NEDU Study

[Shearwater]

Throughout the years of this argument, the only posts you made on this whole subject, has been to insult and attack me with malicious comment on my business, my reputation, my integrity, my work, my home, my lifestyle, and my intentions.


You have not said a word about decompression theory or contributed to this discussion proper in any constructive way.



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Of course not. I actually understand that implementing other people's algorithms doesn't make me an expert on decompression science. You seem to miss that point.

 

[tursiops]

Of course not. I actually understand that implementing other people's algorithms doesn't make me an expert on decompression science. You seem to miss that point.

BaDaBoom

 

[rossh]

Of course not. I actually understand that implementing other people's algorithms doesn't make me an expert on decompression science. You seem to miss that point.

I'm sorry, I just don't see how your level of deco theory understanding, and non participation, that somehow it justifies you to insult and attack me with malicious comment on my business, my reputation, my integrity, my work, my home, my lifestyle, and my intentions, as you have done many times in the past.

 

[rhwestfall]

FWIW, I find it interesting that Shearwater sells a "product" that they apparently don't believe in.....

 

[igor p]

VPM, according to the survey on What Deco Algorithm do you use? (Poll) is down to 3% use. We have seen the same sort of numbers with our data on VPM usage on our computers. From what I can tell, VPM use has been shrinking for a while.

Well Bruce, Look at the link you posted and you will find this (I know it is multichoice but...):

Deep stop practices (or what I understood is grouped under this name):
VPM has 10.10 % and not 3%
Bubble models 3.03%
GF 30/70 or 20/80 has 49.49%
RatioDeco has 9.09%
GF 20/70 has 4.04%

shalow sotp practices (Simons suggestion or near it):
GF 40/80 has 33.33%

It would seem you did not bother to even look at the link you posted.

Just want things are correct.

 

[Dr Simon Mitchell]

Same choice as always.....

a/ the interpretations and opinion positions of a trained Dr., who also publicly promotes his personal agenda for change,

You are fond of portraying me as having an agenda that is "anti-bubble models" and "personal" and somehow unconnected from the science of diving. My only agenda is ensuring that divers do understand the current views of the diving science community. I am entirely consistent in this regard. When we generally believed in the theoretical attraction of bubble models I promoted them. If you don't believe this, then read this article I wrote circa 2001:....

Decompression Strategies: A Changing Philosophy? - www.diveoz.com.au is the biggest and most popular Australian Scuba Diving Resource!

...in which I suggest that bubble models are the coming revolution. And I am being consistent now in the light of an emerging signal in the diving medicine literature that bubble models over-emphasise deep stops. As Victor Zamora has kindly observed, I have allowed my position to be dictated by the evidence. Other scientists have done the same. Wayne Gerth spoke about "losing his religion" in regard to deep stops at the UHMS Deep Stop Workshop. I think that there is abundant evidence that the only player in this discussion with a true "agenda" that is independent of the science is you.

the math and trusted deco science formula that shows the reasoning of a/ above is not correct.

Ross, as stated many times previously, the only relevance of "trusted deco science formula" to this discussion is that like everyone else you use tissue gas pressure calculation methods that are common to all models. How different models apply the results of such calculations differs markedly (which is why they produce different decompression profiles). VPM places emphasis on protecting the fast tissues early in the ascent by imposing deeper stops. This results in greater loading of slower tissues with gas. The NEDU study and subsequent analysis of technical diving profiles in the light of the NEDU study findings has shown that this is almost certainly not the most efficient use of decompression time. That is the state of the evidence as of this date. If further evidence emerges that changes this interpretation, then just as I have done before (see above) I will re-evaluate my position.

Simon M

 

[Dr Simon Mitchell]

VPM-B is not the BVM(3). They are very different, so please don't get it confused. Mathematically, VPM-B is much closer to successful A1 VVAL profile, than the failed BVM A2 profile.

This is all old ground. The mathematical relationship between VPM-B, BVM and VVAL18 is clearly depicted by Dr Doolette, arguably one of the 2 or 3 pre-eminent decompression modellers world-wide, here:

Deep stops debate (split from ascent rate thread) - Page 20

This clearly refutes your claim. Parenthetically, I find it amazing to hear you trying to claim that your bubble model is similar to a gas content model. I suppose it is understandable given that there is evidence that the gas content model is the most successful approach in the NEDU study, but in the early 2000s you were going to great lengths to highlight the differences between VPM and gas content models.

There is no real science to connect the nedu test to VPM-B, or tech diving profiles. The nedu test paper makes no claims to represent anything beyond what it tested.

That is not true. Cautious extrapolation "beyond what it tested" was exactly the point of the cloud diagram (Figure 7) in which the integral supersaturation in representative tissues was evaluated for the two NEDU profiles and approximately 500,000 other possible profiles for decompressing from that dive. On the basis of that evaluation Doolette, Gerth and Gault concluded:

It therefore seems unlikely that any deep stops schedule exists that would result in a probability of DCS discernibly lower than that resulting from the tested shallow stops schedule.

