Intrinsic Laryngeal Muscles Research Articles

The fate of the first avian somite.

We have studied the derivatives of the first somite using the quail-chick marking technique. After transplantation of the somite, the chick embryos were reincubated for periods ranging from 4 h to 11 days. Coronal and sagittal sections of the embryos were prepared for parallel staining with Feulgen-reaction, anti-quail antibody, anti-desmin antibody and QH-1 antibody. The first somite consists of an epithelial envelope surrounding somitocoele cells. Like other somites, it forms sclerotome, dermatome and myotome. Cells contribute to the occipital and parasphenoid bone, the meninges, the dermis in the occipital region and the pharyngeal connective tissue. The contribution of the first somite to bones, meninges, dermis and pharyngeal connective tissue is characterised by sharp anterior and posterior boundaries. In contrast, other derivatives such as connective tissue surrounding the vagus nerve, the carotid artery, and jugular vein exceed 10 to 18 segments. This is also true for myogenic cells participating in the formation of the cucullaris capitis muscle that extends from the temporal bone to the shoulder. In one third of the embryos, myocytes of the intrinsic laryngeal muscles are derived from the grafted first somite. Moreover, endothelial cells originate from this somite and migrate into the head (hind-brain, meninges, dermis), neck (pharynx, connective tissue surrounding the vagus nerve, carotid artery and jugular vein) and thorax. With respect to differentiation and derivatives the first somite is similar to other somites.

Growth patterns of piriform sinus carcinomas.

Advances in functional surgery have encouraged many head and neck surgeons to treat piriform sinus carcinomas, whenever possible, by conservation surgery. An increased understanding of the histopathologic growth pattern and spread of piriform sinus carcionomas is needed to define criteria for appropriate application of voice preservation surgery. The purpose of this study was to analyze the patterns of tumor spread to laryngeal and parapharyngeal structures. A total of 42 specimens obtained by laryngopharyngectomy were subjected to a whole-organ section study. Carcinomas confined to the lateral wall tended to extend laterally beyond the thyroid ala and rarely infiltrated the intrinsic laryngeal muscles. As a result, conservation surgery could be possible in many cases, including T4 carcinomas. Carcinomas confined to the medial wall or occupying the whole piriform sinus tended to infiltrate laryngeal structures early, and hemilaryngeal fixation was observed in 61% of these cases; tumor spread to the contralateral side in 64%. The hemilarynx fixation was due to an invasion of intrinsic laryngeal muscles. An isolated perineural or cricoarytenoid joint involvement was never observed. For these tumors, conservation surgery would be inadequate in most cases, as they often present extensive laryngeal involvement with spread to the contralateral side.

Artificial control of glottic adduction for aspiration by orderly recruitment in the canine.

Laryngeal adduction for swallowing chiefly involves contraction of the thyroarytenoid and lateral cricoarytenoid muscles to seal the glottic chink. Vocal cord elongation supplements closure through cricoarytenoid activation. Relaxation of the posterior cricoarytenoid muscle is also involved in the swallowing process. Recent interest has focused on stimulating the laryngeal nerves to protect the lower airway from conditions where normal muscular coordination may be disrupted (e.g., in aspiration following stroke). Unfortunately, electrical stimulation results in a generalized contraction of all the dependent intrinsic laryngeal muscles because the larger, more excitable axons fire before their smaller counterparts can be activated. In the physiological state, however, the smaller fibers are recruited first. The current study focuses on electronic manipulation of force in the glottic muscles involved in deglutition. We used a stimulator that could selectively activate the intrinsic laryngeal muscles based on their specific motor unit architectures. In 5 dogs, the circuit recruited the axons in the recurrent and superior laryngeal nerves from small to large. The muscles were identified according to the differential recruitment rates of their compound muscle action potentials as they appeared on the graph. The smaller axons in the thyroarytenoid recruited faster than the large ones found in the lateral cricoarytenoid muscles, with intermediate figures observed with the cricothyroid. The posterior cricoarytenoid presented with the slowest recruitment rates, as expected from this muscle's highest contingent of larger motor units. Latencies between the onsets of stimulations and muscle saturations also appeared stable. This approach to manipulating glottic force saves energy because it allows stimulating the adductory muscles with minimal interference from their abductor antagonist.

