Broncho-pulmonary Circuits: a Synoptic Appraisal.

Because pulmonary arteries are end arteries, the circulation within the lung once appeared to be simple. However, an increasing amount of information concerning the systemic contribution to this circulation, mainly through bronchopulmonary anastomoses, has made the picture complex. The intricate network that the bronchial vessels establish between the aorta and the pulmonary arteries on the one hand, and between the pulmonary veins and the caval system via the azygos veins on the other hand, is capable of expansion in various pathological states (Camarri and Marini, 1962). This work is an attempt to classify all the presently recognized situations into five circuits readily visualized and easily remembered. First, the anatomical connexions within the lung will be briefly reviewed; then I shall propose a model of the position these connexions hold in the framework of the whole circulation, and the four pathological aspects of this model. The bronchial arteries normally irrigate the bronchi down to the bronchioles but do not reach the alveoli, which are irrigated solely by the pulmonary vessels proper. Precapillary anastomoses are present between the two types of arterioles, as can be demonstrated in the human lung (Fig. 1), but they are not of functional importance in normal conditions. A second anastomotic pathway results from the absence of a limit between the bronchiolar and the alveolar capillary beds. A third connexion exists at the venous slope of both systems in the form of so-called broncho-pulmonary veins joining the venous bronchial plexus to the pulmonary veins. Towards the hilum this venous plexus forms true bronchial veins that drain into the azygos and caval systems. Thus there are three levels in the pulmonary vessels where systemic blood can enter: pre-, intraand post-capillary (Fig. 2; a, b, and c). Depending on that level, the systemic blood will