Simulations of washout experiments in postmortem rat lungs.

We developed a rat lung model to simulate single-breath and multiple-breath washout experiments performed by Verbanck et al. (J. Appl. Physiol. 71: 847-854, 1991) and González Mangado et al. (J. Appl. Physiol. 71: 855-862, 1991). The multi-branch-point rat lung model is based on anatomic data of the rat airway tree as obtained by Rodriguez et al. (Am. J. Anat. 180: 143-155, 1987). We simulated single- and multiple-breath washout maneuvers and computed the slope of the alveolar plateaus and Fowler and Bohr dead spaces. In general, the comparison between experiments and simulations shows a good agreement, suggesting that the mechanism of diffusion-convection interaction in an asymmetric structure entirely accounts for the ventilation maldistribution in the rat lung. In particular, it is shown that the marked asymmetry of the rat lung structure is responsible for the fact that He slopes are larger than SF6 slopes in rat lungs, as opposed to what is observed in other species.