Site of functional bronchopulmonary anastomoses in sheep

The location of bronchopulmonary anastomoses has long been a topic of discussion, and pre-, post-, and capillary sites have all been demonstrated in postmortem examinations. However, there have been few studies that have provided insight into the patency and function of these anastomoses in the intact lung. To identify these functional sites where the bronchial circulation anastomoses with the pulmonary circulation, we studied sheep lungs in situ serial sectioned with high-resolution computed tomography (CT). Differences in radiodensities of blood, air, and nonionic contrast medium were used to differentiate and localize airways and vessels and to identify the effluent from the bronchial circulation. After an initial series of scans to identify the pulmonary arteries and veins adjacent to airways 2-12 mm in diameter, contrast material was infused into the bronchial artery. In three sheep, the major accumulation of contrast medium was found in pulmonary veins. In one of the sheep, a comparable number of pulmonary arteries and veins contained contrast medium. Serial histologic sections were able to identify small bronchial venules lying within subepithelial bronchial folds that drain directly into pulmonary veins. These results using serial CT and histologic images suggest that drainage from the intraparenchymal bronchial vasculature is predominantly into postcapillary pulmonary vessels.