ALTHOUGH there is extensive literature on the experimental production of bronchial pulmonary arterial anastomoses in animals following pulmonary arterial ligation,1-5 there remains a paucity of information concerning the collateral circulation in the human lung following pulmonary thromboembolism. There are three phases of response to pulmonary embolism: vascular occlusion, pulmonary infarction, and development of a collateral circulation.6 The character and extent of the collateral circulation that develops following pulmonary embolization in man has not been fully defined. The present study was therefore undertaken to determine the distribution and localization of the pathological vascular alterations which occur in the development of this collateral circulation.
Miller7 clearly showed that the only communication between the bronchial and pulmonary arterial system in the normal lung of both man and dog was via capillaries. These anastomoses were shown to occur at two sites: (1) at the level of the respiratory bronchiole, where pulmonary arterial capillaries freely