UTD Ratio deco discussion

[Dan_P]

*says deep stops work*
*gets various studies and explanations of why they don't seem to*
*yes but I think it works, so do more work. What if it was gas density, even if we're far from any known threshold ?! Oh and what if VGE, a deco stress indicator is positive ?*


So either scientists have been wrong all along, or maybe they're somewhat right...

...I feel the discussion of "99% or 95%" is sometimes misinterpreted as "100% or 0%".

I would argue the gas density concern remains legitimate on a 170ft dive with deep stops at 70ft. on air.

You're basically saying that almost certain CO2 retention followed by certain reduction in respiratory capacity in particular disadvantage to deeper divers, couldn't possibly have any impact.

It's hardly easy to fully dismiss that it might on the face of it, even if dismissing that the different permeation coefficient might have an influence.

I've listed some material I find interesting, below.

There's a reason there's controversy about this subject, and it's not because experts agree and some divers don't - it's because experts don't agree.
Otherwise, it'd hardly be controversial, would it.

Astronomers say there's a comet heading for Earth, we should do something about it!
Well, Bob the Barber says we'll be allright, so let's not.
Ah, well, allright then.

No.

This would be a good time to point out I'd be the barber in that analogy, if it were valid - Further, I'm not claiming to "know better". I'm simply unsatisfied that we can fully "debunk deep stops", dismiss CO2 and equate it all to RD.

Deep Stops - Page 7
Relationship between CO2 levels and decompression sickness: implications for disease prevention. - PubMed - NCBI
http://www.dtic.mil/dtic/tr/fulltext/u2/763735.pdf
https://www.nature.com/articles/s41598-017-06678-y
https://www.omao.noaa.gov/sites/default/files/documents/Rebreathers and Scientific Diving Proceedings 2016.pdf
D. E. Busby, Space Clinical Medicine
BEHNKE, A.R.: 1947, A Review of the Physiologic and Clinical Data Pertaining to Decompression
Sickness. NMRI-443-4, U.S. Naval Medical Research Inst., Bethesda, Md.
http://www.dtic.mil/dtic/tr/fulltext/u2/405783.pdf
BLINKS, L.R., TWITTY, V.C., and WHITAKER, D.M., 'Part II. Bubble Formation in Frogs and
Rats', in Decompression Sickness (ed. by J.G. Fulton), W.B. Saunders Co., Philadelphia, pp.
145-164.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670013549.pdf
HARVEY, E.N.: 1965, 'Decompression Sickness and Bubble Formation in Blood and Tissues',
Bull. N. Y. Acad. Med. 21, 505-536.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1870593/

How can you say this?

You take a data set (e.g. depth, time, gas mixes) and you apply a process to that data which produces a result (an ascent plan).

I write software for a living. That is EXACTLY an algorithm, in my book.

If it's not an algorithm, and you teach it to a student, then assign them a "problem" to solve - i.e. give them some dive data and assign them to produce a suitable ascent plan from it - how can you say if their answer is right or wrong?

Isn't the process of checking their answer one where you take the same input data and go through steps (what one might call an "algorithm") to produce your own answer and compare it to theirs? The algorithm is what defines the steps you go through such that the result is repeatable (i.e. you get the same answer as the student).

You have only setpoints that mark relations across times and depths.
One could always make the argument that that's an algorithm, but it's too simplifying.

The point is to move away from the thinking that there is a "right" and "wrong" answer, but you can carry out controls just fine.

 

[Patoux01]

Your points have been addressed already by Simon... I'm not going to parrot him, it would not make sense.

 

[Dan_P]

It's still missing the point.
The point is, principally, this conversation isn't about whether deco is 100% bubble mechanics or 100% dissolved gas.

And it's entirely separate from a discussion on whether one wants an algorithm in a computer, or a setpoint-based system.

 

[stuartv]

You have only setpoints that mark relations across times and depths.
One could always make the argument that that's an algorithm, but it's too simplifying.

The point is to move away from the thinking that there is a "right" and "wrong" answer, but you can carry out controls just fine.

Saying it is not an algorithm, rather than saying it's a somewhat complex and sophisticated algorithm (which is what it clearly is - providing parameters to accommodate things like temperature and workload, just as 2 examples) seems pretty disingenuous. And disingenuousness for a purpose that I cannot fathom - unless it's either for marketing purposes ("we don't want to make it sound too hard") or to avoid accountability ("If we say it's not an algorithm, then they can't say they did it correctly and still got bent").

