Precapillary systemic-pulmonary anastomoses. Thorax

In normal lungs the bronchial arteries communi-cate with the pulmonary arteries through the capillary bed surrounding the respiratory bronchioles (Miller, 1947). Whether precapillary communications exist in normal lungs is open to question, but their development under abnormal circumstances is generally agreed. Liebow, Hales, and Bloomer (1959) have summarized the two main circumstances under which they have been found: (a) obstruction and diminished flow in the pulmonary arteries, and (b) formation of new tissue in the lung. Many different anatomical forms of systemic-pulmonary anastomoses can be found in the lung, but hitherto only a few of these have been described in detail owing to the limitations of the techniques used. Cast preparations have been of great value in identifying the larger communica-tions, but this method has two disadvantages. Firstly, histological verification of anastomoses is impossible, and close apposition of minute vessels may be indistinguishable from their actual continuity. Secondly, the histological study of vessel wall structure and the surrounding tissue is denied. Angiographic studies of whole lungs have been of limited value because systemic-pulmonary anastomoses cannot be distinguished from superimposition of non-communicating vessels. In the present work a microradiographic technique has been developed to study the finer branches of the bronchial arteries and their sites of communication with the pulmonary vascular bed. The findings have been verified by serial sections