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Function of the Posterior Cricoarytenoid Muscle in Phonation: in Vivo Laryngeal Model

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Function of the Posterior Cricoarytenoid Muscle in Phonation: in Vivo Laryngeal Model Function of the posterior cricoarytenoid muscle in phonation: In vivo laryngeal model HONG-SHIK CHOI, MD, GERALD S. BERKE, MD, MING YE, MD, and JODY KREIMAN, PhD, Los Angeles, California The function of the posterior cricoarytenoid (PCA) muscle In phonation has not been well documented. To date, several electromyographlc studies have suggested that the PCA muscle Is not simply an abductor of the vocal folds, but also functions In phonation. This study used an In vivo canine laryngeal model to study the function of the PCA muscle. SUbglottic pressure and electroglottographlc, photoglottographlc, and acoustic waveforms were gathered from fiVe adult mongrel dogs under varying conditions of nerve stimulation. Subglottic pressure. fundamental frequency, sound Intensity, and vocal efficiency decreased with Increasing stimulation of the posterior branch of the recurrent laryngeal nerve. These results suggest that the PCA muscle not only acts to brace the larynx against the anterior pull of the adductor and cricothyroid muscles, but also functions Inhlbltorlly In phonation by controlling the phonatory glottal width. (OTOLARYNGOL HEAD NECK SURG 1993;109: 1043-51.) The important physiologicfunctions of the larynx­ during phonation in some clinical cases. Kotby and protection of the lower airway, phonation, and res­ Haugen? also observed increased activity in the 1 piration - are all mediated by the laryngeal mus­ PCA muscle during phonation and postulated that cles. Intrinsic laryngeal muscles are classified into the muscle is not simply an abductor of the vocal three groups: the tensors, which regulate the length cord. and tension of the vocal folds; the adductors, which Gay et al." observed increased activity in the PCA close the glottis; and the abductor, which opens the muscle during phonation in chest voice at high glottis. The posterior cricoarytenoid (PCA) muscle pitches and concluded that the muscle plays a role is the sole abductor of the glottis and has generally as a tensor of the vocal cords. Hirano" presented been considered a muscle of respiration.P EMG data from the PCA, the cricothyroid (CT), and Several authors have described the function of the the vocalis muscles during singing of ascending and PCA muscle in phonation.v" Faaborg-Anderson' descending scales in modal register by untrained found that electromyographic (EMG) activity in the male subjects. The EMG sample showed that the PCA muscle decreased during sustained phonation, PCA muscle was generally inactive during phona­ but started to increase a few milliseconds before the tion. However, some activity was noted at high end of audible voice. Brewer and Dana' recorded pitches, where the CT muscle was markedly acti­ increased activity from the PCA muscle when ex­ vated. With the use of a pharyngeal surface elec­ perimental animals attempted to whine. Ded06 and trode, Fujita et aLII also noted an increase in PCA Yang? reported increased activity in the PCA muscle muscle activityat the high end of the pitch range. Mu and Yang" observed EMG activity of the PCA muscle during phonation in 11 of 12 dogs. They From the Laryngeal PhysiologyLaboratory, Division of Head and concluded that the PCA muscle has a phonatory Neck Surgery, UCLA School of Medicine. function and that it may play an important role in Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, Washington, D.C., precise glottis control. Sept. 13-17, 1992. The present study used an in vivo canine model of Received for publication Oct. 16,1992; revision received Feb. 5, phonation to study the role of the PCA muscle in 1993;.accepted March 5, 1993. phonation. This model has been described in detail Reprint requests: Gerald S. Berke, MD, Division of Head and elsewhere. 13.14 Phonation was initiated by stimulating Neck Surgery, UCLA School of Medicine, 10833 Le Conte Ave., Los Angeles, CA 90024. the anterior branches of the recurrent laryngeal Copyright © 1993by the American Academy of Otolaryngology­ nerve (RLN). The peAbranch of the RLN was then Head and Neck Surgery Foundation, Inc. stimulated to investigate the effect of the PCA 0194-5998/93/$1.00 + .10 23/10/46950 muscle on laryngeal vibration. 1043 Otolaryngology ­ Head and Neck SUrgery 1044 CHOI el 01. December 1993 METHODS The oral intubating tube was removed. With the use In Vivo Preparation of a small button and a 2-0 silk suture, the epiglottis Five mongrel dogs were anesthetized with an was suspended for better visualization of the larynx. intramuscular injection of 3 ml acepromazine male­ An additional proximal tracheotomy was performed ate as a premedication, followed by intravenous through which a cuffed tracheotomy tube was sodium pentobarbital (Nembutal) titrated to loss of placed, with its tip resting 10 em below the glottis. the corneal reflex.Each animal wasplaced supine on The cuff of the superiorly directed tube was inflated an operating table and direct laryngoscopywas per­ to just seal the trachea. Room air