Estimation of amount of stationary pulmonary blood from carbon monoxide uptake measurements.

A mathematical model of CO uptake from a single alveolus is modified to include stationary pulmonary blood arising from a pulmonary vascular obstruction. From this model an estimator model is developed that produces simultaneous estimations of the diffusing capacity of the lung for CO and the fraction of the pulmonary capillary blood that is stationary. The estimator model was tested using simulated data from uniform and non-uniform simulators and found to be only mildly sensitive to noise and incorrect values for the pulmonary capillary blood volume. Both the estimator model and breath-to-breath changes in the diffusing capacity of the lung for CO (exhaled) were found to be greatly affected by inhomogeneity of diffusing capacity and ventilation. At times both returned false positive results that limit their use as a screening test for stationary pulmonary blood. Although changes in CO uptake may at times indicate the presence of stationary pulmonary blood, the confounding effects of inhomogeneity of ventilation and diffusing capacity make the use of such changes impractical under most circumstances.