A mathematical model of external respiration integrating component models of airway/lung mechanics, pulmonary circulation and gas exchange is presented. The airway system was lumped into: (1) a conducting zone consisting of a rigid compartment in series with a collapsible segment; and (2) a respiratory zone representing respiratory bronchioles and alveolar sacs. Ventilation of the alveolar space was simulated by driving the airway mechanics model with measured intrapleural pressure waveforms obtained experimentally from human subjects in a clinical Pulmonary Function Laboratory (PFL). Pulmonary circulation was described using a lumped tubular compartment with the variation in capillary blood volume being dependent on the surrounding alveolar pressure and the blood flow rates determined by the applied intrapleural pressure and alveolar volume. Gas exchange was described using a one-dimensional spatially distributed model with transport of gas species between air in the alveoli and blood in the pulmonary capillaries driven by the species partial pressure gradient across the alveolar-capillary barrier. The effects of fluctuation in airflow upon the gas composition in the partitioned airway compartments, as well as within the pulmonary capillary, were simulated under conditions of tidal breathing, panting, and forced-vital capacity maneuvers. Results from the model were compared against experimental data obtained in the PFL from normal subjects, and demonstrate the ability of the model in producing reasonable least-squares fits to data using model parameters obtained from a parameter estimation algorithm. The identified model parameters provide a compact description of airway and lung mechanics for an individual subject and may prove useful in assessing pulmonary function and gas exchange abnormalities
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