here. Though lengthy, it is excellent reading for anyone who wants the background thread. It convinced me that the science of decompression was advanced by the NEDU study.

The NEDU study was done by pre-eminent decompression experts who happen to work for the US Navy, such as David Doolette. Commentary is also provided by Simon Mitchell, another decompression researcher.

The main counterpoint to this NEDU study comes from Rossh, who is not a decompression scientist, but the owner of a popular decompression software, which uses "deep stops".

Though Rossh is a software programmer, he seems compelled to argue he knows better than the decompression scientists and the US Navy.

 

[fsardone]

First of all apologies to the MODs for my conspiracy cat/tin foil post ... Thanks for cleaning it up
Also thanks to shoredivr which posted a more mature addition to this thread.

I wish to elaborate on that.

IAll the arguements are here. Though lengthy, it is excellent reading for anyone who wants the background thread. It convinced me that the science of decompression was advanced by the NEDU study.

The NEDU study was done by pre-eminent decompression experts who happen to work for the US Navy, such as David Doolette. Commentary is also provided by Simon Mitchell, another decompression researcher.

What it is really important in the scientific community, is peer review. People that have a background in the issue at stake, review what are the findings of a scientist (or a group, or a particular study) in a critical way in order to find faults. Studies are published only after peer review.
The system is not perfect (see the fake study connecting autism with vaccination, published in a preeminent medicine journal) but thees are soon identified and retracted.

I this case the study was aimed to understand the effect of skewing deco time toward deeper stops:

Classical decompression algorithms limit hypothetical tissue gas contents and prescribe decompression schedules with most of the total stop time (TST) allocated to shallow decompression stops. More recent bubble-model-based algorithms limit hypothetical bubble profusion and size and prescribe decompressions with TST skewed toward deeper stops.

The "bubble algorithms" claim that by keeping under control the bubble size by decompressing deeper, you can achieve a better decompression efficiency (less deco for same bottom time).
Hence the study had to make up a fake deeper profile (resembling a VPM +7) in order to achieve the same decompression time. Remember they wanted to know if redistributing deco time deeper the probability of a DCS hit would be higher or lower. Know if they had used a VPM-B +0 +1 +2 etc profile they would have had a deeper and SHORTER profile therefore two variables.

Result is:

REDISTRIBUTION OF DECOMPRESSION STOP TIME FROM SHALLOW TO DEEP STOPS INCREASES INCIDENCE OF DECOMPRESSION SICKNESS IN AIR DECOMPRESSION DIVES

This was proven by experiments and actually bending people in very controlled situation (environmental conditions). The beauty of the experimental method also called Galilean method (sorry I am Italian and Galileo is one of my heroes) is you can repeat the experiment and confute or confirm it. So right now the only chance Rossh has to refute the experiment is repeat it and come up with different results which then would have to be verified by deco scientists and agreed upon, the published.

The main counterpoint to this NEDU study comes from Rossh, who is not a decompression scientist, but the owner of a popular decompression software, which uses "deep stops".

Though Rossh is a software programmer, he seems compelled to argue he knows better than the decompression scientists and the US Navy.

Rossh, I believe, and I am one of his customers, does make an excellent piece of dive planning software, Multideco. He has a very generous licensing scheme which allowed me to transit from the former V-Planner (only VPM) to Multideco (multiple algorithms) at no charge.
Even he stopped (either by customer demands or personal beliefs) than only VPM was right ... because I licensed V-Planner in 2012 and immediatly after M-Deco came out.
I really like the possibility of comparing profiles by different algorithms in order to decide what amount of risk or extra deco I'd like to add.
But he is not a Deco scholar nor uses methods at par with scientists publishing these studies.

WARNING.
Ignore all references to VPM-B +7. It is FAKE !
They could not make any real connection or faults to VPM-B, so they just made up a FAKE profile.
Pathetic! A deliberate deception. Do not let them trick you.

Fact is that if it walks like a duck and quack like a duck, it exhibits all the needed behaviours to be a duck.
The study was not against VPM, was about skewing deco deeper. VPM +2 would have been shorter in the shallow stops. We would have had (my guess) more bent people.
As somebody said before: do you think shallow deco hurts?

