Nonuniform pulmonary diffusing capacity measured by sequential CO uptake and washout.

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Abstract
Conventional methods for measuring DL (pulmonary diffusing capacity) can yield erroneous results when applied to the non-uniform lung. This paper describes a technique for assessing diffusion nonuniformity, the uptake-washout method, and illustrates its application to computer model-generated data. The method employs a computer analysis of steady-state CO uptake and CO- and He-washout data. Representing the lung as a two-compartment ventilation and diffusion system, the method identifies the range of over-all DL values and compartment characteristics which are compatible with the data. In the presence of diffusion-volume nonuniformity, DL is precisely defined. With diffusion-ventilation nonuniformity the data can be consistent with a variable DL. It is concluded that this approach, by identifying instances in which a range of DL values can explain the data, is more realistic than the DL methods currently employed.