QUANTITATIVE-ANALYSIS OF TRANSPLEURAL FLUX IN THE ISOLATED LUNG

In this study, the loss of inert gas through the pleura of an isolated ventilated and perfused rabbit lung was assessed theoretically and ex perimentally A mathematical model was used to represent an ideal homog eneous lung placed within a box with gas flow (V box) surrounding the lung. The alveoli are assumed to be ventilated with room air (V A) and perfused at constant flow (Q) containing inert gases (x) with various perfusate-air partition coefficients (lambda(p,x)). The ratio of tran spleural flux of gas (V pl(x)) to its total delivery to the lung via p ulmonary artery (V (v) over bar), representing fractional losses acros s the pleura, can be shown to depend on four dimensionless ratios: 1) (lambda>(p,x) 2) the ratio of alveolar ventilation to perfusion (V A/ Q), 3) the ratio of the pleural diffusing capacity (Dpl(x)) to the con ductance of the alveolar ventilation (Dpl(x)/V A beta(g), where beta(g ) is the capacitance coefficient of gas), and 4) the ratio of extraple ural (box) ventilation to alveolar ventilation (V box/V A). Experiment s were performed in isolated perfused and ventilated rabbit lungs. The perfusate was a buffer solution containing six dissolved inert gases covering the entire 10(5)-fold range of lambda(p,x) used in the multip le inert gas elimination technique. Steady-state inert gas concentrati ons were measured in the pulmonary arterial perfusate, pulmonary venou s effluent, exhaled gas, and box effluent gas. The experimental data c ould be described satisfactorily by the single-compartment model. It i s concluded that a simple theoretical model is a useful tool for predi cting transpleural flux from isolated lung preparations, with known ve ntilation and perfusion, for inert gases within a wide range of lambda .