My deco strategy is to plan with both:
VPM and ZHL-16-GF so appreciate the differences but I dive ZHL-16-GF, maybe lowering a bit GF Low according to what came out of the VPM plan. When I first started I was using something around GF low at 25-30 and GF High at 85-95 but then personal feeling and these discussion moved me toward GF lo 35-45 and high at 70-85.
Do I do more deco that strictly needed yes most certainly yes! But I love be underwater .... so?

One final thought. I dive with computers allowing me to set alternate GF and in case of emergency: I can raise my GFs in order to come out of the water quickly maybe bent but alive and able to be sent in a chamber and not a casket. I am not sure if with VPM computers you can achieve same effects, maintaining the support of a calculated deco profile.

Sorry for the long post ... But just my layman understanding of the issue.

 

[Freewillow]

Galileo, my hero with Michelangelo . Forza Italia and thank you for your post.

 

[leadduck]

This would be a concern. Integral supersaturation is a useful "index of decompression stress" when comparing dives that vary only in the distribution of stop time. Doolette has stated this many times (please see this post). It could, and I'd think often would, mislead if used to compare vastly different profiles. That is part, actually a lot, of my reluctance to simply publish the heat map program since in its current form I have no way to limit inputs.

Thanks for the link to this post. I guess (please correct if wrong) that the integral runs from the beginning of the dive to its end, but does not include post-dive supersaturation on the surface, right? So it's during-dive-ISS, not including post-dive-ISS. This would indeed depend on dive time. However, let me then suggest the ultimate deep stop profile: I stay at 170fsw until the 204th minute, then bolt to the surface. Same total dive time, only distribution of stop time is different, and during-dive-ISS is very small. Then I die because of post-dive-ISS.

Integral supersaturation is simple . If you are exposed to 1000mb of supersaturation for 5 minutes, then that would be 5000mb-min of supersaturation exposure (or integral supersaturation). It's just supersaturation x time. It's usually expressed in the form of calculus (integration from 0 to infinity of supersaturation at time t) so can look difficult, but its just a measure of your exposure time to supersaturation.

If the integral runs to infinity, then why is it so important that the dive time is the same; i.e. why is there such a fundamental difference between a stop at 0.001ft and one at 0ft?

 

[rossh]

In that case, here is the Deep Stops thread from RebreatherWorld.

All the arguements are here. Though lengthy, it is excellent reading for anyone who wants the background thread. It convinced me that the science of decompression was advanced by the NEDU study.

The NEDU study was done by pre-eminent decompression experts who happen to work for the US Navy, such as David Doolette. Commentary is also provided by Simon Mitchell, another decompression researcher.

The main counterpoint to this NEDU study comes from Rossh, who is not a decompression scientist, but the owner of a popular decompression software, which uses "deep stops".

Though Rossh is a software programmer, he seems compelled to argue he knows better than the decompression scientists and the US Navy.

I don't know better - I never suggested it.


What you need to know, the nedu tested SHALLOW stops.... not deep stops. Their test outcome applies to extended shallow stop model programs - the kind that only the USN / nedu use. That is a unique problem they have with their models. They did not test deep stops, they did not test tech diving practices. Their results do NOT apply to tech diving practices. Those facts are indisputable.


But some wish to pretend they can morph the results into VPM. The ONLY way they have to do this, is to use FAKE profiles, using made up FAKE and invalid heat graphs. Its a lie, and a sham. A deliberate deception, and devoid of science. You can see we why I get annoyed at so many deliberate lies.

The truth is there is no connection between VPM and the nedu tests !


**********


But... ignore all that for a second. The solution being offered around here, is to "go more shallow ,and go longer shallow".

That proposal is taking you directly towards the very nedu profiles that failed! Hypocrisy...


And the 40/70 profile, as being recommended by many, is almost the same as a VPM-B+3 in most cases. So... Its OK to use VPM model attribute styled profile, as long as we pretend its not? Hypocrisy...

.

 

[rossh]

First of all apologies to the MODs for my conspiracy cat/tin foil post ... Thanks for cleaning it up
Also thanks to shoredivr which posted a more mature addition to this thread.

