Glottic Closure Reflex Research Articles

Superior Laryngeal Nerve Block in Transcutaneous Vocal Fold Injection: A Pilot Study

Topical lidocaine remains the mainstay for anesthesia in transcutaneous vocal fold injection (VFI). While using topical lidocaine, laryngologists sometimes encounter uncontrolled reflexes or poor compliance. Superior laryngeal nerve block (SLNB) provides deep and rapid anesthesia on the larynx above the vocal folds and abolishes the glottic closure reflex. Herein, we present a pilot study to evaluate the feasibility and safety of SLNB for transcutaneous VFI and explored its usefulness. Fifty-nine patients were prospectively anesthetized with SLNB during transcutaneous VFI for unilateral vocal fold paralysis. In the SLNB group, 0.5 to 1 mL of 2% lidocaine was infiltrated on bilateral SLNs through the thyrohyoid membrane. As the control group, we included previous 47 patients who underwent VFI with topical lidocaine. In the control group, 10% lidocaine spray was applied to the laryngopharyngeal mucosa. Demographic data, laryngeal exposure, patient compliance, procedural interruption, and complications were investigated. Patient compliance was evaluated based on the frequency of cough and swallowing during VFI procedures. SLNB enabled endoscopic contact on the epiglottis and pharyngeal wall without gag reflex and provided good exposure of the procedure field on the vocal folds. In the SLNB group, the laryngeal exposure is significantly better than in the control (P=0.005). The frequency of cough and swallowing was significantly lower in the SLNB group than in the control (P < 0.001). The number of procedural interruptions was lower in the SLNB group than in the control (P < 0.001). There was no acute or delayed complication related to SLNB such as bleeding, hematoma, delayed sensory/swallowing problems, or unscheduled hospital visits. SLNB might be safe and effective for anesthesia in transcutaneous VFI. SLNB could be a good anesthetic option for patients with poor compliance despite the sufficient application of topical lidocaine.

Comparison of modified anterior and traditional posterior accesses for ultrasound-guided superior laryngeal nerve block in awake endotracheal intubation: study protocol for a randomised non-inferiority clinical trial

IntroductionAwake tracheal intubation (ATI) involves placing a tracheal tube in an awake, spontaneously breathing patient. Superior laryngeal nerve block (SLNB) can effectively abolish the glottic closure reflex, and blunt the...

Vocal Cord Dysfunction after an Inhalation Exposure

The manuscript embodies case material and the author’s extensive personal experience to address a perceived or actual airborne exposure when incorrectly judged as due to intrathoracic/lung damage when in reality the outcome is the more innocuous extrathoracic/upper airway’s vocal cord dysfunction (VCD). Because of the conviction of possible lung injury, the individual applies the fetal protective glottic closure reflex to counteract an odorant cue instigating acute VCD. Breathing against an obstructed glottis as well as hyperventilation from anxiety, panic and/or fear of personal harm worsens the laryngeal spasm. Spirometer shows flattening of the inspiratory loop of the flow-volume curve and endoscopy, while not done, would reveal adduction of the anterior two-thirds of the vocal cords with posterior chinking creating a diamond shape configuration. Successful therapy and management of VCD requires a speech therapy approach rather than physician prescribed medications.

The functional role of the pharyngeal plexus in vocal cord innervation in humans.

Classical understanding of the function of the pharyngeal plexus in humans is that it relies on both motor branches for innervation of the majority of pharyngeal muscles and sensory branches for the pharyngeal wall sensation. To date there has been no reported data on the role of the pharyngeal plexus in vocal cord innervation. The aim of this study is to evaluate whether or not the plexus pharyngeus contributes to the innervation of the vocal cords. One hundred twenty-five sides from 79 patients (59 female, 20 male) undergoing thyroid surgery with intraoperative neuromonitoring were prospectively evaluated. While vocal cord function was evaluated with endotracheal tube surface electrodes, cricothyroid and cricopharyngeal muscle electromyographic recordings were obtained with a pair of needle electrodes. The ipsilateral pharyngeal plexus, external branch of the superior laryngeal nerve, and recurrent laryngeal nerve were stimulated with a monopolar probe at 1mA. With stimulation of the plexus pharyngeus on 125 operated sides, positive electromyographic waveforms were detected from five ipsilateral vocal cords (accounting for 3.2% of all vocal cords monitored and 6.3% of patients). The mean EMG amplitude of the vocal cords with stimulation of the plexus pharyngeus was 147±35.5 μV (range 110-203). In one case, the long latency time of 19.8ms correlated with innervation by the glottic closure reflex pathway. The short latencies seen in the other four cases [3.9±1.1ms (range 3.2-5.5)] correlated with direct innervation. In some cases, the plexus pharyngeus may contribute to vocal cord innervation by reflex or direct innervation patterns in humans.

