Branching angles in the bronchial tree related to order of branching

Angles of branching in the bronchial tree were measured in one greyhound dog lung cast, and analysed from the data for man, dog, rat and hamster obtained by Raabe et al. (1976). The bronchial trees were ordered by both Strahler's and Horsfield's methods and angles classified by the value of delta, a measure of asymmetric branching defined as the difference in order between the branches forming the angle. Angles were also classified by their position in the bronchial tree, according to the order of the parent branch. It was found that whereas in the greyhound lung mean branching angle decreased with increasing order, there was no consistent trend in the data of Raabe et al., at least down to 3 mm diameter bonchi in man and 2 mm diameter bronchi in beagle dogs. There was, however, a decrease in main branch angle and an increase in minor branch angle with increasing delta.