The Varying Permeability Model, Variable Permeability Model or VPM is an

algorithm In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algo ...

that is used to calculate the decompression needed for ambient pressure

dive profile A dive profile is a description of a diver's pressure exposure over time. It may be as simple as just a depth and time pair, as in: "sixty for twenty," (a bottom time of 20 minutes at a depth of 60 feet) or as complex as a second by second grap ...

s using specified

breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed ...

es. It was developed by D.E. Yount and others for use in

professional A professional is a member of a profession or any person who work (human activity), works in a specified professional activity. The term also describes the standards of education and training that prepare members of the profession with the partic ...

and

recreational diving Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasur ...

. It was developed to model laboratory observations of bubble formation and growth in both inanimate and

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

systems exposed to pressure. In 1986, this model was applied by researchers at the

University of Hawaiʻi The University of Hawaiʻi System is a public college and university system in Hawaii. The system confers associate, bachelor's, master's, and doctoral degrees through three universities, seven community colleges, an employment training center, ...

to calculate diving

decompression tables There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures. Decompression o ...

. Several variations of the algorithm have been used in mobile and desktop dive planning software and om

dive computer A dive computer, personal decompression computer or decompression meter is a device used by an underwater diver to measure the elapsed time and depth during a dive and use this data to calculate and display an ascent profile which, according to ...

Theoretical basis

The VPM presumes that microscopic bubble nuclei always exist in water and tissues that contain water. Any nuclei larger than a specific "critical" size, which is related to the maximum dive depth (exposure

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

), will grow during decompression when the diver ascends. The VPM aims to minimize the total volume of these growing bubbles by keeping the external pressure sufficiently large and the inspired inert gas partial pressures relatively low during decompression. The model depends on the assumptions that different sizes of bubbles exist within the body, that the larger bubbles require less reduction in pressure to begin to grow than smaller ones, and that fewer large bubbles exist than smaller ones. These assumptions can be used to construct an algorithm that provides decompression schedules, designed to eliminate the larger, growing bubbles before they cause problems. ''Varying permeability'' refers to the layer of molecules surrounding the bubbles, which may vary in permeability to gas molecules in the bubble and the surrounding medium, and which affect the diffusion of gases between the surroundings and the bubble, and the variation of compressibility of the bubble under changes of pressure.

Bibliography

This bibliography list was compiled by E.B. Maiken and E.C. Baker as reference material for the V-Planner web site in 2002.

Primary Modeling Sources

* * * *

VPM Research and Development Sources

* * Kunkle, T.D. 1979. Bubble nucleation in supersaturated fluids. Univ. of Hawaii

Sea Grant The National Sea Grant College Program is a program of the National Oceanic and Atmospheric Administration (NOAA) within the U.S. Department of Commerce. It is a national network of 34 university-based Sea Grant programs involved in scientific r ...

Technical Repor
UNIHI-SEAGRANT-TR-80-01
Pp. 108. * * * * * * * * * * Yount, D.E. 1979. Multiple inert-gas bubble disease: a review of the theory. In: Lambertsen, C.J. and Bornmann, R.C. eds. . Undersea Medical Society, Bethesda, 90-125. * * * * * * * *

VPM Dive Planning Software

* V-Planner: VPM-B & VPM-B/E, VPM-B/FBO. * MultiDeco: VPM-B & VPM-B/E, VPM-B/FBO, ZHL-B, ZHL-C, GF, and GFS. * Ultimate Planner: VPM-B, VPM-B/U, VPM-B (Dec-12), VPM-B/U (Dec-12), ZHL-B, ZHL-C, ZHL-D, GF and GF/U. * DecoPlanner: VPM-B. * HLPlanner: VPM-B. * JDeco: VPM-B. * PalmVPM: VPM. * DivePlan: VPM. * Baltic Deco Planner: VPM-B. * Subsurface: VPM-B.

VPM Dive computers

* V-Planner Live: VPM-B & VPM-B/E. * MultiDeco-X1: VPM-B & VPM-B/E, VPM-B/FBO, ZHL-C, GF, and GFS. * MultiDeco-DR5: VPM-B & VPM-B/E, VPM-B/FBO, ZHL-C, GF, and GFS. * Shearwater Research Predator, Petrel, Perdix and NERD models: GF, VPM-B plus GFS. * RATIO Computers: iX3M series and iDive (Tech and Reb) series VPM-B and ZHL16-B. * TDC-3 with MultiDeco-TDC: VPM-B & VPM-B/E, VPM-B/FBO, ZHL-C, GF, and GFS. * HeinrichsWeikamp OSTC4: VPM-B

References

External links

VPM web site

{{authority control Decompression algorithms