Analysis of Bronchial Branching Pattern Using Inflated and Fixed Human Lung : With Special Reference to Comparison Between Daughter Branches and the Other Types of Branches

Numerous studies on bronchial branching pattern were performed in the 1960's using the bronchial cast. Weibel's symmetrical branching model is still very popular and was widely applied for physiological studies. However, it was confirmed by Horsefield et al. that a lot of asym- metrical dichotomy exists in human lungs. In Japan, Yamashita used the term daughter branches for smaller branches of asymmetrical dichotomy. The concept of daughter branches become important as a result of recent advances in the modality of image diagnosis which made it possible to visualize the inner zone in the transaxial plane. Although the outline of the daughter branches has already been reported, detailed measure- ment of daughter branches in comparison with the other types of branching has not yet been done. In this study, we measured the diameter and branching angle of almost all bronchi using a inflated and fixed lung prepared by Heitzman's method. The branching angles were determined using a three-dimensional image analyzing system. The bronchi were classified into several groups accord- ing to the branching patterns. Daughter branches and axial branches are the smaller and larger branches of asymmetrical dichotomy, respectively. Symmetrical branches are branches with sym- metrical dichotomy. The ratio of diameters of daughter, axial and symmetrical branches to parent branches were 0. 54±0.11, 0.91±0.10 and 0.77±0.15 （mean±S. D.）, respectively. The ratio of diameters of daughter, axial and symmetrical branches to other branches bifurcating from the same parent branch were 0. 61±0.15, 1.69±0.33 and 1.03±0.25, respectively. The branching angles of daughter, axial and sym- metrical branches were 56.3±19.6, 21.0±14.9 and 34.8±16.1, respectively. Daughter branches fre- quently exist in S? and S?. Ninety percent of the symmetrical and axial branches supplied the outer layer in the transaxial plane, however, almost the same percentage of daughter branches supplied the inner layer. The favorable ratio of diameters of one branch to another to select daughter branches from dichotomous branches was 0.75. These results are expected to contribute a great deal to the study of the influence of branching pattern on unhomogeneity in the transaxial plane of the human lung.departmental bulletin pape