Loss of large myelinated nerve fibres of the recurrent laryngeal nerve in patients with multiple system atrophy and vocal cord palsy.

OBJECTIVES: Vocal cord palsy seen in some patients with multiple system atrophy may result from neuronopathy of the recurrent laryngeal nerve. METHODS: Six controls and six patients with multiple system...

Activation of intrinsic laryngeal muscles during cough.

We studied the pattern of discharge of the posterior cricoarytenoid (PCA), cricothyroid (CT), thyroarytenoid (TA), and arytenoideus transversus (AR) muscles during cough in 12 anesthetized dogs. Diaphragm electromyographic (EMG) activity was also recorded, together with subglottic and esophageal pressures. Trains of repetitive coughs were induced by mechanically stimulating the tracheobronchial airway. Trials with the upper airway isolated from and connected to the lower airway were performed before and following bilateral sectioning of the internal branch of the superior laryngeal nerve (SLN). The immediate effect of tracheal stimulation was an "apneic" period at FRC, during which the PCA, a laryngeal abductor, showed a progressive increase in activity accompanied by small, variable increases in the activity of the CT and the laryngeal adductors, the TA and AR. The subsequent cough efforts were divided into three phases: inspiration, glottic narrowing, and forced expiration. PCA activity was greatest during the inspiratory phase and CT activity was greatest during the expiratory phase. Peak subglottic pressure occurred during glottic narrowing and coincided with the greatest activation of the TA and AR during the cough effort, and suppression of the PCA and CT. The patterns of EMG activation were not affected by the route of breathing or SLN section. The results suggest the presence of a uniquely central process controlling laryngeal muscles during cough, independent of laryngeal sensory feedback.

鼻腔ｆｌｏｗ刺激の内喉頭筋活動への影響

During the airway reflex deriving from the nose or the larynx, the activities of the respiratory, pharyngeal and intrinsic laryngeal muscles are coordinated. In decerebrate cats, the flow stimulation delivered to the nose prolongs the respiratory cycle time and decreases the amplitude of diaphragmatic activity. The purpose of this study was to analyze whether this nasal flow stimulation influenced the activities of the intrinsic laryngeal muscles.The spontaneous activities of the intrinsic laryngeal muscles and the evoked potentials induced by electrical stimulation to the internal branch of the superior laryngeal nerve (SLN), i. e., the laryngeal reflex, were recorded during nasal flow stimulation in decerebrate cats. A laryngeal reflex was induced by a single SLN stimulation (1Hz).During quiet respiration, the magnitude of the laryngeal reflex recorded from the thyroarytenoid muscle (TA) increased in phase with expiration. In contrast, the magnitude of the laryngeal reflex recorded from the posterior cricoarytenoid muscle (PCA) increased in phase with inspiration. During the period of nasal flow stimulation, TA and PCA activity increased. Moreover, the magnitude of the laryngeal reflex from the TA and PCA during nasal stimulation also greatly increased. These results suggest that the nasal flow stimulation increased the excitability of the motoneurons innervating the laryngeal adductor and abductor muscles. Such an increase in the excitability of the intrinsic laryngeal motoneurons was observed in both the inspiratory and expiratory phases.The functional significance of this phenomenon may be that nasal flow stimulation decreases the inspiratory activity of the diaphragm so as to prevent the inhalation of foreign bodies and increases the activity of the intrinsic laryngeal muscles, thereby increasing the likelihood of the airway reflex.

Occurrence of capillaries with fenestrae in the intrinsic laryngeal muscles of the guinea pig after unilateral denervation.

Capillaries in the posterior cricoarytenoid and the arytenoid muscles of the guinea pig were examined by electron microscopy 3 days after transection of unilateral recurrent laryngeal nerve. The denervated posterior cricoarytenoid muscle had neuromuscular junctions (NMJs) lacking terminal axons, while in the unpaired arytenoid muscle, normal and denervated NMJs coexisted among muscle fibres being seemingly normal. Capillaries in both muscles were almost of the continuous type. However, approximately 10% of capillaries around the denervated NMJs and among some muscle fibres in both muscles, often had a small number (< 10) of fenestrae bridged by a single-layered diaphragm. The untreated normal muscles contained only continuous capillaries. These findings suggest that denervation may induce the fenestrated changes of intramuscular capillaries.