I wish to elaborate on that.



What it is really important in the scientific community, is peer review. People that have a background in the issue at stake, review what are the findings of a scientist (or a group, or a particular study) in a critical way in order to find faults. Studies are published only after peer review.
The system is not perfect (see the fake study connecting autism with vaccination, published in a preeminent medicine journal) but thees are soon identified and retracted.

I this case the study was aimed to understand the effect of skewing deco time toward deeper stops:



The "bubble algorithms" claim that by keeping under control the bubble size by decompressing deeper, you can achieve a better decompression efficiency (less deco for same bottom time).
Hence the study had to make up a fake deeper profile (resembling a VPM +7) in order to achieve the same decompression time. Remember they wanted to know if redistributing deco time deeper the probability of a DCS hit would be higher or lower. Know if they had used a VPM-B +0 +1 +2 etc profile they would have had a deeper and SHORTER profile therefore two variables.

Result is:


This was proven by experiments and actually bending people in very controlled situation (environmental conditions). The beauty of the experimental method also called Galilean method (sorry I am Italian and Galileo is one of my heroes) is you can repeat the experiment and confute or confirm it. So right now the only chance Rossh has to refute the experiment is repeat it and come up with different results which then would have to be verified by deco scientists and agreed upon, the published.



Rossh, I believe, and I am one of his customers, does make an excellent piece of dive planning software, Multideco. He has a very generous licensing scheme which allowed me to transit from the former V-Planner (only VPM) to Multideco (multiple algorithms) at no charge.
Even he stopped (either by customer demands or personal beliefs) than only VPM was right ... because I licensed V-Planner in 2012 and immediatly after M-Deco came out.
I really like the possibility of comparing profiles by different algorithms in order to decide what amount of risk or extra deco I'd like to add.
But he is not a Deco scholar nor uses methods at par with scientists publishing these studies.




Fact is that if it walks like a duck and quack like a duck, it exhibits all the needed behaviours to be a duck.
The study was not against VPM, was about skewing deco deeper. VPM +2 would have been shorter in the shallow stops. We would have had (my guess) more bent people.
As somebody said before: do you think shallow deco hurts?

My deco strategy is to plan with both:
VPM and ZHL-16-GF so appreciate the differences but I dive ZHL-16-GF, maybe lowering a bit GF Low according to what came out of the VPM plan. When I first started I was using something around GF low at 25-30 and GF High at 85-95 but then personal feeling and these discussion moved me toward GF lo 35-45 and high at 70-85.
Do I do more deco that strictly needed yes most certainly yes! But I love be underwater .... so?

One final thought. I dive with computers allowing me to set alternate GF and in case of emergency: I can raise my GFs in order to come out of the water quickly maybe bent but alive and able to be sent in a chamber and not a casket. I am not sure if with VPM computers you can achieve same effects, maintaining the support of a calculated deco profile.

Sorry for the long post ... But just my layman understanding of the issue.

Thanks for your post. Let me touch on a few points;

The nedu did not test VPM-B or RGBM or tech dive practices. They tested their own BVM-3 - which is a SHALLOW stop model. There is no connection to VPM-B.


There test procedure did not test decompression profile stress - profile stress is "fast" deco, with high off gas stress - none of that exists, because they used really long and slow shallow ascent - twice the normal deco. They tested thermal stress - they got the subjects deliberately cold. Thermal stress creates adverse DCS in all model and all profiles.

You imply that if the profiles were shorter there would likely be more injury - that's probably wrong. The diver would be warmer - less thermal stress, better circulation, and conducting normal profiles. If instead, they went even longer than test, they get even colder and more injury occurs. In real world diving, the real profiles are much shorter.... You have it all backwards.


**************

I do not dispute the nedu test result - they got what they tested - cold shallow stops, but no deep stops.

The study conclusion applies to SHALLOW stop models - extending a long shallow stop to deeper state is bad. This is not connected to deep stops.

*****************

My dispute is about all the effort trying to force VPM-B into this shallow test - its these efforts that are invalid.


VPM-B +7 is fake... It was faked up to try to merge a deeper stop design like VPM-B, into a shallow stop design, like VVAL-18 and BVM-3. There is no connection.


