Effect of local antigen inhalation and hypoxia on lobar blood flow in allergic dogs.

To determine the local pulmonary vascular response to inhaled antigen and alveolar hypoxia in canine asthma, 8 of 42 skin-test-positive dogs were selected from a preliminary study of airway reactivity to antigen challenge with an extract of Ascaris suum. In an anesthetized, open-chest preparation subjected to left cervical vagotomy, the proportion of pulmonary blood flow to the left lower lobe (Q lobe/Q lung) was estimated by an insoluble gas-elimination method. Continuous inhalation of antigen to the left lower lobe caused a transient decrease in Q lobe/Q lung during inspiration of a hyperoxic gas mixture; it did not affect the local hypoxic vascular response. The local decrease in blood flow during antigen challenge was positively correlated with the airway responsiveness determined in the preliminary study. There was no evidence that the decrease in blood flow was caused by a change in airway pressure in the left lower lobe. We conclude that the chemical mediators of asthma caused the vascular response to antigen challenge, but did not abolish the local hypoxic vascular response.