Deep Stops Increases DCS

[Kevrumbo]

The "leading experts" are speculating as applied to all mixed gas (Trimix) diving -based on anecdotal reports and extrapolation of data (i.e. "Deep Stops Skew") from the NEDU Study Paradigm- that Deep Stops while keeping Fast Tissue saturation & bubble formation in check, are also supersaturating/loading Slow Tissues significantly which can produce DCS symptoms after completion of a Dual Phase type decompression profile (i.e. RGBM, VPM, Ratio Deco).

The "leading experts" have not yet given a satisfactory explanation about the effects on Fast Tissue Supersaturation, if a Gradient Factor Buhlmann profile is arbitrarily set to moderate or even eliminate the Deepstops segment -but again anecdotally there appears to be no patently detrimental effects (i.g. No acute neuro type II DCS incidence).

Rossh, developer of current V-Planner and Multi-Deco commercial software/firmware platforms vehemently disputes the implied results of the NEDU study because its test paradigm unfairly skews the applications of the base VPM theory & model behind the software.

Again, abridged conclusion the NEDU Study:

(Abstract, p.i). . .Divers wearing swimsuits and tshirts, breathing surface-supplied air via MK 20 UBA, and immersed in 86 °F water were compressed at 57 fsw/min to 170 fsw for a 30 minute bottom time during which they performed 130 watt cycle ergometer work. . . Results indicate that slower tissue gas washout or continued gas uptake offsets the benefits of reduced bubble growth at deep stops. . .
(Conclusion p.18) . . .The practical conclusion of this study is that controlling bubble formation in fast compartments with deep stops is unwarranted for air decompression dives

.

 

[rossh]

Mr. AJ

Have you reviewed or found fault with the basic facts we present above? Can you dispute our claims on a basis of math, physics, or a modelling stance?

 

[PfcAJ]

If I recall correctly, Dr Doolette and Dr Mitchell have already gone line by line and addressed your claims/concerns over on RBW. I'd like to refer you to those posts.

 

[shoredivr]

Rossh, really all this is covered in great detail on the Rebreatherworld thread. You know this. It's kind of sad because you could be running with this new information from NEDU instead of battling subject matter experts.

I learned a huge amount from the RBW thread for which I am thankful. Also thankful that Drs Doolette and Mitchell actually took time to post both there and here.

 

[Dr. Lecter]

I guess re-hashing yesterday's battle in a new forum is a safer bet than addressing the potential issue raised by evolving experience with deeper stop algorithms. I don't care that much about the 1:1 applicability of the NEUD study to whatever windmill Ross is tilting at.

I know that I'm a relatively young, relatively fit diver without a PFO who does a lot of longer dives well below 200' and often below 300'. I know from some unpleasant experiences that despite a moderate to high level of conservatism, VPM-B/E leaves me feeling like after dives much deeper than 200' and/or with more than a hour or so of deco hang, unless I put a 70% GFS on top of it. And I know, having been prompted to experiment by commentary and debate, that limiting the % of helium in my algorithm and running 60/85 GFs leave me feeling a heck of a lot better. Others are putting in 0% helium and diving 85/90 and feeling good; still others report great success with straight VPM models in deeper dives and longer hangs than I'm currently doing.

Everyone else's mileage may vary, but quibbing over exactly what the NEUD study does or doesn't show seems like obfuscationary bull.

 

[shoredivr]

Proof's in the pudding. I recently attended a presentation on Gradient Factors with Steve Lewis. He mentioned paying attention to one's body during and after a dive. Whatever gets you out of the water feeling good is the algorithm that works for you. Given that there are something like 28 factors that effect bubble formation, from hydration to age to fitness levels, and that these can vary, an algorithm that works for one person may not for another.

 

[Kevrumbo]

I guess re-hashing yesterday's battle in a new forum is a safer bet than addressing the potential issue raised by evolving experience with deeper stop algorithms. I don't care that much about the 1:1 applicability of the NEUD study to whatever windmill Ross is tilting at.

I know that I'm a relatively young, relatively fit diver without a PFO who does a lot of longer dives well below 200' and often below 300'. I know from some unpleasant experiences that despite a moderate to high level of conservatism, VPM-B/E leaves me feeling like after dives much deeper than 200' and/or with more than a hour or so of deco hang, unless I put a 70% GFS on top of it. And I know, having been prompted to experiment by commentary and debate, that limiting the % of helium in my algorithm and running 60/85 GFs leave me feeling a heck of a lot better. Others are putting in 0% helium and diving 85/90 and feeling good; still others report great success with straight VPM models in deeper dives and longer hangs than I'm currently doing.

Everyone else's mileage may vary, but quibbing over exactly what the NEUD study does or doesn't show seems like obfuscationary bull.

