LONGITUDINAL DISTRIBUTION OF OZONE ABSORPTION IN THE LUNG - SIMULATION WITH A SINGLE-PATH MODEL

A one-dimensional unsteady state diffusion model was used as a basis f or simulating the absorption (Lambda), breakthrough (V-B), and dispers ion (sigma(2)) of inhaled ozone boluses as a function of penetration ( V-P) into intact human lungs. The model idealized the respiratory syst em as a single equivalent tube with cross-sectional and surface areas that varied as a function of longitudinal position. Longitudinal gas t ransport in the lumen of the equivalent tube occurred by the joint act ion of bulk how and a dispersion coefficient, D. Lateral absorption be tween respired gas and the tube wall was characterized by an overall m ass transfer coefficient, K. By inputting published values of anatomic dimensions scaled to a 160-ml conducting airway volume, D values prev iously reported for inert insoluble gases, and K values equal to gas-p hase transfer coefficients determined in physical lung models, a reaso nable simulation of the Lambda-V-P distribution measured at a 250 ml/s ec respiratory flow was obtained. Simulations of the corresponding V-B -V-P and sigma(2)-V-P distributions both exhibited the correct shapes but underestimated the actual values. Although the addition of an esti mated tissue resistance to K resulted in a poorer simulation of the da ta, an increase in conducting airway volume from a value of 160 ml est imated by the subjects' CO2 dead space to a value of 200 ml substantia lly improved the V-B-V-P and sigma(2)-V-P simulations without sacrific ing the quality of the Lambda-V-P simulation. We conclude that the inc lusion of a tissue diffusion resistance is not necessary to properly s imulate bolus inhalation data during quiet breathing, but a reliable m easurement of conducting airway volume is crucial. (C) 1996 Academic P ress, Inc.