一パーキンソン病患者の音声障害 声のｆｒｅｅｚｉｎｇ現象

薬効ピーク時に移動能力, ADLが向上する一方で, 一時的な起声困難が出現する若年性パーキンソン病患者を経験した.本症例の起声困難はドラッグコントロールにより改善しており, 薬物 (L-DOPA) に起因するすくみ現象による声帯の内転障害と考えられた.同一個体内で歩行と発声という異なる運動間ですくみ現象が時間的解離をもって出現した原因について考察した.結果, 同一個体内においても四肢・体幹と喉頭ですくみ現象の発現機序に相違がある可能性, あるいは薬物の治療閾値がおのおのの筋において異なる可能性を考えた.また, 本症例の起声困難には“kinesie paradoxale”を伴っており, 声帯のすくみ現象には発声を他の目標行動に変換して誘発する方法が有用であった.A 62-year-old man with juvenile Parkinson's disease was reported. When L-Dopa was working the patient felt difficulty in voicing although he could walk smoothly. Meanwhile, when L-Dopa was not working his difficulty in voicing disappeared but he was unable to walk. This discrepancy between voicing and walking is disussed.Laryngofiberscopic examination showed the following intriguing findings. When L-Dopa was working the patient's vocal cords assumed the hyperabduction position. Also, during an attempts at phonation, the vocal cords developed a tendency to adduct but were unable to. This movement seemed to correspond to a“freezing”phenomenon in walking. The adduction tendency of the vocal cords ameliorated temporazily by voluntarily making a cough instead of voicing. Such a phenomenon appeared as a freezing of vocal cord movement with kinesie paradoxale.Two hypotheses were raised to explain this “see-saw” phenomenon between voicing and walking. First, the mechanism of the freezing phenomenon might differ for voicing and walking. Second, the threshold for the effectiveness of L-Dopa might differ for the intrinsic laryngeal muscles controlling voicing and for the limb and truncal muscles controlling walking. The task of hawking which we attempted was very useful in speech therapy on PD patients who exhibited the freezing phenomenon of the vocal cords with kinesie paradoxale.

Cricoarytenoid joint mobility after chronic vocal cord paralysis.

Eleven whole organ laryngeal specimens (10 human and 1 dog) with a history of long-standing (6 months to 17 years) paralysis were studied histopathologically for changes in the cricoarytenoid (CA) joints and the intrinsic laryngeal musculature. In 9 cases the paralysis was unilateral and in 2 bilateral. No evidence of CA joint ankylosis (fibrous/osseous obliteration of joint space or degeneration of articular surfaces) was seen in the specimens. The absence of CA joint ankylosis permits the efficacy of thyroplasty medialization procedures.

Contraction patterns of intrinsic laryngeal muscles induced by orderly recruitment in the canine.

The specific performance of intrinsic laryngeal muscles has been difficult to evaluate, especially in living subjects. To reproduce natural contractions, we artificially induced orderly recruitment of their innervating axons according to the size principle. In 5 dogs, both recurrent laryngeal nerves (RLNs) were stimulated with 50 through 10 Hz, 300 to 1000 microA currents while 600 Hz, 1000 to 0 microA decreasing blocking currents were administered. Surface electromyography electrodes placed on the thyroarytenoid, posterior cricoarytenoid, and lateral cricoarytenoid muscles were used to determine the amplitudes (in mA) of compound muscle action potentials. There was a highly statistically significant difference (P<.004) between the thyroarytenoideus which had the fastest rate of recruitment (8.38%), and posterior cricoarytenoideus, which had the slowest (4.81%). There was an intermediate recruitment rate (6.72%) of the lateral cricoarytenoideus, a divergence attributed to a more equal distribution in fast and slow types of myofibers and a smaller sample. We submit that RLN axons can be recruited in an orderly manner according to their sizes and that the rates are unique to the muscle classes they innervate. The parameters defining these contraction patterns may offer key information for laryngeal pacing.

Hyaluronan localization in the rabbit larynx.

