Decompression theory: Difference between revisions

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If the concentration of the inert gas in the breathing gas is reduced below that of any of the tissues, there will be a tendency for gas to return from the tissues to the breathing gas. This is known as [[outgassing]], and occurs during decompression, when the reduction in ambient pressure or a change of breathing gas reduces the partial pressure of the inert gas in the lungs.<ref name="USNDM R6 3-9.3" />

The combined concentrations of gases in any given tissue will depend on the history of pressure and gas composition. Under equilibrium conditions, the total concentration of dissolved gases will be less than the ambient pressure, as oxygen is metabolised in the tissues, and the carbon dioxide produced is much more soluble. However, during a reduction in ambient pressure, the rate of pressure reduction may exceed the rate at which gas can be eliminated by diffusion and perfusion, and if the concentration gets too high, it may reach a stage where bubble formation can occur in the supersaturated tissues. When the pressure of gases in a bubble exceedexceeds the combined external pressures of ambient pressure and the surface tension from the bubble - liquid interface, the bubblesbubble will grow, and this growth can cause damage to tissues. Symptoms caused by this damage are known as [[decompression sickness]].<ref name="USNDM R6 3-9.3" />

The actual rates of diffusion and perfusion and the solubility of gases in specific tissues are not generally known, and they vary considerably. However, mathematical models have been proposed which approximate the real situation to a greater or lesser extent, and these models are used to predict whether symptomatic bubble formation is likely to occur for a given pressure exposure profile.<ref name="Huggins 1992 Chapter 1" />