Objectives: We sought to examine the neuromuscular basis for ventricular fold function. The primary function of the ventricular folds is to assist in the regulation of intra-abdominal and intrathoracic pressure. They also influence phonation in the setting of vocal fold paralysis or ventricular dysphonia, or after partial laryngectomy. The neuromuscular basis of true vocal fold function has been well studied; however, its neuromuscular correlates in the ventricular folds are ambiguous. The literature is unclear as to whether ventricular fold contraction is passive or active. The musculature and innervation responsible for this action also have not been well defined. The aim of this study was to provide clarity in regard to these mechanisms.
Methods: We examined a whole-organ section of a human larynx from a patient with unilateral vocal fold paralysis. The region of the ventricular folds was compared on both the paralyzed and normal sides. Electrophysiological examination was performed in a porcine model. The superior laryngeal nerve was stimulated, and recording electrodes in both ventricular folds measured the electrical activity. The recurrent laryngeal nerve was then severed, and the experiment was repeated.
Results: The histologic slides from the patient with unilateral vocal fold paralysis demonstrated atrophied ventricularis and thyroarytenoid muscles on the paralyzed side. On the unaffected side, these muscles were of normal size. The electrophysiological examination in the porcine model demonstrated findings consistent with innervation of the ventricularis muscle by the recurrent laryngeal nerve. An association of ventricularis muscle activity with ventricular fold contraction also was demonstrated.
Conclusions: Ventricular fold adduction appears to be a result of ventricularis muscle contraction that is mediated by the recurrent laryngeal nerve.