Superior laryngeal nerve stimulation effects on respiratory movements of the vocal cords.

An animal model was designed to reproduce conflicting effects of the superior laryngeal nerve (SLN) irritation and hypoventilation found in a clinical situation produced by an upper airway foreign body. The effects of continuous stimulation of the SLN on changes in glottic pressure were studied under conditions of a) normoxia and normokapnia , b) hypoxia and hyperkapnia , and c) normoxia and hyperkapnia . Recorded fluctuations of glottic pressure were found to correspond closely to activity of the muscles of respiration. Condition of combined hypoxia and hyperkapnia seemed to protect animals from disruption of breathing caused by the SLN stimulation, while hyperkapnia itself did not influence significantly inhibitory effects of the SLN stimulation. It has been observed that irritation of the SLN may produce reflex swallowing. In certain animals single shocks delivered to SLN in expiratory phase induced additional breaths. The authors emphasize the importance of the larynx as a receptor organ and a trigger zone for a number of clinically important reflexes.