Sina Nasri

Function of the interarytenoid muscle in a canine laryngeal model

Fundamental frequency is controlled by contraction of the thyroarytenoid (TA) and cricothyroid (CT) muscles. While activity of the CT muscle is known to tense and thin the vocal folds, little is known about the effect of the TA muscle on vocal fold vibration. An in vivo canine laryngeal model was used to examine the role of the TA muscle in controlling phonation. Isolated TA muscle activation was obtained by stimulating sectioned terminal TA branches through small thyroid cartilage windows. Subglottic pressure measures, electroglottographic and photoglottographic signals, and acoustic signals were obtained in 5 mongrel dogs during dynamic and static variations in TA muscle activity. Results indicated that TA muscle activation is a major determinant in sudden shifts from high-frequency to modal phonation. Subglottic pressure increased and open quotient decreased gradually with increasing TA activation.

Cross-Innervation of the Thyroarytenoid Muscle by a Branch from the External Division of the Superior Laryngeal Nerve

The neuroanatomy of the larynx was explored in seven dogs to assess whether there is motor innervation to the thyroarytenoid (TA) muscle from the external division of the superior laryngeal nerve (ExSLN). In 3 animals, such innervation was identified. Electrical stimulation of microelectrodes applied to the ExSLN resulted in contraction of the TA muscle, indicating that this nerve is motor in function. This was confirmed by electromyographic recordings from the TA muscle. Videolaryngostroboscopy revealed improvement in vocal fold vibration following stimulation of the ExSLN compared to without it. Previously, the TA muscle was thought to be innervated solely by the recurrent laryngeal nerve. This additional pathway from the ExSLN to the TA muscle may have important clinical implications in the treatment of neurologic laryngeal disorders such as adductor spasmodic dysphonia.

Malignant melanoma of cervical and parotid lymph nodes with an unknown primary site

Forty‐six patients with malignant melanoma metastatic to cervical or parotid lymph nodes with an unknown primary site were treated at UCLA Medical Center from 1964 through 1991. Treatment consisted of parotidectomy and/or neck dissection with or without adjuvant therapy. The initial presentation was a cervical mass in 74% and a parotid mass in 26% of patients. Metastasis distal to the head and neck nodal basins developed in 22% of patients.

Transpharyngeal Approach to Base of Tongue Tumors: A Comparative Study†

Tumors of the tongue base have been traditionally removed by resecting the mandible or using a translabial transmandibular approach. These procedures involve significant morbidity including lip and chin scars, malocclusion, compromised deglutition, chronic aspiration, and altered speech articulation. Therefore alternative techniques have been described to minimize the morbidity associated with transmandibular tongue resection.

Measurement of adductory force of individual laryngeal muscles in an in vivo canine model

In this experiment, the adductory properties of three intrinsic laryngeal muscles (the thyroarytenoid [TA], lateral cricoarytenoid [LCA], and interarytenoid [IA]) were studied and quantified. Using an in vivo canine laryngeal model, a recently developed “tensionometer” was used to measure the adductory force produced by each of these muscles at the vocal process of the arytenoid. Isolated muscle activation was obtained by stimulating selective terminal branches of the anterior division of the recurrent laryngeal nerve. Results indicate that the LCA is the strongest adductory muscle, followed by the TA and the IA Videolaryngoscopy revealed that LCA contraction causes adduction of the vocal fold and vocal process, with the predominant effect on the process. TA stimulation leads primarily to adduction of vocal fold, and the IA adducts mainly the vocal process. Implications of these findings are discussed.

Noninvasive Measurement of Traveling Wave Velocity in the Canine Larynx

Laryngologists have long recognized that assessment of the mucosal wave is an important part of laryngeal evaluation. This is the first report of a noninvasive measurement of vocal fold displacement velocity in an in vivo canine model. a newly developed calibrating endoscopic instrument capable of measuring distances on the vocal fold surface is described. Displacement velocity was determined in three dogs and compared to physiologic measures in the in vivo phonation model. The results indicate that the calculated displacement velocity is linearly proportional to traveling wave velocity and fundamental frequency. Because traveling wave velocity has been shown to reflect vocal fold stiffness, this method may advance the usefulness of stroboscopy for the study of mucosal wave abnormalities.

Physiologic Motion after Laryngeal Nerve Reinnervation: A New Method

In this study a new method of reinnervation for unilateral recurrent laryngeal nerve paralysis was performed in canines, producing physiologic vocal fold motion in each of a small series of animals. During the procedure the left anterior division of the recurrent laryngeal nerve was reinnervated with axons from the thyroarytenoid branch of the contralateral recurrent laryngeal nerve. The posterior branch of the left recurrent laryngeal nerve was divided and sutured to the ansa cervicalis to maintain tone in the posterior cricoarytenoid muscle. In all four animals, the right distal vocalis stump was reinnervated with an ansa cervicalis nerve branch. After 3 months physiologic vocal fold motion and electromyographic activity could be demonstrated during mechanical stimulation of the supraglottis (adduction) and during tracheostomy obstruction (abduction). Acoustic data revealed improvement of jitter, shimmer, signal-to-noise ratio, and vocal efficiency in reinnervated animals compared with paralyzed canines before treatment, although the results lacked statistical significance. This approach to the rehabilitation of unilateral vocal fold paralysis is discussed.

Effects of arytenoid adduction on laryngeal function following ansa cervicalis nerve transfer for vocal fold paralysis in an in vivo canine model

Laryngeal reinnervation with the ansa cervicalis has been proposed as a treatment for human unilateral vocal fold paralysis (UVFP). This study tested the assumption that results from reinnervation could be improved if combined with medialization surgery. Six canine subjects underwent recurrent laryngeal nerve section and reinnervation with a branch of the ansa cervicalis. After reinnervation, vocal function was assessed before and after arytenoid adduction. Although laryngeal function improved significantly following reinnervation, results were significantly enhanced by the addition of medialization surgery. The implications for the treatment of human unilateral vocal fold paralysis are discussed.

Characteristics of an in vivo canine model of phonation with a constant air pressure source

Many previous studies of laryngeal biomechanics using in vivo models have employed a constant air flow source. Several authors have recently suggested that the lung‐thorax system functions as a constant pressure source during phonation. This study describes an in vivo canine system designed to maintain a constant peak subglottic pressure (Psub) using a pressure‐controlling mechanism.

Laryngeal resistance of an in vivo canine model of phonation with a constant air pressure source

Previous studies of laryngeal biomechanics using in vivo models have generally used a constant air flow source. Several authors have recently suggested that during phonation, the lung–thorax system functions as a constant pressure source. The present paper describes an in vivo canine system designed to maintain a constant peak subglottic pressure (Psub) using a pressure‐controlling mechanism. It was found that with a decrease in Psub, the range of recurrent laryngeal nerve stimulation (RLNS) voltage needed to induce phonation was reduced. At a given superior laryngeal nerve stimulation (SLNS) level and Psub, increasing levels of RLNS resulted in a normal distribution of vocal efficiencies. For each SLNS and Psub, minimum and maximum levels of RLNS were determined outside of which no phonation was possible. Levels of RLNS that produced an optimal stable phonation were also identified. Increasing levels of RLNS resulted in significant decreases in glottal air flow. Contrary to a previous report using a cons...