Cricothyroid Muscle Research Articles

Effects of a Semioccluded Vocal Tract on Laryngeal Muscle Activity and Glottal Adduction in a Single Female Subject

Voice training exploits semiocclusives, which increase vocal tract interaction with the source. Modeling results suggest that vocal economy (maximum flow declination rate divided by maximum area declination rate, MADR) is improved by matching the glottal and vocal tract impedances. Changes in MADR may be correlated with thyroarytenoid (TA) muscle activity. Here the effects of impedance matching are studied for laryngeal muscle activity and glottal resistance. One female repeated [pa:p:a] before and immediately after (a) phonation into different-sized tubes and (b) voiced bilabial fricative [β:]. To allow estimation of subglottic pressure from the oral pressure, [p] was inserted also in the repetitions of the semiocclusions. Airflow was registered using a flow mask. EMG was registered from TA, cricothyroid (CT) and lateral cricoarytenoid (LCA) muscles. Phonation was simulated using a 7 × 5 × 5 point-mass model of the vocal folds, allowing inputs of simulated laryngeal muscle activation. The variables were TA, CT and LCA activities. Increased vocal tract impedance caused the subject to raise TA activity compared to CT and LCA activities. Computer simulation showed that higher glottal economy and efficiency (oral radiated power divided by aerodynamic power) were obtained with a higher TA/CT ratio when LCA activity was tuned for ideal adduction.

Recurrent Laryngeal Nerve Palsy on Integrated Positron Emission Tomography-Computed Tomography

A 75-year-old woman with a long-standing history of smoking and emphysema presented with hoarseness and hemoptysis. Computed tomography (CT) scan found a large soft tissue mass involving the superior mediastinum and aortic-pulmonary window (Figure 1). Left main stem biopsy revealed small cell carcinoma. Apart from left vocal cord paralysis, no other laryngeal lesion was identified on bronchoscopy. Co-registered CT-Positron emission tomography (PET) fusion images identified physiologic fluorodeoxyglucose (FDG) uptake in the right vocal cord but no uptake in the left vocal cord (Figure 2). Physiologic tracer uptake in the laryngeal muscles occurs during speech but not when a patient remains completely silent.1 When the recurrent laryngeal nerve is paralyzed, the ipsilateral vocal fold is fixed in a paramedian position due to the unopposed action of the cricothyroid muscle innervated by the superior laryngeal nerve.2 The compensatory movement during phonation of the contralateral vocal cord results in increased workload, and leads to increased local glucose consumption. The combination of a left mediastinal mass with aorto-pulmonary window involvement or at the left lung apex (i.e., the anatomic course of the recurrent laryngeal nerve) and concomitant right-sided increased uptake in laryngeal muscles is a finding that can be seen in patients with recurrent left-sided laryngeal nerve palsy.3 Although FDG-PET is a sensitive imaging modality for lung cancer staging, anatomic localization of lesions detected at PET is suboptimal. Co-registered CT-PET fusion images allow the focal FDG uptake to be reliably localized to the small internal laryngeal muscles.

Establishing a New Animal Model for the Study of Laryngeal Biology and Disease: An Anatomic Study of the Mouse Larynx

Animal models have contributed greatly to the study of voice, permitting the examination of laryngeal biology and the testing of surgical, medical, and behavioral interventions. Various models have been used. However, until recently, the mouse (Mus musculus) has not been used in laryngeal research, and features of the mouse larynx have not been defined. Therefore, the purpose of this study was to qualitatively describe mouse laryngeal anatomy in relation to known human anatomy. Larynges of 7 C57BL mice were examined and photographed under stereotactic and light microscopy. The authors found that mouse laryngeal organization was similar to that of humans. The hyoid bone and epiglottal, thyroid, cricoid, and arytenoid cartilages were identified. An additional cartilage was present ventrally. Thyroarytenoid, posterior cricoarytenoid, lateral cricoarytenoid, and cricothyroid muscles were grossly positioned as in humans. Interarytenoid muscles were not present; however, a functional counterpart was identified. The authors provide an initial description of mouse laryngeal anatomy. Because of its amenability to genetic engineering, the mouse is the premiere model for the study of disease and the testing of interventions. Introduction of the mouse model for laryngeal study offers a tool for the study of normal laryngeal cell biology and tissue response to disease processes.

