Keeping up with Changing Thinking in Scuba

[Dan_P]

I just read the Spisni paper, and given the limitations of the small sample size and limited ability for extrapolation, the author says "Overall, our findings contradict the idea that adding longer and/or deeper stops is useful to achieve a more effective decompression." And that is despite the fact that the ratio deco profile was 12 minutes (17%) longer than the 30/85 GF profile.

I get that the RD1.0 sample got 12 minutes more than the ZH-L16 sample (70 versus 58 minutes) and make that a 20% time addition.
But we can't invert the numbers and thereby determine that RD1.0 is 20% less effective than ZH-L16 with GF 30/85.
Such an exercise has previously been attempted, and for various reasons, is oversimplifying - that's the point I was getting to with my previous comment.

To elaborate; for one, a substantial portion of the added time to the RD1.0 sample, seems to have been arbitrary.
For that dive, (avg. 48m for 25 minutes; 1:1@45m +3m = 25+5 minutes, plus ascend time and deep stops), approximately 35 minutes ascend is warranted, not approximately 45 minutes. RD does not stipulate how any arbitrary time should be distributed - adding it and distributing it as though the initial distribution pattern should be scaled up algorithm-style, sets up a disconnect across the sample and what may or may not hold true for the initial distribution pattern.

Think of it this way; if you do 1 minute deep stop and 3 minutes shallow stop, you can't add an additional 4 minutes arbitrarily with the same distribution ratio (now 2 minutes deep and 6 minutes shallow) and state that the relative result is universal across the initial distribution pattern (1:3).

That's not to say that the study hasn't validity!
It definitely supports that RD1.0 overemphasised deep stops, don't get me wrong on py position there.
It's just that we can't use the Spisni-study to infer by how much and what it means in practical terms.

I think it's a reasonably relevant point to make.

Adding to it, we can't stipulate any specific meaning of increased inflammation other than a (reasonable) assumption that it's not good (conversely, playing the devil's advocate, one might even play with the idea that inflammation goes up during offgassing and until a certain level, is a measure of effectiveness) - regardless, it was a small sample size using just one set of dive parametres, the bubble grade observation wasn't of much use and the results of both metrics can't be extrapolated.

So it's fair to say that there were some serious limitations to the trial - but it would not be fair to dismiss the results, to be certain!

I am failing to see why people keep defending deep stops or ratio deco. Are there any articles that point to deep stops being better? Or is it all "but Rich Pyle... and but AG!"

I find that as for RD, it's catching enough unwarranted flak on internet fora to prompt at least correction of unfair or unbased statements against it.
In fairness though, (to my knowledge) we haven't any articles proving an optimal algorithm anyway, and there's little to suggest that the difference is even practically significant.
Tongue in cheek, I'd say that by the logic employed in this quote, you could argue GF100/100 because "but Buhlmann"
You don't see much of that around. To me, the implication of that is that "most" seem to believe that "some" level of "deep" stop emphasis, is probably "optimal".

I really don't understand how one would think that having to do arithmetic underwater to determine your profile is superior to looking at a computer that will certainly do the work in higher resolution and with fewer errors.

I think it's fair to say there are substantial practical advantages to using Ratio Deco, and if you ask me, one of them relates to training and dive planning as well as predictive dive adjustments.
But there are separate threads about it. Extensive, extensive threads.

I don't understand why people do not use GPS to go their bathrooms when they wake up in the morning. A GPS designed for that purpose will guide you to the bathroom in higher resolution with fewer errors so that you do not bump into the china cabinet along the way.

 

[Cowfish Aesthetic]

I don't understand why people do not use GPS to go their bathrooms when they wake up in the morning. A GPS designed for that purpose will guide you to the bathroom in higher resolution with fewer errors so that you do not bump into the china cabinet along the way.

You must have one of those fancy new government GPSs if yours knows where the china cabinet and bathroom are.

 

[Dr Simon Mitchell]

In fairness though, (to my knowledge) we haven't any articles proving an optimal algorithm anyway, and there's little to suggest that the difference is even practically significant.

Dan,

Sea_ledford has touched on the elephant in the room in relation to the deep stops argument: that is, there was never any evidence in support of them.

It is somewhat ironic that a proponent (you) of a philosophy that dragged decompression practice to one extreme on the basis of NO evidence is basing a case for defending that philosophy on the perceived weaknesses of an emerging body of confluent evidence (multiple studies) suggesting that the philosophy is misguided. Its not a strong position Dan.

My allusions to uncertainty about the practical importance of the differences that are showing up in studies comparing deep and shallower stop profiles (as quoted by Captain Sinbad) are just scientific honesty. They do not mean that the differences are unmeaningful. I can only imagine what Georgitsis would be saying if the result of the Spisni study had been reversed!

Simon M

 

[Jack Hammer]

Hey guys, can we please all just suck up our pride we not start rehashing the deep stop, bubble model, ratio deco, whatever arguments again in this thread? There are plenty of existing and recent threads already on those topics.

