The influence of the vagus nerves on the faradized auricles in the dog's heart

Abstract

The effect of vagus stimulation on the abnormal cardiac activity set up by faradization of the dog's auricle was studied in twenty-three experiments. Faradization of the auricles threw them into a tumultuous activity which in fifteen of the experiments persisted after faradization was discontinued from five minutes to over an hour. In these experiments opportunities were afforded for studying the nature of the abnormal auricular activity set up by faradization and for determining what effect stimulation of each vagus nerve had upon it. In several experiments the effect of cutting the vagi while the abnormal activity was present was observed. In eight experiments in which the abnormal activity could not be established independently, the effect of vagus stimulation was observed by beginning it before ending the faradization of the auricles. When this was done the abnormal auricular activity usually continued until after the end of vagus stimulation and was affected in the same manner as the continuous or established tumultuous activity.

The auricular activity resulting from auricular faradization consisted in very rapid movements, apparently contractions of the whole auricles, which were sufficient to produce definite movements of the recording tambour attached to the auricular myocardiograph. Beside this rapid auricular tachycardia, fine fibrillatory movements in the various fibers could be seen. When the right vagus was stimulated with a faradic current of moderate strength, the coarser movements ceased and the typical fine fibrillations persisted, and when the stimulation was removed the coarser movements could be seen definitely, gradually returning and being coexistent with the fine fibrillation. This effect produced a change in the electrocardiogram and the undulations representing auricular activity became more rapid, blurred and often almost disappeared. This characteristic change in the electrocardiograms occurred in 89.5 per cent. of the experiments.