The larynx is a complex organ composed of different connective tissue elements. So far, the extracellular matrix of the larynx has not been thoroughly described. Hyaluronan is a matrix polysaccharide with physicochemical effects and biological cell functions in soft connective tissues. The histochemical distribution of hyaluronan (hyaluronic acid, hyaluronate) was studied in tissue sections from various levels of the rabbit larynx by means of a hyaluronan-binding protein and avidin biotin peroxidase staining. Microwave-aided fixation was used to retain the extracellular location of hyaluronan. Hyaluronan accumulated chiefly in the subepithelial lamina propria and in the connective tissue enclosing striated muscle fibres of the thyroarytenoid muscle and vocalis muscle. This localization contrasted sharply with the weak staining for hyaluronan in muscles external to the thyroid cartilage. Intensive staining for hyaluronan was found in perivascular and periglandular connective tissue, as in the vacuoles of the hyaline cartilage of the thyroid, cricoid and arytenoid cartilages, and to a lesser extent in the lacunae of the chondrocytes and in the perichondrium of the elastic cartilage of the epiglottis. Hyaluronan was heterogenously distributed in the rabbit larynx. It was abundant in intrinsic laryngeal muscles performing small, precise, and rapid movements and in the subepithelium at the glottic level, where it may facilitate mucosal movements. The abundant hyaluronan in the subglottic region may be involved in the control of vascular leakage and edema formation.

Influence of continuous positive airway pressure on EMG activities of the cricothyroid and posterior cricoarytenoid muscles of the canine larynx.

We investigated the effect of different levels of continuous positive airway pressure (CPAP) on the cricothyroid (CT; a tensor muscle of the vocal folds) and posterior cricoarytenoid (PCA; sole abductor muscle of the vocal folds) muscles in dogs. Prospective, controlled animal study. Nine mongrel dogs of both sexes. University research laboratory. After insertion of a cuffed tracheotomy tube low in the neck the compound EMG responses of the CT and PCA muscles during spontaneous respiration were measured simultaneously under different levels (2, 4, 6, and 8 cmH2O) of positive end-expiratory pressure (PEEP). The CT showed a progressive increase in phasic expiratory EMG activity with the application of graded levels of PEEP. Application of PEEP over 4 cmH2O produced significant increases in the phasic CT activity (P < 0.05). In contrast to the CT, the PCA failed to increase phasic inspiratory EMG activity statistically until a 8 cmH2O of PEEP was applied (P < 0.05). The phasic expiratory CT and inspiratory PCA activities were 297.9 +/- 77.6 and 124.5 +/- 22.9, respectively, at the application of 6 cmH2O of PEEP (percentage of control, mean +/- SD). This study confirms the difference in sensitivity between adductor and abductor laryngeal muscles, demonstrating that the intrinsic laryngeal muscles do not all behave similarly after the application of CPAP.

Experimental study on neurorrhaphy of the recurrent laryngeal nerve in dogs

The effectiveness of anastomosis of a divided recurrent laryngeal nerve was evaluated in six adult mongrel dogs. Videolaryngoscopy and evoked compound muscle action potentials in the intrinsic laryngeal muscles were performed at six months and the posterior cricoarytenoid muscles and recurrent laryngeal nerves were processed for histomorphometric studies. Recovery of compound muscle action potentials in all re-innervated muscles and histomorphometric findings confirmed a good grade of axonal regeneration. The most significant histomorphometric changes observed were: a reactive hypertrophy of type I fibres in the posterior cricoarytenoid muscles of the re-innervated side, and a high nerve fibre density in the distal stump to the anastomosis. However, incomplete recovery of motion and fasciculated movements of the re-innervated vocal folds were observed. Reduction of effective motor units in the re-innervated muscles might be a factor that cause incomplete restoration of vocal fold movements.

Nitrergic Innervation of the Rat Larynx Measured by Nitric Oxide Synthase Immunohistochemistry and Nadph-Diaphorase Histochemistry

We evaluated the involvement of nitric oxide (NO) in the laryngeal innervation of rats using NADPH-diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry. The findings obtained by NADPH-d histochemistry were identical with those obtained by nNOS immunohistochemistry, indicating that NADPH-d is nNOS in the laryngeal innervation system. We found NADPH-d-positive nerve fibers in every region of the larynx. In the epithelia of the mucosa, a small number of NADPH-d-positive nerve fibers were detected. The plexus of NADPH-d-positive nerve fibers was commonly found in the lamina propria, and some of these fibers were clearly associated with blood vessels. We also noted NADPH-d-positive nerve fibers in the region of laryngeal glands. Some of these fibers appeared to terminate in the glandular cells. We found NADPH-d-positive nerve fibers with varicosities in the intrinsic laryngeal muscle and free-ending nerve fibers on the muscle fiber. Motor end plate-like structures were positive for NADPH-d histochemistry. The NADPH-d-positive nerve fibers appeared to terminate at motor end plate-like structures in two of nine rats examined. A cluster of NADPH-d-positive neurons were occasionally present in the lamina propria of the laryngeal mucosa, in the connective tissue between the thyroid cartilage and intrinsic laryngeal muscle, and in the connective tissue near the cricoarytenoid joint. The present findings suggest that NO participates in the autonomic, sensory, and motor innervation of the larynx.

