BLOOD-FLOW TO THE TRACHEA AND BRONCHI - THE PULMONARY CONTRIBUTION

It is generally assumed that when pulmonary vascular pressures are nor mal the pulmonary contribution to central airway blood flow (Qp) is ne gligible compared with systemic blood flow (Qs). However, it has been suggested in recent reports that a substantial portion of central airw ay blood flow is Qp. We have attempted to confirm whether there is a p ulmonary contribution to central airway blood flow and to describe how it is anatomically distributed. Measurements of Qp were made using th e radioactive microsphere technique in anesthetized ventilated dogs (n = 7) and sheep (n = 6). Qs to the central airways was also measured i n another group of sheep (n = 10). At the end of each study, animals w ere killed and the lungs and trachea were excised. Qp to the upper and lower trachea, mainstem bronchi, and lobar bronchi was calculated, an d the relative distribution of Qp and Qs to mucosa, cartilage, and adv entitia was determined. Results showed a progressive increase (P < 0.0 1) in Qp (in ml . min(-1) . 100 g(-1)) from upper trachea to lobar bro nchi in both dogs and sheep. Qp and Qs supplied mainly the airway adve ntitia and the mucosa, respectively. Expressed as a percentage, 89 +/- 4% (SE) of Qp was to the adventitia and 0.1 +/- 0.07% was to the muco sa (P < 0.01), whereas 60 +/- 3.2% of Qs was to the mucosa and 22 +/- 4.6% was to the adventitia. In conclusion, in dogs and sheep there is a pulmonary contribution to central airway blood flow that increases f rom upper trachea to lobar bronchi and that supplies mainly the peritr acheal adventitia.