Attempts at Evaluation of the Function of various Laryngeal Muscles in the Light of Muscle and Nerve Stimulation Experiments in Man

Abstract

Muscle and nerve stimulation experiments have been carried out on a series of 12 human larynges with malignant disease of essentially unilateral involvement. In the course of total laryngectomy tests were applied to several internal and external laryngeal muscles as well as the recurrent and superior laryngeal nerves on both sides. Muscle stimulation experiments were carried out also on the recently excised larynx. The effects were studied on the relatively unaffected side, where vocal fold mobility was apparently free. Stimulation of the sternothyroid muscle constantly led to dilatation of the laryngeal inlet and widening of the glottis. Abduction of the vocal fold occurred only in 50% of the cases (3 out of 6) on stimulation of the posterior crico-arytenoid muscle. Various explanations of these phenomena are discussed. Stimulation of the recurrent laryngeal nerve produced adduction of the vocal fold to the paramedian plane. In two experiments out of seven, however, stimulation of the recurrent laryngeal nerve led to abduction of the vocal fold. In no instance could repeated stimulation of this nerve produce two different responses, abduction and adduction, in the same experiment. Evidence is presented of the existence of both sensory and motor bundles in the recurrent laryngeal nerve. Adduction of the vocal fold to an intermediate position was noticed on stimulation of the superior laryngeal nerve. This was shown to be mediated through its external branch, the effector muscle being the crico-thyroid.