VASCULAR TREE STRUCTURE AFFECTS LUNG BLOOD-FLOW HETEROGENEITY SIMULATED IN 3 DIMENSIONS

Pulmonary arterial tree structures related to blood flow heterogeneity were simulated by using a symmetrical, bifurcating model in three-dim ensional space. The branch angle (Theta), daughter-parent length ratio (r(L)), branch rotation angle (phi), and branch fraction of parent fl ow (gamma) for a single bifurcation were defined and repeated sequenti ally through 11 generations. With phi fixed at 90 degrees, tree struct ures were generated with Theta between 60 and 90 degrees, r(L) between 0.65 and 0.85, and an initial segment length of 5.6 cm and sectioned into 1-cm(3) samples for analysis. Blood flow relative dispersions (RD %) between 52 and 42% and fractal dimensions (D-s) between 1.20 and 1. 15 in 1-cm(3) samples were observed even with equal branch flows. When gamma not equal 0.5, RD% increased, but D-s either decreased with gra vity bias of higher branch flows or increased with random assignment o f higher flows. Blood flow gradients along gravity and centripetal vec tors increased with biased flow assignment of higher flows, and blood flows correlated negatively with distance only when gamma not equal 0. 5. Thus a recursive branching vascular tree structure simulated D-s an d RD% values for blood flow heterogeneity similar to those observed ex perimentally in the pulmonary circulation due to differences in the nu mber of terminal arterioles per 1-cm(3) sample, but blood flow gradien ts and a negative correlation of flows with distance required unequal partitioning of blood flows at branch points.