Deep Stops Increases DCS

[Dr Simon Mitchell]

I don't agree with that.

Simon Mitchell is heavily vested in these arguments, in a different kind of currency - community stature and lasting scientific recognition.

He is a working Dr., and hyperbaric specilaist who has chosen to publish papers and make public opinions. He travels the world giving talks on these and other ideas, based on the strength of his name and reputation. Like others in science, he embarked on a direction and a set of ideas early in his career, and is pursuing that now.

The currency of Simon Mitchell is community stature and lasting scientific recognition. Those are the valuable commodities to academics and take life time to achieve. A career and future prospects hinges on these matters too.

Simon Mitchell is not a neutral or unbiased in any way. He is more heavily invested in the direction this takes, than you or me.
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So, scientists are deemed to have a conflict of interest when they believe what they are writing!? Good luck selling that concept.

In any event, my history proves you wrong. I previously dived VPM. I was a deep stop supporter. Then the evidence emerged that bubble model-imposed deep stops are probably excessive. Like any scientist should I moved with the weight of evidence, which you (complete with massive conflict of interest) then attempted to trash, to the potential detriment of the diving community. All I have ever done is report and defend the evidence. The only reason I may seem heavily invested in an anti-deep stop position is because you have forced me into protracted debates with your persistent ill-informed assault on one of the most important studies ever conducted in diving medicine.

Just as I moved with the evidence previously, and as I have said on these forums multiple times, if the weight of quality evidence shifted in favour of deep stops I would change my view. That is how a scientist works and it would cause me no loss of reputation whatsoever. I have published studies that contradicted my own previous findings on matters far more important than this one, for example:

MITCHELL SJ, PELLETT O, GORMAN DF. Cerebral protection by lidocaine during cardiac operations. Ann Thorac Surg 67, 1117-1124, 1999 (one of the first studies ever to show brain protection by a drug)

...followed by...

MITCHELL SJ, MERRY AF, FRAMPTON C, DAVIES E, GRIEVE D, MILLS BP, WEBSTER CS, MILSOM FP, WILLCOX TW, GORMAN DF. Cerebral protection by lidocaine during cardiac operations: a follow-up study. Ann Thorac Surg 87, 820-825, 2009 (which did not show brain protection by the same drug)

Finally, if you think that my "community stature, lasting scientific recognition, career, and future prospects" are contingent in any way on winning an argument with you about deep stops on the internet you are completely deluded.

Simon M

 

[rossh]

So, scientists are deemed to have a conflict of interest when they believe what they are writing!? Good luck selling that concept.

In any event, my history proves you wrong. I previously dived VPM. I was a deep stop supporter. Then the evidence emerged that bubble model-imposed deep stops are probably excessive. Like any scientist should I moved with the weight of evidence, which you (complete with massive conflict of interest) then attempted to trash, to the potential detriment of the diving community. All I have ever done is report and defend the evidence. The only reason I may seem heavily invested in an anti-deep stop position is because you have forced me into protracted debates with your persistent ill-informed assault on one of the most important studies ever conducted in diving medicine.

Just as I moved with the evidence previously, and as I have said on these forums multiple times, if the weight of quality evidence shifted in favour of deep stops I would change my view. That is how a scientist works and it would cause me no loss of reputation whatsoever. I have published studies that contradicted my own previous findings on matters far more important than this one, for example:

MITCHELL SJ, PELLETT O, GORMAN DF. Cerebral protection by lidocaine during cardiac operations. Ann Thorac Surg 67, 1117-1124, 1999 (one of the first studies ever to show brain protection by a drug)

...followed by...

MITCHELL SJ, MERRY AF, FRAMPTON C, DAVIES E, GRIEVE D, MILLS BP, WEBSTER CS, MILSOM FP, WILLCOX TW, GORMAN DF. Cerebral protection by lidocaine during cardiac operations: a follow-up study. Ann Thorac Surg 87, 820-825, 2009 (which did not show brain protection by the same drug)

Finally, if you think that my "community stature, lasting scientific recognition, career, and future prospects" are contingent in any way on winning an argument with you about deep stops on the internet you are completely deluded.

Simon M

All about the science..?

... like faked up profiles, pretty graphs with no dimensions, plainly false diagrams, unconnected data and other unrelated science that is over hyped all out of proportion..... not to mention the malicious extras you add on at any opportunity.

I don't believe you, Simon. You have left a trail of evidence that shows something else.

The worst part of this, is you try to be judge and jury. You can't stand to have any opposing opinions survive.

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[rossh]

What is Supersaturation? How is it different from tissue tension? How do the different models really work to deal with this?

This diagram format will look familiar to some of you. Here we have added many of the missing pieces. Please refer back to this one, in the coming further slides.

What I hope to do, is demonstrate the various pieces of deco info that David has described for us. it will come in pieces as I build this.

Please correlate what you see here and what David has said below:

.... I have to describe some “Decompression 101” theory, so this may a bit basic for a lot of you, and for brevity I am going to confine the description to diving on a single gas (e.g. air diving, as in the experiment) although it is possible to extend to multiple gas. The purpose of a decompression stop is to limit bubble formation and allow washout of tissue inert gas.....


The "obsession" with supersaturation versus bubble mechanics is well founded. The putative cause of DCS is injury as a result of bubble formation. Supersaturation is a required condition for bubble formation and growth. There is broad (universal?) agreement that modelling tissue gas uptake with a range of exchange rates - as we do for instance with a collection of compartments with mono-exponential gas exchange - captures the essential processes,...

