Nautilus DIVE PLANNER Version 1.0 사용자 설명서
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VERSION 1.0
VERSION 1.0
VERSION 1.0
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VERSION 1.0
3.6 Variable Permeability Model (VPM)
Dr. David Yount created the Variable Permiablilty Model
that takes into account the suspiscion that sub-clinical
bubbling occurs on every dive of significant depth and/or
time. The VPM-A, VPM-B, VPM-E and RGBM models
were derived from this work initially done by Yount and are
very popular with technical divers today.
that takes into account the suspiscion that sub-clinical
bubbling occurs on every dive of significant depth and/or
time. The VPM-A, VPM-B, VPM-E and RGBM models
were derived from this work initially done by Yount and are
very popular with technical divers today.
The following is an excerpt from Eric Maiken who has
done a significant amount of work with VPM
done a significant amount of work with VPM
The Varying Permeability Model (VPM) was developed to
model laboratory observations of bubble formation and
growth in both inanimate (never been alive) and in vivo (soon
dead) systems exposed to pressure. In 1986, this model
was applied by researchers at the University of Hawaii to
calculate Diving Decompression Tables (Reference 1).
Although the original VPM is considered dated by specialists
in hyperbaric medicine, the time lag between the formulation
and public release of the latest decompression methods has
left many divers following ascent schedules that are justified
by obsolete Victorian era physical models. Further
compounding the problem is the widespread use of
commercial decompression software with excessive arbitrary
parameters hiding behind siren-song front-ends that allow
programmers to dish out crucial physiological advice. Finally,
the mathematical and physical bases of the bubble models
have kept them inaccessible to all without degrees in physics
or math and so, apart from reports filtering back from the
front lines, few have understood, seen or used this stuff. So,
caveat emptor —and beware too!
model laboratory observations of bubble formation and
growth in both inanimate (never been alive) and in vivo (soon
dead) systems exposed to pressure. In 1986, this model
was applied by researchers at the University of Hawaii to
calculate Diving Decompression Tables (Reference 1).
Although the original VPM is considered dated by specialists
in hyperbaric medicine, the time lag between the formulation
and public release of the latest decompression methods has
left many divers following ascent schedules that are justified
by obsolete Victorian era physical models. Further
compounding the problem is the widespread use of
commercial decompression software with excessive arbitrary
parameters hiding behind siren-song front-ends that allow
programmers to dish out crucial physiological advice. Finally,
the mathematical and physical bases of the bubble models
have kept them inaccessible to all without degrees in physics
or math and so, apart from reports filtering back from the
front lines, few have understood, seen or used this stuff. So,
caveat emptor —and beware too!
The VPM presumes that microscopic voids, cavities, nuclei
exist in water, and tissues that contain water before the start
of a dive. Any nuclei larger than a specific “critical” size,
which is related to the maximum dive depth (exposure
pressure), will grow upon decompression. The VPM aims
to minimize the total volume of these growing bubbles by
keeping the external pressure large, and the inspired inert
gas partial pressures low during decompression.
exist in water, and tissues that contain water before the start
of a dive. Any nuclei larger than a specific “critical” size,
which is related to the maximum dive depth (exposure
pressure), will grow upon decompression. The VPM aims
to minimize the total volume of these growing bubbles by
keeping the external pressure large, and the inspired inert
gas partial pressures low during decompression.
It is important to note that the total decompression times
generated by the simplified VPM were FORCED to be
similar to the US NAVY Standard/Exceptional Air deco
times. However, much of the decompression time is deeper
than the USN depths. Presumably, a diver would evolve
fewer bubbles using a VPM schedule than on the Navy
table. This is not very stringent once you consider the risky
(O2 & bends) nature of the old USN exceptional exposure
tables. Yount and Hoffman might better have forced the times
to look like Buhlmann’s for conservatism. The parameters
in the open source code produce Bühlmann-like no-stop
times, and total decompression times between the old USN
tables and the Bühlmann tables.
generated by the simplified VPM were FORCED to be
similar to the US NAVY Standard/Exceptional Air deco
times. However, much of the decompression time is deeper
than the USN depths. Presumably, a diver would evolve
fewer bubbles using a VPM schedule than on the Navy
table. This is not very stringent once you consider the risky
(O2 & bends) nature of the old USN exceptional exposure
tables. Yount and Hoffman might better have forced the times
to look like Buhlmann’s for conservatism. The parameters
in the open source code produce Bühlmann-like no-stop
times, and total decompression times between the old USN
tables and the Bühlmann tables.
Why are VPM Decompression Tables so Similar to
the RGBM Tables?
the RGBM Tables?
Why have VPM tables always been so similar to Bruce
Wienke’s RGBM tables? Until 2002, this was simply
because the RGBM was essentially the same as the VPM
for a single decompression dive. Even though Wienke claims
to have “abandoned” VPM, his publications and publicity
from vendor partners belive this as marketing over
substance. Wienke apparently still uses core elements of
Yount and Hoffman’s VPM algorithm as a basis for the
RGBM. Even today, in 2004, it can be demonstrated from
commercial programs that the “full-up” RGBM is still
underpinned by Yount and Hoffman’s iterative algorithm.
With the wide distribution of open source VPM, Wienke
was placed under pressure to differentiate his product by
customers who had paid for material that could be obtained
virtually for free. Since 2002, this has resulted in a new
RGBM model, publicized in dive industry print and venues.
Nonetheless, as demonstrated by the close correlation of
ascent data for VPM and RGBM, this work has actually
only resulted in incremental adjustments of the model. You
pay your money and you take your chances.
Wienke’s RGBM tables? Until 2002, this was simply
because the RGBM was essentially the same as the VPM
for a single decompression dive. Even though Wienke claims
to have “abandoned” VPM, his publications and publicity
from vendor partners belive this as marketing over
substance. Wienke apparently still uses core elements of
Yount and Hoffman’s VPM algorithm as a basis for the
RGBM. Even today, in 2004, it can be demonstrated from
commercial programs that the “full-up” RGBM is still
underpinned by Yount and Hoffman’s iterative algorithm.
With the wide distribution of open source VPM, Wienke
was placed under pressure to differentiate his product by
customers who had paid for material that could be obtained
virtually for free. Since 2002, this has resulted in a new
RGBM model, publicized in dive industry print and venues.
Nonetheless, as demonstrated by the close correlation of
ascent data for VPM and RGBM, this work has actually
only resulted in incremental adjustments of the model. You
pay your money and you take your chances.