From Merriam-Webster: "algorithm: a step-by-step procedure for solving a problem or accomplishing some end."

It looks like a duck. It quacks like a duck. It's an algorithm.

 

[Dan_P]

Saying it is not an algorithm, rather than saying it's a somewhat complex and sophisticated algorithm (which is what it clearly is - providing parameters to accommodate things like temperature and workload, just as 2 examples) seems pretty disingenuous. And disingenuousness for a purpose that I cannot fathom - unless it's either for marketing purposes ("we don't want to make it sound too hard") or to avoid accountability ("If we say it's not an algorithm, then they can't say they did it correctly and still got bent").

From Merriam-Webster: "algorithm: a step-by-step procedure for solving a problem or accomplishing some end."

It looks like a duck. It quacks like a duck. It's an algorithm.

Stuart,
That shoehorn of yours must be red-hot with friction.

As semantics go;
In the fascinating world of software development, I'm sure even love is but a "complex algorithm".

It's "clear" to you that the parameters provided to "accomodate things like temperature and workload", means RD is a "sophisticated algorithm".
Please, elaborate.
Which parameters are those that you know of?

Meanwhile, it remains a massive detour from the matter of CO2 impact on decompression, perceptions of magnitude and interrelation of only loosely associated topics.

 

[Dr Simon Mitchell]

Dan,

Look, I'm sorry, but all of this is essentially a fairy story with its roots in some physiological fact.

You're basically saying that almost certain CO2 retention followed by certain reduction in respiratory capacity in particular disadvantage to deeper divers, couldn't possibly have any impact.

It is not "almost certain" that there was CO2 retention, let alone a difference in CO2 retention in the deep stops compared to the shallow stops in any of the relevant studies. In the NEDU study the deepest stop on the deep and shallow stops profiles were 70' and 40' respectively.

The maximum breathing capacity at 100' (4 ATA) during air breathing is about 100L/min. A diver resting on deco probably breathes 12 - 15 L/min. So, it is clear that divers on either profile were not materially affected by a "reduction in respiratory capacity".

The density of air at 70' is about 3.1g/L and at 40' is about 2.2g/L, Both figures are substantially less than the 6g/L risk threshold for CO2 retention identified in Gavin Anthony's data, and that risk was in working divers. The divers were at rest on decompression in the relevant studies.

It follows from the above that there is no basis for an assumption that divers on the deep stops profiles were more affected by CO2 retention. And that is before we get to the issue of whether CO2 truly is a risk factor for DCS. That is a highly controversial matter, with conflicting evidence. Some researchers have actually hypothesised that high CO2 levels during decompression might be an advantage (by causing vasodilation and increased tissue outgassing). A couple of studies in animals did not support this idea (they did not show a disadvantage either), but you get the point.

You seem determined to find any thread to cling to, no matter how tenuous, that would justify a disbelief in the evidence that deep stops are being overemphasised by RD, when there is logical and highly plausible explanation for that evidence based on concepts indisputably central to decompression physiology (tissue inert gas supersaturation). The irony is that you are doing this to defend a strategy that sounded good in theory, but which has never been supported by evidence.

I totally accept your point that your personal appreciation of the utility of RD outweighs concerns about decompression efficiency. That's fine, and I don't even consider it reckless in any way. We make those sorts of risk vs benefit decisions all the time. But I do find this scrambling to defend a pseudo-religious practice using extremely tenuous links and extrapolations between established scientific concepts to be unhelpful, and somewhat reminiscent of how we came to believe in deep stops in the first place.

Simon M

 

[Dan_P]

Hi Simon,

Thanks for your insights.

By "almost certain CO2 retention", I referred to the 170ft portion and inferred a potential disadvantage to divers subsequently on deep stops, but be that as it may;

As you know, Ratio Deco was adjusted shallower by several mechanisms after the Spisni-study but I'm happy that you appreciate my point on utility in using a system to frame dives.

Personally, I've adapted to err on the shallow side within that framework based on the works we've discussed, so if my concerns with CO2 come across as a hell-bent dedication to maintain deep stops at any cost, I am sorry that my intent hasn't been clearer;

I am most interested in the developments within the field, but simply am disappointed that the ensuing discussion generally has taken on form as though evidence concisely "debunks" gas mechanics in total (that is, a perception that m-values certainly being the only measure of importance, rather than some balance across concepts).

