Evolving Thoughts on Deep Decompression Stops

[dmaziuk]

I mean deep, deeper than otherwise - I dunno - again, trying to learn and understand.

I forget who's presentation it was, Dr Pollock maybe, showing tissue saturation graphs after two different deco strategies, one with deeper stops than the other. The graphs really made it easy to see the different end result and made sense, that's why I was serious about sitting in a chair watching tissue graphs in a chamber......

For the same total ascent time if I'm not mistaken. Well, sure, no argument there, but you yourself showed that 10/100 adds 10% more time to your ascent. So it's not at all the same thing.

 

[dorsal]

John. Thank you for using your reduction funnel to distill all that research into a great article

 

[stepfen]

I am very far from understanding let alone having a say on deco matters, however yesterday I saw this video that seems interesting:
It is about a study that took place in Italy few years ago comparing Buhlmann to ratio deco (which to my understanding favors deep(er) stops). Unfortunately the results are not shown in the video, but somebody asked about them in the comments to get the following reply from the publisher:
"The outcome was positive towards Ratio Deco. And we learned so much that we could adjust our Ratio Deco to be even more precise."
Maybe somebody here can access the paper itself to see the results.
Once more I want to make clear that I am not implying anything for or against deep stops. I just saw the video yesterday and I wanted to bring it to your attention.
Cheers

 

[tursiops]

I am very far from understanding let alone having a say on deco matters, however yesterday I saw this video that seems interesting:
It is about a study that took place in Italy few years ago comparing Buhlmann to ratio deco (which to my understanding favors deep(er) stops). Unfortunately the results are not shown in the video, but somebody asked about them in the comments to get the following reply from the publisher:
"The outcome was positive towards Ratio Deco. And we learned so much that we could adjust our Ratio Deco to be even more precise."
Maybe somebody here can access the paper itself to see the results.
Once more I want to make clear that I am not implying anything for or against deep stops. I just saw the video yesterday and I wanted to bring it to your attention.
Cheers

That study was mentioned in John's article, as "Spisni," it is his Reference 8. The published results are at: A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco.
The interesting thing is that the published results -- and John's summary -- are exactly the opposite of what you report from the publisher of that video.

 

[rjack321]

That study was mentioned in John's article, as "Spisni," it is his Reference 8. The published results are at: A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco.
The interesting thing is that the published results -- and John's summary -- are exactly the opposite of what you report from the publisher of that video.

In other words, the video version is a gigantic lie to save face on a flawed approach. Only slightly more contrite and conciliatory about their erroneous assumptions than the author of v-planner.

 

[tursiops]

In other words, the video version is a gigantic lie to save face on a flawed approach. Only slightly more contrite and conciliatory about their erroneous assumptions than the author of v-planner.

Well, to be generous, perhaps they had not yet done the full analysis. I know, that's pretty generous.

 

[stepfen]

Wow! That's a pity because I like this guy's videos (apart from this one obviously).

Well, maybe what he means by: "... we learned so much that we could adjust our Ratio Deco to be even more precise." is that they learned not to trust that much deep stops any more.

He should have clearly emphasized that his method was proven wrong and not let viewers think that the study was positive for deep stops.

Thanks guys for all this info.

 

[thetechnicaldiver]

Great article John, also helped me discover your blog, i'll add it to my site

 

[dmaziuk]

He should have clearly emphasized that his method was proven wrong and not let viewers think that the study was positive for deep stops.

Aside from the relationship between ratio deco and deep stops, or gradient factors and deep stops for that matter:

I wouldn't rush to that conclusion based on N=23 on one profile with one trimix/EAN combo: it is interesting but until they start testing everyone's blood and work out reproducible and verifiable trends, I'll stick to these:

Didn't somebody recently show that in presence of gas switches, differently spaced/timed deco stops produce lower ISS? -- That could be why the other group had less inflammation markers, and not because they spent "less time" decompressing. And the numbers for RD group were no different than those for no-stop divers on air, so they weren't "worse than usual", it's the other group that "scored better" on the blood test... "proven wrong" is a bit of an overstatement IMO.

We've been through this already: the newfangled doppler ultrasound showed that bubbles were always present, traditional model failed, and we needed the new and improved one that controlled bubbles while keeping the overall deco time shorter. And look what happened.

 

[UWSojourner]

... by the same logic, if 50/75 is "safe enough", then any combination of GF Lo <= 50 and GF Hi <= 75 is also safe enough: 5/75, or 50/7.5 can't be "less safe" than your upper limit of 50/75.

This statement ignores the additional gas loading the diver incurs if they lower the low GF. In the Spinsi trials both groups surfaced at about the same GF, but UTD-RD suppressed the low GFs at all the in water stops (typical of bubble models). And that approach showed to be less effective by the criteria established by the study.

So if, for example, a 70/90 profile has probability of DCS = p, it does not follow that 10/90 or 20/90 will have probability of DCS <= p. I would expect, as in the Spinsi trials, that there could be areas where the additional time given to the 10/90 profile (for example) would not be enough to counter the detrimental effects of the additional gas loading.