A modeling approach to the estimation of CO diffusing capacity.

Standard methods of measuring the diffusing capacity of the lung for CO are susceptible to inhomogeneity and to errors in the performance of a breathing maneuver by the subject. A mathematical model of CO uptake from a single alveolar lung is developed and used as the basis for an estimation procedure to measure both lung volume and diffusing capacity during a rebreathing maneuver. Because this estimator-model uses the exact flow generated by the subject, errors in such factors as breath-hold times or depth of inspiration do not result. The estimator-model was tested using simulated data from uniformly and nonuniformly ventilated models and was found to be insensitive to noise and inhomogeneity, in contrast to the diffusing capacity of the lungs for CO (exhaled). The estimator-model makes greater use of the available data than traditional methods by utilizing both the slope of the alveolar plateaus for CO and the relative heights of such plateaus in a rebreathing experiment.