Injection of Botulinum Toxin into External Laryngeal Muscles in Pediatric Laryngeal Paralysis

I undertook to demonstrate the effect of injecting botulinum toxin type A (BTA) into cricothyroid, sternothyroid, and sternohyoid muscles in cases of bilateral laryngeal paralysis (BLP). Tracheostomy remains the consistently reproducible and accepted method to salvage the airway obstruction in BLP. The bypass, however, acknowledges the current lack of knowledge and consensus on the pathogenesis. I performed a retrospective chart review of BLP cases treated with BTA in a tertiary care pediatric center. The injections were performed under direct vision through an open transcervical approach. The main outcome measures used were improvement of airway symptoms and endoscopic findings, tracheostomy requirement, and incidence of recovery of function. In total, 24 patients with BLP were identified. Over a 2-year period, 7 patients were treated with BTA. Six patients had congenital idiopathic BLP. One of these had trisomy 7. One patient acquired the paralysis after cardiac surgery. No patients required a tracheostomy, except for the infant with trisomy 7. Six patients recovered function completely, and the seventh recovered it partially (range, 4 weeks to 12 months). Injection of BTA into external laryngeal muscles may be an alternative to tracheostomy in BLP. It is proposed that the toxin relaxes the glottic aperture by paralyzing the cricothyroid and strap muscles and that it may aid in appropriate reinnervation of the larynx via mechanisms beyond the neuromuscular junction.

R429 – Irradiation Changes MyHC Expression in Rat Larynx

Problem Laryngeal cancer treatment involves radiotherapy, laser treatment, and/or surgery. Radiotherapy does not impair voice quality as much as laser treatment or surgery but can induce muscle wasting, fibrosis, and dry mouth symptoms. To elucidate the molecular mechanisms involved in such changes, we investigated the effect of irradiation on myosin heavy chain (MyHC) expression in laryngeal muscles. Methods Rats were irradiated with one dose of 10, 15, 20, 25, 30, or 35 Gy and sacrificed 2 weeks later. Other rats were irradiated with 20 Gy and sacrificed 3 days or 2, 4, or 12 weeks later. The thyroarytenoid (TA), posterior cricoarytenoid (PCA), cricothyroid (CT), and digastric (DG) muscles were subjected to SYBR Green real time-reverse transcriptase-PCR. Results Radiation exceeding 20 Gy killed all rats within 7-12 days. Two weeks after irradiation with 10, 15, or 20 Gy, MyHC type IIa expression had decreased in a dose-dependent manner in the PCA and CT muscles and in a dose-independent manner in the TA muscle. The expression of MyHC IIx and IIL also decreased but in a dose-dependent manner in the TA muscle and a dose-independent manner in the PCA and CT muscles. In the 20 Gy-irradiated rats, MyHC IIx, IIL, and especially IIa expression declined over 12 weeks. Conclusion The laryngeal muscles responded differently to radiation but showed a time-dependent and long-lasting decrease in the expression of all MyHC isoforms. MyHC IIa expression in the PCA and CT muscles may be more sensitive to irradiation than the other MyHC isoforms. Significance All of these observations together support the notion that if the radiation-induced changes in MyHC expression in the larynx can be ameliorated by an as-yet undefined method, it may be possible to restore to normal the laryngeal muscles of larynx cancer patients who have been trated with radiation therapy, therepy presevering their voice quality. Support This work was supported by the Korea Research Foundation Grant funded by the Korea Govement (MOE-HRD)” (KRF-2006-331-E00235).

