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Concept
Bühlmann decompression algorithm
Summary
The Bühlmann decompression set of parameters is an Haldanian mathematical model (algorithm) of the way in which inert gases enter and leave the human body as the ambient pressure changes. Versions are used to create Bühlmann decompression tables and in personal dive computers to compute no-decompression limits and decompression schedules for dives in real-time. These decompression tables allow divers to plan the depth and duration for dives and the required decompression stops.
The sets of parameters have been developed by Swiss physician Dr. Albert A. Bühlmann, who did research into decompression theory at the Laboratory of Hyperbaric Physiology at the University Hospital in Zürich, Switzerland.
The results of Bühlmann's research that began in 1959 were published in a 1983 German book whose English translation was entitled Decompression-Decompression Sickness. The book was regarded as the most complete public reference on decompression calculations and was used soon after in dive computer algorithms.
The model (Haldane, 1908) assumes perfusion limited gas exchange and multiple parallel tissue compartments and uses an inverse exponential model for in-gassing and out-gassing, both of which are assumed to occur in the dissolved phase.
Building on the previous work of John Scott Haldane (The Haldane model, Royal Navy, 1908) and Robert Workman (M-Values, US-Navy, 1965) and working off funding from Shell Oil Company, Bühlmann designed studies to establish the longest half-times of nitrogen and helium in human tissues. These studies were confirmed by the Capshell experiments in the Mediterranean Sea in 1966.
The basic idea (Haldane, 1908) is to represent the human body by multiple tissues (compartments) of different saturation half-times and to calculate the partial pressure of the inert gases in each of the compartments (Haldane's equation):
with the initial partial pressure , the partial pressure in the breathing gas (minus the vapour pressure of water in the lung of about 60 mbar), the time of exposure and the compartment-specific saturation half-time .
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