Is the External Branch of the Superior Laryngeal Nerve Dispensable in Thyroid Surgery?

There is growing evidence that the external branch of the superior laryngeal nerve (eSLN) participates in thyroarytenoid (TA) contraction, but little data quantify its role in vocal cord adduction. Injury to the eSLN, such as in thyroid surgery, is difficult to diagnose and likely underappreciated. It is the authors' belief that eSLN injury contributes to aspiration by depriving its contribution to the laryngeal plexus. The goal of this study was to measure the glottic closing force (GCF) from eSLN stimulation in a porcine model. The recurrent laryngeal nerve (RLN) and eSLN were identified bilaterally in four porcine necks. Bilateral RLNs and eSLNs were stimulated simultaneously to obtain a control GCF using a pressure transducer placed in the glottis. Subsequently, bilateral eSLNs were stimulated and the GCF measured to quantify its percent contribution to the control value. Stimulation of the RLNs and the eSLNs each led to TA muscle contraction and a measureable GCF in all four porcine necks. The control GCF was 1000.1 mmHg, while the eSLN mediated CGF was 800 mmHg. The percentage GCF attributable to the eSLN was thus 800/1000 = 80%. Reflex glottic closure is one of the most important mechanisms for the prevention of aspiration during deglutition. The biomechanical quantification of glottic closure can be shown as the GCF. This study has shown that the eSLN contributes in a significant way to the GCF in a porcine model, a finding that has not been quantified to the best of the authors' knowledge. Therefore, greater focus should be placed on preserving this nerve in thyroid surgery.

The pharyngeal plexus-mediated glottic closure response and associated neural connections of the plexus.

There continues to be a paucity of data regarding the pharyngeal plexus (PP) and its interconnectivity with the laryngeal nerves and function. To identify the specific neural pathways involved in the glottic closure reflex (GCR)-like pathway of the PP and other pathways to the thyroarytenoid (TA) muscle in the porcine model. Animal experimental study from September 2013 to June 2014 conducted in a tertiary academic medical center on male Yorkshire pigs. Contraction of the TA was detected with electromyography (EMG) during electrical stimulation of the PP in 7 porcine necks. Subsequently, the external branch of the superior laryngeal nerve (eSLN), communicating nerve of Galen (NG), and the recurrent laryngeal nerve (RLN) were sequentially transected to help elucidate the path of neural conduction. Confirmation of TA muscle contraction by EMG. Stimulation of the PP evoked a response from the TA muscle in 6 of 7 subject animals. In 3 of 7 subjects, a long latency response (mean, 14.62 milliseconds) was identified, which was eliminated only after transection of the RLN. In 3 of 7 subjects, a short latency response (mean 3.05 milliseconds) was identified, which disappeared in 1 subject each by eSLN, RLN, and NG transection. We identified the specific neural pathway involved in the PP's GCR-like pathway. We also noted a variable direct pattern of innervation to the TA.

Stimulation of denervated muscle promotes selective reinnervation, prevents synkinesis, and restores function

