Effects of local and systemic hypercapnia on the discharge of stretch receptors in the airways of the dog.

We have investigated the effects of local and systemic administration of 8% CO2 on the afferent discharge from slowly adapting stretch receptors located in a functionally isolated, in situ segment of trachea and extrapulmonary bronchi in dogs. Stretch receptors situated in the trachea were not affected by hypercapnia. Discharge from bronchial stretch receptors was diminished by local CO2 administration, especially at low airway transmural pressures. Systemic hypercapnia was generally ineffective. The results indicate that stretch receptors in extrapulmonary bronchi are more accessible to CO2 in the airway lumen than to perfusion with hypercapnic blood.