Effect of hypoxia on bronchial reactivity in dogs

The effect of hypoxia on bronchial reactivity was studied in six anesthetized dogs. Bronchial reactivity was obtained by inhalation of histamine aerosol in stepwise incremental concentrations during fixed tidal volume breathing. Two kinds of hypoxia were induced by inspiration of nitrogen until the end-tidal oxygen concentration (FETO2) reached 15% (mild) and 10% (severe hypoxia). Pulmonary resistance (RL) was measured by the 3 HZ forced oscillation technique in the open chest condition. Before histamine challenge, hypoxia did not increase RL in any of the dogs with mild hypoxia (FETO2 15%) and increased it in one dog with severe hypoxia (FETO2 10%). There was synergy between hypoxia and inhaled histamine in all dogs with both mild and severe hypoxia. The magnitude of synergy was significantly higher in severe than in mild hypoxia (p less than 0.05). With vagi cut, hypoxia did not increase RL compared with normoxia at any histamine concentration. It is suggested that hypoxia enhanced bronchial reactivity through the vagal nerves.