Branching architecture of canine pulmonary arteries: a quantitative cast study

The purpose of this investigation is to analyze the branching pattern of pulmonary artery. The excised right lower lobes of six mongrel dogs were fixed by perfusion with 1.2% glutaraldehyde solution. Pressure of the pulmonary artery, vein and airway were controlled during perfusion. After fixation, resin was injected manually into the artery. When resin was completely polymerized, the lung was placed in 15 N NaOH solution to remove lung tissue. The diameters and lengths of branches were measured by stereomicroscopy. The results obtained were as follows: The basically dichotomous pulmonary arteries showed not only fairly regular dichotomies but monopodies, in the latter of which the diameter of parent branch was almost the same as that of its larger daughter branch. The diameter of monopodial branch was less than 500 microns, even when the parent branch was a large central segment. In arteries of over 1,000 microns in diameter, 75% or more of branchings were monopodies, whereas in small arteries of 200-300 microns in diameter, half the bifurcations were monopodies. At a bifurcation, the average daughter-to-parent diameter ratio was 0.8-0.9 for the larger daughter branch and 0.5 for the smaller one. The average length of branches was in proportion to their average diameter.