Intrinsic Laryngeal Muscle Reinnervation Using the Muscle-Nerve-Muscle Technique

This study was performed to investigate the muscle-nerve-muscle reinnervation technique in the larynx, in which a nerve conduit implanted into an innervated muscle conducts axonal sprouting into a denervated muscle while maintaining function of the donor muscle. In this study, the muscle-nerve-muscle technique was used to direct superior laryngeal nerve axons to reinnervate intrinsic laryngeal muscles by implanting the recurrent laryngeal nerve stump into the cricothyroid muscle in 8 dogs. In 4 of the dogs, the recurrent laryngeal nerve trunk to the adductor muscles was divided so that all axonal sprouting was directed to the posterior cricoarytenoid muscle. Six-month electromyography data were obtained from 6 of the 8 dogs. All 6 dogs showed evidence of successful reinnervation of the thyroarytenoid or posterior cricoarytenoid muscles with action potentials that corresponded to spontaneous respiratory efforts, while the donor cricothyroid muscles retained their phasic contraction. These responses were obliterated when the recurrent laryngeal nerve conduit was divided. Histologic examination of the intrinsic laryngeal muscles demonstrated successful reinnervation. The results confirm that intrinsic laryngeal muscles may be successfully reinnervated by the superior laryngeal nerve with the muscle-nerve-muscle technique, without sacrifice of function of the cricothyroid muscle. This method offers an alternative source of appropriately firing axons for laryngeal reinnervation procedures.

Estimation of the number and size of motor units in intrinsic laryngeal muscles using morphometric methods

The number and size of motor units in the intrinsic laryngeal muscles were estimated by morphometric methods. Laryngeal muscles with their respective nerve branches were obtained from 64 fresh cadavers (32 older than 60 years, mean age 74 +/- 9 years and 32 younger than 60 years, mean age 51 +/- 8 years). Myelinated nerve fibers and the total number of muscle fibers were counted. Motor unit size was estimated by dividing the total number of muscle fibers by the total number of motor units in each case. The mean number of motor units ranged from 268 +/- 1.3 (interarytenoid muscle) to 431 +/- 1.6 (cricothyroid muscle). Thyroarytenoid and cricothyroid muscle presented the smallest (9.8 +/- 0.2) and largest (20.5 +/- 0.9) motor unit size, respectively, suggesting that thyroarytenoid muscle has a greater capacity to fine-tune its total force compared with the other intrinsic laryngeal muscles. No differences in motor unit number or size were observed between the right and left sides or between younger and older subjects. It is suggested that synaptic rearrangements may occur at the level of the neuromuscular junction in the human larynx that may explain the age-related changes in motor units reported by clinical methods.

The Human Cricothyroid Muscle: Three Muscle Bellies and Their Innervation Patterns

We hypothesized that the phonatory and respiratory functions of the human cricothyroid (CT) muscle are subserved by separately controlled muscle bellies. In this work, 30 autopsied adult human hemilarynges were used to determine the neuromuscular organization of the CT muscle using microdissection, histology, and Sihler's stain. The results showed that the human CT was composed of three bellies: rectus, oblique, and horizontal. External superior laryngeal nerve (ESLN) was found to enter into the CT muscle as a single trunk (37.5%) or multiple (two to five) branches (62.5%). Within the CT muscle, the ESLN gave off three to seven branches to innervate the rectus belly and one or two branches to supply the oblique and horizontal bellies, respectively. Notably, ESLN also gave off branches to innervate the ipsilateral thyroarytenoid muscle (46%) and subglottic mucosa (67%) or connect with the recurrent laryngeal nerve (25%). These findings suggest that the CT bellies appear to be functionally designed for different motor tasks. The data are also useful for further clarifying the functions of the CT bellies and the ESLN branches and for developing belly-based reinnervation procedures to treat laryngeal paralysis.

Recurrent Laryngeal Neuropathy in a Systemic Lupus Erythematosus (SLE) Patient

A 41-yr-old woman with hoarseness, multiple joint pain, and generalized myalgia was diagnosed with systemic lupus erythematosus (SLE) 7 mos before visiting our clinic. SLE-related vocal cord palsy of the left side was identified after otolaryngologic evaluation. We performed laryngeal electromyography (LEMG) on both cricothyroid and thyroarytenoid muscles. The findings indicated left recurrent laryngeal neuropathy with ongoing processes of denervation and reinnervation. Laryngeal involvement is a rare complication of SLE, but it is of clinical significance because serious consequence such as upper-airway obstruction can occur. LEMG identified this complication and precisely defined the neuromuscular status, and this information assisted in creating a therapeutic plan. LEMG may be useful for evaluating the neuromuscular status in vocal cord palsy.

