My DCS Hit

[UWSojourner]

Hello UWS

Hello.

Your analysis in seeking to compare what are perceived to be three equivalent dives (two different GFs and one VPM) may not be a correct equivalence because equal run time is the wrong measure of decompression risk equivalence for the two models.

I was not trying to compare 3 equally risky profiles. The analysis shows in all probability that VPM-B+3 is the riskier of the profiles shown. It would be difficult, unless you've already drank the kool-aid, to see how 44% greater supersaturation exposure and surfacing GFs exceeding 130 is not clearly a riskier proposition.

The reason you compare profiles with the same run time is to see what each decompression method does with the allotted time. I am sure that given enough extra time we could cure the VPM-B+3 profile. That's what current research is indicating -- deep stops as recommended by bubble models require MORE, not less, decompression time to achieve the same risk. But showing what results from the same run time highlights how each perform given the same time to work with.

The outcome of your analysis (higher levels of supersaturation with VPM as compared to GF models for the same run time) is merely a necessary and expected outcome of comparing two decompression risk models requiring different quantum of decompression stops for dives of the same working depth.

What you are saying is correct. VPM-B does require a different amount of stop time for the same dive to achieve the same risk -- more stop time. That is the definition of an inefficient decompression model..

... if I was to say that a bubble model would result in a shorter dive run-time; no one should be surprised if that is an inherent differentiating characteristic of the two models.

Actually, they would be surprised that you attempted to say that at all. Current research says clearly that the deep stops generated by bubble models require MORE, not less, decompression time to achieve the same level of risk.

... all that matters is how close a model aligns with the evidence on observed decompression injury rates.

I agree.

And as Dr. Mitchell has summarized nicely here, all current research, including closely monitored human trials, points to the conclusion that bubble-model-style deep stops are inefficient, meaning their injury rates will be higher than a profile of the same run time that spreads some of that time toward shallower stops.

 

[Tony_Q]

Hello UWS,

Thank you for your detailed comments on my post.

If different dive models are requiring substantially different quantities of decompression as occurred in your example, then I don't think you can directly translate a VPM surface supersaturation level directly to an equivalent dissolved tissue model supersaturation level e.g. like quoting a 130GF factor for the VPM dive. This would be equivalent to saying that the GF dives reporting a surface 80 GF had an effective surface GF of say 40 based upon a VPM model (in a VPM model on this data, 130GF would equal 100GF on VPM scale of 100 being its safe maximum in GF speak). With the VPM model reporting its surface supersaturation at 100GF (assuming no conservative setting). The numbers other the VPM 100 GF are made up to illustrate the two different perspectives/GF scales.

Dissolved tissue and bubble models exist as two discrete mathematical models or intellectual constructs to explain decompression risk. The definition of what something means in one construct does not necessarily have the same meaning in the other or even exist. Some elements are absolute e.g temperature, pressure; others can be relative e.g Gas Supersaturation (requires an actual and a reference point). Reference points can be different between models and variable within models.

For intra-model dive profile comparison purposes, no potential conflict in construct elements or their definition can arise so your methodology works well. Even for inter-model comparison purposes, if the quantity of decompression required is similar, methodology should still work well as the concept of allowable supersaturation should be consistent (inferred from similar required decompression obligations). However if there are significant variations between definition of what constitutes allowable supersaturation in the models, then direct conversion of model parameters between models is not possible or meaningful.

It is not a matter of consuming any kool-aid, just a question of whether GF models have a tendency to become more conservative with depth, bubble models to become more aggressive with depth or some combination of the two. Only empirical evidence will resolve this question.

Regards,
Tony

 

[UWSojourner]

Dissolved tissue and bubble models exist as two discrete mathematical models or intellectual constructs to explain decompression risk. The definition of what something means in one construct does not necessarily have the same meaning in the other or even exist.

They may exist in separate mathematical models, but they don't exist in separate realities. Pointing out that VPM-B+3 is recommending surfacing at GF over 130 means you need to really believe it's doing something incredibly smart in the profile to allow that. Based on the available research, that belief is not well founded.

