Site of functional bronchopulmonary anastomoses in sheep

The location of broncrhopulmonary anastomoses has long been a topic of disc ussion and pre-, post-, and capillary sites have all been demonstrated in p ostmortem examinations. However, there have been few studies that; have pro vided insight into the patency and function of these anastomoses in the int act 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). Difference s in radiodensities of blood, air, and nonionic contrast medium were used, to differentiate and localize airways and vessels and to identify the efflu ent from the bronchial circulation. After an initial series of scans to ide ntify the pulmonary arteries and veins adjacent to airways 2-12 mm in diame ter, contrast, material was infused into the bronchial artery. In three she ep, 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 dr ain directly into pulmonary veins. These results using serial CT and histol ogic images suggest that drainage from the intraparenchymal bronchial vascu lature is predominantly into postcapillary pulmonary vessels. Anat Rec 254: 360-366, 1999. a 1999 Wiley-Liss, Inc.