The chronotropic effect of hypercapnia in dogs depends on the initial heart rate and the type of anesthesia used, mediated by both central and peripheral mechanisms.
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. hypercapnia; effect of anesthetics; mechanism of action; CO2-site of action; interaction between initial rate and rate response Submitted on May 14, 1964
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Mithoefer et al. (1964) studied this question.
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