Son of Deep Stops *or* Waiting to be merged with the mother thread...

[rossh]

From Tech Diving Conference Proceedings, page 120. Clearly VGE is correlated to risk of DCS and obviously a sharper rise in risk is associated with Grade 3+.

View attachment 380580

... Clearly VGE is correlated to risk of DCS...


Are you sure about such a hard position is appropriate?.


The text says...

"....the incidence of DCS was around 15%. This association is not strong enough to use VGE grades to predict DCS incidence,..."


And the graph also shows a 2 or 3% event rate of DCS with zero(0) VGE.


All this predictive and finger pointing is greatly discouraged in the recommendations of the "Consensus guidelines for the use of ultrasound for diving research" paper


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[David Doolette]

Its referencing to conditions like Pulmonary DCS, which is certainly life threatening. However its unlikely to a problem for normal everyday diving procedures.


From the sentence prior... which is the more normal conditions.... "The detection of bubbles in any individual is not diagnostic for decompression sickness (DCS).


The false association is that VGE are some kind of a direct measure or profile stress. They are not. VGE are associated with profile stress only, but not correlated - huge variations exists across individuals, or profiles ,or gas types ,age , prior history and a dozen other variables. There is no 1:1 connection with VGE and stress. Anyone trying to make predictions from that is reading tea leaves.


If the readers stop trying to measure DCS probability from VGE counts, then we can all settle down... but until then, that miss-understanding has to corrected.

This is just wrong, Ross.

Rather than engage in the surreal exercise of arguing with you about the meaning of a statement I wrote, let me set you some home work based on documents I know you have. The statement in Mollerløkken A, Blogg SL, Doolette DJ, Nishi RY, Pollock NW. Consensus guidelines for the use of ultrasound for diving research. Diving Hyperb Med 2016;46:26-32 “bubble load detected in large systemic veins and, in particular, in the mixed venous blood is considered to be correlated with the probability of DCS” is based on data from decompression trials such as those data from DCIEM using Doppler detected VGE and data from NEDU using 2-D echocardiography. Those latter data were presented at the workshop and appears in Table 2 of Doolette DJ. Venous gas emboli detected by two-dimensional echocardiography are an imperfect surrogate for decompression sickness. Diving Hyperb Med 2016;46:4-10, which I reproduce here:

VGE_Grade #_ Dives #_ DCS %_DCS
0 134 0 0%
1 141 2 1%
2 178 4 2%
3 215 15 7%
4 200 10 5%

The increasing DCS incidence with increasing VGE grade is a demonstration of the correlation between VGE grade and probability of DCS. These data are derived from the dive trials described in Gerth WA, Ruterbusch VL, Long ET. The influence of thermal exposure on diver susceptibility to decompression sickness. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2007 Nov. Report No.: NEDU TR 06-07 and and Doolette DJ, Gerth WA, Gault KA. Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2011 Jul. 53 p. Report No.: NEDU TR 11-06. Each of these reports provides case descriptions of the DCS cases. The DCS had many manifestations, ranging from mild pain-only symptoms through to more serious CNS symptoms, just like any compilation of DCS cases. Have a read through and report back how many are pulmonary DCS. There might be one, but I do not remember any.

 

[C Dub]

This thread is very educational if you use the "ignore" function built into the forum software.

 

[lowviz]

3.1 vs 4.6 ata
So you're holding deco time constant ....

Yes, in this instance just to make a point.

... But going about 48% more atas deeper
And get less than half the bottom time
If depth were all equally stressful you'd only have 48% less bottom time when you actually have 42% less BT.

In other words, you're illustrating how even within recreational depths still 50ft deeper is 6% more stressful from a gas loading perspective. A bigger depth difference would magnify this divergence.

Such is my suspicion, but I have no way of knowing what the noise is in that table. A 5 minute NDL is good from 150' to 200' in that table. Hmmm. Is that just a Navy "run down there and retrieve something" thing, or is it based on trials?

If a bubble model is really that important, then it stands to reason that the effect should be large enough to see it in spite of the noise in the table. The only thing that I lack is any connection with human bubble model data. But we can't use bubble scores because they have no relationship to deco stress. My head hurts...

 

[rossh]

This is just wrong, Ross.

Rather than engage in the surreal exercise of arguing with you about the meaning of a statement I wrote, let me set you some home work based on documents I know you have. The statement in Mollerløkken A, Blogg SL, Doolette DJ, Nishi RY, Pollock NW. Consensus guidelines for the use of ultrasound for diving research. Diving Hyperb Med 2016;46:26-32 “bubble load detected in large systemic veins and, in particular, in the mixed venous blood is considered to be correlated with the probability of DCS” is based on data from decompression trials such as those data from DCIEM using Doppler detected VGE and data from NEDU using 2-D echocardiography. Those latter data were presented at the workshop and appears in Table 2 of Doolette DJ. Venous gas emboli detected by two-dimensional echocardiography are an imperfect surrogate for decompression sickness. Diving Hyperb Med 2016;46:4-10, which I reproduce here:

VGE_Grade #_ Dives #_ DCS %_DCS
0 134 0 0%
1 141 2 1%
2 178 4 2%
3 215 15 7%
4 200 10 5%

The increasing DCS incidence with increasing VGE grade is a demonstration of the correlation between VGE grade and probability of DCS. These data are derived from the dive trials described in Gerth WA, Ruterbusch VL, Long ET. The influence of thermal exposure on diver susceptibility to decompression sickness. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2007 Nov. Report No.: NEDU TR 06-07 and and Doolette DJ, Gerth WA, Gault KA. Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2011 Jul. 53 p. Report No.: NEDU TR 11-06. Each of these reports provides case descriptions of the DCS cases. The DCS had many manifestations, ranging from mild pain-only symptoms through to more serious CNS symptoms, just like any compilation of DCS cases. Have a read through and report back how many are pulmonary DCS. There might be one, but I do not remember any.

