Determination of D CO by the single breath method in inhomogeneous lungs: Theory

Abstract

The effects of functional inhomogeneities in the lungs upon the single breath CO diffusing capacity were studied in theory. Non-uniform distribution of the alveolar tidal volume to the alveolar volume and unequal distribution of the diffusing capacity to the alveolar volume or to the pulmonary capillary flow were found to reduce the apparent single breath co, i.e. the D CO calculated ignoring the presence of such unequal distributions. The characteristic feature in the presence of unequal distributions of the diffusing capacity is a decrease of the apparent D CO with increasing times of apnoea. Approaches are described to arrive at the true D CO in presence of functional inhomogeneities in the lungs from data obtained from measurements of D CO by the single breath method.