Deep Stops Increases DCS

[Dr Simon Mitchell]

OK, I am curious, can you please point me to the data that shows that 99.95% of divers that present with DCS have no issue with VGE? I don't think that any such data exists of course..but hey I may be wrong. If there is no data I don't understand why and how you can make such a statement

Hello Cerich,

I think he is saying that most dives result in some VGE and that 99.95% of those dives don't result in problems. But your question gets to the point of what I am saying. There is overwhelming evidence (see the studies I listed earlier) that VGE transferred into the arteries across a PFO contribute to development of spinal, cerebral and inner ear DCS. Ross seems to be saying that we don't need to worry about that even though there may be relatively efficient ways of mitigating that risk. Obviously he has never had to tell a diver that they will never walk again, or (much more commonly) that they can never dive again.

Simon M

 

[cerich]

Hello Cerich,

I think he is saying that most dives result in some VGE and that 99.95% of those dives don't result in problems. But your question gets to the point of what I am saying. There is overwhelming evidence (see the studies I listed earlier) that VGE transferred into the arteries across a PFO contribute to development of spinal, cerebral and inner ear DCS. Ross seems to be saying that we don't need to worry about that even though there may be relatively efficient ways of mitigating that risk. Obviously he has never had to tell a diver that they will never walk again, or (much more commonly) that they can never dive again.

Simon M

Aye, and what % of the population have a PFO again? ;-)

 

[Shotmaster]

Aye, and what % of the population have a PFO again? ;-)

Although the prevalence of PFO is about 25 percent in the general population, this increases to about 40 to 50 percent in patients who have stroke of unknown cause. Oct 20, 2015
Patent Foramen Ovale (PFO) - American Heart Association

 

[UWSojourner]

No, your trying to play both side now, and pretend they are the same... no.

Ross, I don't see two sides in this "debate".

I see one side backed by considerable research and the world's best decompression minds all saying the same thing about VGE and deep stops. Way off in the distance I see you screaming at the horizon for allowing the sun to rise. It is quite something, but it's not two sides.

 

[rossh]

OK, I am curious, can you please point me to the data that shows that 99.95% of divers that present with DCS have no issue with VGE? I don't think that any such data exists of course..but hey I may be wrong. If there is no data I don't understand why and how you can make such a statement

These are the standard rates. 1 in 5,000 to 10,000 is the rate often quoted in many texts. The DHM had a 12 year survey of tech cave divers in Australia 1:3,700.... Another multi-year review study in Denmark just published - same kind of numbers. Many other sources too - not going to reference.

But of that 0.05% of injured, is has to be further spilt into all the different types of DCS. So VGE are far less of a problem still - maybe 0.02% ??


Compare that to known VGE. We know 25% have a PFO, and are potential arterialized VGE (artVGE) candidates. We know that up to half of us will make artVGE from post dive exercise. We know that most of can make some artVGE after a dive,

That's a huge gap between the conditions of artVGE, and the injury from the same ... 25 to 50% vs 0.02%. That needs to be explained, and trying to make every one do double deco today, is not the answer.

This in NOT a deep stop problem. This is not a new problem . This is not a problem for 99.97% of us, at all.

This is a condition that has been with us since we got in the water. Almost every tech diver has these, regardless of model. Half of all recreation divers have these conditions too. Millions of successful dives every year, with this condition.



*****


What about the handful of people who seem to be more susceptible? They usually suffer skin rash, (see DAN PFO workshop report). They already know who they are from troubles in their NDL diving days. They already know they cannot tolerate the increased stress of tech diving. Tough luck for them - not everyone is made equal. They can either do an abundance of extra deco time, or go find a new hobby.

.


Commercial footnote: We make a program called MultiDeco. It has most of the current deco models and variatios availabe for you to choose from. Your welcome to do as much, or as little deco time as you want - its your choice.

 

[Storker]

Back in post #1215 I said:

I expect Ross to give us a list of his peer reviewed papers accepted in reputable scientific journals.

Of course I didn't really expect that, for obvious reasons. A few quick Web of Science searches give the following results:

• Author: Mitchell SJ: 30 references related to hyperbaric medicine, of which one Cochrane review.
• Author: Doolette DJ 24 references related to hyperbaric medicine
• Author: Hemingway Ross: 0 references

For those who aren't familiar with the Cochrane Database of Systematic reviews, here's what Wikipedia says about it:

Cochrane, previously known as the Cochrane Collaboration, is an independent, non-profit, non-governmental organization consisting of a group of more than 37,000 volunteers in more than 130 countries. The group was formed to organize medical research information in a systematic way to facilitate the choices that health professionals, patients, policy makers and others face in health interventions according to the principles of evidence-based medicine

[...]

