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.