Deep Stops Increases DCS

[ajduplessis]

Hello Kev,

You cannot draw any conclusions about causation of inner ear DCS without first knowing whether the diver has a large PFO. Over 90% of IEDCS cases have a large spontaneous shunt and the only profile that will be protective in the presence of a large shunt will be one that reduces the formation of venous inert gas bubbles (that might cross the PFO and be carried to the inner ear).

Doc, can you please cite the data you referenced for the above claim? I cant find it anywhere, but I am sure you have it.

---------- Post added January 5th, 2015 at 09:47 AM ----------

Just to clarify, this is NOT what AG used. He used something similar to 30/80 plus arbitrary deep stops because diving without deep stops is "way too dangerous." That attitude infuriates me beyond belief fir afew reasons:
1) A HUGE portion of the tech community is going away from deep stops and claiming they feel better. Clearly low gf of 30 isn't that dangerous. 2) He is testing a scientific principle in the least scientific manner possible... by ruining the chances of the one that will prove him wrong.
3) Why does he think his arbitrary addition of deep stops is an improvement despite the findings of the world's leading deco experts?
4) Many deep Trimix divers, including some of the world's leading deco experts are diving 40/70 and 50/70 and even just nitrox divers are using 30/70 due to gf high of 80 being too aggressive. Why use 30/80 PLUS deep stops (which would make it worse and more aggressive) if you're being honest?

I could go on and on, but it's a poor comparison and shows me that it's not an agency or a leader I have any interest in following.

Everyone is "obsessed" with the HUGE amount of divers moving away from deep stops, where can i view this data source? Some divers on RBW indicate feeling better without deep stops, some divers here feel better using something else. Are these (handful) the HUGE numbers we are talking about? WTF??
Secondly, not all deco experts are in agreement on the findings, neither do they dive shallow stop profiles.

 

[Dr Simon Mitchell]

Doc, can you please cite the data you referenced for the above claim? I cant find it anywhere, but I am sure you have it.

Hi AJ,

Sure. Klingmann et al 2003 reported 11 cases of IEDCS in 9 divers all of whom (100%) had a major right to left shunt. Cantais et al 2003 reported 34 cases of IEDCS of whom 24 (~71%) had a major shunt and another 4 (~12%) had a lesion that did not spontaneously shunt; a total of 83% with a right to left shunt. It is notable that the same authors found a major shunt in only 12% of control divers who had never suffered DCS. Ignatescu et al 2012 reported 30 cases of IEDCS who underwent PFO testing in which 24 (80%) were positive. Peter Wilmshurst told me recently that he thinks it is virtually 100% and that the few IEDCS victims who don't show a PFO just didn't have their test done properly! That is not published though. Anyway "90%" is a ball park figure, and I was thinking in particular of Klingmann's paper, but there are multiple studies supporting the contention that it is very high.

Refs:

Klingmann C et al. Embolic inner ear decompression illness. Correlation with a right to left shunt. Laryngoscope 2003;113:1356-61.

Cantais E et al. Right to left shunt and risk of decompression illness with cochleovestibular and cerebral symptoms in divers: a case-control study in 101 consecutive dive accidents. Critical Care Medicine 2003;31:84-8.

Ignatescu M et al. Susceptibility of the inner ear structure to shunt related decompression sickness. Aviation Space and Environmental Medicine 2012;83:1145-51.

I have these papers if you would like them.

---------- Post added January 5th, 2015 at 09:47 AM ----------

Secondly, not all deco experts are in agreement on the findings, neither do they dive shallow stop profiles.

I think the truth of this matter is that there would be few, if any, un-conflicted decompression scientists or diving physicians who do not believe there is an important signal in the NEDU study results. By specifying "un-conflicted", I recognise the possibility that there may be one or two who might disagree, but who have a financial interest in deep stop models. That is not to say that their opinion is invalid, but it does raise the possibility of an understandable bias.

