Experiments dealing with the relation of the sinus node to the effects of stimulation of the vagus nerves

Abstract

Experiments by a number of investigators on the sino-auricular node have warranted the conclusion that this structure is responsible for stimulus production and the maintenance of the rate of the heart. Flack thought that this node formed a station in the pathway, both of the vagus and of the accelerator nerves, and that through its agency they exercised their influence on the heart. He attempted to show that exclusion of the node from function consequently interrupted impulses passing over the nerves.

It is the purpose of this paper to report that a large number of experiments have been performed on dogs to determine the relation of the vagus nerves to the sinus node. The experiments were performed under ether; a small opening in the chest was made by resecting one or two ribs, and both vagus nerves were dissected, cut and laid on shield electrodes. Records were taken electrocardiographically. The results of stimulation of both vagus nerves were first registered. Then the sinus node was carefully clamped off with a suitable T-shaped clamp, all the tissue surrounding the node being crushed. Stimulation of both vagus nerves was repeated and records were obtained.

In the greater number of experiments, it could be shown that stimulation of the vagus nerves after clamping the node was effectual in producing effects on the rate and on the rhythm of the heart in a way similar to that seen before the clamp was placed. In a number of cases the effect of stimulation was more profound after than before the clamping. The conclusion is therefore warranted that the sinus node does not represent a simple relay in the course of the vagus nerves.

These experiments will be published in detail later, and the histological examinations of the areas at which the clamp was applied will be reported.