Effect of carbon dioxide on heart rate

¹ Cardio-Pulmonary Laboratory, Mary Imogene Bassett Hospital, Cooperstown, New York

Pentobarbital, by its sympathomimetic effect, produces tachycardia in the dog which is slowed by hypercapnia. The parasympathomimetic effect of chloralose anesthesia, in the intact dog, results in a slow heart rate which is increased by hypercapnia. This opposite response to CO₂ appears related to the opposite autonomic effects of the two agents, since when tachycardia is induced in dogs anesthetized with chloralose, they then respond to hypercapnia by cardiac slowing. In experiments reported here and in data available in the literature, there appears to be a correlation between prehypercapnic heart rate and the chronotropic effect of CO₂. Results reported here suggest that cardiac slowing by hypercapnia occurs through a direct effect of CO₂ rather than pH and that the mechanism has both central and peripheral mediation; the former transmitted by vagal pathway with a specific site of action at the sinus node.

Submitted on May 14, 1964