Yes I saw you had an attempt to make the nedu test and cold water testing, result verified as a VGE surrogate dcs end point. The conclusion was, it was not achievable, and gave warnings about not using these to diagnose DCS, and must be interpreted cautiously.

All the tests, for years, end up with the same basic conclusions. VGE are extremely vague, indicative of almost nothing in any reliable sense, we don't know how, why or where they form. They cannot be used for an absolute measure (ie. deco models / predictions). etc..


But here you and Simon are again desperately trying to make some sense out of VGE. But why? It adds nothing to the predictive power of an existing model and its supersat / tissue value / microbubble load levels of predictions. Existing model tracking / predicting methods are the vastly superior and more reliable, than VGE can ever be. So why the rush to try to invent more value from VGE?? Oh yeah ... so one can pretend that some kinds of deco are worse than others, and then start on a whole new scare tactic.

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[cerich]

Existing model tracking / predicting methods are the vastly superior and more reliable, than VGE can ever be. So why the rush to try to invent more value from VGE?? Oh yeah ... so one can pretend that some kinds of deco are worse than others, and then start on a whole new scare tactic.

.

but yet earlier this evening you said

"Why new models? Because the current ZHL side is worn out. the GF method is abused to excess, and needs fixing."

So doesn't one statement somewhat negate the other?

Is it more about the general consumer psychology of "newer=better" and desire to have the newest? I know I do new models because of that, I also try really hard to make better product that can be quantified.

 

[lowviz]

...//... trying to make some sense out of VGE. But why? It adds nothing to the predictive power of an existing model and its supersat / tissue value / microbubble load levels of predictions. ...

Here is where I'm getting lost. From my empirical take on most non-quantum, non-nuclear physical phenomena, nature almost always provides a range of values. If you want tight and tidy then it will be biological.

So VGE's are just the tail of the Bell curve that contains microbubbles. That is a strong correlation, No?

 

[rossh]

Here is where I'm getting lost. From my empirical take on most non-quantum, non-nuclear physical phenomena, nature almost always provides a range of values. If you want tight and tidy then it will be biological.

So VGE's are just the tail of the Bell curve that contains microbubbles. That is a strong correlation, No?

Spencer discovered them in the 70's, and today we know very little more then he did back then.

It seems so simple ... just count the bubbles and deco is all done. Problem is, it doesn't work that way.

The only hard fast rule you can rely on, is VGE are not reliable to predict anything. It all been tried before.

Virtually all tech diver gets them - half of all rec NDL get them. They vastly change (50% + ) from person to person, from daily, from gas type, from age, from vibration and heat, from prior history... just to name a few. You and me can do the same dive - you come back wit ha grade 3 and I come back with 0. Happens regularly.

There was a test just recently - rabbits - they skipped 4 hours real deco time (8 hours Mitchell deco time), and made a direct ascent. half made VGE and died, the other half had not much to none ,and were terminated anyway. Which demonstrated the predictive power of a grade 3 VGE is somewhere between harmless, and death with in 10 minutes. Kind of shows how useless VGE can be.


Trying to use VGE as a predictive / measuring tool is doing it all backwards. Its just not up to the job - never has been.

Fortunately the specialists in this area recognize those limitations and warn against other researchers trying to over value VGE. Sadly we have a few here, that need to re-learn the rules.

VGE are everywhere - almost 100% of us on most every dive. Up to 50% of us can arterilaize them, and do so at some stage in most dives. yet the real world injury rate is a tiny 0.05%, so VGe can manage to vanish on there own or we absorb or dissolve them somehow naturally. We clearly have a good tolerance for them.

VGE origins and growth locations (intravascular) are unknown mostly. No real documents to describe ordinary everyday VGE that we all get. A few exploided rabbit and other animal photos, but that's not what we need to know. They are not tissue bubbles (extravascular) that have escaped. They are not monitored or watched by deco model. They are NOT what bubble models compute. VGE are ignored in all our planning and deco tools today - either ignored outright, or recognized as not harmful and allowed to exist.

Sorry .. don't have time to fetch links to studies just now.

 

[lowviz]

OK. But did not each and every VGE originate as a microbubble?

 

[rossh]

OK. But did not each and every VGE originate as a microbubble?

Thats what these VGE are venous microbubbles. .. But not tissue growth type 2 DCS forming microbubble - those are most likely different. . VGE are venous growth microbubbles, not unlike the ones in a glass of coke. They exists concurrently in dissolved off gassing, in the same venous flow. Clearly the gas comes from dissolved gas in transit in the veins, but where they are located and planted when they start to form is unknown. Why in some people they tend to form more or less is unknown.

If we had some of these answers, then one could know the actual meaning and value of VGE andthen do something with em. But right now its all guess work and vague and not nmuch real value at all.

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