Numerical modelling of respiratory and inert gas exchange in healthy human lungs
Abstract
The mechanisms of gas transport in the lung occur within the detailed morphometry of the conducting airways. A computer model of the lung was developed based on the simultaneous convection-diffusion equation modified by the addition of a source term, which describes gas exchange between alveolar gas and blood, and a net alveolar flux boundary condition at the terminal lung generation, which allows for the evolution or uptake of the respiratory gases at the alveolar membrane in balance with body metabolism. The model was able to generate CO$\sb2$, O$\sb2$, and infused inert gas expirograms in a variety of morphometric models, including Weibel's model A, the model of Hansen and Ampaya, and models taken from Haefeli-Bleurer and Weibel. The model was used to study the effect of varying respiratory and morphologic parameters on dead space and phase III slope of the washout curve. Experimental data of expired tidal O$\sb2$, CO$\sb2$, He, and SF$\sb6$ during the continuous intravenous infusion of saline saturated with a mixture of the latter two gases in normal volunteers was obtained. The numerical model was able to generate expirograms with the same general shape as that obtained experimentally. Calculated phase III alveolar slope and dead spaces were significantly effected by airway geometry. In general, more rapidly flaring airways resulted in flatter slopes of phase III and smaller dead space fractions. Cardiac output had almost no effect on the calculated dead space. The phase III slopes and calculated dead spaces were inversely related to the gas diffusion coefficient. The model was able to show that the slope of the alveolar plateau of the CO$\sb2$ expirogram reflects persistence of concentration differences between inhaled gas and residual gas within the FRC and is exquisitely sensitive to changes which alter diffusive mixing in the distal airways.
Recommended Citation
Sherif R Gobran,
"Numerical modelling of respiratory and inert gas exchange in healthy human lungs"
(January 1, 1991).
Dissertations available from ProQuest.
Paper AAI9125652.
http://repository.upenn.edu/dissertations/AAI9125652
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