It is not a matter of consuming any kool-aid, just a question of whether GF models have a tendency to become more conservative with depth, bubble models to become more aggressive with depth or some combination of the two. Only empirical evidence will resolve this question.

Your appeal for more evidence neglects the evidence already there. But in any case, the way VPM-B calculates profiles GUARANTEES increasing risk as dives become more extreme. It's just baked into VPM-B. Showing a profile with a surfacing GF over 130 is just one manifestation of that issue described here.

 

[JonG]

Gents as well as looking at the comparative stress between the 2 models, I think many of us are interested in whether there is any demonstrable physiological benefit to any form of deep stop incorporated into any model?

Also what impact does a fixed/higher setpoint have in comparison with the oc studies on faster tissues during ascent.

Or are these as yet unknowns?

 

[Tony_Q]

They may exist in separate mathematical models, but they don't exist in separate realities. Pointing out that VPM-B+3 is recommending surfacing at GF over 130 means you need to really believe it's doing something incredibly smart in the profile to allow that. Based on the available research, that belief is not well founded.


Your appeal for more evidence neglects the evidence already there. But in any case, the way VPM-B calculates profiles GUARANTEES increasing risk as dives become more extreme. It's just baked into VPM-B. Showing a profile with a surfacing GF over 130 is just one manifestation of that issue described here.

Hello UWS,
That VPM is showng a more aggressive approach to dealing with decompression obligations is not the key issue, it is how this additional aggression translates to any increased incidence of decompression injury. Logically more decompression should be safer from a decompression risk perspective, but if residual decompression injury risk is still within acceptable risk levels for a particular diver, then all should be fine. If it pushes risk above what a diver wants to accept then it is not okay. I appreciate these are not hard numbers, but just illustrate the principle.

If VPM is pushing aggression too far, then notwithstanding the generally low levels of decompression injury observed in the general diving population, some observable increase in decompression injury rates for divers using a VPM profile on deep dives as compared to divers using a more conservative GF model profile should be occurring. I acknowledge that the smaller population of divers undertaking these type of dives makes determining statistically significant variations difficult to determine.

Based upon previous posts from Ross and Simon, neither appeared able to point to any studies showing such evidence of how well the reality of outcomes in the diving population are aligning with the relative risks identified in the available research.

Hopefully one day (in the not too distant future) we will have the empirical evidence to settle the matter.

Regards,
Tony

 

[Simon Mitchell]

Hello Tony,

One of Ross's strategies in these threads is to identify people he thinks are vulnerable to being influenced behind the scenes and he starts pm'ing them. This is something he has clearly done with you. I would caution you that you are dealing with someone who has no relevant training, whose views are markedly at odds with the experts in the field, and who has revealed multiple times (including in this thread) that his knowledge of the relevant physiology and pathophysiology is extremely poor. He is ignored by the scientific community. He has a financial interest in the outcome of this debate, and is obsessed with being considered correct. He will effectively say anything he feels may help him in pursuit of that goal. He constantly accuses true experts in the field of lying, data fabrication, and misleading the public when there is no plausible reason (not to mention any evidence) for any of these accusations being true. You should consider very carefully who you are dealing with.

Moving on from that, I think UWSojourner has hit the nail on the head with a number of his responses to you.

These debates are fundamentally about the most efficient use of decompression time. There is no other debate worth having. If you believe we should not be comparing decompressions of the same length generated by different models (as you indicate in one of your posts above) then we might as well give up on this discussion. What, for example, would be the point of comparing DCS risk between a VPM decompression and a GF decompression with GFs chosen to give you an hour more deco than the VPM decompression?

Put another way, if you are a VPM user and it gives you X amount of decompression time for a particular dive, the question you should be asking is, "is there another way of distributing my decompression stops in that same X time that reduces my risk of DCS"? That is the key question and same if you are a GF user. We all know you can make a decompression safer if it is longer, but the strategy for distributing the stops across depth is the key question.

