Cardiac output during excitation of chemoreflexes in the cat.

In cats under chloralose anaesthesia the reflex fall of blood pressure and heart rate caused by injection of veratrine, amidines, diphenhydramine, or ethyl acetoacetate was accompanied by a fall in cardiac output. After veratrine and amidines there was a fall in mean pulmonary arterial pressure and after veratrine no significant change in pulmonary vascular resistance. After diphenhydramine and ethyl acetoacetate there was a rise in mean pulmonary arterial pressure and after diphenhydramine an increase in pulmonary vascular resistance. The effects of veratrine and amidines, but not those of diphenhydramine and ethyl acetoacetate, were abolished by section of the vagi. The main change leading to the fall of cardiac output after amidines was bradycardia.