A MODEL OF FLUID, ERYTHROCYTE, AND SOLUTE TRANSPORT IN THE LUNG

A mathematical model of fluid, solute, and red cell transport in the l ung has been developed that includes the effects of simultaneous chang es in lung vascular and interstitial volumes. The model provides separ ate arterial, microvascular, and venous pulmonary regions and a system ic vascular region in addition to a pulmonary interstitial compartment . Pressure, volume, hematocrit, flow, and concentration of up to 12 so lutes and tracers can be computed in each compartment. Computer code i s written in the C programming language, with Microsoft Excel serving as a user interface. Implementation is currently on PC-486 microcomput er systems, but the core program can easily be moved to other computer systems. The user can select different models for the blood-interstit ial barrier (e.g., multiple pore, nonlinear Patlak equation), osmotic pressure-concentration relationships (e.g., Nitta, Navar-Navar), solut e reflection coefficients, interstitial macromolecule exclusion, or ly mph barrier characteristics. Each model parameter or a combination of parameters can be altered with time in a predetermined fashion. The mo del is particularly useful in interpreting lung experimental data wher e simultaneous changes occur in vascular and extravascular compartment s. Several applications are presented and discussed, including interpr etation of optical filtration experiments, venous occlusion experiment s, external detection of macromolecular exchange, and blood-lymph stud ies that use exogenous tracers. A number of limitations of the model a re identified and improvements are proposed. A major strength of the m odel is that it is specifically designed to incorporate newly discover ed relationships as the field of lung physiology expands.