Slow tissue on gas from stops

[Dan_P]

Your posts seem to have conceded that the research shows that bubble-model-style deep stops increase the risk of DCS. But evidently you've concluded that the risks are only increased by 1 in 1000, and thus irrelevant. Given the wide range of diving that occurs that estimate seems simplistic in the extreme.

Substantial dives are occurring where stop distribution will matter as demonstrated by the research (not just the NEDU's). It seems irresponsible, given the available data, that an instructor of any agency would attempt to discount available information in such a cavalier manner. Perhaps it points to a larger problem within the agency itself. In any case, in my opinion the chances that the increased risk of the deeper stops imposed by RD and bubble models is limited to 1 in 1000 are remote indeed.

There is NO advantage to deep stops per se. They increase gas requirements, keep divers deeper than needed, and, even as conceded by you, increase the risk of DCS.

No, you're putting words in my mouth, apparently to fit a preconceived bill.

The only thing I'm conceding is that if I were doing a cold deep air dive in speedos and a t-shirt and also had nothing to decompress on but air, I'd emphasise shallower.
How very groundbreaking indeed.

For you to extrapolate so freely on that as to state I've conceded anything to the effect of deep stops being generally unsafe, is quite frankly, out of order.

But, seeing it as your ridiculous statements about person and agency, while convoluted with "maybe" and "seem", build on some notion that the NEDU-trial dives were representative, let me ask you how often you do 30 minute dives to 170ft. wearing a t-shirt in relatively cold water, and using nothing but air throughout?

And saying there is no advantage to deep stops, is inaccurate. Even if there really are zero benefits in physiological terms, practical considerations have a place in this too - now, some might say that, well, you can conjure some ratio somewhere in an ascend for a each dive, to achieve having a ratio on that specific dive. That's missing so many points to RD that I'm genuinely amused by it

The point is 1) don't put words in my mouth, and 2) if you really want to have an expert's opinion on whether what you're saying is valid, try aksing Dr. Mitchell if using RD is irresponsible because of the level of emphasis it presently has on deep stops.

My take on it is, as significant as NEDU were, you're probably overestimating what it shows and what it doesn't.
In all respect, the scale of things seems to be lost in your interpretation of things.

 

[Patoux01]

And saying there is no advantage to deep stops, is inaccurate. Even if there really are zero benefits in physiological terms, practical considerations have a place in this too - now, some might say that, well, you can conjure some ratio somewhere in an ascend for a each dive, to achieve having a ratio on that specific dive. That's missing so many points to RD that I'm genuinely amused by it

 

[Dr Simon Mitchell]

Hello Dan,

I put it to you that the play to an unsophisticated superficial appraisal of the NEDU study methodology here:

The only thing I'm conceding is that if I were doing a cold deep air dive in speedos and a t-shirt and also had nothing to decompress on but air, I'd emphasise shallower.
How very groundbreaking indeed.

and here...

how often you do 30 minute dives to 170ft. wearing a t-shirt in relatively cold water, and using nothing but air throughout?

....is beneath your usual standard of debate.

Have you read the NEDU report? If so, did you appreciate that they showed that the shallower stops profile had less total integral supersaturation and less slow tissue supersaturation than the deep stops profile. Can you not appreciate that this is, overwhelmingly, the most obvious and plausible explanation for the results? Can you also not appreciate that in comparing any two other profiles the identification of the same characteristics (less total supersaturation and less supersaturation in slow tissues) in one of them would suggest that to be the most successful profile? And have you not cottoned on to the fact that evaluations of same-length bubble model vs GF decompressions of unquestionable relevance to everyday tech diving have identified exactly those characteristics in the GF profile?

I also find it surprising that your arguments focus almost exclusively on the NEDU study and completely ignore the fact that there has been a DIRECT COMPARISON of a GF decompression and a deeper stop decompression prescribed by the approach you seem so passionate about defending. That study is a powerful illustration of how wrong blind acquiescence to cult-like decrees can be. I believe this characterisation is not unfair: RD appears to be the product of one divers opinion (he says it himself - see video link below); it has no basis in experimental validation whatsoever. Yet you appear to believe in it despite considerable evidence suggesting that you should at the very least be sceptical.

I honestly think you should reset yourself. I would start by watching the video here. Be sure to watch the whole thing (it is only 6 minutes long) because some of the most outrageous over-confident presumptions of a positive outcome appear near the end. Then read the Spisni study (that showed the opposite to those presumptions) again, reflect on the disconnect between the aggressive promotion of fantasy in the video and the reality of the study, and ask yourself, "why would I trust anything that UTD says about decompression methodology"? I mean this genuinely, and I am not trying to be cute. The conclusions any rational person would draw are obvious. I know they changed RD after that study, but that is missing the point. The same confident predictions that RD2 is better are being made in the complete absence of evidence, and so the cycle begins again.

Having said all that:

if you really want to have an expert's opinion on whether what you're saying is valid, try aksing Dr. Mitchell if using RD is irresponsible because of the level of emphasis it presently has on deep stops.

