Distribution of vascular resistance and compliance in a dog lung lobe

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Abstract
The left lower dog lung lobe was modeled as 3 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. 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 3 compartments could be determined. The central compartment had 46% of the lobar vascular resistance and 75% of the lobar vascular compliance under control conditions. Serotonin and histamine, which increased the resistance proximal and distal to the central compartment, respectively, did not increase the central resistance. Apparently, 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.