An editorial in the Canadian Medical Association Journal in 2004 noted that Cochrane reviews appear to be more updated and of better quality than other reviews and due to their standardized methodologies, was "the best single resource for methodologic research and for developing the science of meta-epidemiology." Their work has also led to methodological improvements in the medical literature.

In short, Cochrane reviews are high-quality systematic reviews of research and are very highly regarded in the scientific community.

Since it has been argued several times about the "peer review process" and proper interpretation of scientific results, I thought this little tidbit of information might help the audience in this thread to evaluate the merits and competence of the different participants to the discussion.

 

[rossh]

• Author: Hemingway Ross: 0 references

Correct.

The really sad part is amateur readers and participants, like you and me, are able to see the errors of the explanations and incorrect connections being shown to us, and the errors in changes being made and proposed, by the trusted credentialed science posters.

 

[Storker]

amateur readers and participants, like you and me, are able to see the errors of the explanations and incorrect connections being shown to us, and the errors in changes being made and proposed, by the trusted credentialed science posters.

Speak for yourself.

I have a lot more trust in the "credentialed science posters" than in "amateur readers and participants, like you and me". Those "credentialed science posters" have the necessary competence to soundly interpret the data, they have no economic ties to one specific decompression model and they're also the ones who present current research and their interpretation of the data in a way that is decently clear and understandable to me. And finally, the behavior of the the "credentialed science posters" in response to extremely offensive accusations by "amateur readers and participants, like you and me" has been commendable. In fact, it has dramatically exceeded what one could reasonably expect from them.

 

[Dr Simon Mitchell]

That's a huge gap between the conditions of artVGE, and the injury from the same ... 25 to 50% vs 0.02%. That needs to be explained

Both of your figures can be disputed: it is the much smaller fraction of divers with a large PFO that are at most risk (probably < 5% of divers) and the proportion who arterialise bubbles that you cite presumably comes from the Split study in which the divers had very high VGE grades (which is a significant risk factor for VGE arterialisation). The proportion of divers who arterialise VGE is lower in the "all VGE grades" general diving population. On the other side of your the equation the 0.02% of dives with shunt-related DCS is probably an underestimate for technical divers (for example, the vast majority of cutaneous DCS goes unreported in my experience).

Nevertheless, while we could debate the actual numbers it would be largely pointless because I do agree that there is a substantial discrepancy between presence of VGE + PFO and the actual development of DCS. We have known this for years and David and I addressed it to some extent in our 2009 paper (see below). I have pointed out potential explanations for the discrepancy to you many times, but you never seem to process information that you claim to want. One of my figures from the DAN PFO conference summarises some of the plausible ones:

This is discussed in some detail in this publication.

MITCHELL SJ, DOOLETTE DJ. Selective vulnerability of the inner ear to decompression sickness in divers with right to left shunt: the role of tissue gas supersaturation. J Appl Physiol 106, 298-301, 2009

I would be happy to send a copy to anyone who wants it.

and trying to make every one do double deco today, is not the answer.

Well, it could be one answer, but that is not what is being advocated in this discussion. Remember, the discussion was about efficiency of decompression and if you have two approaches that are equal length but one produces more VGE than the other, then the one conferring the lowest risk of serious neurological DCS is almost certainly the one with less VGE.

This in NOT a deep stop problem.

It certainly could be if a deep stop approach to decompression produces more VGE than a viable alternative - especially if that alternative is not a longer decompression - just a different distribution of stop time.

This is not a problem for 99.97% of us, at all.

If I have interpreted your earlier working correctly I think you have mistakenly based your crude estimate of the proportion of divers affected on the incidence of DCS by number of dives (which overinflates the denominator). But even if we let that go, there are lots of rare devastating diseases that "not a problem" for the vast majority of us that we are still intensely interested in preventing.

Simon M

 

[BDSC]

Correct.

The really sad part is amateur readers and participants, like you and me, are able to see the errors of the explanations and incorrect connections being shown to us, and the errors in changes being made and proposed, by the trusted credentialed science posters.

Anyone else see the irony in this statement?