My opinion? No its not "irresponsible". You have your reasons for using it. Fine. I also agree that we are not in a position to accurately define the absolute reduction in risk that would accrue from (for example) a GF approach with less emphasis on deep stops vs RD. It may be small, or it may be bigger than you think. But that too misses the point. Setting unresolvable arguments about the magnitude of differences in risk aside, if divers seek the "truth in the universe" about the most efficient approach to decompression (least risk in the same decompression time), all the current evidence suggests that approaches which emphasise deep stops are not it. I don't think you would disagree with that, and there is not much point in arguing about it ad infinitum.

Simon M​

 

[Dan_P]

Hi Simon,

First, let me say that I sympathise with your statement that my "play to an unsophisticated superficial appraisal of the NEDU study methodology.......is beneath your usual standard of debate." - they were retorts to a (baseless) statement effectively on the lines of me having conceded to using RD being "irresponsible".
But you're right that my retort came off belittling of the work involved in the NEDU-study, which was neither my intent or reflective of my position.

Let me further say that I understand your antipathy towards the video you refer to. I gather that it's a big part of the motivation for the present evolutionary branch of the debate as is - and I'm not going to argue the contrast across the video's content and much of the content you often refer to, which has become the mainstay of my daily reading.
This includes of course NEDU, Spisni, Blatteau, etc.

And please note I'm not arguing with you over statements to the effect of present evidence showing that bubble models and other methods (RD or GF) with similarly high deep stop emphasis probably are suboptimal in terms physiology pure (below).

Personally, I was initially taught tech diving within a mainstream organization when bubble mechanics were at the peak of it's vogue, but as the debate goes, by my own admission, I consider my exposure to the debate surrounding them in medias res, at best.
But I'm not diving RD because I've seen a video with an anecdotal narrative that it feels good, or dismiss the body of knowledge available to us. I trust that you'll give me the credit of assuming I speak the truth when I say that.

What I'm after isn't dismissing what we have. Rather, it's looking at what we have and seeing what we have.
As such, I'm perfectly happy with this paragraph below:

My opinion? No its not "irresponsible". You have your reasons for using it. Fine. I also agree that we are not in a position to accurately define the absolute reduction in risk that would accrue from (for example) a GF approach with less emphasis on deep stops vs RD. It may be small, or it may be bigger than you think. But that too misses the point. Setting unresolvable arguments about the magnitude of differences in risk aside, if divers seek the "truth in the universe" about the most efficient approach to decompression (least risk in the same decompression time), all the current evidence suggests that approaches which emphasise deep stops are not it. I don't think you would disagree with that, and there is not much point in arguing about it ad infinitum.

Suboptimal but practical works fine for me. I have no problem with that.
So long as it's not called "irresponsible" or "unsafe" with reference to the body of knowledge we have on hand at present.
That's all.


Best Regards,

Dan

 

[shoredivr]

Why anybody would chose suboptimal is unclear to me.

 

[PfcAJ]

Why anybody would chose suboptimal is unclear to me.

I can see picking something that’s “suboptimal” in one area but makes up the difference in areas of practicality.

Standard gases are a good example. They aren’t “optimal” compared to best mix, but VERY practical.

RD ascents are very practical. I can come up with a decent deco plan very quickly that has an acceptable level of risk. Is it optimal? Perhaps not. BUT if I can make some adjustments to move it toward optimal, I will, and I wrote about how to do that earlier in this thread. Digging your heels in the ground and only focusing on the “practical” seems a bit foolish to me.

 

[rsingler]

Have resisted commenting.
Nothing to add from a theoretical or medical standpoint. Endless discussion, that like a vortex, just keeps swirling and swirling.
But I am reminded of an old phrase I was taught about failed plans, in military leadership training:
"Culture eats strategy for breakfast!"

One may have a strategy (to wean off deep stops, perhaps?) that is based upon logic, or science, or whatever is most convincing/compelling to you (and therefore can't really be argued by those whom you wish to influence, you think).

But if you come up against a contrary culture, you are dead in the water.
Our scuba culture will change, over time. But for many of us, that change is painfully slow. And as in the military, I fear some lives may be lost in the process.

 

[100days-a-year]

So can anyone help me set the GFs on my EDGE so I dive a more optimal profile,I'm afraid I may be doing something that resembles a deep stop at 60' as the ascent warning starts flashing and don't want to offend anyone.TIC

 

[rsingler]

I loved that old thing!
Hasn't been a display yet that's more descriptive of what's theoretically happening in your tissues.

And the best part was, I could carry 4# less lead!

 

[tursiops]

So can anyone help me set the GFs on my EDGE so I dive a more optimal profile,I'm afraid I may be doing something that resembles a deep stop at 60' as the ascent warning starts flashing and don't want to offend anyone.TIC

If you leave your EDGE at 60 ft and dive henceforth without it, it will be happy.