Reduced Gradient Bubble Model
Encyclopedia
The reduced gradient bubble model (RGBM) is an algorithm
developed by Dr Bruce Wienke for calculating decompression stops needed for a particular dive profile
. It is based on the Varying Permeability Model
.
It is used in several dive computer
s, particularly those made by Suunto
, Mares, HydroSpace Engineering, and Underwater Technologies Center. It is characterised by the following assumptions: blood flow (perfusion
) provides a limit for tissue gas penetration by diffusion
; an exponential distribution
of sizes of bubble seeds is always present, with many more small seeds than large ones; bubbles are permeable to gas transfer across surface boundaries under all pressures; the haldanean tissue compartments range in half time
from 1 to 720 minutes, depending on gas mixture
.
Manufacturers such as Suunto have also devised approximations of Wienke's model. Suunto uses a modified haldanean nine-compartment model with the assumption of reduced off-gassing caused by bubbles. This implementation offers both a depth ceiling and a depth floor for the decompression stops. The former maximises tissue off-gassing and the latter minimises bubble growth.
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...
developed by Dr Bruce Wienke for calculating 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 is based on the Varying Permeability Model
Varying Permeability Model
The Varying Permeability Model, Variable Permeability Model or VPM is an algorithm that is used to calculate the decompression stops needed for a particular dive profile. It was developed by D.E. Yount and others for use in professional diving and recreational diving...
.
It is used in several dive computer
Dive computer
A dive computer or decompression meter is a device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.- Purpose :...
s, particularly those made by Suunto
Suunto
Suunto Oy, based in Finland, is a company that produces and markets sports precision instruments for Diving, Training and Outdoor sports. Headquartered in Vantaa, Suunto employs more than 500 people worldwide, and its products are sold in over 100 countries...
, Mares, HydroSpace Engineering, and Underwater Technologies Center. It is characterised by the following assumptions: blood flow (perfusion
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
) provides a limit for tissue gas penetration by diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
; an exponential distribution
Exponential distribution
In probability theory and statistics, the exponential distribution is a family of continuous probability distributions. It describes the time between events in a Poisson process, i.e...
of sizes of bubble seeds is always present, with many more small seeds than large ones; bubbles are permeable to gas transfer across surface boundaries under all pressures; the haldanean tissue compartments range in half time
Half time (physics)
The half time is the time taken by a quantity to reach one half of its final value, where the rate of change is proportional to the difference between the present value and the final value....
from 1 to 720 minutes, depending on gas mixture
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
.
Manufacturers such as Suunto have also devised approximations of Wienke's model. Suunto uses a modified haldanean nine-compartment model with the assumption of reduced off-gassing caused by bubbles. This implementation offers both a depth ceiling and a depth floor for the decompression stops. The former maximises tissue off-gassing and the latter minimises bubble growth.