Thanks,

- Jeff

Edit: fixed missing word

 

[MichaelMc]

boulderjohn asked a really good question, we got a bit distracted by the example he used, and I admit my role in furthering that distraction.

So, how do we keep up with changing thinking?

 

[CAPTAIN SINBAD]

Hi Doc Simon Mitchell. I was waiting to see how long it would take for you to join in. Glad to see you here.

I give credit to UTD for going ahead and doing the Italian study. Without the Italian study, we wont be able to have the discussion that we are having right now. It is UTD's own research that enables us to be critical of their past practices and that is saying something about an agency that is considered "unscientific." There are not a lot of certification agencies that have invested in their own decompression research so I am not sure why one of the few that has done it be perceived that way.

They have also accommodated the results of their own research into their diving practices by moving the stops shallower. I personally would have liked the first stop to be shallower than where it is in RD 2.0 and the way Ratio Deco is evolving, I am willing to bet you that in Ratio Deco 3.0 version they would go shallower. Still as you mentioned, whatever safety margin they will be creating with these modifications adds such a tiny safety increment that it would be like arguing if a plunge from the balcony of a 200 story skyscraper is a better way to commit suicide than a plunge from 220 story sky scraper. In the end, they both get you killed but scientifically, in the light of Newtons laws of motion and theory of gravity the guy who is jumping from 220 floor is on a better path to killing himself. Would this make me climb another 20 stories if I was committing suicide? I dont think I would bother. Would I deserve the same persecution for not climbing the twenty stories that UTD does for not moving their stop a few feet higher?

A lot of people who are critical of UTDs ascent strategy have this exaggerated perception of safety margin (of moving the stops shallower) and that perception is more unscientific in my view than UTDs ascent.

But then if the guy jumping from 200 floor made a video in which he claimed that his plunge will be more effective in killing him than the guy jumping from 220 floor (just like Andrew did) then the uproar may be quite understandable.

Thoughts?

 

[Dan_P]

Hi Simon,

I'll be happy to revert to the matter at hand, but I feel I should address first that I found this quote to be a tad shoehorning for what I was saying:

Dan,

Sea_ledford has touched on the elephant in the room in relation to the deep stops argument: that is, there was never any evidence in support of them.

It is somewhat ironic that a proponent (you) of a philosophy that dragged decompression practice to one extreme on the basis of NO evidence is basing a case for defending that philosophy on the perceived weaknesses of an emerging body of confluent evidence (multiple studies) suggesting that the philosophy is misguided. Its not a strong position Dan.

I think I've been clear on my position that Spisni and other studies indicate an overemphasis on deep stops (we can say "at least in RD1.0's case") - allow me to repeat;

"That's not to say that the study hasn't validity!
It definitely supports that RD1.0 overemphasised deep stops, don't get me wrong on my position there.
It's just that we can't use the Spisni-study to infer by how much and what it means in practical terms."

My allusions to uncertainty about the practical importance of the differences that are showing up in studies comparing deep and shallower stop profiles (as quoted by Captain Sinbad) are just scientific honesty. They do not mean that the differences are unmeaningful. I can only imagine what Georgitsis would be saying if the result of the Spisni study had been reversed!

Simon M

I understand what you're saying. My point is there is no backing to tell us how much RD1.0 overemphasised deep stops, or what the practical appplication of it may be, as I wrote.

Hey guys, can we please all just suck up our pride we not start rehashing the deep stop, bubble model, ratio deco, whatever arguments again in this thread? There are plenty of existing and recent threads already on those topics.

Yes, let's.

 

[RayfromTX]

My research has shown that discussing RD and/or the emphasis of deep stops to reduce early bubble formation on ascent in yet another thread, is 35% less effective than moving on to other important issues, such as the topic of this thread.

Staying on topic often requires us to refrain from reacting to every sentence that may imply that our pet issue is in danger of being misrepresented.

 

[Rhone Man]

What I find interesting is not how much diving changes (even in tec), but how little. A sport we evolve with agonising slowness.

If a tec diver awoke today after 20 years in a coma, I don't think it would take him or her too long to get up to speed before strapping on a twinset and launching back in.

For a rec diver, you could comfortably add another 10 years to that.

 

[sea_ledford]

Back to the original topic, when covering the methods of staying up to date on emerging knowledge, I mention that at the technical level, divers can't reasonably expect the agencies to keep up. They don't update materials often enough. Perhaps with the increasing use of e-learning the text can be updated more often than before, since an always current version of the text is one of the selling points of elearning. But I'm not holding my breath.

It is up to the divers to keep up and adopt new techniques and strategies as they understand and see fit. The changing of gradient factors is an excellent example of this. There is also a gap in knowledge and technology. Dr. Mitchells work with helium penalties is the most current example I know of. If my memory serves me correctly, the summary was: there is no helium penalty, but we are probably still doing the appropriate amount of deco, just not for the reasons we think.

I'm looking forward to an update on that next weekend at TekDiveUSA!

-Chris