Chronotropic and dromotropic components of cardiac reflexes in rabbits

The relationships between dromotropic and chronotropic components of five reflexes were studied in rabbits: intravenous and intraarterial blood injections, occlusion of the carotid arteries, Aschner maneuver, and stimulation of depressors. All these stimuli reduced heart rate (except carotid artery occlusion, which induced approximately equal number of tachi- and bradycardic responses). The former three stimuli also reduced atrioventricular (AV) conduction velocity, the changes in these two parameters were proportional. Changes in heart rate induced by Aschner maneuver were more pronounced than changes in AV conduction. Stimulation of depressor induced co-directed shifts in these parameters during the first seconds, but then AV conduction increased, while heart rate remained decreased; bradycardia and AV acceleration persisted for long time after termination of stimulation. Our findings attest to independent regulation of heart rate and AV conduction velocity and to the absence of a strict relationship between these two parameters.