Fig. 1.

Schematic sketch of the modeling approach, with a scale separation distinguishing between the larger airways and blood vessels and the peripheral smaller respiratory and vascular units in the lung parenchyma. The larger airways and blood vessels are modeled as discrete zero-dimensional networks with the transported respiratory gases oxygen and carbon dioxide (shown on the top right), and the smaller respiratory and vascular units are modeled through a porous medium. The phases (tissue, air, and blood) and species ($O_2$ and $C{O}_2$) present in the porous domain are outlined on the bottom right