This brings us to the point that UWSojourner has quite correctly made: you have entered this discussion as though a state of equipoise exists on the matter and you are ignoring (or are unaware of) the relevant evidence that has emerged over the last 10 years. To summarise, the only comparative human studies of deeper vs shallower approaches to decompression that have been performed have all shown that there is no apparent advantage from the reduction of fast tissue supersaturation that occurs when deeper stops as prescribed by bubble models or similar algorithms are performed, and that outcomes from the deeper stop dives are worse based on primary endpoints of DCS and / or VGE and / or inflammatory activation (depending on the study). In one of the studies, that was despite the fact that the deeper stop decompression was substantially longer than the shallower stop approach.

Integral supersaturation evaluations of the type performed by UWSojourner on this thread have correctly predicted the outcomes of all of these studies, and it follows that this approach provides a plausible means of comparing profiles for risk. His concerns about high surfacing gradient factors (and correspondingly high post surfacing integral supersaturation) in the VPM profile he analysed in his examples above arise from the fact that there is no evidence whatsoever from the extant studies (and they are the only studies) that deep stops do anything to magically prepare the diver to better tolerate this physiological insult. In fact, it is this higher supersaturation in the slower tissue later in the decompression and after surfacing that is by far the most plausible explanation for worse outcomes in the deeper stop study dives. Bubble models were a fashion based entirely on a theoretical attraction (an attraction that drew all of us in for a while) that has started to look very shaky as real evidence has started to emerge.

Now, I totally agree with you that the evidence we have is not as comprehensive as it could be. I applaud your idea of trying to gather more. But do not be under any misapprehension that we are currently in a state of equipoise; because we are not. There is evidence, and so far it is all saying the same thing. It is strong enough that the only full time professional decompression modelers in the world recommended that the US Navy not incorporate bubble models into their operational diving. But we do need more evidence because holes in our knowledge remain; not least being that the deeper stops of any approach to decompression have to start somewhere, and we currently don't know exactly where that sweet spot is.

I am sceptical that databases of decompression dives and outcomes will ever be the answer, because dives rarely strictly follow the prescriptions of a particular model, and reporting of dives and outcomes to such databases are subject to considerable potential biases. That is why PDE started out with observers actually on the boats to make sure ALL dives conducted and their outcomes were recorded. But there could be value in it if done properly. Unfortunately this sort of research is very hard to do.

That VPM is showng a more aggressive approach to dealing with decompression obligations is not the key issue it is how this additional aggression translates to any increased incidence of decompression injury.

Actually, it is a key issue because we have no means of comparing the incidence of DCS in use of different algorithms in the wider community but we do have strong evidence from carefully controlled studies that bubble model decompressions are not optimal, AND the more aggressive tolerance of high surfacing supersaturations (and greater total supersaturations) provide a highly plausible explanation as to why.

Based upon previous posts from Ross and Simon, neither appeared able to point to any studies showing such evidence of how well the reality of outcomes in the diving population are aligning with the relative risks identified in the available research.

True, but this does not mean there is equipoise in the available research. As I allude to above, the reality is far from it. We actually know quite a lot about this issue. Ross just does not like it.

Hopefully one day (in the not too distant future) we will have the empirical evidence to settle the matter.

That would be great, but for the reasons I articulated above, it will be a tough ask.

Simon M

 

[Mark Chase]

Exactly.

From my viewpoint, seems most people arguing against vpm, are arguing academically, and may never even have actually dove using vpm I may be wrong, but that's how it seems, as I don't see deep stops, rarely even anything below 100ft, that wasn't already burned off on ascent.

Asked above why we use vpm, the answer was already in my post. Longer bottom times, less deco.. We set one computer to 50/90 and for short dives, it was pretty close to vpm. But deeper and longer, they dramatically diverged. Dives we could do in 2.5-3 hours, were not even doable, and became more like 5 with all the deco. Deeper- Longer dives it diverges badly. In our 2 weeks in truk, we probably averaged about an extra 15-20m of bottom time on the deep wrecks.

