MEASUREMENT OF PULMONARY BLOOD-FLOW BY FRACTAL ANALYSIS OF FLOW HETEROGENEITY IN ISOLATED CANINE LUNGS

Regional heterogeneity of lung blood flow can be measured by analyzing the relative dispersion (RD) of mass (weight)-flow data. Numerous stu dies have shown that pulmonary blood flow is fractal in nature, a phen omenon that can be characterized by the fractal dimension and the RD f or the smallest realizable volume element (piece size). Although infor mation exists for the applicability of fractal analysis to pulmonary b lood flow in whole animal models, little is known in isolated organs. Therefore, the present study was done to determine the effect of blood flow rate on the distribution of pulmonary blood flow in the isolated blood-perfused canine lung lobe by using fractal analysis. Four diffe rent radiolabeled microspheres (Ce-141, Nb-95, Sr-85, and Cr-51), each 15 mu m in diameter, were injected into the pulmonary lobar artery of isolated canine lung lobes (n = 5) perfused at four different flow ra tes (flow 1 = 0.42 +/- 0.02 l/min; flow 2 = 1.12 +/- 0.07 l/min; flow 3 = 2.25 +/- 0.17 l/min; flow 4 = 2.59 +/- 0.17 l/min), and the pulmon ary blood flow distribution was measured. The results of the present s tudy indicate that under isogravimetric blood flow conditions, all reg ions of horizontally perfused isolated lung lobes received blood flow that was preferentially distributed to the most distal caudal regions of the lobe. Regional pulmonary blood flow in the isolated perfused ca nine lobe was heterogeneous and fractal in nature, as measured by the RD. As flow rates increased, fractal dimension values (averaging 1.22 +/- 0.08) remained constant, whereas RD decreased, reflecting more hom ogeneous blood flow distribution. At any given blood flow rate, high-f low areas of the lobe received a proportionally larger amount of regio nal flow, suggesting that the degree of pulmonary vascular recruitment may also be spatially related.