SERIAL DISTRIBUTION OF AIRWAY DIAMETERS FROM INPUT IMPEDANCE AND COMPUTED-TOMOGRAPHY

Indirect measures of airway diameter such as respiratory system input impedance (Z(in)) have been widely used to infer or quantify bronchoco nstriction, or bronchodilation. One such measure, Z(in) above 100 Hz h as been shown to be primarily influenced by airway geometry and airway walls but not by lung and chest wall tissues. We used a recently deve loped method based on a complex asymmetrically branched network of tub es with nonrigid walls to analyze Z(in) from 100 to 2,000 Hz in contro l and bronchoconstricted (histamine injection) dogs. The resulting est imates of airway diameters indicated that peripheral airways were cons tricted far more (approximate to 30% of their control diameters) than central airways (i.e., 0% in the trachea). Separate measurements of ch anges in airway diameters were made in an excised dog lung using high resolution computed tomography. The observed changes in airway diamete r between lung volumes of total lung capacity (TLC) and functional res idual capacity (FRC) were quantitatively consistent with those obtaine d from Z(in) data in our control dogs at FRC. We conclude that this sy stems identification method can be used to estimate the distribution o f airway diameters from Z(in).