In this study we propose, and implement in the time domain, an anatomically consistent model of the respiratory system in critical care conditions that allows us to evaluate the impact of different ventilator strategies as well as of constrictive pathologies on the time course of acinar pressures and flows. We discuss the simplifications of the original Horsfield structure (Horsfield, K., et al. Models of the human bronchial tree. J. Appl. Physiol. 31:207-217, 1971), which were needed to enable the model implementation. The model has a binary tree structure including large airways represented as a combination of wall compliance and laminar resistance, small airways that have the same arrangement but can be heterogeneously constricted, and alveolar compartments that are viscoelastic second-order models to represent the stress adaptation behavior of lung tissue. We have described patient-ventilator interactions modeling the ventilator and the endotracheal tube. In conclusion this model makes it possible to investigate realistically the effect of homogeneous versus heterogeneous constrictive pathologies and the impact of different ventilatory patterns on pressure and flow distribution at the acinar level in the mechanically ventilated patient.