Will http://www.ncbi.nlm.nih.gov/pubmed/25525213 change deco procedures?

[Dr Simon Mitchell]

Latest poll also shows thousands of people believing in Bigfoot. Seriously, is a poll your "go to place" to show it MUST be so?

Thank you for your constructive post.

You asked whether we had done any good. I provided some metrics that suggested we had successfully defended good science among a group of your diving peers.

Also, I reported a proportion (>90% of respondents) while your Bigfoot example cites an absolute number. There's a difference. Your argument might have been more convincing had you been able to report that 90% of sensible people believe in Bigfoot which, of course, you can't.

Simon M

 

[ajduplessis]

Like VPM +7 ?

 

[Dr Simon Mitchell]

Like VPM +7 ?

Yes, like that, and all the other concepts that were carefully explained on that thread.

 

[Shearwater]

...
David didn't talk much about things connected to tech diving (or explain the above). In fact he shied away from the question. But he did stomp all over the DCIEM tables. I think if the original DCIEM people were still around, David might have a harder time of getting away with such negativity.
...

This is a minor thing, but Ross doesn't seem to have any need to make statements that are factual. Imaginary arguments work fine for him.


Ron Nishi, who is considered to be the father of DCIEM, is very much "still around."

In fact he made a presentation at the CUHMA meeting in Toronto Oct 23-25 2015. Lynn and I sat next to him for all three days, so I'm pretty confident it was really him.

Bruce

 

[boulderjohn]

It probably should have no impact at this stage. David and his colleagues have performed studies in both animals and humans that appear to refute the assumed need to penalise helium use with longer decompressions in the type of deep bounce diving we do. HOWEVER, we have reason to suspect that those penalties for helium may have resulted in appropriate decompressions from deep dives where helium is typically used; in other words, deep dives need longer decompressions irrespective of the gas you use. We can't rule that out at this stage anyway. So, we do not recommend that anyone goes out and starts shortening their usual decompression from deep dives, or that we start messing with our computers by telling them we are breathing nitrogen when we are really breathing helium. In the fulness of time we will elucidate a sensible application of this new knowledge in the optimisation of decompression, but now is not the time to be making changes. Hope this helps.

Thank you very much. It does help.

 

[UWSojourner]

Like VPM +7 ?

You can start here to read the debate about VPM+7. That post was my conclusion that we had moved beyond the idea that VPM-B+7 was somehow an invalid idea. For more, see posts 611-617, 626, 636, 638, 646, 665, and 703.

Among the arguments tried by Ross in the deep stop thread, for me this was the weirdest. It was strange simply because if Ross wins the point, VPM is busted. Calling into question VPM's theory for limiting bubble growth is a bad strategy for showing its superiority.

We did get past that, although it continues to pop-up here and there (as in your post).

 

[ajduplessis]

You mean to say that data was "adjusted" to derive a setting that actually does not exist? The rest is just blah blah blah.

 

[UWSojourner]

You mean to say that data was "adjusted" to derive a setting that actually does not exist? The rest is just blah blah blah.

As I said, if the core idea behind VPM is just "blah blah…" and you're willing to junk it, I'm fine with that.

As to "does it exist" ...

simply open up Ross's software, go to "Config\Advanced\Allow me to control the advanced configuration settings". Then choose VPM-B as the model and put 84% in the "Conservatism" box. That is VPM-B+7 -- alive and well in Ross's software.

 

[boulderjohn]

You can start here to read the debate about VPM+7. That post was my conclusion that we had moved beyond the idea that VPM-B+7 was somehow an invalid idea. For more, see posts 611-617, 626, 636, 638, 646, 665, and 703.

I think a lot of people who are not members of that forum, do not want to become members of that forum, and do not want to wade through the whole discussion would greatly appreciate a summary.

 

[UWSojourner]

I think a lot of people who are not members of that forum, do not want to become members of that forum, and do not want to wade through the whole discussion would greatly appreciate a summary.

Sorry John, I thought visitors could see the thread without having to become members. But quickly ...

VPM hypothesizes a distribution of bubble seed sizes that are present at the start of a dive. For illustration, let's say a diver has bubble seed sizes {0.55, 0.63, 0.67, 0.71, 0.83, 1.03, 1.4, 1.8 }. The "critical radius" setting in VPM promises to prohibit bubbles at the critical radius size and smaller from initiating growth during the diver's ascent to the surface. Bubble's of greater size are allowed to grow, but since you can change the critical radius it shouldn't be a problem. If that part of the bubble distribution starts to become a problem, just stop them from growing by increasing the critical radius size. So the critical radius is the primary VPM parameter that attempts to manage the total volume a bubble growth.

So, for example, a critical radius of 0.71 would not allow bubbles {0.55, 0.63, 0.67, 0.71} to grow. The others would experience supersaturation pressures that could initiate growth, but by adjusting the critical radius you hope to control the total volume of bubbles (free gas). You can find MUCH more technical descriptions, but for our purposes that's the gist of it

Ross defines the critical radius in his software by defining + values. For example, VPM-B+3 corresponds to a critical radius that is larger (i.e. should prohibit larger bubbles from growing), than VPM-B+1. That's why it is thought to be more conservative. As you increase the critical radius size you should be cutting off more and more of the hypothesized bubble distribution from initiating growth. And larger critical radii imply lengthening deco times.

Those objecting to VPM-B+7 seem to be saying VPM can effectively limit growth of only part of the hypothesized bubble distribution. In other words, VPM only works up to a point (usually defined by Ross as his VPM-B+5 … which of course is completely arbitrary). That admission is extremely odd if you're trying to defend VPM which is why I was so stunned they were even attempting to make the argument.

The reason he didn't want to admit VPM-B+7 is a valid VPM profile is because it is VERY similar (not identical) to the A2 deeper stop profile tested by the NEDU (which is part of what the deep stops thread showed). The A2 profile was considerably more risky than the A1 shallower stop profile that was also tested. And, it turns out, the A1 profile was very similar to GF 53/53. So we have actual dive trials showing, at least for that case, that a GF profile would likely have performed considerably better than one generated by VPM-B … not a comfortable outcome for deep stop proponents.

But, it's all here for the reading, and a good presentation from Dr. Doolette is here.