Your statement: "I totally accept your point that your personal appreciation of the utility of RD outweighs concerns about decompression efficiency.", sums it up well.
I fully appreciate that there is an increased and growing body of knowledge shifting emphasis shallower, particularly compared to pre-Spisni levels.
I'm still sceptical of 100/100, though.

 

[CAPTAIN SINBAD]

I can see why Dan_P believes the RD is not an algorithm. If we were to do a google search of "Decompression Algorithms" then the following show up:

Buhlmann
Recreational Dive Planner
Reduced Gradient Bubble Model
Thalmann Algorithm etc

Ratio Deco will not show up because initially during its GUE days it was simply an attempt to replicate the above. Then UTD argued that it was not merely enough to replicate any one of the above algorithms but deco time was to split between bubble models (deep stop) and dissolved gas (shallow stops.) Oxygen window was also a big thing in those days and thus time taken from deep and shallow was used to pad the middle (S-curve.) The result was an ascent profile that did not mimic any single algorithm but attempted to accmodate three different theories, deep stops, oxygen window and dissolved gas at the depths where they mattered.

In an era where science was not sure about what is actually happening inside the body we can appreciate the intent behind this "risk distribution" exercise. We have to keep in mind that UTD was not the only one thinking along these lines. Steve Lewis (Doppler) who is as far removed from UTD as they come, also wrote an article on Ratio Deco as an alternative way to look at decompression.

Another Way to Look at Decompression | SDI | TDI | ERDI

Then as our understanding of decompression progressed, S-curve went away and deep stops also fell from grace. The new RD 2.0 is designed along shallower stops without S-curve. The question that remains today is not whether deep stops should happen or not but how shallow should the first stop be? In other words, if scientific community could give an ideal GF-Lo that is backed by solid research then that would be the kind of "debunking" that scubaboard really really needs.

 

[leadduck]

Ratio Deco will not show up because initially during its GUE days it was simply an attempt to replicate the above. Then UTD argued that it was not merely enough to replicate any one of the above algorithms but deco time was to split between bubble models (deep stop) and dissolved gas (shallow stops.) Oxygen window was also a big thing in those days and thus time taken from deep and shallow was used to pad the middle (S-curve.) The result was an ascent profile that did not mimic any single algorithm but attempted to accmodate three different theories, deep stops, oxygen window and dissolved gas at the depths where they mattered.

I think these two different interpretations of the terms "Ratio Deco" (or "Deco on the Fly") can be confused:

1. The high-level idea of approximating any deco algorithm with some simple arithmetic rules that the diver can do in his head or on wetnotes during the dive. Nothing said so far what ascent profile exactly we want to approximate; could be GF10/90, could be VPM-B+3, could be GF60/80, could be some mix of all.
   
   vs.
   
   
2. A precise particular procedure (aka algorithm) how to calculate an ascent profile, taught by some training agency.

Of course any criticism about RD overemphasizing deep stops can mean only the latter; blurring the definition are weasel tactics IMO.

I like this presentation about it (in German only unfortunately):
http://techdiving-network.de/wp-content/uploads/2014/05/Ratiodeco_et_al.pdf

Anyone got a description of UTD RD 2.0 calculation rules to share? Or is it something they want to hide from public scrutiny?

 

[Dan_P]

The question that remains today is not whether deep stops should happen or not but how shallow should the first stop be? In other words, if scientific community could give an ideal GF-Lo that is backed by solid research then that would be the kind of "debunking" that scubaboard really really needs.

Exactly my thought.

I think these two different interpretations of the terms "Ratio Deco" (or "Deco on the Fly") can be confused:

1. The high-level idea of approximating any deco algorithm with some simple arithmetic rules that the diver can do in his head or on wetnotes during the dive. Nothing said so far what ascent profile exactly we want to approximate; could be GF10/90, could be VPM-B+3, could be GF60/80, could be some mix of all.
   
   vs.
   
   
2. A precise particular procedure (aka algorithm) how to calculate an ascent profile, taught by some training agency.

Of course any criticism about RD overemphasizing deep stops can mean only the latter; blurring the definition are weasel tactics IMO.

I like this presentation about it (in German only unfortunately):
http://techdiving-network.de/wp-content/uploads/2014/05/Ratiodeco_et_al.pdf

Anyone got a description of UTD RD 2.0 calculation rules to share? Or is it something they want to hide from public scrutiny?

Speaking of blurred lines, I'm not sure if that was a genuine question or an expression of a view that anyone in disagreement with you must effectively be a convolusive weasel.

Unofficial materials have been shared by link in this very thread already.
If you want official materials, I'm sure you'll buy them.