For 6 years we ran+2,but now run+3, but for no real reason than to just buffer abit. I think it added maybe 5m. I can tell no difference.

I am struggling to make sense of your statements?

A no deep stop 100m for 30min dive running 80/80GF would look like this

Decompression model: ZHL16-C + GF
DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 80/80
Dec to 100m (5) Diluent 10/70 0.70 SetPoint, 18m/min descent.
Level 100m 24:27 (30) Diluent 10/70 1.30 SetPoint, 17m ead, 25m end
Asc to 51m (35) Diluent 10/70 1.30 SetPoint, -9m/min ascent.
Stop at 51m 0:33 (36) Diluent 10/70 1.30 SetPoint, 3m ead, 14m end
Stop at 48m 2:00 (38) Diluent 10/70 1.30 SetPoint, 3m ead, 13m end
Stop at 45m 2:00 (40) Diluent 10/70 1.30 SetPoint, 2m ead, 12m end
Stop at 42m 2:00 (42) Diluent 10/70 1.30 SetPoint, 1m ead, 12m end
Stop at 39m 2:00 (44) Diluent 10/70 1.30 SetPoint, 0m ead, 11m end
Stop at 36m 3:00 (47) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 33m 3:00 (50) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 30m 5:00 (55) Diluent 10/70 1.30 SetPoint, 0m ead, 9m end
Stop at 27m 5:00 (60) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 24m 6:00 (66) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 21m 9:00 (75) Diluent 10/70 1.30 SetPoint, 0m ead, 7m end
Stop at 18m 9:00 (84) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 15m 13:00 (97) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 12m 17:00 (114) Diluent 10/70 1.30 SetPoint, 0m ead, 5m end
Stop at 9m 23:00 (137) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 6m 32:00 (169) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 3m 53:00 (222) Diluent 10/70 1.30 SetPoint, 0m ead
Surface (223) Diluent 10/70 -3m/min ascent.


First stop depth 51m for 33 seconds and you would probably pass that with progressive ascent so first proper stop is 48m


Same dive on VPMB3

Decompression model: VPM - B
DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 3
Dec to 100m (5) Diluent 10/70 0.70 SetPoint, 18m/min descent.
Level 100m 24:27 (30) Diluent 10/70 1.30 SetPoint, 17m ead, 25m end
Asc to 78m (32) Diluent 10/70 1.30 SetPoint, -9m/min ascent.
Stop at 78m 0:33 (33) Diluent 10/70 1.30 SetPoint, 11m ead, 20m end
Asc to 57m (41) Diluent 10/70 1.30 SetPoint, -3m/min ascent.
Stop at 57m 2:00 (41) Diluent 10/70 1.30 SetPoint, 5m ead, 15m end
Stop at 54m 2:00 (43) Diluent 10/70 1.30 SetPoint, 4m ead, 14m end
Stop at 51m 2:00 (45) Diluent 10/70 1.30 SetPoint, 3m ead, 14m end
Stop at 48m 3:00 (48) Diluent 10/70 1.30 SetPoint, 3m ead, 13m end
Stop at 45m 2:00 (50) Diluent 10/70 1.30 SetPoint, 2m ead, 12m end
Stop at 42m 3:00 (53) Diluent 10/70 1.30 SetPoint, 1m ead, 12m end
Stop at 39m 4:00 (57) Diluent 10/70 1.30 SetPoint, 0m ead, 11m end
Stop at 36m 4:00 (61) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 33m 4:00 (65) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 30m 5:00 (70) Diluent 10/70 1.30 SetPoint, 0m ead, 9m end
Stop at 27m 6:00 (76) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 24m 7:00 (83) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 21m 8:00 (91) Diluent 10/70 1.30 SetPoint, 0m ead, 7m end
Stop at 18m 10:00 (101) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 15m 13:00 (114) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 12m 15:00 (129) Diluent 10/70 1.30 SetPoint, 0m ead, 5m end
Stop at 9m 21:00 (150) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 6m 28:00 (178) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 3m 41:00 (219) Diluent 10/70 1.30 SetPoint, 0m ead
Surface (220) Diluent 10/70 -3m/min ascent.


