EFFECTS OF PULMONARY BLOOD-FLOW ON THE FRACTAL NATURE OF FLOW HETEROGENEITY IN SHEEP LUNGS

The spatial heterogeneity of pulmonary blood flow can be described by the relative dispersion (RD) of weight-flow histograms (RD = SD/mean). Glenny and Robertson (J. Appl. Physiol. 69: 532-545, 1990) showed tha t RD of flow in the lung is fractal in nature, characterized by the fr actal dimension (D) and RD for the smallest realizable volume element (RD(ref)). We studied the effects of increasing total pulmonary blood flow on D and RD(ref). In eight in situ perfused sheep lung preparatio ns, 15-mu m radiolabeled microspheres were injected into the pulmonary artery at five different blood flows ranging, in random order, from 1 .5 to 5.0 1/m. The lungs were in zone 2 at the lower flows and in zone 3 at the higher flows. The lungs were removed, dried, cut into 2 X 2 X 2-cm(3) pieces, weighed, and then counted for microsphere radioactiv ity. Fractal plots of log(weight) vs. log(RD) were constructed by iter atively combining neighboring pieces and then calculating RD with the increasingly larger portion size. D, which is one minus the slope of t he fit through this plot, was 1.14 +/- 0.09 and did not change as bloo d flow increased. However, RD(ref) decreased significantly (P < 0.01) as total flow increased. We conclude that the fractal nature of pulmon ary blood flow distribution is not altered by changes in overall flow.