UTD Ratio deco discussion

[mikeny9]

Do you expect everyone who dives Buhlmann GFs to be able to compute m-values and fractions of them? I would imagine not. It's more the idea and reasoning behind it that's important.

 

[PfcAJ]

Do you expect everyone who dives Buhlmann GFs to be able to compute m-values and fractions of them? I would imagine not. It's more the idea and reasoning behind it that's important.

im not asking you to computer anything, just explain how you got to 66%.

"bubble theory" isn't how you end up with 66%.

 

[Diver0001]

I think the explanation is as easy as changing the rule from "divide by 4" to "divide by 3". How do we know that's right? Because AG said it was right.

I honestly think that this is how some of this stuff gets decided.

R..

 

[decompression]

An interesting read.....

Review of Deep Stops - Shearwater Research

 

[Kevrumbo]

Explain the math behind arriving at 66% and why its no longer 75%

im not asking you to computer anything, just explain how you got to 66%.

"bubble theory" isn't how you end up with 66%.

.

75% of max depth was a very conservative delta ambient pressure gradient estimate of the leading 5min Fast Tissue Compartment in which it just starts to barely desaturate.

The old rule of thumb was based on the leading 5min Fast Tissue Compartment being saturated to 75% in 2 half-lives. This new rule of 66% seems to be based on a lesser value of 1.5 half-lives. (See post #158 and #157 for reference of the UTD Ratio Deco Deepstops Paradigm: UTD Ratio deco discussion).

Whether this is "enough" of a deepstops de-emphasis is open to debate (@Dr Simon Mitchell 's opinion is that this rollback is a starting point, but still may be too deep. . .)

 

[PfcAJ]

75% of max depth was a very conservative delta ambient pressure gradient estimate of the leading 5min Fast Tissue Compartment in which it just starts to barely desaturate.

The old rule of thumb was based on the leading 5min Fast Tissue Compartment being saturated to 75% in 2 half-lives. This new rule of 66% seems to be based on a lesser value of 1.5 half-lives. (See post #158 and #159 for reference of the UTD Ratio Deco Deepstops Paradigm: UTD Ratio deco discussion).

Whether this is "enough" of a deepstops de-emphasis is open to debate (@Dr Simon Mitchell 's opinion is that this rollback is a starting point, but still may be too deep. . .)

Kev, you're like that kid that reminds the teacher that she forgot to collect the homework.

 

[Patoux01]

Really? Where is the science that "debunks" it?

There's never been science that "bunked" the oxygen window in the first place.

 

[Kevrumbo]

Simple Explanation of the Oxygen Window
by George Irvine
As a dope's explanation of the oxygen window concept for you Marines, the best gas differential would be a vacuum relative to a partial pressure, right? Oxygen is the next best as it creates a similar effect in that the sum of the gas partial pressures is unbalanced by the fact that some of the oxygen is metabolized, more in a fit person. The greater the difference between the oxygen and the other gases up to the max differential described by the metabolism ( maximum window ) , the greater the propensity for whatever is in the cells to come out and be displaced. For a fit person, the widow is wider and by definition so is his vascularity and perfusion, so he decompresses better. These things are all tied together.

You open the widow as wide as possible subject to 1) risk of tox or damage, 2) how long before the vaso constrictive effect offsets the benefit, 3) how long before the asthma like reaction sets in. You then alternate the process back to open up the vessels and lungs again, and repeat. All part of a good deco. Also it can be said that the sum of the inert gases is the other side of the oxygen window minus the metabolism drop of oxygen- there is no benefit to combining inerts - they act like one gas. Oxygen can be pushed to above its partial pressure effectiveness as a result of this imbalance for a "window" that then exceeds what would be the net effect of the partial pressures of the gases, and this is especially important in diminishing bubbles of inert gas as the pressure of the bubble can always be faced with a negative gradient or "tension" on the outside due to the fact that metabolized oxygen is creating a "vacuum" in the total sum of the partial pressures of the gases, leaving a consistent imbalance between bubble pressure and surrounding tension of any given inert.

This is why oxygen (pure, not 80/20) works so well in DCS cases after the fact to reduce bubbles, as well as the fact that saturation with oxygen tends to move that gas to where it is needed even if the vessels are blocked by damage.

Simple Explanation of the Oxygen Window | Global Underwater Explorers

Enlarging the oxygen window can only occur when PaO2 is increased to a maximum tolerated value, either by increasing depth or increasing FiO2 of the gas mix, or both. Although enlarging the oxygen window may not directly affect tissue gas removal, it does directly affect tissue on-gassing during decompression, which affects the amount of time required to decompress the tissue. . . (Breathing [100%] oxygen at a deeper depth has the advantage of a greater hydrostatic pressure to hold dissolved gas in solution. . . [but] Oxygen toxicity clearly limits the oxygen window to much lower values during in-water diving operations).

Furthermore, inert gas elimination is independent of depth during [100%] oxygen breathing. . . The gas partial pressure gradient for movement from tissue into blood is not controlled by ambient pressure; it is controlled by the gas partial pressure in the tissue and in arterial blood. As long as the arterial [inert] gas partial pressure is zero, the gradient for [inert] gas removal from tissue is maximal . . .It should be intrinsically obvious that removal of a gas from tissue can be speeded by elimination of the gas from the inspired mixture. If the arterial partial pressure of a gas is zero, then no gas will diffuse into tissue while the gas is diffusing out of the tissue. . .

Gas Exchange, Partial Pressure Gradients, and the Oxygen Window, Johnny E. Brian, Jr., M.D.

 

[Patoux01]

Sigh. Since what @boulderjohn already explained/telled in this thread did not work, I'll go for a pragmatic answer.

Why do you think no one is implementing an S-curve except UTD? Does only UTD understand deco? Why did GUE step away (as far as I understood that story) from the S-curve?
Isn't even UTD stepping back from it in UTD-RD 2.0 ?

 

[Kevrumbo]

Sigh. Since what @boulderjohn already explained/telled in this thread did not work, I'll go for a pragmatic answer.

Why do you think no one is implementing an S-curve except UTD? Does only UTD understand deco? Why did GUE step away (as far as I understood that story) from the S-curve?
Isn't even UTD stepping back from it in UTD-RD 2.0 ?

S-Curve in UTD RD 2.0 looks like it's more time weighted towards the 9m stop on Eanx50 in an attempt to "emulate" an ascending Buhlmann schedule stair-step profile shape.

In the original Classic RD version, the emphasis of the S-curve was deeper at the Eanx50 switch depth of 21m and at 18m -but again even with the change to a higher ppO2 of 1.6 at 21m on Eanx50, there's still that "NEDU/Time Integral of Supersaturation" effect acting on the slow tissues already loaded from the deepstops starting at what was then the 75% max depth rule.

So for example, for 20min of deco time in a S-curve starting from 21m over five deco stops to 9m depth on Eanx50, classical RD had a progression like: 6,6,2,2,4.

UTD RD 2.0 -if I understand @mikeny9 correctly- now does the S-curve something like: 3,3,4,4,6. (More weighted toward the 9m stop)

GUE still does (?) the straight linear progression: 4,4,4,4,4.