Your observation that many deco experts don't dive shallow stop models (per se) is valid. But the evolution of "expert" decompression practice in response to the emerging evidence reflects sensible caution in the face of incomplete data. My own response to the current situation has been articulated in a number of places, and I recall UWSojourner linked to a couple of those a few posts ago. I think it is also fair to say that many other knowledgeable scientists are changing their practice, but cautiously so.

Simon M

---------- Post added January 5th, 2015 at 09:57 PM ----------

Dr Mitchell, we really appreciate you coming on here and clarifying the information for us. Thanks so much for your patient responses!

Thank you. Its an important subject to discuss. Can I also acknowledge the contribution that UWSojouner has made here and on other threads. His depictions of some of the physiology have enhanced understanding for many divers.

Simon M

---------- Post added January 5th, 2015 at 10:10 PM ----------

Simon, I'm simply not willing to risk bubble nucleation & formation in my Fast Tissues for the sake of not loading/supersaturating my Slow Tissues later on in the deco profile (per indication of those "heat maps" by UW Sojourner); essentially a "Robbing Peter to pay Paul" dilemma.

And yes, I have plenty of time and an 11L Alu full of O2 to clean-up those Slow Tissues. . .

Hello Kev,

I guess this is the sticking point. It is an article of faith for you that allowing fast tissues to supersaturate early in a profile that places less deep stops in your ascent is harmful, and there is probably nothing I can do to change your mind on that. However, I must point out that you only believe that because someone has told you it is so. It is an attractive theoretical assumption that many people believe(d) in the absence of any confirmatory data. The point is, that there is now data that challenge the idea. As UWSojourner's heat maps have illustrated the NEDU deep stops profile did reduce fast tissue supersaturation compared to the shallow stops profile, but this did not result in better outcomes. If tight control of fast tissue supersaturation early in the ascent is as important as you believe, why did the profile with the best control of fast tissue supersaturation early in the ascent produce the highest DCS rate?

Anyway bud, if you do what you say you are going to do and significantly pad your shallow oxygen decompression it may not matter too much what you do earlier. Just don't have a seizure please!

I hope you have a fabulous trip. I may have mentioned I am going back with Pete Mesley in November.

Simon

 

[ajduplessis]

Thanks for the feedback, I would appreciate if you can share the papers.

With regards to "finacial interest" in deep stop models; any of the current providers will jump onto a new model/idea if there is money to be made. Just because they have investments in a current model does not make them biased, any oppertunity to generate money is an business oppertunity. I would however love to see who and what finacial interests will come from this study by those not already "playing" in this market.

If I understand it correct the NEDU study in question was conduct around 2008? Why the delay if the data was so straight forward?

I appreciate your comments.

 

[victorzamora]

Everyone is "obsessed" with the HUGE amount of divers moving away from deep stops, where can i view this data source? Some divers on RBW indicate feeling better without deep stops, some divers here feel better using something else. Are these (handful) the HUGE numbers we are talking about? WTF??
Secondly, not all deco experts are in agreement on the findings, neither do they dive shallow stop profiles.

I'm by no means obsessed with these "HUGE" number of divers, but do believe that the very-deep Trimix divers are currently swaying away from deep stops as a whole. Besides those on RBW, TDS, and here, several acquaintances regularly doing 300ft+ dives and friends doing 200ft+ cave dives with very long exposures are all moving towards shallower stops.....anywhere from 30/70 to 50/70, and one friend has even started playing with 40/60.

I have yet to see a diver in the last 18 months legitimately give 40/70 a try and not claim to feel better over VPM. Purely subjective, and not a data source. Also, there really aren't "huge numbers" of divers doing 300ft+ dives anyway. "HUGE portion" is a different phrase, and is what I said and meant. It seems to me like VPM was "in vogue" starting ~10yrs ago, and most divers doing those dives went the way of VPM. It seems like now, many of those same divers are slowly switching back to Buhlmann, but with very different GFs than they had previously tried out.

