Slow tissue on gas from stops
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We only had 8 cases of DCS in the small group of UTD divers I was associated with, so I guess it was effective for the ones who didn't get bent, right?
UWSojourner
Contributor
It's difficult to see anything exaggerated, although I admit I don't have your talent for verbal gymnastics.
- The UTD-RD profile was given 44% more decompression time to work with
- Despite the additional time provided to the UTD schedule, the study concluded that the Ratio Deco Strategy "has the disadvantage of decompression-associated increased secretion of chemokines involved in the development of vascular damage." And "our findings contradict the idea that adding longer and/or deeper stops is useful to achieve a more effective decompression."
- In response to the study UTD came out with UTD-RD 2.0
). I just said it would be difficult to put the label "effective" on it, which is far from a stretch.
ajduplessis
Contributor
I guess so...
Which takes me back to my earlier post about deco plans falling somewhere on the equivalent of an archery target. The higher percentage of DCS in our small group suggests to me that the deco plan we were using was somewhere on an outer circle, one which holds the plans that have a much higher possibility of people getting bent.
It reminds me of an analogy I used to use in workshops I used to conduct (on a very different topic). I created something of a parable in which someone who survived Pickett's Charge at the Battle of Gettysburg Went on to teach military strategy after the war. Pickett's Charge is considered one of the worst military decisions in the history of warfare, with that division suffering greater than 50% casualties and accomplishing nothing. An old friend drops by one day while he is teaching, and that old friend is horrified to see him teaching the students to use the strategy Pickett had been ordered to use on that charge. The survivor/instructor responds, "It worked for me."
The fact that you survived a battle does not mean the battle strategy was a good one. The fact that you survived a dive without getting DCS does not mean the strategy you used was particularly good. Every known decompression strategy will have survivors. That does not make them all equally effective.
Dan_P
Contributor
That's the stretch I was on about before.
I'm not arguing that RD1.0 placed too great emphasis on deep stops, but there's a difference between that statement and saying RD is defetive. That's all.
If "small" means 8 or less, that's a 100% DCS rate in that group?
This is wildly disproportionate.
And, the results of using RD, as we'll see prominent experts in the field state previously in this thread, can't be considered unsafe on the basis of what we have at our disposal, including the Spisni trial.
In all respect, I believe Occam's Razor would have us hypothesise that it was not RD that caused the problem, but the group itself.
Dan_P
Contributor
Actually, I'm saying if a scenario brings about X% cases of DCS with a given decompression method, and those results cannot be replicated elsewhere using the same decompression method, likely it's another factor than decompression method in that scenario that caused those cases of DCS.
Right--that is indeed how they explained to me.
That said that the proof that RD works is that people don't get bent using it. When I pointed out the number of people in our small group who got bent, they said they did not count, because they got bent for some other reason. What was that other reason? Don't know. How do you know it was not RD? Because people don't get bent using RD, so any case in which it happens has to be caused by something else.
Hard to beat that kind of logic.
Now these dives were all done at altitude, so I was concerned at that time with using RD at altitude. We were told specifically and emphatically that altitude was not a factor in decompression, so RD could be used without changing at altitude. As Andrew explained it to me, he knows this to be true because he dives at Lake Tahoe using RD, and he is fine. It has therefore been empirically tested by none other than Andrew himself.
I was not convinced, and i started a thread on ScubaBoard in which I described this situation and asked for input on altitude considerations for decompression. I was then threatened by a UTD instructor, who said that I should have said that none of those cases were caused by RD, because RD does not lead to DCS, either at sea level or at altitude. I was told that if I were to post anything like that again (as I am now), I would be reported to PADI for disparaging UTD. PADI professionals are not allowed to disparage other agencies, and I was told that a public mention of people getting bent while using RD would be disparaging the agency, and I could be expelled and lose my PADI instructor status.
Hello Dan,
Since you are referring to me I just want to clarify this.
I did not state RD should not be characterised as `unsafe`; you did. The post in which that appeared was generally well reasoned, and I `liked` it, but you shouldn`t infer that I would `state` everything you said in the post.
To the specific point, I think we have ample evidence pointing to the fact that RD as it stood when Georgitsis confidently predicted its superiority was less efficient and therefore less safe than available alternatives. Whether that constitutes unsafe depends on how one would define unsafe, and we do not have the data (relative DCS rates) to resolve the debate no matter what that definition is, which is why I said:
Dr Simon Mitchell:
If an individual diver (such as you Dan) has a reason to use RD based on its utility in specific situations I would not consider that irresponsible, and I could not put my hand on my heart and give you an evidence-based reason to call it unsafe (we have no data on DCS rates). But I would definitely be comfortable (based on existing evidence) to say that you are sacrificing decompression efficiency and therefore some degree of safety for whatever perceived utility exists for using it.
Simon M
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