UTD Decompression profile study results published

[Kevrumbo]

Hello,

The UTD decompression profile project results were published in Diving and Hyperbaric Medicine this month.

Spisni E et al. A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco. DHM 2017;47(1):9-16.

This study attracted a lot of discussion after Andrew Georgitsis posted a video on You Tube that strongly (but incorrectly as it turns out) assumed an advantage for ratio decompression in this investigation:


The authors compared a ratio deco and GF30:85 approach to decompression from a 50m 25 min trimix dive with nitrox 50 and oxygen decompression. There were 51 dives (28 ratio deco and 23 GF deco) and the end points were venous bubbles and assays of inflammatory markers suggestive of vascular injury.

Despite having a longer decompression the ratio deco profile was associated with greater production of inflammatory markers after the dive. The ratio deco profile produced grade 3 or 4 bubbles in 4/28 (14.3%) divers and the GF profile produced grade 3 or 4 bubbles in 2/23 (8.7%) divers. The differences in inflammatory marker production were statistically significant, but the difference in the proportion of divers producing high bubble grades was not.

The ratio decompression profile puts greater emphasis on deep stops in comparison to the GF profile, and the results constitute further evidence that the "love affair" we had with deep stops in the early 2000s has resulted in over-emphasis of the strategy by some algorithms. For clarity, and to avoid misinterpretation, the study does not establish GF 30:85 as optimal decompression. It simply indicates an advantage for that algorithm over one which places more emphasis on deep stops.

Simon M

If I remember right, AG added arbitrary deep stops to the 30/85 profile. Is there going to be a public release of the write-up of the test methods, curves, and results? Or is it staying behind the steep paywall?

Comparing Profiles: Adapted Buhlmann GF 30/80 vs RD 1:2 (UTD Study). . .

 

[huwporter]

A quick analysis of the two profiles as taken from the video through the lens of Buhlmann theory.

First the GF profile:

...a conventional GF profile as expected.

Then the UTD profile:

So the UTD profile ends up kinda a bit comparable to a heavily butchered gradient factors 1/80 but over 10 minutes longer.

(Common assumptions: 15m/min descent, 9m/min to first stop, immediate ascent from 6m.)

Edited to fix up mistake (missing 3m stop) in the UTD profile.

 

[Diver0001]

The ratio decompression profile puts greater emphasis on deep stops in comparison to the GF profile, and the results constitute further evidence that the "love affair" we had with deep stops in the early 2000s has resulted in over-emphasis of the strategy by some algorithms. For clarity, and to avoid misinterpretation, the study does not establish GF 30:85 as optimal decompression. It simply indicates an advantage for that algorithm over one which places more emphasis on deep stops.

Simon M

Thank you. One follow up question. He's talking about the "immune system" response as being one of the crucial factors in DCS.

Over the last years I've personally become more and more skeptical regarding what the DIR people say about deco theory or ascent strategies. He appears to be saying that bubble lead to an immune response and that the immune response leads to DCS. I've always been told (and believe) that bubbles are a problem in and of themselves because they can get lodged in the blood vessels and generally disrupt bloodflow.

My question is, is there something important about the immune system response that we need to remember as tech divers or is this just more smoke being blown up the proverbial back end?

R..

 

[chillyinCanada]

Immune response causes inflammation. Perhaps the inflammation makes it even that much more difficult for bubbles?

I'm not good at this stuff but I'd swear we had a thread that addressed the relationship not too far back.

 

[Diver0001]

Immune response causes inflammation. Perhaps the inflammation makes it even that much more difficult for bubbles?

I'm not good at this stuff but I'd swear we had a thread that addressed the relationship not too far back.

I understand that but I am personally very skeptical of DIR concepts. Since 2002 I have had severe reservations and from about 2007 onward I have been becoming more and more skeptical of DIR "concepts" as related to deco. It seemed like more of a throw-back to the 1980s than anything else. ... like going backwards instead of going forwards....

The thorough inability of DIR to process a "paradigm change" was, for me the final nail in the coffin. Holding on to an old paradigm despite incontrovertible evidence to the contrary shows clear problems with thinking/logic.

R..

 

[The Chairman]

The thorough inability of DIR to process a "paradigm change" was, for me the final nail in the coffin. Holding on to an old paradigm despite incontrovertible evidence to the contrary shows clear problems with thinking/logic.

Anecdotally speaking, of the few people I know who have had incidents with DCS, clearly half of them were on RD. Of all the divers I know, less than one percent utilize RD. That disparity speaks volumes to me. That one of the more vocal proponents of RD has been bent using it two or three times is truly ironic. Their minds are made up, so please, please don't confuse them with statistics or reason!

@Dr Simon Mitchell, could you define "aggressive deco" for us? Is it referring to accumulating lots of deco or blowing off a goodly amount by using RD?

 

[victorzamora]

Comparing Profiles: Adapted Buhlmann GF 30/80 vs RD 1:2 (UTD Study). . .

Thanks, Kev. I had only seen one video, much shorter than the one you linked, where AG spoke briefly and vaguely about adding deep stops in a manner that seemed arbitrary.

It seems like they went with 30/80 (as opposed to 40-50/70-80) AND gave RD the benefit of longer deco and it STILL performed notably better. I'm really curious to know how something like an unmodified GF50/70 would've done.

Edited: Seems like there's no arbitrarily-added deep stops on top of the GF30/80 profile.

 

[PfcAJ]

UTD deco nonsense.

Hopefully this helps put the kibosh on some of the crazy stuff they're teaching.

 

[stuartv]

I'm really curious to know how something like an unmodified GF50/70 would've done.

Edited: Seems like there's no arbitrarily-added deep stops on top of the GF30/80 profile.

I took AG's statements about being a "tweaked" Buhlmann to mean Gradient Factors. I.e. when he talked about "pure Buhlmann" he was talking about Buhlmann with no GF used at all.

 

[victorzamora]

I took AG's statements about being a "tweaked" Buhlmann to mean Gradient Factors. I.e. when he talked about "pure Buhlmann" he was talking about Buhlmann with no GF used at all.

In the first video I watched (before the paper was published, before/during the initial dives), his phrasing was more along the lines of "Buhlmann 30/80, tweaked to add deeper stops because it'd be unsafe otherwise." It's unclear if the tweaks he's referencing are simply the GF adjustments (widely accepted model for adding conservatism) or if he's talking about adding other tweaks.

The report and the longer video KevRumbo posted make it clear to me that he's simply talking about GFs, but has little respect for them.

My point remains, though, about wanting to see how 50/70 would've done compared to RD and 30/80, as well as VPM-B+2.5 (as VPM+2 is slightly shorter and VPM+3 is slightly longer, or something like 50/75 compared to VPM-B+2).

I'm looking at some plots for ascent curves and the UTD RD is very different from the ZHL curves but is also pretty different from the VPM curve. I'll see if I can post a couple graphs.

Edit: I added a PDF attachment (hopefully) that should come through. I made a couple decisions that make it look non-standard, but it was to get smooth curves for visual comparison. It looks a little goofy and is nothing complicated, but should show the different ascent strategies.