Bronchial Circulation

The bronchial circulation is the systemic vascular supply to the lung, and it supplies blood to conducting airways down to the level of the terminal bronchioles as well as nerves, lymph nodes, visceral pleura, and the walls of large pulmonary vessels. Within the airway wall, the circulation is composed of parallel vascular plexuses adjacent to airway smooth muscle. The density of this vascular network predicts its role in the clearance of aerosols delivered to the airway mucosa. As in other systemic vascular beds, inflammatory cells are recruited to the airway wall through postcapillary venules. Inflammatory proteins are largely vasodilatory in their effect on bronchial vascular smooth muscle tone. Most vasodilatory action is mediated at least partially through endothelial cell-derived nitric oxide. Inflammatory proteins play a major role in the loss of bronchial endothelial barrier function causing airway wall edema, as demonstrated in conditions of asthma and allergy. The most prominent pathologic feature of the bronchial circulation is its proliferative capacity. Unlike the pulmonary vasculature, the bronchial circulation is pro-angiogenic in asthma, chronic pulmonary thromboembolism, interstitial pulmonary fibrosis, cystic fibrosis, and other inflammatory conditions. Although the recruitment of new bronchial vessels to ischemic lung parenchyma may prove beneficial, hemoptysis resulting from rupture of abnormal, bronchial vessels can be life-threatening.