Repeatedly successful closure of the larynx for the treatment of chronic aspiration with the use of botulinum toxin A.

Botulinum toxin A was used preoperatively to temporarily paralyze the intrinsic laryngeal muscles to hinder movements during the healing period after operation. In addition, toxin was injected into the cricopharyngeal muscle to allow a better passive drainage of the saliva into the esophagus. We treated six patients. Three suffered from chronic aspiration problems after multiple lower cranial nerve lesions, and three patients were apallic (after stroke and major brain injury). Two weeks before scheduled operation, we injected the toxin into the posterior cricoarytenoid muscles, the aryepiglottic muscles, and the vocalis muscle on both sides, as well as the cricopharyngeal muscle. The amount of injected toxin varied between 1.0 and 1.4 mL, equal to 200 to 280 units of botulinum toxin A (Dysport). After a complete palsy of these muscles (controlled by direct electromyography), a closure of the larynx was performed. After laminotomy and exposure of the intralaryngeal structures, the false vocal cords were mobilized and adapted with sutures. Because involuntary movements of the intralaryngeal musculature were absent, primary healing without complications occurred in all cases. Aspiration and related complications disappeared in all patients. In addition, the intensity of patient care could be considerably reduced. Preoperative use of botulinum toxin A allows sufficient laryngeal closure. This procedure is especially useful in the treatment of children and young adults, preserving the ability of later speech rehabilitation because of the return of voluntary movements of the intrinsic laryngeal muscles 6 months after the injection. Furthermore, this technique, as minimal surgical intervention, can be performed in high-risk patients.

Laryngeal Muscle Activity During Speech Breaks in Adductor Spasmodic Dysphonia

To determine the laryngeal muscle activation abnormalities that are associated with speech symptoms in adductor spasmodic dysphonia (ADSD), electromyographic measures of extrinsic and intrinsic laryngeal muscles during speech compared 1) muscle activity when ADSD patients had breaks in words with when they produced the same words without breaks; and 2) muscle activity in ADSD patients during speech without voice breaks with normal control producing phonetically similar words. Simultaneous electromyographic recordings were made from the thyroarytenoid (TA), cricothyroid (CT), sternothyroid (ST), thyrohyoid (TH) and the posterior cricoarytenoid (PCA) muscles during speech testing in 11 ADSD patients and 10 control subjects. Speech breaks were identified and mean muscle activity measured starting 100 ms preceding a voice break and for the remainder of the word. Mean muscle activity level was significantly greater on break than non break words in ADSD patients only for the thyroarytenoid muscle (p<.001). No significant differences were found between the ADSD and control subjects during non break words for any of the laryngeal muscles studied. The results demonstrated that 1) only the thyroarytenoid, of the muscles tested, was affected in ADSD, 2) that muscle activation abnormalities were spasmodic, only appearing when symptoms occurred and 3) no imbalances of muscle tone were evident when speech disruptions did not appear.

Feasibility and design of a battery powered EMG/nerve conduction velocity instrument

Summary: The clinical picture of a paralyzed vocal fold often has the same appearance as a subluxated arytenoid, with anterior and medial displacement of the arytenoid and a foreshortened and lax vocal fold. Previous work by the authors has shown that a subluxated arytenoid may be permanently repositioned by reduction and selective injection of the intrinsic laryngeal musculature with botulinum toxin. The injection changes the forces within the larynx, allowing the arytenoid to be brought back to proper position on the cricoid cartilage. This concept has been extended to the paralyzed vocal fold. It has been noted that even a clinically paralyzed vocal fold has voluntary motor units that may still act on the arytenoid through residual action from the interarytenoid and synkinesis. These forces are significant enough to manipulate the arytenoid and, thus, the vocal fold, into its correct, adducted position. In this paper, the arytenoid is mobilized to free any fibrosis. The thyroarytenoid and lateral cricoarytenoid muscles are then injected to prevent any forward synkinetic pull on the arytenoid. Next, a Gelfoam injection medializes the vocal fold to create glottic closure. This rebalancing sufficiently positions the arytenoid, so that valvular function is permanently restored. In the ten patients studied for over 1 year, there was a 90% success rate as measured by videostroboscopy, phonation time, and V-RQOL analysis. There were no untoward complications. All the materials used are nonpermanent. The procedure does not limit other techniques from being performed at a later time.

