UTD Ratio deco discussion

[ajduplessis]

The proof that the NEDU study clearly did NOT have too much deco, however, is in the pudding: Real-life human beings got bent at a rate notably higher than what I'd consider acceptable in my diving.

please remind me again of the notably higher DCS rate, 10%, 5%, 2%, <0.1 ?

 

[RayfromTX]

100%?

 

[ajduplessis]

Sorry to hear, I did not know you bend on all dives prior to the study.

Keep safe.

 

[victorzamora]

please remind me again of the notably higher DCS rate, 10%, 5%, 2%, <0.1 ?

I think you've misinterpreted the sentence you quoted. I'm not saying "normal" recreational Tech divers were getting bent at a high rate. I'm saying that the divers of the NEDU study got bent at a higher rate than I'd consider comfortable during the study.

One of the main arguments by the deep stop advocates is that there was far too much deco being done by the divers in the NEDU study. Divers in the NEDU study doing "way too much deco" were getting bent at rates high enough to stop the experiment early. Even the shallow-stop was producing DCS at a higher rate than I'd be happy with.

Those high DCS rates (both deep and shallow stop models) are not due to "excessive" deco. It's due to insufficient deco.

ETA: The rates of DCS in the study were 5.56% and 1.56% for the Deep and Shallow stop models, respectively. Even 1.56% is too much risk for my liking. The argument that they were doing "too much" deco is silly to me.

 

[RayfromTX]

So based on those numbers the deep stops divers were bent at a rate 356% higher than the shallow stops? I only remembered it being about 100% higher rate. That would be the higher rate I was referring to. There was really no need for the snarky response from ajduplessis. We should be able to discuss these issues in a positive and informative way. We are on the same side. No one has the answers.

 

[victorzamora]

So based on those numbers the deep stops divers were bent at a rate 356% higher than the shallow stops? I only remembered it being about 100% higher rate. That would be the higher rate I was referring to. There was really no need for the snarky response from ajduplessis. We should be able to discuss these issues in a positive and informative way. We are on the same side. No one has the answers.

The numbers from the study were 11/198 for the Deep Stops model and 3/192 DCS incidents in the Shallow Stops model. See here.

And yeah, I agree completely.

 

[Kevrumbo]

Going back to Erik C. Baker's excellent article explaining the trade-offs of utilizing Deepstops:

This is what GF 20/75 would look like for a 90msw depth, 20min BT (and by the implications of the NEDU Deepstop Study would still claim to be too deep):

Conversely, this tissue compartment graph would be a radical interpretation & application of the results of the NEDU Study with a much shallower first stop at 33msw (i.e. the first intermediate deco gas Nitrox36 switch). Note the huge over pressure gradient and supersaturation of the first five Fast Tissue Compartments.

(Anybody try this 90msw profile in figure 1 yet?)


The point is that @Dr Simon Mitchell 's suggestion of GF 50/80 seems to be a happy medium and better conservative starting value of gradient factors used in the de-emphasis of deepstops.

 

[Kevrumbo]

Found a "version" of the new Ratio Deco 2.0 Deep Stops Table:
http://www.utdspain.com/wp-content/uploads/2017/10/Ratio-Deco-2.0-Deepstop.pdf

UTD Instructors @Dan_P and @decompression , care to comment ?

 

[decompression]

Found a "version" of the new Ratio Deco 2.0 Deep Stops Table:
http://www.utdspain.com/wp-content/uploads/2017/10/Ratio-Deco-2.0-Deepstop.pdf

UTD Instructors @Dan_P and @decompression , care to comment ?

Hey Kev, just saw this recently, I still have issues in comparison knowing the standard gases used in the UTD dives as compared to the Air + Deco Air dives for the NEDU study.. I think you’re even better school’d than I am in how different gases affect the body.

 

[Kevrumbo]

Hey Kev, just saw this recently, I still have issues in comparison knowing the standard gases used in the UTD dives as compared to the Air + Deco Air dives for the NEDU study.. I think you’re even better school’d than I am in how different gases affect the body.

Yeah, but even the gas kinetics of Helium that RD presumed to be faster than Nitrogen in the body's representative tissue compartments is under attack:

. . .These findings have implications for decompression algorithms. The majority of decompression algorithms model the kinetics of inert gases in a collection of compartments with different time constants spanning the range of tissue kinetics relevant to decompression sickness. Decompression algorithms that accommodate multiple gases may assign different time constants to nitrogen and helium for the same compartment. This structure is appropriate for compartments with slow gas exchange, as evidenced by slower whole-body washout of nitrogen than of helium (3, 14). This slower washout of nitrogen than helium from tissues with slow gas exchange probably underlies the slower required decompression from nitrogen-oxygen than from helium-oxygen saturation dives (15). Saturation dives are hyperbaric exposures of sufficient duration that all body tissues have equilibrated with inspired inert gas partial pressure, and the slowest washout of gas from tissues limits the rate of decompression from such dives. However, some decompression algorithms assign faster time constants for helium than for nitrogen in all compartments (6). The present findings indicate this latter structure is not appropriate because nitrogen and helium exchange at similar rates in some tissues. For the best of the present models, the slowest compartment time constant for a normal blood flow state was V1/Q = 24 min [Note: Original Ratio Deco used 30min Tissue Compartment Half Time], which is relatively fast in terms of the collection of time constants used in decompression algorithms. The extent of gas uptake into compartments with fast time constants determines the deepest required de- compression stop for dives of insufficient duration for all body tissues to reach equilibration with inspired inert gas partial pressure (bounce dives). A deeper first decompression stop results in longer total decompression time. In model structures with faster helium than nitrogen uptake into fast compartments, a deeper first decompression stop and longer total decompression results from a helium-oxygen bounce dive than from a nitrogen-oxygen bounce dive to the same depth for the same bottom time. This behavior may be inappropriate, but few data exist that directly compare the decompression obligation resulting for helium-oxygen and nitrogen-oxygen bounce dives of identical depth and duration. . .
http://www.physiology.org/doi/pdf/10.1152/japplphysiol.00944.2014