Take a look at these;

Does the Green part equal the RED part ??? No, not even close.


Where is the connection to deep stops / VPM-B ??? Not there.

There are no deep stops in the nedu test.

.

 

[Macan]

What it is really important in the scientific community, is peer review. People that have a background in the issue at stake, review what are the findings of a scientist (or a group, or a particular study) in a critical way in order to find faults. Studies are published only after peer review.

I agree with @fsardone.

AND There is a peer review of the NEDU study. See link below posted by @leadduck.

B.R.Wienke and T.R. O'Leary: "Recent Deep Stop Data and Tests". Deep Stops and Decompression Workshop, Salt Lake City, June 2009
https://www.researchgate.net/profil...cf265693cef0185.pdf?origin=publication_detail

See Table 6.

https://www.researchgate.net/profil...cf265693cef0185.pdf?origin=publication_detail

This recent paper by Dr. Bruce Wienke appears to support what Ross is saying. Shouldn't the discussions in this thread focus on the merits/demerits of Dr. Wienke's paper? What it is saying is that both Deep and Shallow stops are ok but Deep Stops are more efficient.

My view however is this. When you do decompression dives, you only have two choices:

1. You protect the fast tissues by doing deep stops. The trade off is you have higher supersaturation in the slower tissues when you surface.

2. You protect the slow tissues by doing shallow stops. The trade off is you have increased supersaturation in the fast tissues when you surface.

Bottom line, is its one or the other. You can't have it both ways (i.e. protect both fast and slow tissues). You can however, PAD your last stop by extending it and depending on your earlier profile, this padding may or may not help bring down the supersaturation levels in the fast or slow tissues. Padding is also inefficient as it extends your time in the water not to mention higher accumulation of CNS% and OTUs from your deco gas.

For me, at this point, tend to agree with the NEDU conclusions that protecting the slow tissues (i.e. shallow stops) is the safer option. But, I'm open to exploring ideas that may differ from this such as the recent study in the link above from Dr. Wienke.

 

[rossh]

I agree with @fsardone.

AND There is a peer review of the NEDU study. See link below posted by @leadduck.



https://www.researchgate.net/profil...cf265693cef0185.pdf?origin=publication_detail

This recent paper by Dr. Bruce Wienke appears to support what Ross is saying. Shouldn't the discussions in this thread focus on the merits/demerits of Dr. Wienke's paper? What it is saying is that both Deep and Shallow stops are ok but Deep Stops are more efficient.

My view however is this. When you do decompression dives, you only have two choices:

1. You protect the fast tissues by doing deep stops. The trade off is you have higher supersaturation in the slower tissues when you surface.

2. You protect the slow tissues by doing shallow stops. The trade off is you have increased supersaturation in the fast tissues when you surface.

Bottom line, is its one or the other. You can't have it both ways (i.e. protect both fast and slow tissues). You can however, PAD your last stop by extending it and depending on your earlier profile, this padding may or may not help bring down the supersaturation levels in the fast or slow tissues. Padding is also inefficient as it extends your time in the water not to mention higher accumulation of CNS% and OTUs from your deco gas.

For me, at this point, tend to agree with the NEDU conclusions that protecting the slow tissues (i.e. shallow stops) is the safer option. But, I'm open to exploring ideas that may differ from this such as the recent study in the link above from Dr. Wienke.

You can't have it both ways..... Correct. And no model tries to skip that.

Our models today (ZHL, VPM-B) use the Haldane and Schriener equations to govern on /off gas tracking. All models use this method, or a variation of it. The purpose of these formula is to track tissue state, and they do this continuously through the dive and in all kinds of ascents - deep / shallow, multi levels, wobbly, anything. Models then take this info and make ascent limits - it all works perfectly just as it is.

ALL models on gas in the slow tissues - this is not limited to VPM or deep stops - it happens everywhere. All models correctly account for this.

There is no "choice" to be made - the model and gas tracking already do this job for you - stop fiddling with it.


The nedu test did NOT test fast or slow tissue pressure stress. There is almost none present in any of the test profiles. They tested effects of thermal stress.


.