Previously, electrical stimulation of denervated canine laryngeal muscle was shown to promote reinnervation by native over foreign motoneurons. The goal of this study was to assess the effect of different stimulus paradigms on reinnervation quality and functional recovery. A prospective study of six canines over 8 to 20 months. A clinical model of laryngeal paralysis was used, where recurrent laryngeal nerves of the animals were sectioned and ventilation compromised. The abductor, posterior cricoarytenoid (PCA) muscles were implanted bilaterally with electrodes from an implantable pulse generator. Animals were randomly assigned to three groups to assess the effect of different stimulus paradigms: 1) 40 pulses per second (pps) train, 2) 10 pps train, 3) no stimulation. Spontaneous vocal fold movement was measured endoscopically during hypercapnia. Exercise tolerance was measured on a treadmill using pulse oximetry. In the terminal session, electromyography (EMG) potentials were recorded during superior laryngeal nerve stimulation to index foreign reinnervation of the PCA by reflex glottic closure (RGC) motoneurons. After reinnervation started, nonstimulated and stimulated 40 pps animals displayed paradoxical closure of the glottis during hypercapnia and severely decreased exercise tolerance due to faulty reinnervation. In contrast, stimulated 10 pps animals displayed minimal paradoxical closure and normal exercise tolerance (12 minutes up to 8 mph). EMG findings in this group demonstrated significantly less PCA reinnervation by foreign RGC motoneurons. PCA stimulation with low frequency reduced synkinetic reinnervation by foreign RGC motoneurons. Paradoxical closure of the glottis with inspiration was reduced and exercise tolerance restored to normal.

Modulating Effects of Hypoxia and Hypercarbia on Glottic Closing Force

Aspiration has been identified as one of the independent risk factors for development of respiratory tract infections, the incidence of which varies from 10% to 65% in patients in intensive care units. The primary defense mechanism for protection of the lower airway is the glottic closure reflex (GCR), elicited by stimulation of the internal branch of the superior laryngeal nerve. This reflex, once considered highly stable, is now considered vulnerable to a growing number of clinical factors. This study was designed to explore the biomechanical effects of hypoxia and hypercarbia, common occurrences among critically ill patients, on the GCR. Five adult male Yorkshire pigs were used in the study. Both internal superior laryngeal nerves were simultaneously stimulated with bipolar platinum-iridium electrodes. The glottic closing force (GCF) was then measured by placing a pressure transducer between the adducting vocal folds under 3 different protocols: protocol 1 (control), protocol 2 (hypoxia: partial pressure of arterial oxygen [PaO2] levels of 90, 70, and 50 mm Hg), and protocol 3 (hypercarbia: partial pressure of arterial carbon dioxide [PaCO2] levels of 60 and 70 mm Hg). Six readings were recorded under each experimental paradigm, and Student's t-test was applied to calculate the statistical significance against the control. Hypoxia reduced the GCF to 75%, 40%, and 29% of control for PaO2 levels of 90, 70, and 50 mm Hg, respectively, and hypercarbia reduced the GCF to 40% and 27% of control for PaCO2 levels of 60 and 70 mm Hg, respectively. This is the first study that highlights the biomechanical impact of hypoxia and hypercarbia on the GCR, providing a unified explanation for the increased incidence of life-threatening aspiration in critically ill patients with such alterations.

Characteristics of Glottic Closure Reflex in a Canine Model

PurposeThe most important function of the larynx is airway protection which is provided through a polysynaptic reflex closure triggered by the receptors in the glottic and supraglottic mucosa, evoking the reflex contraction of the laryngeal muscles especially by strong adduction of vocal cords. Based on the hypotheses that central facilitation is essential for this bilateral adductor reflex and that its disturbance can result in weakened laryngeal closure, we designed this study to elucidate the effect of central facilitation on this protective reflex.Materials and MethodsSeven adult, 20 kg mongrel dogs underwent evoked response laryngeal electromyography under 0.5 to 1.0 MAC (minimum alveolar concentration) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles.ResultsIpsilateral reflex closure was consistantly recorded regardless of anesthetic levels. However, contralateral reflex responses disappeared as anesthetic levels were deepened. Additionally, late responses (R2) were detected in one animal at lower level of anesthesia.ConclusionsDeepened level of anesthesia affects central facilitation and results in the loss of the crossed adductor reflex, predisposing to a weakened glottic closure response. Precise understanding of this effect may possibly provide a way to prevent aspiration in unconscious patients.

