Cardiac responses to stimulation of discrete loci within canine sympathetic ganglia following hexamethonium.

In dogs which had been administered hexamethonium, localized stimulation with bipolar electrodes in the middle cervical and stellate ganglia as well as ganglia in the caudal pole nerve and ventral ansa elicited alterations in cardiodynamics. The middle cervical and stellate ganglia were divided into 30 discrete regions in order to provide a standardized map of these ganglia. Of all the responses elicited. 5% consisted of increased heart rate while 38% consisted of augmented inotropism without accompanying chronotropic changes. Both rate and force were augmented in 57% of the responses. The sites in which stimulation consistently elicited chronotropic responses were located in right-sided ganglia. Loci which consistently generated force changes on stimulation were in the middle cervical and stellate ganglia bilaterally. Cardiac chronotropism and inotropism were augmented by stimulation of ganglia located in the ventral subclavian ansae or the left caudal pole nerve. No cardiac responses were elicited by stimulation within the superior cervical ganglia. It is concluded that localized stimulation of specific sites in the major thoracic ganglia or smaller mediastinal ganglia can alter cardiac chronotropism and/or inotropism.