ABSTRACT
The bronchial circulation is one of the double arterial and venous systems of the
lung. The other “pulmonary” circulation arises from the pulmonary artery,
supplies the alveolar capillary surface, and is the main functional artery of the
lung. The “bronchial” circulation should correctly be called the airway circulation
as it provides nutrient supply to the trachea, the bronchi, and peripheral airways up
to the level of the terminal bronchiole. The origin of the airway circulation is from
systemic arteries, and there is considerable interspecies and intraspecies
variability (1-5). Here, the description is restricted to the human. In the fourth
week of gestation, primitive bronchial arteries arise from the dorsal aorta in the
neck and are distributed to the airways (6). By the sixth week of gestation, airway
branching is at the segmental or lobar level, and at this time, the primitive
bronchial arteries disappear. Definitive bronchial arteries arise from the thoracic
aorta between the T3 and T7 vertebrae during the ninth to twelfth weeks of
gestation. In about 40% of individuals a single bronchial artery is present for each
lung. The right bronchial artery may arise directly from the aorta or from an
intercostal, subclavian, or internal thoracic artery. On the left, about 70% of
people have two or more bronchial arteries, generally arising directly from the
aorta. The bronchial arteries supply the distal trachea and carina, and they ramify
within the walls of the bronchi and intrapulmonary airways. The branches form
a plexus in the peribronchial space by anastomosing with each other, and small
arterioles penetrate the muscular wall of the airway to form a submucosal plexus.
The two plexuses (submucosal and peribronchial) travel along the entire airway
up to the level of the terminal bronchiole, where the bronchial arteries give off
capillaries that communicate with pulmonary capillaries in airway walls (Fig. 1).
The normal diameter of the bronchial artery at the hilum is less than 2 mm (8), and
in its intrapulmonary portion, it is much smaller than the diameter of the
accompanying pulmonary artery. Venous drainage of intrapulmonary airways
(70% of the total) is via pulmonary veins into the left atrium, resulting a small
degree of venous admixture (Fig. 2) (9). Thus, elevation of left heart pressure
causes congestion not only of the alveolar region but of the intrapulmonary
airways as well. True bronchial veins drain blood from large hilar structures and
extrapulmonary airways to the right atrium.
