Videostroboscopy of the canine larynx: the effects of asymmetric laryngeal tension.

The effects of simulated paralysis of the peripheral laryngeal nerves on patterns of vocal cord vibrations were studied. Videostroboscopy was used in seven anesthetized mongrel dogs to record laryngeal vibrations during direct electrical stimulation of the recurrent and superior laryngeal nerves under conditions of constant airflow. Stroboscopic images obtained from both supraglottic and subglottic aspects were analyzed frame-by-frame. Results indicated that simulated paralysis of the recurrent laryngeal nerve or combined paralysis of the recurrent and superior laryngeal nerves produced a diminished mucosal wave bilaterally, with loss of the two-mass system of vibration and diminished lateral excursion of the normal cord. In contrast, simulated paralysis of the superior laryngeal nerve was characterized by an abnormally exaggerated vertical movement of the paralyzed cord in relation to the normal cord and a horizontal shifting of the glottis from the paralyzed to the normal side during each vibratory cycle. Clinical implications are discussed and the literature reviewed.