Early stages in the development of collateral circulation to the lung in the rat.

IT HAS been shown repeatedly that the bronchial arteries enlarge considerably following occlusion of branches of the pulmonary artery by either embolism (Virchow,' and others) or experimental ligation (Sehlaepfer, Liebow et al., Ellis et al., and others). The expanded bronehial arteries have been demonstrated by various anatomic methods, including bronchovascular casts and microscopic sections. Physiologic studies revealed that this bronchial collateral blood supply to the lung deprived of the pulmonary artery was able to participate in the gas exchange in this lung, and must, therefore, have reached the alveolar capillaries (Bloomer et al.). Liebow et al. concluded that under these conditions a considerable amount of blood was circulating only on the left side of the circulation, entering the lung through bronchial arteries, going through the lung capillaries and pulmonary veins back to the left heart and into the aorta. This increased left cardiac output, as compared with the right cardiac output, seems, however, to be without any influence on the size and configuration of the heart in normal animals (Loring and Liebow).