Blood flow to the trachea and bronchi: the pulmonary contribution

It is generally assumed that when pulmonary vascular pressures are normal the pulmonary contribution to central airway blood flow (Qp) is negligible compared with systemic blood flow (Qs). However, it has been suggested in recent reports that a substantial portion of central airway blood flow is Qp. We have attempted to confirm whether there is a pulmonary contribution to central airway blood flow and to describe how it is anatomically distributed. Measurements of Qp were made using the radioactive microsphere technique in anesthetized ventilated dogs (n = 7) and sheep (n = 6). Qs to the central airways was also measured in another group of sheep (n = 10). At the end of each study, animals were killed and the lungs and trachea were excised. Qp to the upper and lower trachea, mainstem bronchi, and lobar bronchi was calculated, and the relative distribution of Qp and Qs to mucosa, cartilage, and adventitia was determined. Results showed a progressive increase (P < 0.01) in Qp (in ml.min-1 x 100 g-1) from up...