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More up to date information of method of measuring the diffusing capacity |
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In practice, the test is performed by having the test subject blow out all of the air that they can to reach [[residual volume]]. The person then takes a full [[vital capacity]] inhalation of a test gas mixture that contains a small amount of carbon monoxide (usually 0.3%) and some helium or other non-absorbed tracer gas. The test gas is held in the lung for about 10 seconds and then is exhaled from the lung. The first part of the expired gas is discarded and the next portion which represents gas from the alveoli is collected. By analyzing the concentrations of carbon monoxide and helium in the inspired gas and in the exhaled gas, it is possible to calculate how much carbon monoxide was taken up during the breath hold, and the partial pressure of carbon monoxide was during the breath hold. This method is known as the single-breath diffusing capacity test.
Other methods that are not so widely used at present can measure the diffusing capacity. These include the steady state diffusing capacity that is performed during regular tidal breathing, or the rebreathing method that requires rebreathing from a reservoir of gas mixtures. A more sophisticated "three-equation method" which involves fast responding analysers for the carbon monixide and a tracer gas such as helium has been developed. It monitors all parameters continuously and solves some of the technical problems of the traditional method but is more expensive to implement.
==Interpretation==
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