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

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

 that is used to calculate the decompression stops needed for a particular dive profile

Dive profile

A dive profile is a two dimensional graphical representation of a dive showing depth and time.It is useful as an indication of the risks of decompression sickness and oxygen toxicity and also the volume of open-circuit breathing gas needed for a planned dive as these depend in part upon the depth...

. It was developed by D.E. Yount and others for use in professional diving and recreational diving

Recreational diving

Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...

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

In vivo

In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

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

University of Hawaii

The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...

 to calculate diving decompression tables.

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

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

), will grow upon decompression (when the diver ascends again). 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.

VPM model description articles:

• VPM Explained by Corrado Bonuccelli. An illustrated, easy to follow description of VPM principles and operation.
• VPM for Dummies by Kevin Watts. This article, published in both English and French in the International Cave Diving Magazine Plongeesout, provides divers a good working understanding of VPM.

Primary Modeling References

• Yount, D.E. and Hoffman, D.C. 1984. Decompression theory: A dynamic critical-volume hypothesis. In: Bachrach A.J.
  Arthur J. Bachrach
  Arthur J. Bachrach is an American psychologist and administrator, who was Professor and Chairman of the Department of Psychology at Arizona State University, and Director of the Environmental Stress Program and Chair of Psychophysiology at the Naval Medical Research Institute at the Naval Medical...
  
   and Matzen, M.M. eds. Underwater physiology VIII: Proceedings of the eighth symposium on underwater physiology. Undersea Medical Society
  Undersea and Hyperbaric Medical Society
  The Undersea and Hyperbaric Medical Society is the primary source of information for diving and hyperbaric medicine physiology worldwide.-History:The Undersea Medical Society grew from the close associations of a small group of scientists...
  
  , Bethesda, 131-146.
• Yount, D.E. and Hoffman, D.C. 1989. On the use of a bubble formation model to calculate nitrogen and helium diving tables. In: Paganelli, C.V. and Farhi, L.E. eds. Physiological functions in special environments. Springer-Verlag, New York, 95-108.
• Yount, D.E., Maiken, E.B., and Baker, E.C. 2000. Implications of the Varying Permeability Model for Reverse Dive Profiles. In: Lang, M.A. and Lehner, C.E. (eds.). Proceedings of the Reverse Dive Profiles Workshop. Smithsonian Institution, Washington, D.C. pp. 29–61.

VPM Research and Development References

• Kunkle, T.D. 1979. Bubble nucleation in supersaturated fluids. Univ. of Hawaii Sea Grant Technical Report 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. Isobaric Inert Gas Counterdiffusion Workshop. Undersea Medical Society
  Undersea and Hyperbaric Medical Society
  The Undersea and Hyperbaric Medical Society is the primary source of information for diving and hyperbaric medicine physiology worldwide.-History:The Undersea Medical Society grew from the close associations of a small group of scientists...
  
  , Bethesda, 90-125.
• Yount, D.E. and Hoffman, D.C. 1983. On the use of a cavitation model to calculate diving tables. In: Hoyt, J.W., ed. Cavitation and multiphase flow forum-1983. New York: American Society of Mechanical Engineers
  American Society of Mechanical Engineers
  The American Society of Mechanical Engineers is a professional body, specifically an engineering society, focused on mechanical engineering....
  
  , 65-68. ISSN: 9993289434

VPM Dive Planning Software

• Ultimate Planner VPM-B & VPM-B/U
• V-Planner VPM-B & VPM-B/E
• DecoPlanner VPM-B
• HLPlanner VPM-B
• JDeco VPM-B
• PalmVPM VPM
• DivePlan VPM
• Baltic Deco Planner VPM

VPM Dive computers

• V-Planner Live VPM-B & VPM-B/E
• MultiDeco-X1 VPM-B & VPM-B/E, with GF
• MultiDeco-DR5 VPM-B & VPM-B/E, with GF

External links

• VPM web site
• VPM development time line