Abstract:
Rationale Efficient gas exchange depends on the close matching of blood and air delivered to the parenchymal tissue. Ventilation (V) and perfusion (Q) distributions are influenced by airway/vasculature geometry, by pressures to which the conduits are exposed, and by tissue deformation. We have developed computational models of V and Q, coupled to soft−tissue mechanical deformation. This modeling approach allows us to predict distributions in any posture, and provides quantification of gradients and heterogeneity. Method Computational models for airflow and blood flow through the airways and pulmonary arteries, respectively, are used to predict regional V and Q. Local tethering pressure and tissue compliance are obtained from a model that describes lung tissue deformation under gravity. Fluid flow is governed by conservation of mass and a modified 1D Poiseuille flow equation that includes a gravitational term, energy losses at bifurcations, and empirical pressure−area relationships describing conduit distensibility. Results Both V and Q are distributed preferentially to the gravitationally−dependent regions in all postures. There is a larger flow gradient in the gravitational direction in the supine posture compared to the prone posture, and significant isogravitational heterogeneity in V, Q, and V/Q matching. Whole lung heterogeneity compares well with measurements from imaging studies. Conclusions The difference in supine and prone flow gradients is due to the effect of the tree branching structures and a noticeable difference in regional tissue compliance in the two postures. Heterogeneity of results in isogravitational slices results from variability in path resistance in the asymmetric trees and heterogeneity in regional tissue compliance.
