ANATOMIC DISTRIBUTION OF PULMONARY VASCULAR COMPLIANCE

Previously, the pressure changes after arterial and venous occlusion h ave been used to characterize the longitudinal distribution of pulmona ry vascular resistance with respect to vascular compliance using compa rtmental models. However, the compartments have not been defined anato mically. Using video microscopy of the subpleural microcirculation, we have measured the flow changes in similar to 40-mu m arterioles and v enules after venous, arterial, and double occlusion maneuvers. The qua si-steady flows through these vessels after venous occlusion permitted an estimation of the compliance in three anatomic segments: arteries >40 mu m, veins >40 mu m, and vessels <40 mu m in diameter. We found t hat similar to 65% of the total pulmonary vascular compliance was in v essels <40 mu m, presumably mostly capillaries. The transient portions of the pressure and flow data after venous, arterial, and double occl usion were consistent with most of the arterial compliance being upstr eam from most of the arterial resistance and most of the venous compli ance being downstream from most of the venous resistance.