On the VPM profile you get a similar 33 second stop but that's at 78m and the first proper stop is 57m


The overall run time with VPM is 219minsd and with GF is 222mins so virtualy the same in water time but with the VPM shallow stops from 9m and up you have a total of 90mins shallow stops where as with the GF profile you have 108mins of shallow stops


If I manipulate the GF to match the shallow deco time Id need to go to 80/95 so with the VPMB3 dive you have a final GF of 95

However If I manipulate the GFs to give me a first stop depth of 57m (the same as VPMB3) I will go over 100GF inorder to match the deep stop profile

Decompression model: ZHL16-C + GF
DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 50/100
Dec to 100m (5) Diluent 10/70 0.70 SetPoint, 18m/min descent.
Level 100m 24:27 (30) Diluent 10/70 1.30 SetPoint, 17m ead, 25m end
Asc to 60m (34) Diluent 10/70 1.30 SetPoint, -9m/min ascent.
Stop at 60m 0:33 (35) Diluent 10/70 1.30 SetPoint, 6m ead, 16m end
Stop at 57m 2:00 (37) Diluent 10/70 1.30 SetPoint, 5m ead, 15m end
Stop at 54m 2:00 (39) Diluent 10/70 1.30 SetPoint, 4m ead, 14m end
Stop at 51m 2:00 (41) Diluent 10/70 1.30 SetPoint, 3m ead, 14m end
Stop at 48m 2:00 (43) Diluent 10/70 1.30 SetPoint, 3m ead, 13m end
Stop at 45m 2:00 (45) Diluent 10/70 1.30 SetPoint, 2m ead, 12m end
Stop at 42m 2:00 (47) Diluent 10/70 1.30 SetPoint, 1m ead, 12m end
Stop at 39m 2:00 (49) Diluent 10/70 1.30 SetPoint, 0m ead, 11m end
Stop at 36m 2:00 (51) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 33m 3:00 (54) Diluent 10/70 1.30 SetPoint, 0m ead, 10m end
Stop at 30m 5:00 (59) Diluent 10/70 1.30 SetPoint, 0m ead, 9m end
Stop at 27m 5:00 (64) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 24m 6:00 (70) Diluent 10/70 1.30 SetPoint, 0m ead, 8m end
Stop at 21m 8:00 (78) Diluent 10/70 1.30 SetPoint, 0m ead, 7m end
Stop at 18m 9:00 (87) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 15m 12:00 (99) Diluent 10/70 1.30 SetPoint, 0m ead, 6m end
Stop at 12m 16:00 (115) Diluent 10/70 1.30 SetPoint, 0m ead, 5m end
Stop at 9m 20:00 (135) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 6m 28:00 (163) Diluent 10/70 1.30 SetPoint, 0m ead, 4m end
Stop at 3m 45:00 (208) Diluent 10/70 1.30 SetPoint, 0m ead
Surface (209) Diluent 10/70 -3m/min ascent.


Looking at the two profiles your some 52mins below 21m on VPMB3 and only 43mins below 21m on the 50/100GF profile


And you claim to prefer VPMB3 to GFs because you get better bottom time to deco time but infact if you ran 50/100 you would have 10mins less deco than VPMB3?


Ad how different are the profiles?

Stop at 57m 2:00 (37) VPMB 2 GF 80 0 +2
Stop at 54m 2:00 (39) VPMB 2 GF80 0 +2
Stop at 51m 2:00 (41) VPMB 2 GF80 0 +2
Stop at 48m 2:00 (43) VPMB 3 +1min GF80 2
Stop at 45m 2:00 (45) VPMB 2 GF80 2
Stop at 42m 2:00 (47) VPMB 3 +1min GF80 2
Stop at 39m 2:00 (49) VPMB 4 +2min GF80 2
Stop at 36m 2:00 (51) VPMB 4 +2min GF80 3
Stop at 33m 3:00 (54) VPMB 4 +1min GF80 3
Stop at 30m 5:00 (59) VPMB 5 GF80 5
Stop at 27m 5:00 (64) VPMB 6 +1min GF80 5
Stop at 24m 6:00 (70) VPMB 7 +1min GF80 6
Stop at 21m 8:00 (78) VPMB 8 GF80 9
Stop at 18m 9:00 (87) VPMB 10 +1min GF80 9
Stop at 15m 12:00 (99) VPMB 13 +1min GF80 13
Stop at 12m 16:00 (115) VPMB 15 + 1min GF80 17
Stop at 9m 20:00 (135) VPMB 21 +1min GF80 23
Stop at 6m 28:00 (163) VPMB 28 GF80 32
Stop at 3m 45:00 (208) VPMB 41 -3mins GF80 53