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[Dr Simon Mitchell]

I don't believe you, Simon. You have left a trail of evidence that shows something else.

I don't much care what you believe Ross. There certainly is a trail of evidence that I disagree with you, but attempting to argue that a scientist has a conflict of interest simply because they persist in disagreeing with you is ludicrous.

The worst part of this, is you try to be judge and jury. You can't stand to have any opposing opinions survive.

One could easily make the same argument about you Ross. You are repetitively taking a position that is contrary to the best available evidence on a matter of potential relevance to diving safety. I make no apology for continuing to point that out.

What is Supersaturation? How is it different from tissue tension? How do the different models really work to deal with this?

Since your post begins with the question "What is supersaturation?", you might want to correct the error in defining supersaturation pressure. Supersaturation pressure should be a vertical line. It is the difference between tissue gas pressure and ambient pressure at a given ambient pressure.

Simon M

 

[rossh]

. I previously dived VPM. I was a deep stop supporter. Then the evidence emerged that bubble model-imposed deep stops are probably excessive. ......

Simon M

Really - you used VPM? How ? Lets see now.

The nedu study came out in 2006. So you were between 2002 and end 2005?
You were never my customer back then, so that's not it,
The VR3 version only came out in late 2005, and it was really a GF plan pretending to be VPM-B/E, so that's not it,
Way too early for X1's and Shearwater's,

I'm stumped. How did you do it Simon?


Once again I'm inclined not to believe you.

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[David Doolette]

This actually makes a lot of sense.

FWIW, I'm a padder. I'm almost always going to pad my last stop by five minutes. I've cut tables before I dive mostly to determine gas requirements, but not often and I always let my PDC du jour take over. Most of my deco is on cave dives and usually amounts to less than 45 minutes, including the padding. Furthermore, I won't do deco dives for more than two days without a break and then usually only one a day.

I simply don't get the push it, push it, push it mentality. I certainly don't intend to derail this lively discussion, but I think there's a number of people like myself that are wondering if this discussion is relevant to us at all? So what kinds of run times are going to become problematic? If I'm below 80, I'll do a 2 minute half stop. I hardly ever see 200 anymore, but that will change as I am hoping to do trimix on my SF2 in the next couple of months and I'll be using my Petrel IIs for that. So, what's my take-a-way here? Is it this is way beyond what I need to worry about? If not, what should I be changing.

Caveat, probably against most sage advice, I usually dive only in a bathing suit and t-shirt. The cave dives are getting a bit chilly towards the end now, so I have a wet suit on order. I'm also obese by anyone's standard. Kind of like a deco Buddha.

NetDoc

The simple take away from my perspective is that your two minute stop at half depth does not allow you to shorten your shallow stops and overall decompression time (to be fair, very few people here are arguing the contrary). Your two minute stop at half depth will be a good thing if you appropriately lengthen the subsequent decompression, which you say you are doing by padding your shallow stops (and your dive computer may already be doing).

 

[Dr Simon Mitchell]

The VR3 only came out in late 2005, and it was really a GF plan pretending to be VPM-B/E, so that's not it.
I'm stumped. How did you do it Simon? Once again I'm inclined not to believe you.

I purchased my second VR3 specifically BECAUSE it had the VPM option. What you and Kevin had going between you is irrelevant. It was portrayed as a VPM implementation. If you were not happy with the way it was portrayed I'm surprised you did not take legal action. Or is this a stance-of-convenience that you are taking now? Anyway, the relevant point is that I purchased that computer because it had VPM. And as you are well aware, I am a user of your products subsequently, and have commented positively about them on line.

If I were you I would be more concerned about the fact that you have begun your lecture on supersaturation (post 823) with an incorrect depiction of supersaturation. Maybe focussing on that would be a better use of your time than worrying about how I came to use VPM.

Simon M

 

[igor p]

I purchased my second VR3 specifically BECAUSE it had the VPM option. What you and Kevin had going between you is irrelevant. It was portrayed as a VPM implementation. If you were not happy with the way it was portrayed I'm surprised you did not take legal action. Or is this a stance-of-convenience that you are taking now? Anyway, the relevant point is that I purchased that computer because it had VPM. And as you are well aware, I am a user of your products subsequently, and have commented positively about them on line.

If I were you I would be more concerned about the fact that you have begun your lecture on supersaturation with an incorrect depiction of supersaturation. Maybe focussing on that would be a better use of your time than worrying about how I came to use VPM.

Simon M

In the time that VPM came out on VR3 it was known in diving comunity that VR3 VPM was a simulation of true VPM only.

But ok as an misinformed user of VR3 you used "VPM".

 

[rossh]

VR3 was nothing to do with us - they just wanted sell more products. It was longer than real VPM-B/E. So you have not dived VPM-B.


But Simon, you told us the nedu study convinced you in 2006, and most likely you knew about its progress before then. So... something still does not fit right.


Added later:

If I were you I would be more concerned about the fact that you have begun your lecture on supersaturation (post 823) with an incorrect depiction of supersaturation. Maybe focussing on that would be a better use of your time than worrying about how I came to use VPM.

Simon M

Really? David seems to think its OK now.

But how interesting that you suddenly seem to understand these important differences... now - when it suits you. Your youtube "presentation", is devoid of such distinctions and uses that to incorrectly make conclusions that are not there.

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[igor p]

Looking at Baker graph I think Ross's graph is correct. Or I missed something...