Pulmonary and systemic contribution to canine tracheobronchial blood flow

To investigate the quantity and pathophysiological relationship of pulmonary and bronchial artery supply to the tracheobronchial tree in dogs in absence and in presence of increased tissue metabolic requirements, pulmonary and bronchial blood flow to the trachea and bronchi was determined by the radioactive microsphere method in nine adult mongrel dogs. Microspheres were injected into the right atrium of three dogs (pulmonary injection group) and into the left ventricle of four dogs (systemic injection group) just before and three, eight and fourteen days after resection and anastomosis of the right main bronchus. The remaining two dogs served as controls without surgery. After the fourth injection, the tracheobronchial tree was harvested, divided into segments, and the radioactivity counted in each segment. At baseline the systemic flow to the tracheobronchial tree expressed as percentage of cardiac output was 0.188% +/- 0.121 and the pulmonary blood flow was 0.007% +/- 0.004 (mean +/- S.D.). Three, eight and fourteen days after transection and anastomosis of the right main stem bronchus, the systemic blood flow to the bronchial segments proximal and distal to the anastomosis increased significantly whereas pulmonary blood flow did not change. Depending on the anatomical segment considered the systemic contribution was between 5 and 100 times larger than the pulmonary one, both at baseline and after transection and anastomosis of the right main stem bronchus, but the ratio diminished in more distal segments where pulmonary blood flow was larger. It is concluded that the systemic blood contribution to the canine tracheobronchial tree is larger than the pulmonary one and that, in the presence of increased metabolic needs, it responds more promptly with increased blood flow.