 

[Tony_Q]

Hello Simon,

Thank you for your thoughtful reply.

You misinterpret my intentions, it was not to suggest that there is some equivalence in risk between VPM and GF models (quite the opposite intention actually); that one model is better than the other, or question available research on perceived benefits/effectiveness of deep versus shallow decompression stops. My position is quite different to Ross in that I have no commercial interest in any specific decompression model.

My queries to UWS were about the potential difficulties/suitability of trying to describe outcomes of one model in the language/construct of another in certain circumstances. They in no way were meant to say the substantive points he was trying to make on relative risks were in error.

I knew the point I was trying to make was quite an abstract conceptual point and rather difficult to explain. I tried my best but clearly botched the attempt as UWS and yourself have not understood what I was trying to say. This is my failing in communication, not yours in understanding and I will waste no more time on the matter.

Your point on difficulty in obtaining relevant statistically significant empirical evidence is noted and I totally agree with it. However nothing will be lost by trying to have a go at seeing what can be found.

Regards,
Tony

 

[rossh]

There's nothing theoretical about VPM-B+3 generating a profile with a surfacing GF greater than 130; or that every compartment 9-16 is over a GF of 100.

Given that current research says deeper stops require MORE, not less, decompression time, a profile with a GF over 130 truly has gone off the rails.

Your theory is flawed. You hold GF / ZHL up as an absolute measure of correctness. Its not. ZHL is no more correct than any other measure. However, from these deep dive examples, we have proof that ZHL is grossly incorrect, and cannot be trusted or used. To make anything useful from ZHL at this depth, it has to be severely modified directly towards the bubble model attributes.

Conversely, the bubble model attributes - unmodified, works well at these depths...

In reality, you should be holding up the VPM-B as the standard, and asking why ZHL is so badly out of tune with the needs of deep dives.

.

 

[UWSojourner]

Your theory is flawed. You hold GF / ZHL up as an absolute measure of correctness.

When I respond to your posts I'm not really responding to YOU. I know your faith in VPM-B, or its hold on your wallet, will not be shaken. I'm responding to those whose minds might not yet be settled on the matter.

You are correct that ZHL/GFs is not an absolute measure of correctness. But GFs are a commonly known measure. In an era when most divers see a surfacing GF of 90 or 95 as being pretty aggressive, showing that your recommendation to divers has a surfacing GF over 130 is, well, an interesting data point.

My bet is that in most divers the cognitive dissonance created by a recommended surfacing GF at those levels will make them stop and think, "Something's obviously not right here." And that would be an entirely correct conclusion.

 

[Jeff Pack]

I am struggling to make sense of your statements?

A no deep stop 100m for 30min dive running 80/80GF would look like this

Depends on the GF used. You can putz around with GF and get similar to VPM, as you did, but where here is anyone running these GFs? I think the answer is almost no one.
Most are running 30/70 or 80, or 40/70-80.

 

[Jeff Pack]

I know your faith in VPM-B, or its hold on your wallet, will not be shaken..

this argument always amuses me when brought up. Its not like you pay extra to get VPM or anything, you use Multi Deco, you use VPM or not. Ross makes the same.

 

[UWSojourner]

I know your faith in VPM-B, or its hold on your wallet, will not be shaken.

this argument always amuses me when brought up. Its not like you pay extra to get VPM or anything, you use Multi Deco, you use VPM or not. Ross makes the same.