The Supraglottic Nerve Supply: An Anatomic Study With Clinical Implications

To describe the course of the superior laryngeal nerve (SLN) and its branches, in particular, with regard to supraglottic motor and sensory functions. In 30 normal human hemilarynges, the SLN with its internal (intSLN) and external branch (extSLN) were dissected under microsurgical conditions and marked with acrylic dye. All anatomic structures of the larynges (muscles, cartilages, and ligaments) were dissected in detail. The intSLN subdivides into three branches. The superior branch (I) runs to the lingual (extralaryngeal) part of the epiglottis and sends small fibers through the epiglottic foramina to the laryngeal surface. The middle branch (II) runs through the aryepiglottic fold into the ventricular fold, and the inferior branch (III) to the piriform sinus and to the postcricoid region, forming various anastomoses (e.g., ansa galeni) with the recurrent laryngeal nerve (RLN). The extSLN runs to the cricothyroid muscle (CT) and sends a branch through the CT along the lower rim of the thyroid cartilage into the larynx and up to the ventricular fold. This ventricular branch is a potential candidate for the innervation of the ventricular muscle (VM). Our results may contribute to a better understanding of supraglottic actions that provide primary functions of the larynx (such as swallowing, coughing, and breathing). An enhanced knowledge of neurolaryngology also provides a basis for interpreting disorders or paralyzes following surgical treatments (e.g., thyroid surgery, partial laryngectomy) and helps to lower the risks.

P075: Prognostic Indicator of Unilateral Vocal Fold Paralysis

Objectives: To determine what factor would be helpful in determining prognosis of unilateral vocal fold paralysis (UVFP) and to reconfirm the feasibility of published laryngeal electromyography (LEMG) decision rules in assessing prognosis of UVFP Methods: A cohort study with retrospective data analysis was conducted at voice clinic of a tertiary medical center from Nov. 2004 to Jun. 2006. Independent variables including patient gender, age, laterality of UVFP, etiology, symptom duration, or LEMG findings for 30 patients diagnosed as idiopathic or iatrogenic UVFP were collected. The LEMG was performed between 3 weeks and 6 months from the onset of symptoms and patients were followed for a minimum of 6 months after symptom onset and 3 months after LEMG to check the motion of the diseased vocal fold. Univariate analysis, logistic regression and Receive Operating Characteristic curve were used to decide the significant prognostic indicators. Results: According to the LEMG decision ruling proposed by Dr. Munin normal or nearly normal motor unit recruitment and absence of spontaneous activities gave a good prognosis. The predictive values for negative test and positive test, sensitivity, specificity and accuracy of LEMG were 75%, 80.8%, 95.5%, 37.5%, and 80% respectively. Univariate analysis and logistic regression showed that symptom duration and overall LEMG result significantly correlated with outcome of UVFP (p the prognostic role of electromyography in laryngeal paralysis. Otolaryngol Head Neck Surg.1994;111:770-775. 9 Munin MC, Rosen CA, Zullo T. Utility of laryngeal electromyography in predicting recovery after vocal fold paralysis. Arch Phys Med Rehabil. 2003; 84:1150-1153. Bibliography From Nov. 2004 to Jun. 2006, medical records of 30 patients diagnosed as idiopathic or iatrogenic UVFP who received LEMG between 3 weeks and 6 months from the onset of symptoms were retrospectively reviewed after institutional review board approval was obtained. The office-based LEMG (Fig. 1) was all performed by the first author; a laryngologist familiar with the anatomy of intrinsic laryngeal muscles. The LEMG findings were all interpreted by the second author; a neurologist with 15 years experience in electrodiagnostic medicine. All LEMG examinations were performed by a machine (Cadwell Sierra 6200A, Cadwell Laboratories, Inc., 909 North Kellogg Street, Kennewick, Washington, 99336) with a computer-based electrodiagnostic system. The cricothyroid (CT) muscle and thyroarytenoid (TA) muscle were both approached transcutaneously without local anesthesia, while only the signals representing recurrent laryngeal nerve function obtained from TA muscle were used to predict prognosis of UVFP. TA muscle was approached by inserting a needle through the cricothyroid ligament approximately 0.5 cm from the midline. The needle was then angled superiorly 30° to 45° to an approximate depth of 1-2 cm. The position of the needle was validated by asking the patient to say a sustained vowel /i/ with the absence of activation during respiration and neck flexion. The outcome measurement of vocal fold motion (Fig. 2) was done with flexible laryngoscope or video-stoboscope at least 3 months after LEMG and at least 6 months after onset of symptoms. These criteria gave patients at least 3 months (ranging from 3 to 5 months) follow up duration to observe the predictive ability of LEMG in this time window. Methods and Materials Table 2 Table 3