Reflex Vocal Fold Adduction in the Porcine Model: The Effects of Stimuli Delivered to Various Sensory Nerves

The aim of this study was to identify a panel of sensory nerves capable of eliciting an evoked glottic closure reflex (GCR) and to quantify the glottic closing force (GCF) of these responses in a porcine model. In 5 pigs, the internal branch of the superior laryngeal nerve (iSLN) and the trigeminal, pharyngeal plexus, glossopharyngeal, radial, and intercostal nerves were surgically isolated and electrically stimulated. During stimulation of each nerve, the GCR was detected by laryngeal electromyography and the GCF was measured with a pressure transducer. The only nerve that elicited the GCR in the 5 pigs was the iSLN. The average GCF was 288.9 mm Hg. This study demonstrates that the only afferent nerve that elicits the GCR in pigs is the iSLN, and that it should remain the focus of research for the rehabilitation of patients with absent or defective reflex vocal fold adduction.

Comparison of the Glottic Closure Reflex in Traditional “Open” Versus Endoscopic Laser Supraglottic Laryngectomy

Comparison of the Glottic Closure Reflex in Traditional “Open” Versus Endoscopic Laser Supraglottic Laryngectomy

Effects of Altered Consciousness on the Protective Glottic Closure Reflex

The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal folds. We hypothesize that central facilitation is an essential component of a bilateral brain stem-mediated adductor reflex and that its disturbance by altered consciousness or physiologic sleep could result in weakened sphincteric closure. In 10 adult pigs the glottic closure response was evaluated under light and deep isoflurane anesthesia. The internal branch of the left superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. The force of evoked glottic closure was measured with a pressure transducer positioned between the vocal folds. Consistent threshold responses (>90%) were obtained ipsilaterally from 0.5 to 2.0 minimal alveolar concentration (MAC) anesthesia. However, the contralateral reflex responses declined to 6.4% in successive trials as anesthetic levels approached 1.5 to 2.0 MAC. Furthermore, glottic closing force closely reflected these electromyographic changes, declining from 383 mm Hg at 0.5 to 1.0 MAC to 114 mm Hg at 1.5 to 2.0 MAC. Alteration of central facilitation by progressively deeper loss of consciousness abolishes a lower brain stem-mediated crossed adductor reflex, predisposing the subject to a weakened glottic closure response.

Comparison of the Glottic Closure Reflex in Traditional “Open” versus Endoscopic Laser Supraglottic Laryngectomy

Cancer of the supraglottic larynx may be surgically treated with either traditional "open" supraglottic laryngectomy (OSL) or endoscopic laser supraglottic laryngectomy (ELSL). Pharyngeal dysphagia is a well-documented consequence of traditional OSL from which near-normal swallowing characteristically recovers 14 to 40 days after surgery. Conversely, ELSL results in the resumption of serviceable swallowing within 2 to 7 days after surgery. A prospective assessment of the glottic closure reflex in 6 consecutive patients who had ELSL was performed by fiberoptic endoscopic evaluation of swallowing with sensory testing. All 6 patients with ELSL demonstrated an intact glottic closure reflex both before surgery and 48 to 72 hours after surgery. In contrast, 7 of 8 historical control patients who had OSL demonstrated a persistent absence of the glottic closure reflex 3 weeks to 12 years later. Although a number of clinical factors influence swallowing recovery, one important factor separating our patient groups was the preservation of the glottic closure reflex in patients who underwent endoscopic laser resection. Because the loss of the glottic closure response persists for years after traditional OSL, it is concluded that the sensory field deficit caused by superior laryngeal nerve section is largely not recoverable; however, compensatory mechanisms remain important in serviceable recovery, even if delayed after operation. Indeed, preservation of the glottic closure response appears to enhance swallowing recovery when equivalent compensatory mechanisms are used.

Utility of Fiberoptic Assessment in the Differential Diagnosis of Glottic Impaction versus Reflex Glottic Closure with the Laryngeal Mask Airway

Utility of Fiberoptic Assessment in the Differential Diagnosis of Glottic Impaction versus Reflex Glottic Closure with the Laryngeal Mask Airway

A Proposed Algorithm for the Management of Airway Obstruction with the Proseal??? Laryngeal Mask Airway