And I know for myself after 21 consecutive days of Deep Air deco diiving -ten of those consecutive days with two deco dives per day- that if I reset for a surfacing GF of 60 or lower (i.e. longer O2 deco profiles at 6m), then I come out surfacing much cleaner of inert gases and free of prompt or delayed acute DCS symptoms.

This is what Simon Mitchell M.D. Ph.D implied to me as I understood it, as an alternative plan -on our 2013 Bikini Atoll Expedition as my attending Emergency/Hyperbaric Physician- if I still decided to use Deep Stops in my deco profiles (i.e. to extend the Oxygen deco as needed).

That's the best most useful and practical advice to take from the Nedu Study, notwithstanding all the other Bullscatology posted on Rebreather World. .

 

[Dr. Lecter]

And I know for myself after 21 consecutive days of Deep Air deco diiving -ten of those consecutive days with two deco dives per day- that if I reset for a surfacing GF of 60 or lower (i.e. longer O2 deco profiles at 6m), then I come out surfacing much cleaner of inert gases and free of prompt or delayed acute DCS symptoms.

This is what Simon Mitchell M.D. Ph.D implied to me as I understood it, as an alternative plan -on our 2013 Bikini Atoll Expedition as my attending Emergency/Hyperbaric Physician- if I still decided to use Deep Stops in my deco profiles (to extend the Oxygen deco as needed).

That's the most useful and practical advice to take from the Nedu Study, notwithstanding all the other Bullscatology posted on Rebreather World. .

Yes, if you think doing the deep stops provides a meaningful DCS risk reduction that offsets the huge increase in CNS loading from the shallow stop time necessary to compensate for them, that works fine. Given the depths and runtimes I'm doing and seeing done on things from 60/80 to 85/90, I'd question the value of those deeper stops and thus whether keeping them in adds anything worth the CNS loading - especially over a long period of repetitive diving.

Are you dropping the working ppO2 for your dives to (in part) compensate for your increase in O2 time? Obviously that just adds to your inert loading and deco obligations...

 

[lv2dive]

Seems like whenever Steve is in FL, I'm in GA, and I'm bummed we haven't caught up in a while... because of this kind of attitude! One of the the things I like the most about Mr. Lewis' approach to diving is something that sometimes is hard to find: good old-fashioned common sense. I could not agree more with this statement!: "paying attention to one's body during and after a dive. Whatever gets you out of the water feeling good is the algorithm that works for you."

Obviously, this has to be taken in the context of buddies, etc... But anyone with much experience tech diving *should* know what works best for them. I know that I feel better with a higher low GF. On a dive with 30-60 minutes of deco, it doesn't make much difference, so I'm ok going with the flow... But once the deco time starts adding up, we are going to have to come up with a plan bc I'm only going so low with that low GF.

Proof's in the pudding. I recently attended a presentation on Gradient Factors with Steve Lewis. He mentioned paying attention to one's body during and after a dive. Whatever gets you out of the water feeling good is the algorithm that works for you. Given that there are something like 28 factors that effect bubble formation, from hydration to age to fitness levels, and that these can vary, an algorithm that works for one person may not for another.

 

[Kevrumbo]

And I know for myself after 21 consecutive days of Deep Air deco diiving -ten of those consecutive days with two deco dives per day- that if I reset for a surfacing GF of 60 or lower (i.e. longer O2 deco profiles at 6m), then I come out surfacing much cleaner of inert gases and free of prompt or delayed acute DCS symptoms.

This is what Simon Mitchell M.D. Ph.D implied to me as I understood it, as an alternative plan -on our 2013 Bikini Atoll Expedition as my attending Emergency/Hyperbaric Physician- if I still decided to use Deep Stops in my deco profiles (i.e. to extend the Oxygen deco as needed).

That's the best most useful and practical advice to take from the Nedu Study, notwithstanding all the other Bullscatology posted on Rebreather World. . .(along with Steve Lewis' (Doppler's) advice above)

Yes, if you think doing the deep stops provides a meaningful DCS risk reduction that offsets the huge increase in CNS loading from the shallow stop time necessary to compensate for them, that works fine. Given the depths and runtimes I'm doing and seeing done on things from 60/80 to 85/90, I'd question the value of those deeper stops and thus whether keeping them in adds anything worth the CNS loading - especially over a long period of repetitive diving.

Are you dropping the working ppO2 for your dives to (in part) compensate for your increase in O2 time? Obviously that just adds to your inert loading and deco obligations...

No. All deep dives from the latest Truk trip were Open Circuit with mostly Air Bottom Mix to a max depth of 60m and ppO2 of 1.5 (see Post#329 above). I actually discarded the S-curve profile shape of the Intermediate Deco Stops on Nitrox50, demphasizing the time at high ppO2 exposures at 21m and 18m which reduced the total overall CNS loading as tracked by a Petrel Dive Computer.