The Pars Interna/Media Anatomy and Histology in the Human Larynx

The pars interna/media (PIM) is a small muscle found in the human larynx that has not been successfully described in contemporary literature on laryngeal structure. The objective of this study was to describe the PIM’s anatomy in detail. Thirteen human larynges obtained from postmortem examination were cleaned and preserved. Exposure of the PIM was through a lateral disarticulation of the cricothyroid joint and reflection of the cricothyroid muscle and the thyroid lamina. In the human, the PIM was found to be strap-like in form and to have two bellies with attachments to the medial surface of the thyroid cartilage at the root of the inferior horn and anteriosuperior cricoid arch. It appears to be innervated by a middle division, vestibular branch, of the internal superior laryngeal nerve. The average fiber diameter is 40 µm. Its type 1-to-type 2 fiber ratio places it within the range of other intrinsic laryngeal muscles. A muscle spindle was identified in medial bundle at the PIM’s thyroid attachment. Thyroid medial surface attachment is within few millimeters of the muscular process of the arytenoid cartilage. These data show that the PIM is a robust muscle and deserves attention anatomically. Its orientation within the thyroid and nonrecurrent laryngeal nerve innervations of the human PIM may place it in the vocal fold tensor group rather than the laryngeal sphincter group. It is possible the PIM reports on cricothyroid distance and right versus left cricothyroid joint stresses. Electromyographic examination of the PIM in the Rhesus larynx may help elucidate its physiology to elaborate its human physiology.

Laryngeal Electromyography in Adults With Parkinson's Disease and Voice Complaints

To study the laryngeal electromyography (LEMG) pattern in patients with Parkinson's disease (PD) and vocal complaints. Twenty-six adults with PD and vocal complaints and 26 controls with presbyphonia underwent videolaryngoscopy (VL) and LEMG. No tremor was found on LEMG of the cricothyroid and thyroarytenoid muscles, even in cases with clinical and VL tremor. LEMG hypertonicity during voice rest was the typical feature observed in 73% of the patients with PD versus 23% of the controls. This difference was statistically significant. The severity of the disease, diagnosis, and the time of treatment did not correlate with LEMG findings. This is the first study reporting the use of LEMG in a large series of patients with PD and vocal complaints. Patients with PD presented spontaneous intrinsic laryngeal muscle activity during voice rest. The typical patterns in LEMG suggest this to be a valuable diagnostic tool in PD.

Sleep‐related stridor due to dystonic vocal cord motion and neurogenic tachypnea/tachycardia in multiple system atrophy

