Distribution of vascular resistance and compliance in a dog lung lobe

We have modeled the left lower dog lung lobe as three serial compartments, each containing resistance (R) and compliance (C). The intracompartmental arrangement of R and C was chosen to permit their evaluation from pressure data obtained following occlusion of the venous outflow. We found that two mathematically distinct models permitted evaluation of the distribution of R and C. The models were complementary in that when used together the R and C of the three compartments could be determined. The central compartment had 46% of the lobar vascular resistance and 75% of the lobar vascular compliance under control conditions. We found that serotonin and histamine, which increased the resistance proximal and distal to the central compartment, respectively, did not increase the central resistance. Therefore, we conclude that the central compartment includes the capillary bed. The equilibrium pressure (Pd), obtained when arterial inflow and venous outflow were simultaneously occluded, was in close agreement with the average preocclusion pressure of the central compartment, indicating that Pd is close to the pulmonary microvascular pressure.