Bronchial artery circulation
The bronchial arteries derive from the descending aorta.
They follow the bronchial tree deeply into the lung parenchyma forming a peribronchial plexus, and small arterioles penetrate the muscularis to form a submucosal plexus. The bronchial arteries also contribute arterial blood supply to the visceral pleura, the walls of the pulmonary arteries and veins as vasa vasorum, the mediastinal tissue, esophagus, mediastinal and hilar lymph nodes, pericardium, vagal and sympathetic nerves and even branches to the myocardium can be found in humans.
Studies of the microvascular anatomy has found the venous drainage to be partially to the azygos and hemiazygos veins and partially through anastomoses between the broncial arteries and pulmonary alveolar microvessels, called bronchopulmonary anastomoses (figure 1). These anastomotic vessels have been described by one investigator as being coiled, possibly because of spiral musculature in their walls and suggested that this structure "might help to regulate the pressure gradient from bronchial to pulmonary vessels". Also communications between the bronchial arteries and the pulmonary veins have been described.
Figure 1
A little more schematically the flow in bronchial artery system comes from the bronchial arteries and supply the structures mentioned above and drains to the azygos vein (returning blood to the right atrium) or the pulmonary veins (returning blood to the left atrium).
Schematical normal bronchial artery flow
The bronchopulmonary anastomosis are important vessels shunting blood from the systemic (high pressure circulation) to the pulmonary (low pressure) circulation. These shunts are believed to function as a back-up system in case of lung embolism.
After lung transplantation without direct revascularization of the bronchial arteries, the transplanted airways are believed to be supplied by venous blood from the pulmonary arteries (low pressure) through retrograde flow in the bronchopulmonary anastomoses. The drainage goes exclusively to the pulmonary veins since the azygos vein has been closed during transplantation.
Bronchial artery flow in transplanted lungs without BAR
After lung transplantation with bronchial artery revascularization the bronchial artery circulation receives oxygenated blood of systemic pressure. The flow only differs from the normal bronchial artery circulation in respect to venous drainage, which is no longer possible through the azygos vein.
Bronchial artery flow in transplanted lungs with BAR