Sleep-disordered breathing and sleep-related motor phenomena are part of the clinical spectrum of multiple system atrophy (MSA). Stridor has been attributed to denervation of laryngeal muscles or instead to dystonic vocal cord motion. We studied 3 patients with nocturnal stridor in the setting of MSA. All patients underwent nocturnal videopolysomnography (VPSG) with breathing and heart rate, O(2) saturation and intra-esophageal pressure recordings, and simultaneous EMG recordings of the posterior cricoarytenoid, cricothyroid, and thyroarytenoid muscles and continuous vocal cord motion evaluation by means of fiberoptic laryngoscopy. VPSG/EMG and fiberoptic laryngoscopy documented normal vocal cord motion without denervation during wake and stridor only during sleep when hyperactivation of vocal cords adductors appeared in the absence of significant O(2) desaturation. All patients had tachycardia and tachypnea and paradoxical breathing during sleep, erratic intercostalis and diaphragmatic EMG activity and Rem sleep behavior disorder. One of the patients had restless legs syndrome with periodic limb movement during sleep and excessive fragmentary hypnic myoclonus. In conclusion, our patients with MSA had nocturnal stridor due to sleep-related laryngeal dystonia. Stridor was associated with other abnormal sleep-related respiratory and motor disorders, suggesting an impairment of homeostatic brainstem integration in MSA.

Refinements in modeling the passive properties of laryngeal soft tissue

The nonlinear viscoelastic passive properties of three canine intrinsic laryngeal muscles, the lateral cricoarytenoid (LCA), the posterior cricoarytenoid (PCA), and the interarytenoid (IA), were fit to the parameters of a modified Kelvin model. These properties were compared with those of the thyroarytenoid (TA) and cricothyroid (CT) muscles, as well as previously unpublished viscoelastic characteristics of the human vocal ligament. Passive parameters of the modified Kelvin model were summarized for the vocal ligament, mucosa, and all five laryngeal muscles. Results suggest that the LCA, PCA, and IA muscles are functionally different from the TA and CT muscles in their load-bearing capacity. Furthermore, the LCA, PCA, and IA have a much larger stress-strain hysteresis effect than has been previously reported for the TA and CT or the vocal ligament. The variation in this effect suggests that the connective tissue within the TA and CT muscles is somehow similar to the vocal ligament but different from the LCA, PCA, or IA muscles. Further demonstrating the potential significance of grouping tissues in the laryngeal system by functional groups in the laryngeal system was the unique finding that, over their working elongation range, the LCA and PCA were nearly as exponentially stiff as the vocal ligament. This paper was written in conjunction with an online technical report (http://www.ncvs.org/ncvs/library/tech) in which comprehensive muscle data and sensitivity analysis, as well as downloadable data files and computer scripts, are made available.

A Complex Muscle Fiber Network in the Cricothyroid Muscle: A Scanning Electron Microscopic Study

To examine the three-dimensional ultrastructure of cricothyroid (CT) muscle fibers to elucidate their morphologic characteristics with regard to the specific functions of the muscle. An anatomic animal study. The CT muscles of five adult rats were processed using the HCl-hydrolysis method to remove the peri- and intramuscular connective tissue components. The fine muscle fiber arrangements were observed by scanning electron microscopy. Complex muscle fiber interconnections (myomyous junctions) were identified in the muscles. Myomyous junctions were characterized by the connection of many villous processes that were 1 to 2 mum in diameter and 2 to 4 mum in length with a serrated appearance at the ends of a lateral branch or a bifurcating trunk of the muscle fibers. Myomyous junctions form a complex muscle fiber network, which is thought to synchronize the activity of the CT muscle fibers. This is the first three-dimensional demonstration of the muscle fiber network in the CT muscle; this network may play a major role in the functional specificity of the CT muscle.

Magnetoelastic sensors as a new tool for laryngeal research

Conclusions. The use of custom-built magnetoelastic sensors designed for insertion in the larynx to measure the force of transverse deformation of the thyroarytenoid and cricothyroid muscles was examined. Objectives. The availability of sensors that transduce deformation force into an electrical current (measurable in millivolts) suggested that such sensors could be used to study muscle function in the canine larynx. This study aimed to obtain information about the force exercised by larynx muscles on the sensor in an experiment in vivo. Materials and methods. The results of six surgical interventions in three dogs using four magnetoelastic sensors are described. The sensor and insertion technique were atraumatic. One dog underwent surgery four times to study the morbidity, reliability and reproducibility of the technique. An electromyographic recording was made at the same time that sensor response was registered to compare results with a standardized technique. Results. We obtained 584 regular responses: 256 deglutitions (150 thyroarytenoid and 106 cricothyroid recordings) and 328 phonations (223 thyroarytenoid and 105 cricothyroid recordings). No signs of injury or functional deficit were observed after any intervention. In the dog that underwent four interventions, results were consistent after each intervention.

