REFLEX BRONCHIAL VASODILATION IN DOGS EVOKED BY INJECTION OF A SMALL-VOLUME OF WATER INTO A BRONCHUS

Injection of water into a lobar bronchus stimulates airway C-fibers an d rapidly adapting receptors and evokes airway defense reflexes. To de termine whether this stimulus also evokes a reflex increase in bronchi al blood flow (Qbr), we injected 1-2 ml of water into a lobar bronchus in anesthetized dogs. Injection decreased arterial pressure but incre ased Qbr from 9 +/- 1 to 21 +/- 3 ml/min. The increase had a latency o f 6-8 s and reached a peak after approximately 20 s; Qbr returned to c ontrol after 60-90 s. Airway mucosal blood flow, measured by colored m icrospheres, increased in proportion to Qbr. In contrast, flow in an a djacent intercostal artery that did not supply the airway decreased sl ightly. Injection of isosmotic saline had little effect. In 13 of 16 d ogs, the water-induced increase in Qbr was abolished by cutting or coo ling the cervical vagus nerves and hence was entirely dependent on cen trally mediated vagal pathways. When the vagus nerves were intact, abo ut one-third of the vasodilator response remained after pharmacologica l blockade of muscarinic and adrenergic receptors. We conclude that in dogs the defense response to water in the lower airways includes a la rge increase in Qbr that is partly due to activation of nonadrenergic noncholinergic autonomic pathways.