Asymmetry of the laryngeal reflex responses to superior laryngeal nerve stimulation unrelated to the length of the recurrent nerves in the porcine model.

Electrical stimulation of the superior laryngeal nerve (SLN) can elicit reflex responses in the cricothyroid (CT) and thyroarytenoid (TA) muscles. We made bilateral recordings of the responses evoked in these muscles in piglets by the stimulation of either the right or the left superior laryngeal nerve (SLN). The stimulus intensity was gradually increased to study the "persistence" of the responses. We observed a direct, ipsilateral response in the CT muscle, and reflex, ipsilateral and crossed responses in both CT and TA muscles. The ipsilateral or contralateral responses obtained in TA muscles, following stimulation of the left SLN, were significantly delayed in comparison with those evoked by stimulation of the right SLN. This delay cannot be explained by the difference in length between the right and the left recurrent laryngeal nerves, but rather by an asymmetry in the sensory afferent pathway. The functional significance of this observation remains to be determined.