To the Editor: Airway obstruction is a common problem after ProSeal™ laryngeal mask airway insertion, with a frequency of between 2% (1) and 10% (2). The management depends on the etiology, which includes reflex glottic closure (deepen anesthesia or administer a muscle relaxant), epiglottic downfolding (reinsertion with maintained laryngoscopy (3) or jaw thrust (4)), glottic/supraglottic compression (5) (jaw thrust, cuff deflation or reinsertion using a smaller size), infolding of the ventral cuff (6) (cuff deflation or reinsertion using a smaller size), and malposition (reinsertion using a guided technique) (7). Distinguishing among these etiologies are the tests for malposition and mechanical obstruction. The malposition tests are only required after nonguided insertion and comprise: (i) checking for air leaks up the drain tube during positive pressure ventilation, (ii) assessing the position of the bite block in relation to the incisors (8), and (iii) the suprasternal notch tap test (9). The mechanical obstruction tests comprise: (i) jaw thrust, which decompresses the pharynx and elevates the epiglottis, and (ii) deflating the cuff, which decompresses the glottis and reduces cuff infolding (10). The algorithm synthesizes these tests to facilitate the diagnosis and management of airway obstruction with the ProSeal™ laryngeal mask airway (Fig. 1).Figure 1.: Algorithm synthesizing tests to facilitate the diagnosis and management of airway obstruction with ProSeal™ laryngeal mask airway.J. Brimacombe, MD Department of Anaesthesia and Intensive Care James Cook University Cairns Base Hospital Cairns, Australia [email protected] C. Keller, MD Department of Anaesthesia and Intensive Care Medicine Leopold-Franzens University Innsbruck, Austria

Glottic closing force: impact of thyroplasty on vocal cord paralysis in a pig model.

Reflex glottic closure is an essential component of a normal swallow. A lesion of the unilateral recurrent laryngeal nerve weakens this reflex response, affecting the essential protective functions of the larynx and potentially resulting in aspiration pneumonia, sepsis, or death. Thyroplasty has been advocated to reduce glottic incompetence due to unilateral vocal cord paralysis (UVCP). Although medialization thyroplasty has traditionally been evaluated in terms of its phonatory effect, its role in improving protective glottic closure has never been studied. The present study was designed to evaluate the effect of UVCP and thyroplasty type I on the glottic closing force (GCF). Five male Yorkshire pigs weighing approximately 40 kg were used in this study. Both internal superior laryngeal nerves were simultaneously stimulated with bipolar platinum-iridium electrodes, and the force of evoked glottic closure was measured with a pressure transducer positioned between the vocal cords. Initial pressure readings (GCF) obtained with bilaterally intact recurrent laryngeal nerves served as a control. The GCF was then measured after the right recurrent laryngeal nerve was sectioned to simulate the conditions of UVCP. Finally, thyroplasty type I was performed on the affected side, and the GCF was measured again to evaluate its quantitative effect on reflex glottic closure. The mean GCF was reduced by UVCP to approximately 22.5% (49.71 mm Hg) of the control GCF (220.25 mm Hg). Thyroplasty enhanced the GCF to 57.7% (127.08 mm Hg) of the control GCF. These measures underscore the profound effect that UVCP exerts on the GCF and the limitations of vocal cord medialization in fully restoring it.

Central facilitation of the glottic closure reflex in humans.

The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal cords. We hypothesize that central facilitation is an essential component of a bilateral adductor reflex and that its disturbance could result in weakened sphincteric closure. Five patients during supraglottic laryngectomy underwent evoked response laryngeal electromyography under 0.5 and 1.0 minimal alveolar concentration (MAC) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. Consistent threshold responses were obtained ipsilaterally from 0.5 to 1.0 MAC anesthesia. However, the contralateral reflex responses approached 0% in successive trials as anesthetic levels approached 1.0 MAC. In human subjects, alteration of central facilitation by deepening anesthesia abolishes the crossed adductor reflex, predisposing to a weakened glottic closure response. A precise understanding of this effect may improve the prevention of aspiration in patients emerging from prolonged sedation or under heavy psychotropic control.

Mapping of brain stem neuronal circuitry active during swallowing.

