A continuum mechanics analysis of pulmonary vascular interdependence in isolated dog lobes.

The pressure-diameter (PD) behavior of intact pulmonary vessels was measured roentgenographically at several fixed deflation transpulmonary pressures (Ptp). At any constant vascular pressure (Pv), the intact-vessel diameter was larger for higher Ptp. The behavior of the parenchyma was described by a nonlinear analysis. An excised-vessel PD behavior was computed which was consistent with both nonlinear parenchymal behavior and measured intact-vessel PD behavior. Estimates of Px', the difference between the perivascular pressure and the pleural pressure, as a function of Ptp and Pv were obtained. For physiological values of Pv, mean values of Px' for arteries were -1 cmH2O at Ptp of 4 cmH20 and decreased almost linearly to -15 cmH20 at Ptp of 25 cmH2O. Veins showed a similar behavior, but Px' was more positive. Increasing Pv raised Px' and decreasing Pv lowered Px' at all values of Ptp. These results indicate that the interdependence effect is small at functional residual capacity, increases with lung inflation, and is greater for arteries than veins.