I think you'd have to classify that as simply a comment.

The argument is that the recommended VPM-B+3 profile ...

1. with its surfacing GF in excess of 130
2. with its 34-44% higher total supersaturation exposure compared to the two GF profiles shown
3. and with its 50% higher surface supersaturation exposure

... is unlikely to be seen by divers as a profile with "extra safety" (as +3 is described by Ross). And if the VPM-B+3 profile were properly tested, based on what we've learned from prior research, a reasonable person would expect it to be the riskier profile. That's the argument.

 

[rossh]

I think you'd have to classify that as simply a comment.

The argument is that the recommended VPM-B+3 profile ...

1. with its surfacing GF in excess of 130
2. with its 34-44% higher total supersaturation exposure compared to the two GF profiles shown
3. and with its 50% higher surface supersaturation exposure

... is unlikely to be seen by divers as a profile with "extra safety" (as +3 is described by Ross). And if the VPM-B+3 profile were properly tested, based on what we've learned from prior research, a reasonable person would expect it to be the riskier profile. That's the argument.

...all of which are obviously beneficial or meaningless or just plain irrelevant or wrong..... i.e. junk info derived from invalid measures and junk science test methods. Your home made measures and metrics clearly do not represent stress and risk as you claim.

I remind you again... VPM-B and similar GF style plans work this deep, beacuse fast tissues do matter, and deeper stops are essential in some places. While your "new, more efficient" deco method does not work - it failed horribly in Don's dive example here.

Your suggested "new, more efficient and lower risk" method put the guy in a wheel chair and 3 months of spinal DCS injury.....

You and Mitchell are peddling a concept and self claimed improvement, that plainly fails when put to the real test. So maybe your self serving interpretations of the science papers was wrong all along, and you lot need to reassess your interpretations..

Because this thing you are doing now - spin doctoring, mass marketing false information, attempting to hide the failed test of your deco theory behind another smoke screen, is transparent and shows desperation. Worst of all it will get more people that follow your failed deco method and theories, will be seriously injured.
.



.

 

[Simon Mitchell]

However nothing will be lost by trying to have a go at seeing what can be found.

Tony, agreed!

 

[jason drake]

Ross I am a deeply concerned diver. Are you telling us that UWSojourner and/or Simon Mitchell have directly recommended their own deco method to the public? And claimed that it is newer and more efficient? Could you link me to where they made those statements please? I can't find them. Also can you link me to the incident where the "new, more efficient and lower risk" approach injured someone please. That's a really very serious allegation. What possible motivation could they have to do this? Any ideas?

 

[Simon Mitchell]

...all of which are obviously beneficial or meaningless or just plain irrelevant or wrong..... i.e. junk info derived from invalid measures and junk science test methods. Your home made measures and metrics clearly do not represent stress and risk as you claim.

Except they are the same methods used and endorsed by the worlds leading decompression modelers to interpret their own research, and to calibrate a risk function in some of their own models. And if they "clearly do not represent stress and risk", how have they been able to correctly predict the outcomes of all the controlled deep vs shallow stop studies?

I remind you again... VPM-B and similar GF style plans work this deep, beacuse fast tissues do matter, and deeper stops are essential in some places. While your "new, more efficient" deco method does not work - it failed horribly in Don's dive example here.

Two points. First, yes, fast tissues matter, but the best evidence we currently have strongly suggests that they don't matter as much as bubble models assume they do. Second, show us your data that demonstrate that "VPM-B and similar GF style plans work this deep", or that other methods don't. The truth is that this is a wildly speculative claim based on nothing. There is no database of dives of known outcome for ANY approach to decompression from extremely deep dives.

Your suggested "new, more efficient and lower risk" method put the guy in a wheel chair and 3 months of spinal DCS injury.....

You keep saying this, and others keep pointing out that Don's dive did not conform to anything anyone recommended, which is demonstrably correct and Don himself has said it. But, as is the case with many demonstrably correct arguments that don't support your position, you just ignore them. That is one of the reasons you have totally destroyed any credibility you may once have had.

