A human acinar structure for simulation of realistic alveolar plateau slopes

We simulated the intra-acinar contribution to phase III slope (S-acin) for gases of differing diffusivities (He and SF6) by solving equations of diffusive and convective gas transport in multi-branch-point models (MBPM) of the human acinus. We first conducted a sensitivity study of S-acin to asymmetry and its variability in successive generations. S-acin increases were greatest when asymmetry and variability of asymmetry were increased at the level of the respiratory bronchioles (generations 17-18) for He and at the level of the alveolar ducts (generations 20-21) for SF6, corresponding to the location of their respective diffusion fronts. On the basis of this sensitivity study and in keeping with reported acinar morphometry, we built a MBPM that actually reproduced experimental S-acin values obtained in normal subjects for He, N-2, and SF6. Ten variants of such a MBPM were constructed to estimate intrinsic S-acin variability owing to peripheral lung structure. The realistic simulation of S-acin in the normal lung and the understanding of how asymmetry affects S-acin for different diffusivity gases make S-acin a powerful tool to detect structural alterations at different depths in the lung periphery.