Regardless, my point wasn't that "All good divers think deep stops are stupid." My point was AG and UTD have a seemingly endless arrogance to make a statement like "Buhlmann is OBVIOUSLY dangerous without adding arbitrary deep stops." It's unscientific, dishonest, and unfair. If you're going to test your model against another, use one that's actually "in vogue" and properly representative of what those supporters are diving.....and don't ruin it by adding arbitrary time. Period. I also never claimed that all deco experts were in agreement...simply that some/many deco experts disagreed, which is a true statement.

 

[ajduplessis]

The reason behind the question is that I dont know of any divers (at least here) that are moving away from VPM profile. We have many divers completing 200-400ft dives routinely.

 

[UWSojourner]

The reason behind the question is that I dont know of any divers (at least here) that are moving away from VPM profile. We have many divers completing 200-400ft dives routinely.

Are they diving straight "VPM-B+x" or other iterations such as BE, or GF tail, extended O2 stop, etc.?

One adjustment that I think is clear is that many people are talking about extending shallow stops, even if not yet intentionally deemphasizing deep stops. My recollection is that the dialogue used to often be about how a "smart profile" (i.e. deep stops) would reduce your total deco obligation. And that the shallow padding was unnecessary, but fine if someone wanted "extra protection", or had issues of their own.

Now, though, I think you'd have to say the dialogue has shifted. Even with Kevrumbo, he's keeping the deep stops but padding the profile down to GF 60 on exit. That sounds like an adjustment in the face of shifting data/opinions, and perhaps experience, but it is a far cry from VPM-B+2 or 3 (as reference: on kevrumbo's deeper profile discussed above VPM-B+2 would exit at about GF 110, or VPM-B+3 at about GF 100).

As has been acknowledged countless times, deep stops don't kill a profile. The data just suggests that heavy emphasis on the fastest compartments likely requires more, not less, shallow time to maintain the same level of risk.

 

[C Dub]

Kev, did you watch the slide presentation above? Doulette (sp?) specifically said that the deep stop made things worse. It seems like your rate of DCS hits are up, so logic dictates you do something more conservative. I see that you posted that you are considering doing only 1 Deco dive a day, and taking a day off after 3 days. It would be great if you could post how that works out, or whatever you decide to tweak. And thanks for your continued posting on this issue, the discussions have been enlightening.

I would continue doing Deep Stops -with the caveat impressions of the NEDU Study and attending Expedition Physician/Hyperbaric Specialist Dr. Simon Mitchell noted (and definitely not the histrionics of Vic Zamora above)- along with the extended O2 Profiles with my Truk Dive Guides. For the upcoming return trip to Truk 18Jan - 08Feb, I might take a break dive-day-off after three consecutive days of deco dives, or maybe elect to only do one deco dive per day and take a day-off at the end of a week.

 

[LiteHedded]

Not to rehash old stuff, but does Gue offering a JJ course change this jab into a bit of crow to eat?

no. they've been teaching the JJ for a long time now. what i'm driving at is he certainly cant take it because he doesn't meet the prerequisites and it shows in his posts

 

[tomfcrist]

no. they've been teaching the JJ for a long time now. what i'm driving at is he certainly cant take it because he doesn't meet the prerequisites and it shows in his posts

I wasn't poking at you, it was a legit question. Thanks for the response.

However, I must ask another question. Since that stab was directed at the configuration of the unit, why would he certainly not be able to use that configuration? What do GUE course Pre- Req's have to do with diving a configuration?

 

[Dr Simon Mitchell]

Thanks for the feedback, I would appreciate if you can share the papers.

No problem, just pm me an email address.

Just because they have investments in a current model does not make them biased

I think there is a vast history in science that proves you wrong on this point. Not really worth debating, but the scientific community places great emphasis on declaration of financial conflicts of interest precisely because of the bias it introduces.

If I understand it correct the NEDU study in question was conduct around 2008? Why the delay if the data was so straight forward?

There has been no delay. The data were presented at multiple diving science conferences (eg the Deep Stops Workshop in 2008, and the Technical Diving Workshop in 2010). The definitive technical report was published in 2011. The study gets discussed when threads like this pop up on the internet, which may look to some people like it is new information, but it has been around for a while now.

Simon M