The ischemic lung: Role of the bronchial arteries in lung function

A patient with a dissecting aortic aneurysm, Type 1, developed acute pulmonary edema unexplained by the usual etiologic factors. Pathologic evidence that bronchial arterial circulation was interrupted led us to hypothesize that pulmonary edema could be due to ischemia of the bronchial circulation. To test this hypothesis, two chronic studies were done in dogs. The first study consisted of selective ligation of the right posterior bronchial artery at its origin at the fifth or sixth intercostal artery. After recovery from surgery, biopsies were taken from the ipsilateral and contralateral lung at time periods from 5 hours to 11 days. Ischemic damage was found in seven of eight dogs (87.5%), and was confined to the right lung. Histological examination revealed initial congestion within 8 hours, followed by pulmonary edema within 72 hours, and finally, disruption of alveolar septa with small emphysematous bullae on the eleventh postoperative day. The left lung remained normal in histological appearance. The second study consisted of transplanting the bronchial artery to the pulmonary artery to create a low pressure system and low O(2) content, and to simulate a regional shock situation. In five of six dogs (83.3%), the anastomosis was occluded within 72 hours, probably due to pressure competition from small collateral bronchial circulation. However, in these five dogs, pulmonary vascular resistance increased by 53%, intrapulmonary shunting increased by 83%, and the alveolar-to-arterial oxygen gradient increased by 150 mm Hg. Pulmonary edema was again confined to the right lung. Bronchial arteriograms demonstrated the extensive and variable distribution of the bronchial circulation in dogs. In the sixth dog, the anastomosis remained patent with a left-to-right shunt, due to a larger bronchial arterial collateral circulation. In this animal, the pulmonary arterial resistance, intrapulmonary shunting, and alveolar-arterial O(2) gradient were normal. Pulmonary edema was absent in lung biopsies. Bronchial circulation is discussed with respect to its clinical implications for lung transplants, shock, thoracic aneurysms, and mediastinal surgery. The results of this study suggest that the systemic bronchial circulation is important for normal lung function.