A poorly understood neural circuit in the brain stem controls swallowing. This experiment studied the swallowing circuit in the rat brain stem by means of fos immunocytochemistry. The fos protein is a marker of activated neurons, and under experimental conditions, repetition of a behavior causes the fos protein to be produced in the neurons involved in that behavior. The fos technique has been successfully used to delineate neural circuits involved in reflex glottic closure, cough, and vocalization; however, the technique has not been used to map the swallowing circuit. Nine rats were used in this study. Swallows were evoked in anesthetized rats for 1 hour, then, after a 4-hour delay to allow maximum fos production, the rats were painlessly sacrificed by perfusion. The brain stems were removed and sectioned in the frontal plane, and every fourth section was immunoreacted for fos protein. All sections were examined by light microscopy, and cells positive for fos were marked on drawings of brain stem structures for different levels throughout the brain stem. Control animals underwent sham experiments. After subtraction of the areas of fos labeling seen in controls, all experimental rats showed fos-labeled neurons in very discrete and localized areas, including practically all regions implicated by prior neurophysiology studies of swallowing. The distribution of labeled neurons was more dispersed through the brain stem than current theories of swallowing would suggest. Specifically, recent studies of swallowing control have focused on the nucleus of the solitary tract (NST) and the region surrounding the nucleus ambiguus (periambigual area) just rostral to the obex. These areas contained fos-labeled neurons, but unexpectedly, heavy labeling was found in the same areas caudal to the obex. Areas containing the heaviest labeling were specific subnuclei of the NST and surrounding reticular formation; the periambigual area; and the intermediate reticular zone in the pons and caudal medulla. Interestingly, none of these anatomic structures had uniform fos labeling; this finding suggests that the unlabeled areas are involved in other oromotor behaviors, or that the specific protocol did not activate the full population of swallowing-related neurons. A notable finding of this study is a candidate for the central pattern generator (CPG) of swallowing. Careful lesioning studies in cats strongly suggest that a region in the rostral-medial medulla contains the CPG for swallowing, although the exact location of the CPG was never pinpointed. In the homologous region of the rat brain stem, fos labeling was only found in a small group of neurons within the gigantocellular reticular formation that may be a candidate for the CPG. In summary, correlation with prior physiology experiments suggests that this experiment appears to have delineated many, if not all, of the components of the swallowing circuit for the first time in any mammal. In addition, other areas were found that might also be swallowing-related. One notable example is a small group of fos-labeled cells that may be the CPG for swallowing. Further studies are required to clarify the specific roles of the fos-labeled neurons seen in this study.

Critical role of central facilitation in the glottic closure reflex.

The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal cords. We hypothesize that central facilitation is an essential component of a bilateral adductor reflex and that its disturbance could result in weakened sphincteric closure. Six adult 50-kg pigs underwent evoked response laryngeal electromyography under 0.5 to 1.0 minimal alveolar concentration (MAC) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. Consistent threshold responses were obtained ipsilaterally from 0.5 to 1.0 MAC anesthesia. However, the contralateral reflex responses approached 0% in successive trials as anesthetic levels approached 1.0 MAC. Alteration of central facilitation by deepening anesthesia abolishes the crossed adductor reflex, predisposing to a weakened glottic closure response. A precise understanding of this effect may improve the prevention of aspiration in patients emerging from prolonged sedation or under heavy psychotropic control.

ラット内喉頭筋におけるsuperfast myosin heavy chainの発現

The existence of superfast myosin heavy chain (MHC), found in jaw-closing muscle and extraocular muscle (EOM), was also found in rat laryngeal muscles. Immunostaining and western blot using anti-EOM superfast MHC antibody were performed to identify and localize superfast MHC in rat laryngeal muscles. Specific reactivity of laryngeal II L MHC was confirmed by western blot. By immunostaining, all fibers in the thyroarytenoid muscle reacted with EOM superfast MHC antibody. A scattered pattern of positive fibers was observed in the vocalis, the posterior cricoarytenoid and the lateral cricoarytenoid muscles. EOM superfast MHC was not detected in thecricothyroid muscle. Co-expression of EOM superfast MHC and type II B MHC was observed, and expression of EOM superfast MHC was seen in laryngeal muscle innervated only by recurrent laryngeal nerve, with the highest density of EOM superfast MHC in the thyroarytenoid muscle. The expression of EOM superfast MHC in rat laryngeal muscle is consistent with the functional demands for airway protection and glottic closure reflex. The MHC phenotype, or relative composition of myosin heavy chains, reflected the physiologic demands on each laryngeal muscle.