Changes in myocardial performance induced by pancuronium and gallamine in hypercapnic and hypocapnic dogs

Changes in myocardial performance after administration of gallamine 1.5 mg kg-1 and pancuronium 0.1 mg kg-1 were investigated in hypercapnic (PaCO2 = 7.08 kPa) and hypocapnic (PaCO2 = 2.74 kPa) dogs anaesthetized with thiopentone, nitrous oxide and halothane. Administration of pancuronium during hypocapnia caused a decrease of 25% in dP/dt max (corrected for changes in preload, afterload and heart rate). This change was not seen during hypercapnia, probably because of the associated sympathetic stimulation. By contrast, gallamine was without effect on dP/dt max in both groups. The increase in heart rate and cardiac output caused by the atropine-like action of both groups. The increase in heart rate and cardiac output caused by the atropine-like action of these relaxant drugs differed in the hypercapnic and hypocapnic group of dogs, with the more pronounced response in the latter group. The duration of the chronotropic changes was the same in both groups.