We have always accepted and stated many times that in dives with a lower risk of DCS (less work, warmer, oxygen decompression etc) the difference between approaches is likely to be smaller and perhaps impossible to detect in study of pragmatic size, but the direction of relative risk is highly unlikely to be any different.

The attempted explanations and positions to make any tech connection so far, by all involved, are opinion based theory only. But when put to analysis, they have failed.

No, the "tech connection" is an extrapolation from solid experimental evidence. It is backed up by outcomes of other studies looking at bubble production in deep vs shallow stop approaches to decompression diving. In other words, the current evidence is all trending in the same direction and for that reason should not be ignored. I can hardly see why you would deem the explanations "failed". In contrast, the elephant in the room on your side of the argument is that there is not a shred of evidence that bubble models are more successful than approaches which emphasise deep stops to a lesser degree, or any approach for that matter.

Simon M

 

[UWSojourner]

Well Bruce, Look at the link you posted and you will find this (I know it is multichoice but...):

Deep stop practices (or what I understood is grouped under this name):
VPM has 10.10 % and not 3%
Bubble models 3.03%
GF 30/70 or 20/80 has 49.49%
RatioDeco has 9.09%
GF 20/70 has 4.04%

shalow sotp practices (Simons suggestion or near it):
GF 40/80 has 33.33%

It would seem you did not bother to even look at the link you posted.

Just want things are correct.

Igor, since you're looking for accuracy, I think the idea that VPM, GF30/x, and GF20/x should be grouped under the "deep stop" banner should be considered inaccurate. I've said this before, but GF in almost ANY configuration accomplishes the "shallower stop" goal when compared to VPM.

To illustrate, consider a CCR dive to 270ft 20min 10/70 1.2 1.6@20. If you use VPM-B+2 then GF20/90, GF30/88, and GF50/82 all match the run time.

Now look at the supersaturation-time chart below for that dive.

Anyone can see looking at this chart that the decompression stress of GF20/90, GF30/88, and GF50/82 are far closer than between VPM-B+2 and GF20/90. In fact about 80% of the "gain" obtained by switching from VPM-B to GF50/82 is also enjoyed by GF20/90.

You see the same thing looking at peak GF by depth:

Clearly, this chart also shows the 3 GF profiles are more closely related to each other than any of them are to VPM. The large VPM-B "sag" on the line represents the deeper stops that cause the need for the high surfacing gradient factor (i.e. the high surfacing GF is the "cost" of the continued on-gassing, delayed off-gassing, during the deeper stops).

So in the spirit of being correct, it makes more sense to group VPM-B, bubble models, and ratio deco together under the label "deep stop". The others should be under the shallower stop label. That would put deep stop practices at about 22% and shallower stop practices at 78%. My guess is that Bruce actually has a better handle on the pulse of dive practices than this relatively small poll given his business and contacts, but even that poll puts deeper stop practices in a clear minority.

Again, just for the sake of accuracy.

 

[Dr Simon Mitchell]

FWIW, I find it interesting that Shearwater sells a "product" that they apparently don't believe in.....

Hello Bob,

I certainly don't purport to speak for Shearwater, but I think this observation exemplifies an unfortunate consequence of the way Ross has chosen to frame this debate over a long period now. His repeated attacks on a scientifically sound and influential study have forced a vigorous defence from the scientific community side, and this has made the argument seem more polarised than it really is. The "anti-VPM" sentiment that pervades the threads comes more from him accusing me (and others) of harbouring such sentiment than from direct "anti-VPM" messages from us. He has put VPM in the firing line by trying to claim that that the NEDU study bears no relevance to VPM when this is almost certainly not true. But, we have always been very cautious in drawing hard conclusions about practical changes to diving behaviour. I don't think anyone has prospectively set out to condemn VPM or issue an edict against its use.

Which brings me to the Shearwater thing. I suspect that it not a case of not "believing in" VPM (after all, it will work fine the majority of the time), but more a case of perceiving that it is probably not the optimal approach to decompression. I don't seen anything wrong in offering it despite such a perception. After all, if you are going to offer multiple decompression platforms it is inevitable that not all of them can be optimal. Bruce is a very analytical guy and I suspect that what upsets him about this issue is Ross's refusing to consider that this may be the case in the face of substantial evidence that he should do so. It is highly likely that VPM is not be the optimal approach to decompression but I would certainly not consider the evidence strong enough to "ban" it. I personally see nothing wrong with offering VPM on any computer for users who want it.

Simon M

 

[rossh]

Readers, be very careful about reading the graphs by UWSojourner (Kevin Watts). He uses a measure he made up called Integral Super Saturation (ISS).

This is not a recognized scientific measure. It has not been tested, validated, calibrated, or shown to be valid for this purpose. It does not appear in other place. Even worse is he sums up the data from concurrent cells into one big number, but the model structure is strictly a parallel cell design and does not function as a serial or interconnect design.

Bottom line... this integral super saturation (ISS) measure is one big meaningless number - junk science.

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