Lung mechanical effects on the bronchial circulation.

The bronchial circulation, like the pulmonary circulation, is subjected to the mechanical effects of lung inflation with each breath. Lung inflation, in all species studied, decreases the bronchial blood flow. This is due to changes in both lung volume and transpulmonary pressure. With this reduction of flow there is also a relative increase in the proportion of bronchial blood flow drained from the lung through systemic veins. These changes are probably due to purely mechanical effects on the systemic-to-pulmonary anastomotic bronchial blood vessels with both compression and stretching of the vessels.