Arterial Baroreceptor Fibers in the Recurrent Laryngeal Nerve

Abstract

Stimulation of the larynx, as during intubation, can produce significant cardiac arrhythmias. Investigation of the cause of these arrhythmias has led us to believe that they are in part due to stimulation of a baroreceptor reflex pathway which passes through the larynx rather than to initiation of a simple reflex in the larynx itself. Pressure sensors (baroreceptors) in the aortic arch form part of a system which monitors systemic blood pressure. Stimulation of these baroreceptors produces, via a medullary reflex arc, a slowing of the heart rate, a decrease in sympathetic vascular tone, and as a result a drop in blood pressure. The pathway from the aortic arch baroreceptors has heretofore been thought to run directly through the vagus nerve. We have shown, however, that in the rat a significant number of fibers from aortic arch baroreceptors run in the left recurrent laryngeal nerve (RLN), through the larynx into the left superior laryngeal nerve (SLN), and only then into the vagus. Blocking or cutting the left RLN produces a significant drop in overall baroreceptor reflex activity, and furthermore, nerve fibers have been isolated in the left RLN which show exactly the same patterns of discharge as those from arterial baroreceptors elsewhere. It is our belief that at least some of the arrhythmias produced during laryngeal manipulation can be explained on the basis of mechanical compression producing stimulation of the baroreceptor fibers as they pass along the thyroid cartilage through the ramus communicans between the RLN and SLN. Further work needs to be done to show that compression does in fact stimulate the baroreceptor pathway, but there is now little doubt that, in experimental animals, such a pathway exists.