Sunday, October 09, 2005

Pearls from the Past - REDUCED GRADIENT BUBBLE MODEL

In our DiveMed Newsletter for Feb 15, 2002, we had the following question and answer(s). These have initiated a really great response from Bruce Wienke et al regarding the differences between the VPM and RGBM bubble models.

Q: Can you explain the difference between VPM and RGBM deco models?
A:
The RGBM is based on the VGM. (Variable Permability Model)
You can read articles by Bruce Wienke on the RGBM here:
http://www.abysmal.com/pages/articles.html . Wienke's book on decompression theory, Basic Decompression Theory and Application (out of print) has additional information and graphs.


While there is little information on the RGBM there is extensive information on the earlier VPM algorithm. Eric Baker's articles and Fortran source code can be found here:
ftp://ftp.decompression.org/pub/Baker/

Along with the information and source codes for the VPM algorithm there is a page discussing aspects of the RGBM with graphs.
http://www.decompression.org/maiken/VPM/VPM_Publications.htm

Useful Articles for tech diving, DIR, Deep stops, etc
http://www.geocities.com/Pipeline/Shore/4331/articles.htm


Here is Bruce Wienke's response to our answers:

Just read your Newsletter Mailbox answer to question about RGBM vs VPM. There is quite a bit more all should know (major differences) -- actually the RGBM abandons the gel physics of the VPM as NOT applicable in toto to blood and tissue. With all due respects to my friend and decreased colleague, David Yount, I must go on record as NOT accepting that VPM gel dynamics apply routinely to the body, nor the properties he studied. Such VPM type bubble seeds have NEVER been found in the body -- nor outside of "gel-like" media. RGBM (EOS) bubbles do recover VPM bubbles in limiting circumstance of material strength and pressure, but that is not important to the RGBM. Naturally occuring bubble "seeds" in the atmosphere and oceans are NOT akin to VPM gel bubbles -- NOR should they be. The body, oceans, and atmosphere are NOT gel.

Consider comments:

1) RGBM does NOT use (VPM) gel bubbles as model for tissue and blood bubbles;

2) RGBM deduces bubble persistence time scales (how long they hang around) FROM seed skin structures (lipid or aqueous), not a-priori weeks as ASSUMED in the VPM;

3) RGBM bubbles are permeable to gas transfer DEPENDING on their skin structure always, NOT at some cutoff pressure as in the VPM gel studies;

4) biophysical equations-of-state (EOS) for lipid and aqueous substances relate seed pressure, temperature, diffusivities to gas transfer, and skin structure in the RGBM, and, as such, are OUTSIDE the VPM;

5) the RGBM transfers gas across the bubble interfaces, the VPM does NOT;

6) See new book "Technical Diving In Depth" by Wienke (Best) for more on same subject.

7) RGBM tables (NAUI Tec nitrox, heliox, trimix Tables), meters (Suunto, Plexus, HydroSpace, "new" ones), and commercial software (ABYSS and some Tim O'Leary and I will release) ABOUND (the past 3 - 4 years), and collectively have logged many 10,000s of technical and recreational dives with only a 2 reported cases of DCS So, RGBM DCS incidence rate is virtually zero, especially on the technical envelope where it matters most as a model test. NOT SO to my best knowledge for the VPM as far as validation, testing and use, though the crude dynamics are likely similar.

8) RGBM successes span technical deco, altitude, and mixed gas diving, which are the real test of any model. Recreational diving is a rather simple limit point for the RGBM -- albeit, an important one just considering diver numbers, but one that tests virtually nobody's deco or staging mode, except for repetitive and reverse profile diving maybe.

9) the RGBM bootstraps parameters to diving data (DCS rate) using maximum likelihood, the VPM does NOT.

10) NAUI RGBM Tables for the recreational diver on air, EAN32, EAN36, from sea level to 10,000 ft elevations have been tested over the past few years, and are being released as simple, no-calc, no group, no-bull tables with simple rules for repets, flying-after-diving, SIs, etc, etc. Check with NAUI Hdqts, or NAUI Tec Ops

11) NAUI RGBM Tec Tables have been forged over the past 8 yrs from operations of the LANL Countermeasures Team, NAUI Tec Instructor Training Courses, reported WKPP extreme diving profiles, and 100s of field reports graciously sent to me (us) by the technical community. (see TDID for more here).

12) Deep stops are natural to both the RGBM and VPM, but RGBM deep stops have NAUI Tec tests and stamps of approval down to 300 fsw on trimix -- ditto for the LANL Team.

13) RGBM modified Haldane meter algorithms are bubble folded schemes that exist in some deco meters, and have been used very successfully for repetitive, reverse profile, and multiday apps, but NOT so with the VPM.

NAUI Worldwide currently has trimix and hyperoxic trimix RGBM tables imbedded within the currently published NAUI trimix instructor guide (since 1998). These tables range from 100 fsw to 240 fsw.

Altitude tables from 2000 to 5000 feet and 5000 to 10000 feet for air and nitrox 32 and 36.

Trimix tables from 80 fsw to 350 fsw with mixes of 16/40 and 10/60

Constant PO2 tables (1.3 and 1.4) for nitrox and trimix from 60 fsw to 350 fsw with bottom times up to 180 minutes. Nitrox tables for FO2's of 28, 30, 32, 36, 40, 50 RGBM Hyperoxic trimix for depth between 80 and 150 fsw with and with out oxygen deco.

Recreational No stop , no calculation RGBM tables are also being published on plastic by NAUI Worldwide for air and nitrox from sea level to 10000 altitude.
These tables are full up RGBM and will not include RNT's and Pressure groups as seen in dissolved gas models. But will instead have delta P's with no stop limits for repts.

Drs Wienke and Tim O'Leary have kindly provided us with the following pdf articles that should be quite helpful in clearing up any confusion.
REDUCED GRADIENT BUBBLE MODEL:
DIVING ALGORITHM, BASIS, AND COMPARISONS (without formulae)
http://www.scuba-doc.com/rgbmim.pdf

REDUCED GRADIENT BUBBLE MODEL:
DIVING ALGORITHM, BASIS, AND COMPARISONS (with formulae)
http://www.scuba-doc.com/rgbm.pdf