Dan,
Since this is effectively a critique of one of my posts, I feel compelled to respond.
Your posts earlier in this thread make it clear that you still do not understand the message that the scientific community has taken from this study. Specifically, it challenges the belief that protecting the fast tissues from supersaturation early in the ascent by imposing deep stops outweighs any disadvantage arising from greater supersaturation of slow tissues later in the ascent. This pattern of supersaturation distribution is inevitable if you have a fixed amount of decompression time and you favour a deeper distribution of your stops, no matter what gases you use. Obviously there needs to be a deepest stop somewhere, but the available evidence suggests that bubble models and RD place that stop too deep.
While I understand your responding, I hope the least negative meaning of the word "critique" is what has come across in my previous response.
I understand clearly the expressed concern of overemphasis towards fast tissues versus slow tissues in general motivation for deep stop application. This mainly thanks to a presentation by yourself, which very aptly explained it. So firstly, thanks are in order for taking the time to make readily available that presentation.
My concern is based in another of your own presentations, on the topic of deep air and CO2-retention. As this is a most useful ressource in conversations about deep air, I feel thanks are in order for making that available, also.
In explanation of my concern, I feel it's based in a notion that the density of air on the deep stops (of the NEDU study) poses an issue in terms of isolating factors in the study;
If deep air is an issue, surely that is grounds for reasonable concern that deep stops on air may well be relatively less effective than deep stops on a lighter gas mixture, irrespective of various gases' on/off-gassing properties, simply due to density at depth.
If that concern is apt, it would prompt a natural assumption that deep stops with lower gas densities would be more effective, gas/depth irrespective.
Would you say this is an unreasonable concern on my part, please?
Yes, and it is the study that, with great fanfare and confidence on a UTD video, Georgitsis announced was going to prove that RD was better than Buhlmann GF. The study found the opposite, to be clear, a disadvantage for RD. So what is your point?
My point is a comparative study across "a lot of deep stop" and "quite a lot of deep stop" is a poor measure for the validity of deep stops in general.
We can speak about the general issues in the framing of the parametres of the dives in that study, as I'm sure we both have several points to bring up that would or could have skewered results, but that's a different matter from the principle of deducting from, say,
"X minus 20 leading to slightly worse results than X minus 19" that
"X minus 10 is better", which seems to be the effect.
This is a sentence from the introduction in which the authors are describing the rationale for conducting their study. Do you not think it might be more relevant (and honest) to quote the actual result - which was not favourable to deep stops?
A fair point. I did not mean to obscure anything, and am happy to elaborate.
I believe the correct reference for this is "Blatteau JE, Hugon M, Gardette B, et al. Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops. Aviat Space Environ Med 2005; 76:490 –2";
This was, however, also a deep air trial. Surely, any concern over gas densities, principally apply here, too?
Fair enough. The unpublished studies have been presented at multiple diving medical conferences and I have not misrepresented them, but clearly you have not had the chance to hear the presentations.
Indeed I have unfortunately not had the chance to hear the presentations, and therefore have zero foundation to comment on them.
Perhaps the most important point that seems to be forgotten by those who attempt to debunk the evidence against deep stops is that they / you are defending a decompression approach that has not a SHRED of supportive evidence and that all studies that are relevant to this general issue suggest that it is not optimal (that is, it over-emphasises deep stops). None of the studies are perfect for our purposes, but when multiple imperfect studies all say the same thing, the chances are it is correct.
I feel the term "deep stops" has become inadequate for the purpose of this conversation in that deep stops are widely accepted as a reasonable approach by way of no-one advocating GF-lo=100 and at the same time, deep stops are widely unaccepted as a reasonable approach as bubble models such as VPM or RGBM have not proved able to bring about the results expected by particularly many in the 2000's.
I feel the discussion should be focused on "what is the balance" between dissolved gas impact and bubble mechanics impact on decompression, and I appreciate of course that a study to support endeavouring such questions, would require significant scope and scale - probably more than I envision.
As for separating the understanding of RD and bubble models, please allow me to reiterate that if we had availble "the perfect algorithm", I would still prefer a tool that approximated it but allowed the benefits of RD at the expense of
some accuracy.
On a final and entirely
personal note, Ratio Deco does allow and does indeed prompt diver decisions in allocation of
some deco time within pre-determined segments;
Only at very specific depth-time-ratios is all deco time pre-determined within the (even then, still adaptable) RD framework.
At all other depth-time-ratios, I actively take into account the body of knowledge available from sources such as the ones mentioned, and drive emphasis in a direction I find reasonable.
For your contributions towards helping me make those decisions, I thank you.
Best Regards,
Dan
