A porous medium model of alveolar gas diffusion

A mathematical model based on the volume-averaging technique is derived for simulating the diffusion process within the alveolar region of the lung. T he derivation of this macroscopic model leads to a lung effective diffusivi ty that depends on the diffusivity and on the interface geometry of each al veolar constituent Unfortunately, describing the internal geometry of the a lveolar region for estimating the lung effective diffusivity is impractical . We found, however that the steady-state solution of the macroscopic model can be used to obtain the lung effective diffusivity once the lung diffusi ng capacity is known. A preliminary investigation considering a hypothetica l cubic domain representing the alveolar region of the lung is undertaken f or demonstrating the applicability of the method. Using characteristic valu es of capillary red blood cell density, alveolar volume, and lung diffusing capacity, the representative lung effective diffusivity is computed and sa tisfactorily compared with the molecular diffusivity of each constituent of the alveolar region.