Pulmonary gas transport characterization by a dynamic model

Abstract

A mathematical model is developed which describes and predicts pulmonary transport of N 2 and CO. The model is structured as a system of five well-mixed compartments, four of which have variable volumes, arranged in parallel and series. For this structure, the unsteady, mass-balance equations are derived and the effect of parameters investigated. The model may be used to simulate experiments of nitrogen washout and carbon monoxide uptake with normal subjects and those with chronic obstructive lung disease (COLD). With each subject, these experiments are conducted at several levels of tidal volume and frequency under controlled conditions. When all experiments of a subject are simulated, a set of parameter values is obtained that characterizes the volume and distensibility distributions in airways and alveoli and the CO mass transport across the pulmonary membrane. The model has been applied to analyze the differences between normal subjects and those with COLD. The parameters yield quantitative information about abnormal transport which is caused by greater volume inhomogeneities, more distensible airways, and apparently less effective surface area of the membrane. Finally, model and experimental studies show how the effective ventilation of a subject with COLD having a large FRC is improved by increasing Vt/Frc.