was bubbled formed to confirm normal laryngeal anatomy. through 5 em H20 at 37° C for warming and hu­ A 7 mm oral endotracheal tube was inserted and midification and was then passed through the ceph­ connected to a respirator. After the animal was alad tracheotomy tube. shaved, prepared, and draped, a vertical midline All animal protocols were approved by the UCLA incision was made, and the strap muscles and ster­ Animal Care and Use Committee and were per­ nocleidomastoid muscles were retracted laterally to formed in compliance with the local, state, and expose the larynx and trachea. The external branch federal regulations for the humane use ofanimals in ofthe superior laryngeal nerve (SLN) was isolated at research. its entrance into the cr muscle. After twitch of the cr muscle was confirmed by nerve stimulation, Glottography. Pressure. and Intensity speciallydesigned rubber electrodes (custom-made, Measurements monopolar, flexible, conductive neoprene with sili­ Electroglottography electrodes (Synchrovoice, cone, coated with insulative silicone KE45W) were Briarcliff Manor, N.Y.) were placed in direct contact applied around the nerve (Fig. 1,B). The RLN was with the cartilage itself. The reference electrode was isolated at the tracheoesophageal groove and was sutured to the inside of the skin flap. confirmed with electrical stimulation. The inferior A photosensor (Centronics OSD 50-2, Mountain­ constrictor muscle was cut at the lateral margin of side, N.J.) was placed on the trachea approximately the thyroid cartilage. The sternothyroid muscle was 3 em below the larynx.A halogen flashlight provided cut. The RLN was dissected superiorly to identify supraglottic illumination for photoglottography. the anterior and posterior branches and Galen's A catheter-tipped pressure transducer (Millar anastomosis after the posterior larynx was rotated. model no. SPC 330, Houston, Texas) was inserted The three branches (anterior, posterior, and Galen's through the upper tracheostoma and rested 2 em anastomosis) were confirmed with electrical stimu­ below the glottis. The transducer was calibrated lation. The anterior branch, which contracts the against a manometer from 0 to 100 mm Hg pressure adductor muscles, was cut just distal to the PCA before insertion. branch. A rubber electrode was attached to the Phonatory intensity was measured with a linear distal stump of the anterior branch proximal to the scale sound level meter (Quest Electronics model interarytenoid branching. Galen's loop was cut after no. 208L,Oconomowoc, Wis.),which was positioned confirmation. Another electrode was applied to the 30 em from the canine larynx. Photoglottography, trunk of the RLN for stimulation of the posterior electroglottography, subglottic pressure, and acous­ branch (Fig. 1, A). tic signals were low-pass filtered at 3 kHz and dig­ This procedure was then repeated on the opposite itized at 20 kHz with a 12-bit analog-to-distal con­ side of the animal. Electrodes attached to both sides version board. The signals were verified on an os­ of the SLN were connected to a Grass model 54H cilloscope (Tektronix 5116, Beaverton, Ore.) before stimulator (Grass Instruments, Quincy, Mass.). digitization, Files were stored on disks, and 0.5 to Electrodes attached to the anterior branches and 2.4-second samples of stable phonation were ex­ trunks of the RLN on both sides were connected to cerpted for analysis. A multipurpose computer pro­ separate channels of a second nerve stimulator (cus­ gram (CSpeech, version 3.1, P. Milenkovic, Madi­ tom-made, two-channel, constant-voltage, direct­ son, Wis.) was used to analyze subglottic pressure, current stimulator). A ground electrode was in­ glottography, and acoustic signals (Fig. 2). serted into the subcutaneous tissue of the neck flap. Nerves were stimulated by an 80 Hz pulse with 1.5 Vldeostroboscopy ms duration. Stimulation intensity varied from 0 to Stroboscopic imagesof vocal fold movements dur­ 2 volts, as will be described. ing phonation were recorded with the use of a Karl A distal tracheotomy was performed and an en­ Storz laryngostrobe unit (model 8000). A Storz zero­ dotracheal tube was connected to the respirator. degree telescope was connected to the stroboscope VTolaryngology - Head and Neck Surgery CHOt et 01. 1045 Volume 109 Number 6 A TA BRANCH LCA BRANCH \\...._- - - RLN Fig. 1. A, Posterior view of canine larynx. Anterior branch of RLN was cut just distal to peA branch (large arrow). 8, Photograph of canine larynx. Rubber electrodes applied to anterior branch (arrow) and trunk (open arrow) of RLN and external branch of SLN (arrowhead). TA, Thyroarytenoid muscle; LeA, lateral cricoarytenoid muscle; IA. interarytenoid muscle. Otolaryngology ­ Head and Neck Surgery December 1993 1046 CHOI et at OireclCaFfJUterized Di9ilolizOlion Flow MeIer Humidi'ie.!YamlAir VWrlilolor Fig. 2. SChematic drawing of experimental set-up. EGG. Electroglottography: PGG. photo­ glottography. by means of fluid-filled cables. The image from the OQ. Separate regressions were undertaken for each telescope was recorded with a Storz CCD (charge­ dependent measure. coupled device) video camera (model 9000, Storz Static study.
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