Multiple Gradient factors?

[Jaap]

I have been thinking a bit about how gradient factors are used when mulitple inert gases are present in a mix, such as during trimixdiving.

Has anyone heard of someone using two sets of Low/Hi-GF, one for the He and one for the N2?

My thinking is that the maximum tolerable gradients could be different depending on if the leading tissue is limited by He or by N2. Can the tolerance be dependent on more than just the M-value of the different gasses? If there is a individual factor that is dependent on the type of gas this could merit another set of GFs?

Of course this would lead to even more parameters and make diveplanning more complex so my question is more on the theoretical level.

Another way of looking at another set of GFs for exach inert gas would be as a way of avoiding a He-induced DCS while in the water? As I have understood things a He-induced DCS could sometimes manifest itself a lot faster than a N2-DCS? By being more conservative on a He-GF one could maybe minimize the risk of getting a rapid DCS while still in the water?

Am I wrong here or? I just came to think about this possibility so I haven't made any deeper resarch into the question.

 

[padiscubapro]

Jaap once bubbled...
I have been thinking a bit about how gradient factors are used when mulitple inert gases are present in a mix, such as during trimixdiving.

Has anyone heard of someone using two sets of Low/Hi-GF, one for the He and one for the N2?

My thinking is that the maximum tolerable gradients could be different depending on if the leading tissue is limited by He or by N2. Can the tolerance be dependent on more than just the M-value of the different gasses? If there is a individual factor that is dependent on the type of gas this could merit another set of GFs?

Of course this would lead to even more parameters and make diveplanning more complex so my question is more on the theoretical level.

Another way of looking at another set of GFs for exach inert gas would be as a way of avoiding a He-induced DCS while in the water? As I have understood things a He-induced DCS could sometimes manifest itself a lot faster than a N2-DCS? By being more conservative on a He-GF one could maybe minimize the risk of getting a rapid DCS while still in the water?

Am I wrong here or? I just came to think about this possibility so I haven't made any deeper resarch into the question.

Do some more reading on Gfs.. You don't understand them.. the GF-low and GF high settings set the initial and final limits and determine the slope of the deco curve.. the GF factor is linearly adjusted from the gf-low up to the gf high...

Also basic deco theory treats inert gas loading as the total gas loading of a compartment, the inert gas doesn't matter its the total thats important..

Also the minumum bends depth for helium is always deeper than that of nitrogen...

 

[Jaap]

I'm sorry but I found your answer to be quite indirect? Or is it so that you didn't really read my question?

My question is about if anyone has been thinking of alternative ways of thinking on multiple inert gas loadings. Like if there is a possibility that the tolerance of the tissue could be related to the kind of inert gas and not just the total gas saturation of a compartment as the general theories state.

Would you care to elaborate on you statement- 'Also the minumum bends depth for helium is always deeper than that of nitrogen...' I don't really see how that answers my second question?

 

[Kendall Raine]

Sorry, but I'm not quite clear what you're asking. Are you suggesting different GF's for different inert gasses? If so, please know that the models use different coefficients (e.g. M's and R's), in both dual and dissolved phase models, specific to the inert gas used. For dissolved phase models, I believe these adjustments drive off relative solubility and diffusion properties. In dual phase (e.g. RGBM) other coefficients for bubble surface tension, excitation radii, etc are used to recognize that different inert gasses behave differently. In short, I'm not sure why different GF's would be needed.

If your question was do models recognize that inert gasses may not be inert (react, or cause metabolic reaction) differently, I think the only way this is really done is via the empirical tweaking, using Doppler studies, etc. that gets done to the coefficients ex- post. If you think about it, the empirical tweaking approach is the only one which makes sense since trying to figure out knock-on effects (e.g. complement system activation, differential blood filterability, etc.) is probably beyond the current state of the art.

Does this address your question?

 

[BRW]

Trying to tweak GFs for He and/or N2 separately
or together is a little like Russian Roulette.
Especially in the mixed gas, deco world.

GFs are not self-consistent, tested, nor rotely
applicable across the full diving spectrum. They
do not (cannot) generally do a complete job of
emulating full phase mechanics (dissolved gases
and bubbles).

Beware how you use them in their present state.

To see how they might be validated, check out
our early RGBM paper(s) on retrofitting GFs for
recreational diving and data,

"Reduced Gradient Bubble Model", B.R. Wienke,
Int J Biomed Comp 26, 237-256 (1990)

"Numerical Phase Algorithm For Decompression
Computers And Application", B.R. Wienke, Comp
Biol Med 22, 389-406 (1992)

Plus the refs listed there. These pubs are
the FIRST to introduce GFs in a tractable mode.
And only within recreational diving.

One day we may do the same for mixed gas and
deco diving.

In the deco world, full up phase models are
now a better choice than arbitrary GF knobs.

Saner, safer, and self-consistently tested.
As released in RGBM tables, meters, and software,
for instance.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[BRW]

Folks,

Also need to point out that how to handle GFs in the
shallow zone where long deco tails arise in pure Haldane
staging is FAR more critical then using them to juxtapose
deeps stops. While deep stops mainly hold down bubble inflation
in the early parts of the deco path, the shallow stops control
BOTH bubble growth and dissolved gas elimination, and remain
important (and while still eliminating much of the Haldane
deco tail). To do this, the whole deco profile needs an
integrated model approach, not just hodge podge GF patches
along the deco glide path.

BW

Earlier post

Trying to tweak GFs for He and/or N2 separately
or together is a little like Russian Roulette.
Especially in the mixed gas, deco world.

GFs are not self-consistent, tested, nor rotely
applicable across the full diving spectrum. They
do not (cannot) generally do a complete job of
emulating full phase mechanics (dissolved gases
and bubbles).

Beware how you use them in their present state.

To see how they might be validated, check out
our early RGBM paper(s) on retrofitting GFs for
recreational diving and data,

"Reduced Gradient Bubble Model", B.R. Wienke,
Int J Biomed Comp 26, 237-256 (1990)

"Numerical Phase Algorithm For Decompression
Computers And Application", B.R. Wienke, Comp
Biol Med 22, 389-406 (1992)

Plus the refs listed there. These pubs are
the FIRST to introduce GFs in a tractable mode.
And only within recreational diving.

One day we may do the same for mixed gas and
deco diving.

In the deco world, full up phase models are
now a better choice than arbitrary GF knobs.

Saner, safer, and self-consistently tested.
As released in RGBM tables, meters, and software,
for instance.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr