BRW
Contributor
Guys And Gals,
Just a quicky here. If you have seen, please move past.
Fumbling thru a couple of mailboxes, I got requests to
spell out differences between RGBM and VPM (again). Here's
a copy of that post on another site.
Thanks for all that great RGBM feedback and discourse.
But really thanks for pointing out differences/problems
with VPM vs RGBM. In the past, I have stepped on toes
explaining the whys and wherefores, and your observations
here underscore some probs and require me to once more
explain some points and major differences. Unlike some
comments that RGBM and VPM are siblings, they are really
distant. Neither the original VPM, nor the present incarnation
of Yount's original VPM. BTW, Yount did nice pioneering
bubble work which sent a wakeup call to the overall diving
community. And that was a great thing.
But onto RGBM vs VPM differences, which some already
have heard from me.
Important major fact is that RGBM for diving HAS BEEN
published, validated, tested, linked to diving data, and
released in Tables, meters, and software. VPM HAS NOT
(though the original VPM was published by Yount and
co-workers, but never tested, validated, folded over
data. etc). There were some probs with the original
VPM, and you guys have stumbled on one. There are others
for mixed gas, and constant ppO2, extended and shallow
range, plus others. On the application side, RGBM extrapolates
fairly well, and VPM does NOT from beaucoup comments.
RGBM has seen no DCS incidence in 100,000s of dives across
the rec and tec community. That's vitally important too.
Next onto nitty-gritty reasons for differences.
This is explained in RGBM In Depth, but I can touch on
some salient features here (also in Tech Diving In Depth
and Basic Deco Theory And Apps 2nd Ed):
1 -- RGBM is based on tissue and blood bubbles (lipid and
aqueous substances), while VPM uses info from gel
bubbles (colloids) in lab experiemts. Tissue and blood
bubbles have LITTLE in common with gel bubbles,
structure wise, formation wise, and reponse wise.
RGBM assigns what is called an equation of state (EOS)
to the skins (surfactants) coating the bubbles, and can be
mono to many molecular layers thick. The EOS depends
on pressure and temperature. VPM assigns NO structure
to the skins, and separates observed behavior in gels
into two regions, called permeable and impermeable,
and these two regions only correspond to bubbles
in colloidal solutions for gels;
2 -- RGBM DIFFUSES gas into and out of the bubbles using
the EOS to define diffusion lengths for gas transport,
that is, inert and active gases. VPM does NOT (because
the skins have no assigned structure nor diffusion lengths).
RGBM bubbles grow and contract as gas diffuses into and
out of them. The VPM bubble does NOT contract and
expand under gas diffusion across tissue bubble interfaces.
3 -- RGBM TRACKS Boyle expansion-contraction under pressure
changes using the EOS to link pressure, temperature
and bubble volume. VPM CANNOT do this (correctly) without
an EOS for the skin structures. Boyle response in real
tissue and blood bubbles is not the "ideal" case --
if pressure doubles, bubble volume does not half. It's
less, and RGBM uses the EOS to describe how much less.
4 -- RGBM TRACKS ALL bubbles excited into growth by pressure
changes to give a separated phase volume to control
staging. The RGBM excitation radius is a function of EOS
for skins, pressure, temperature, and gas mix. VPM's
radius is NOT, and uses an experimentally determined
radius for gel bubbles and pressure (deduced from
selected experimental range). And does NOT integrate
over the excited bubble distribution.
5-- RGBM extends to altitude, reverse profiles, short SIs,
multiday diving using EOS properties and bubble mechanics
folded over data. Original VPM did NOT address such. Can't
say what purveyors of VPM have done now. Nothing published
in reviewed journals.
There are some other points, but this covers major differences.
And these differences often show up dramatically when applied
to profiles and staging. And sometimes not.
I am mostly unaware what VPM code keepers today have
done to Yount's original model, but RGBM is spelled out in its
entirety in Technical Diving In Depth, RGBM In Depth, and
Basic Deco Theory And Apps, including field testing, validation,
references, and reported data in the RGBM Data Bank.
Cheers, and I am out of here for a bunch,ut:
Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr
Just a quicky here. If you have seen, please move past.
Fumbling thru a couple of mailboxes, I got requests to
spell out differences between RGBM and VPM (again). Here's
a copy of that post on another site.
Thanks for all that great RGBM feedback and discourse.
But really thanks for pointing out differences/problems
with VPM vs RGBM. In the past, I have stepped on toes
explaining the whys and wherefores, and your observations
here underscore some probs and require me to once more
explain some points and major differences. Unlike some
comments that RGBM and VPM are siblings, they are really
distant. Neither the original VPM, nor the present incarnation
of Yount's original VPM. BTW, Yount did nice pioneering
bubble work which sent a wakeup call to the overall diving
community. And that was a great thing.
But onto RGBM vs VPM differences, which some already
have heard from me.
Important major fact is that RGBM for diving HAS BEEN
published, validated, tested, linked to diving data, and
released in Tables, meters, and software. VPM HAS NOT
(though the original VPM was published by Yount and
co-workers, but never tested, validated, folded over
data. etc). There were some probs with the original
VPM, and you guys have stumbled on one. There are others
for mixed gas, and constant ppO2, extended and shallow
range, plus others. On the application side, RGBM extrapolates
fairly well, and VPM does NOT from beaucoup comments.
RGBM has seen no DCS incidence in 100,000s of dives across
the rec and tec community. That's vitally important too.
Next onto nitty-gritty reasons for differences.
This is explained in RGBM In Depth, but I can touch on
some salient features here (also in Tech Diving In Depth
and Basic Deco Theory And Apps 2nd Ed):
1 -- RGBM is based on tissue and blood bubbles (lipid and
aqueous substances), while VPM uses info from gel
bubbles (colloids) in lab experiemts. Tissue and blood
bubbles have LITTLE in common with gel bubbles,
structure wise, formation wise, and reponse wise.
RGBM assigns what is called an equation of state (EOS)
to the skins (surfactants) coating the bubbles, and can be
mono to many molecular layers thick. The EOS depends
on pressure and temperature. VPM assigns NO structure
to the skins, and separates observed behavior in gels
into two regions, called permeable and impermeable,
and these two regions only correspond to bubbles
in colloidal solutions for gels;
2 -- RGBM DIFFUSES gas into and out of the bubbles using
the EOS to define diffusion lengths for gas transport,
that is, inert and active gases. VPM does NOT (because
the skins have no assigned structure nor diffusion lengths).
RGBM bubbles grow and contract as gas diffuses into and
out of them. The VPM bubble does NOT contract and
expand under gas diffusion across tissue bubble interfaces.
3 -- RGBM TRACKS Boyle expansion-contraction under pressure
changes using the EOS to link pressure, temperature
and bubble volume. VPM CANNOT do this (correctly) without
an EOS for the skin structures. Boyle response in real
tissue and blood bubbles is not the "ideal" case --
if pressure doubles, bubble volume does not half. It's
less, and RGBM uses the EOS to describe how much less.
4 -- RGBM TRACKS ALL bubbles excited into growth by pressure
changes to give a separated phase volume to control
staging. The RGBM excitation radius is a function of EOS
for skins, pressure, temperature, and gas mix. VPM's
radius is NOT, and uses an experimentally determined
radius for gel bubbles and pressure (deduced from
selected experimental range). And does NOT integrate
over the excited bubble distribution.
5-- RGBM extends to altitude, reverse profiles, short SIs,
multiday diving using EOS properties and bubble mechanics
folded over data. Original VPM did NOT address such. Can't
say what purveyors of VPM have done now. Nothing published
in reviewed journals.
There are some other points, but this covers major differences.
And these differences often show up dramatically when applied
to profiles and staging. And sometimes not.
I am mostly unaware what VPM code keepers today have
done to Yount's original model, but RGBM is spelled out in its
entirety in Technical Diving In Depth, RGBM In Depth, and
Basic Deco Theory And Apps, including field testing, validation,
references, and reported data in the RGBM Data Bank.
Cheers, and I am out of here for a bunch,
ut:Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr
