Distributions of vascular volume and compliance in the lung

The ether- and dye-dilution methods were used to estimate the arterial, capillary, and venous volumes anc compliances in isolated dog lung lobes. In the range of arterial pressure from ~7 to 14.5 Torr and venous pressure of 1.4 to 10.8 Torr, the total lobar blood volume ranged from ~2 to ~2.6 ml/kg body wt. About 19% of the lobar vascular volume was in the arteries, ~59% was in the capillaries, and ~22% was in the veins. The lobar vascular compliance was ~0.065 ml·Torr^-1·kg body wt^-1 with an arterial-capillary-venous distribution of ~30:49:21. These results suggest that the largest fractions of the intralobular blood volume and compliance are in the capillary bed. The segmental compliances along with outflow occlusion data were used to place lower and upper bounds on the arterial, capillary, and venous resistances. These bounds were 13.6 and 61.4% of the total vascular resistance for the arteries, 0 and 59.4% for the capillaries, and 5.5 and 64.9% for the veins, respectively. These bounds are rather broad, but they help to put the information content of the occlusion data under the conditions of these experiments into perspective.