PRESERVATION TECHNIQUE FOR EXTERNAL LARYNGEAL NERVE IN THYROID SURGERY

A prospective comparative study conducted at Basrah Teaching Hospital in Basrah between December 2000 and February 2002. Eighty patients included, they were 13 (16.2%) male and 67(83.7%) female patients, most of the patients aged between 20-50 year (81%). The patients were allocated in two groups, each comprises 40 patients. The external laryngeal nerve (E.L.N) is a motor nerve to cricothyroid muscle of the larynx which concerned with high pitch voice. The incidence of injury to this nerve during thyroid surgery is between 11-25% in the literature. This study aimed to compare the incidence of ELN injury in thyroid surgery between the ordinary approach and the nerve stimulator approach in two groups, and to evaluate the efficacy of nerve preservation technique using nerve stimulator. In the first group, thyroid surgery was done with the aid of nerve stimulator, while in the second group the surgery was done in classical way; we found that the incidence of ELN injury in rthe first group was zero while in the second group was 12.5% (5/40). We Also found increase risk of injury to ELN in thyrotoxic patient and it was about 30.7% (4/13). We concluded that nerve stimulation is an effective method for preservation of ELN in thyroid surgery and we recommend its use in every thyroidectomy specially in cases having thyrotoxicosis, thyroiditis, huge goitre and in certain professional groups like teachers, lectureres singers and female patients.

Intrinsic laryngeal muscles are spared from myonecrosis in the mdx mouse model of Duchenne muscular dystrophy

Intrinsic laryngeal muscles share many anatomical and physiological properties with extraocular muscles, which are unaffected in both Duchenne muscular dystrophy and mdx mice. We hypothesized that intrinsic laryngeal muscles are spared from myonecrosis in mdx mice and may serve as an additional tool to understand the mechanisms of muscle sparing in dystrophinopathy. Intrinsic laryngeal muscles and tibialis anterior (TA) muscle of adult and aged mdx and control C57Bl/10 mice were investigated. The percentage of central nucleated fibers, as a sign of muscle fibers that had undergone injury and regeneration, and myofiber labeling with Evans blue dye, as a marker of myofiber damage, were studied. Except for the cricothyroid muscle, none of the intrinsic laryngeal muscles from adult and old mdx mice showed signs of myofiber damage or Evans blue dye labeling, and all appeared to be normal. Central nucleation was readily visible in the TA of the same mdx mice. A significant increase in the percentage of central nucleated fibers was observed in adult cricothyroid muscle compared to the other intrinsic laryngeal muscles, which worsened with age. Thus, we have shown that the intrinsic laryngeal muscles are spared from the lack of dystrophin and may serve as a useful model to study the mechanisms of muscle sparing in dystrophinopathy.

Simulation of phonation control using a tensile vocal-fold model

The vocal folds act as an energy transducer that converts aerodynamic power into acoustic power. Therefore, modeling the vocal-fold vibration could provide valuable information for voice synthesis. In previous vocal-fold lumped models, the vocal-fold was simplified as a spring oscillator; the restoring force due to lateral deflection of vocal-fold tissue is represented by equivalent lateral springs. However, the vocal-fold tissue actually contains an intricate extracellular matrix, composed of longitudinal elastin, which lies parallel to the vocal fold. Thyroarytenoid, lateral cricoarytenoid, and cricothyroid muscles control the elongation of these longitudinal elastin and further determine the voice pitch, dysphonia, and rough voice. In this study a tensile vocal-fold model is proposed to simulate vocal-fold vibration. In this model the lateral tissue deflection is represented by lateral spring and the longitudinal elastin elongation is described by nonlinear longitudinal springs. Differential equations are developed to describe the tensile vocal-fold model. The fundamental frequency and phonation threshold pressure are predicted by the proposed vocal-fold model. Numerical simulations prove that the proposed tensile vocal-fold model can accurately describe the muscles control on phonation pitch and so on. [Work supported by NIH.]