Pharmacological factors influencing permeability of the bronchial microcirculation.

The bronchial microcirculation is organized as a network of interconnected superficial and deep small blood vessels that extend throughout the bronchial tree. The close proximity of the bronchial venules to the origin of the pulmonary lymphatics suggests a role in fluid balance in the lung. The responsiveness of the venous segment of this network to agents influencing permeability clearly indicates a role in the genesis of certain types of noncardiogenic interstitial edema. The responsiveness of the venous segment of the bronchial circulation to neural and humoral stimuli raises the possibility of a significant role in the distribution of blood flow between the mucosa and peribronchial space. Such control may play a significant role in heat and water exchange between blood and air. Thus, these observations indicate that the bronchial microcirculation is involved with aspects of pulmonary function other than the nutrition of the bronchi, nerves, pleura, and large pulmonary blood vessels.