Effect of verapamil on pulmonary reflexes in the vascularly isolated canine lung: physiology

Breathing frequency (BF) may be affected by changes in the percent inspired CO2 administered to vascularly isolated lungs. Pulmonary CO2 probably affects BF, in part, through a secondary effect of CO2 on airway smooth muscle. To further determine the role of pulmonary mechanics in the pulmonary CO2-mediated BF response, Verapamil, a Ca++ blocking agent which blocks hypocapnic airway constriction, was administered to the vascularly isolated lungs of the dog. Verapamil blocked the hypocapnic airway constriction which occurred when pulmonary CO2 was reduced; however, the decrease in BF was not only blocked but in some animals there was an increase in BF. Also, the decrease in BF produced by hyperinflation of the lungs (Hering-Breuer reflex) was either blocked or an increase in BF occurred after administration of Verapamil.