Nitrergic neurons in the canine intrinsic laryngeal muscle

Nitrergic ganglionic cells located in the canine intrinsic laryngeal muscle were studied by NADPH-diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry. Cells intensely stained by NADPH-d histochemistry were found between the striated muscle fibers of the intrinsic laryngeal muscle. Most of these cells were bipolar or pseudounipolar in form. Some NADPH-d negative cells were observed to be enveloped in a mesh by varicose NADPH-d positive nerve fibers. The findings obtained by nNOS immunohistochemistry corresponded well with those obtained by NADPH-d histochemistry, indicating that NADPH-d activity in the ganglion in the intrinsic laryngeal muscle is nNOS. The present findings clearly indicate that some of the ganglion cells located in the canine intrinsic laryngeal muscle are nitrergic, and that the ganglionic cells synapse together with the participation of nitric oxide in integrating ganglionic cells.

ラット内喉頭筋線維の生後変化

The purpose of this study was to analyse the postnatal development of the intrinsic laryngeal muscle fibers using the myosin ATPase stain method. We measured the ratio of type IIc fibers in all of the intrinsic laryngeal muscle fibers in postnatal-day (PND) 1, 3, 7, 14, 21 and mature Sprague-Dawley rats.Type IIC fibers disappear at PND 14 in most intrinsic laryngeal muscle fibers. However, the decreasing rate of the fibers is different for various intrinsic laryngeal muscles. Decreases in type IIc fibers are observed most in the lateral compartment of the thyroarytenoid muscle (1-TA), and then in the posterior cricoarytenoid muscle (PCA), cricothyroid muscle (CT), lateral cricoarytenoid muscle (LCA), interarytenoid muscle (IA) and the medial compartment of the thyroarytenoid muscle (m-TA).These results suggest that the differentiation of the intrinsic laryngeal muscle fibers in rats is nearly accomplished by the end of the second week.

Differential effects of propofol, thiamylal and ketamine on the cricothyroid and posterior cricoarytenoid muscles of the canine larynx

To measure the electromyographic (EMG) responses of the phasic discharge in the cricothyroid (CT; a tensor muscle of the vocal folds) and the posterior cricoarytenoid (PCA; sole abductor muscle of the vocal folds) following intravenous infusion of propofol 1.0 mg.kg-1.min-1, thiamylal 1.0 mg.kg-1.min-1, or ketamine 0.5 mg.kg-1.min-1 for five minutes. Prospective, nonrandomized, controlled animal study. University research laboratory. Fifteen mongrel dogs, including three groups of five animals in each group. Under 0.2-0.3% halothane and oxygen anesthesia with spontaneous ventilation, phasic EMG activities of the CT and PCA muscles were recorded in an identical manner after the administration of each drug. Propofol infusion produced almost equal suppression of EMG activity of the CT and the PCA with time and three minutes after the start of infusion of propofol there was a significant depression of the phasic activities in the both muscles; EMG activity of the CT and the PCA was 33.8 +/- 21.2 and 36.6 +/- 22.9% (% of control, mean +/- SD) respectively P < 0.05). Thiamylal selectively reduced rhythmic discharges in the CT muscle during spontaneous breathing and significant depression of discharge in the CT muscle was observed three minutes after the drug (47.3 +/- 24.9%, P < 0.05). In contrast, both phasic EMG activities of the CT and the PCA were rhythmically active and the differential sensitivity between the CT and the PCA muscles was not observed after ketamine, even after ten minutes of administration. This study confirms a difference in sensitivity between the CT and the PCA muscles, demonstrating that the intrinsic laryngeal muscles do not behave similarly after the administration of conventional intravenous anaesthetic agents.