Because this thing you are doing now - spin doctoring, mass marketing false information, attempting to hide the failed test of your deco theory behind another smoke screen, is transparent and shows desperation. Worst of all it will get more people that follow your failed deco method and theories, will be seriously injured.

Leaving aside the fact that "the failed test" you refer to (Don's dive) was not of anything that anyone has recommended, does the position you are taking here indicate that you believe a single bad outcome can prove a decompression strategy is wrong? Because I can certainly provide examples of dives using your model and other bubble models / deep stop approaches that resulted in DCS. Does any one of these cases prove that deep stops are bad? Are you really this ignorant of what can and can't be concluded from one case of DCS, or do you actually understand it, thus implying this whole thing is just a cynical exploitation of one diver's misfortune to try to look authoritative on the internet and for your own financial gain?

In a related vein, since you continue to apportion blame for Don's case to me, can you please answer the question about whether you now accept blame for every case of DCS that has occurred using deep stop approaches to decompression? And if not, why not?

Finally, while I have your attention, can I get an answer on another question I put earlier that I think you are quietly hoping everyone will forget. Based on the arguments I put in this post, do you still claim that supersaturation at the surface doesn't matter? Over the years you have become skilled at sounding authoritative, but from time to time the level (or more correctly the lack) of your knowledge gets revealed in scarcely believable ways. The recent scubaboard thread where you insisted that it is tissue half times not perfusion (blood flow) that determines inert gas kinetics in tissues was a great example (for example, the last sentence in your post here). For reader's information, it is one of this field's most basic concepts and 100% proven that tissue perfusion is a critical determinant of a tissue's half time, and it is abundantly clear from the thread I linked to that Ross did not understand that. And we have another example in this thread with your characterization of surfacing supersaturation as inconsequential (as if a developing bubble can tell whether the supersaturation driving its growth is present before or after arriving at the surface!). Another absolute clanger that reveals how superficial your knowledge really is. Yet here you are portraying yourself as expert.

So, do you still claim that supersaturation at the surface doesn't matter?

Simon M

 

[rossh]

Ross I am a deeply concerned diver. Are you telling us that UWSojourner and/or Simon Mitchell have directly recommended their own deco method to the public? And claimed that it is newer and more efficient? Could you link me to where they made those statements please? I can't find them. Also can you link me to the incident where the "new, more efficient and lower risk" approach injured someone please. That's a really very serious allegation. What possible motivation could they have to do this? Any ideas?

I guess you have not being paying attention to the last 5 years of marketing and noise, and distractions and fallacy attacks they produce? Or are you just a fan boy trying to start a distraction from the obvious, and let these two off the hook.

No matter how much they try to deny it.... This dive is a direct test of Simon's / Kevin's own deco theories that they have derived from their false interpretations of science papers, and the invalid assumptions they have made as a consequence. Tough luck for them, and you the public. It seems their "new, more efficient, lower risk" deco method when put to a serious test like this one, fails.

.

 

[jason drake]

I'm not trying to distract Ross. I'm really disturbed by what seem like serious allegations. What have they been marketing for 5 years? As in, what are they selling? Do Simon Mitchell or UWSojourner sell dissolved gas models or products using them? And when you use quotation marks ( "new, more efficient, lower risk" ) are you quoting someone else's words? Did Simon Mitchell or UWSojourner write that? I can't find that post. Do Simon Mitchell and/or UWSojourner have their own deco model? One that is separate from Buhlmann's theories? Did Don follow a dive profile suggested to him by Simon Mitchell or UWSojourner? Do we have evidence of this? Sounds pretty serious.

 

[DSix36]

My dive profile and planning was NOT recommended to me by anyone. It was done totally on my own using what knowledge and experience I had at the time.

Everyone needs to keep in mind that there were several things, other than the plan or profile, that were not optimum for a dive like this and any one (or combination of) could have been the cause for my DCS. Maybe tomorrow the profile would work just fine for me, maybe not?