The drainage routes of the bronchial blood flow in anesthetized dogs

It is generally accepted that the bronchial blood flow from extrapulmonary airways drains to the systemic veins through the bronchial veins, while that from the intrapulmonary airways drains into the pulmonary vasculature and eventually the left heart. This concept has not been confirmed by physiologic studies in live animals. We measured the routes taken by radionuclide-labeled Diethylenetriamine pentaacetate (DTPA) deposited in the extrapulmonary and the intrapulmonary airways in dogs. In living, anesthetized open chest animals, the pulmonary circulation of the left lower lobe was isolated and perfused with autologous heparinized blood. 99mTc DTPA was deposited on the mucosa of the extrapulmonary left mainstem bronchus just beyond the main carina (extrapulmonary deposition) and 111In DTPA on that of an intrapulmonary left lower lobe segmental bronchus (intrapulmonary deposition). Sequential blood samples from the right heart and from the isolated left lower lobe pulmonary circuit were counted for radioactivity, corrected for the volume in which they were distributed and for the bronchial blood that flowed into the isolated left lower lobe circuit, and expressed as the ratio of systemic to pulmonary drainage from each deposition site. The extrapulmonary tracer drained mostly to the systemic veins (84% of total) but also into the pulmonary circulation (16% of total). The intrapulmonary tracer drained mostly into the pulmonary circulation (70% of total) but also into the right heart (30% of total). Since tracers from both deposition sites drained to both circulations, the bronchial vasculature is continuous between the systemic (right heart) and the pulmonary circulation. Thus, it may provide a pathway for blood flow between the right and left heart.