Lateral Cricoarytenoid Research Articles

Diffusion of Aniline Blue Injected into Thyroarytenoid Muscle

Objective: Intralaryngeal injection of botulinum toxin into the thyroarytenoid (TA) muscle is one of the methods for the treatment of laryngeal focal dystonia. The side effects and the modification of the laryngeal configuration are probably due to the diffusion of the botulin toxin to nearby structures. Aim: Analyze the diffusion of aniline blue (liquid substance) injected into the TA to the adjacent intrinsic laryngeal muscles. Method: Study Design: Experimental. Eighteen excised cadaveric larynges were analyzed after injection of aniline blue (0.2 mL) into the TA, using the intralaryngeal technique. After fixation by formaldehyde and decalcification using nitric acid, the larynges were sectioned in the coronal plane in 4 slices and the intrinsic muscles analyzed. Results: The aniline blue spread to the lateral cricoarytenoid muscle, the cricothyroid muscle and the posterior cricoarytenoid muscle 94.3%, 42.9%, and 8.6%, respectively. Gender, height, and width of the TA had no effect on the likelihood of diffusion to any of the muscles. Conclusion: The present study showed that, based on the methodology proposed, the diffusion of a solution injected into the TA occurs in almost all cases toward the CAL muscle. The CT muscle was affected in half of the cases. Although rarely, it can also achieve the PCA muscle.

A muscle spindle abnormity in one laryngeal muscle would be sufficient to cause stuttering

Muscle spindles are increasingly recognized as playing a pivotal role in the cause of dystonia. This development and own laryngeal observations that support the idea of causally “well-intentioned” stuttering motivated us to present the following hypothesis: stuttering events compensate for a sensory problem that arises when the abductor/adductor ratio of afferent impulse rates from the posterior cricoarytenoid and lateral cricoarytenoid muscle spindles is abnormally reduced and processed for the occasional determination of the vocal fold position. This hypothesis implies that functional and structural brain abnormalities might be interpreted as secondary compensatory reactions. Verification of this hypothesis (using technologies such as microneurography, dissection and muscle afferent block) is important because its confirmation could relink dystonia and stuttering research, change the direction of stuttering therapy and destigmatize stuttering radically.

Neuromuscular control of fundamental frequency and glottal posture at phonation onset.

The laryngeal neuromuscular mechanisms for modulating glottal posture and fundamental frequency are of interest in understanding normal laryngeal physiology and treating vocal pathology. The intrinsic laryngeal muscles in an in vivo canine model were electrically activated in a graded fashion to investigate their effects on onset frequency, phonation onset pressure, vocal fold strain, and glottal distance at the vocal processes. Muscle activation plots for these laryngeal parameters were evaluated for the interaction of following pairs of muscle activation conditions: (1) cricothyroid (CT) versus all laryngeal adductors (TA/LCA/IA), (2) CT versus LCA/IA, (3) CT versus thyroarytenoid (TA) and, (4) TA versus LCA/IA (LCA: lateral cricoarytenoid muscle, IA: interarytenoid). Increases in onset frequency and strain were primarily affected by CT activation. Onset pressure correlated with activation of all adductors in activation condition 1, but primarily with CT activation in conditions 2 and 3. TA and CT were antagonistic for strain. LCA/IA activation primarily closed the cartilaginous glottis while TA activation closed the mid-membranous glottis.

Ultrasonographic evaluation of Cricoarytenoideus lateralis muscle in Standardbred horse

The cricoarytenoideus lateralis muscle (CALM) is an adductor of the arytenoid cartilages but is not directly involved in the pathogenesis of recurrent laryngeal neuropathy (RLN) as the abductor cricoarytenoideus dorsalis muscle (CADM) is. Nevertheless, the CALM is the first muscle to experience a neurogenic atrophy in the course of RLN and this feature explains its potential importance in RLN diagnosis. On 30 gelding and 30 female Standardbred horses weighing about 500 kg and aged between 3 and 9 years, an ultrasound examination of the larynx was performed in order to assess shape, size, and echogenicity of the CALMs. The mean width, thickness, and area of the muscle were respectively 1.42 cm, 1.23 cm, and 1.36 cm^2 for the right side and 1.40 cm, 1.21 cm, and 1.34 cm^2 for the left side. No differences were found in relation to sex, age, or difference between right and left muscle. Focal calcifications of thyroid cartilage prevented visualization of the muscles, especially in females.

The clinical interest of the ary‐thyro‐cricoid fascicle

The aim of this work was to study the prevalence and form of the ary-thyro-cricoid (ATC) muscular fascicle, a variable muscular slip connecting the oblique and/or transverse arytenoid muscles with the thyroarytenoid (TA) and/or lateral cricoarytenoid (LCA) muscles resembling a sphincter encircling the glottis. Thirty larynges obtained from necropsies of individuals with no known laryngeal pathology were dissected. The ATC fascicle was observed in 96.7% of the larynges. It appeared bilaterally in 60% of subjects and unilaterally in 36.7%. The posterior attachment of the muscular slip was observed to be in common with either the transverse arytenoid (34%), or the oblique arytenoid (28%) or both muscles (38%). Its fibers terminated by intermingling with either those of the LCA muscle (10.6%), or the TA muscle (38.3%) or both (51.1%). These variable attachments mean that there are nine possible variants of this muscular fascicle. The ATC fascicle was supplied by branches originating bilaterally from the recurrent laryngeal (RLN) and internal laryngeal nerves. The existence of this ATC fascicle could explain the variable position (intermediate, paramedian or lateral) adopted by the vocal folds after lesion of the RLN. The bilateral disposition and innervation of the fascicle could also complicate the interpretation of electromyographic techniques used for testing laryngeal nerve function.

Laryngeal Electromyography: Electrode Guidance Based on 3-Dimensional Magnetic Resonance Tomography Images of the Larynx

Laryngeal electromyography (LEMG) is an important tool for the assessment of laryngeal nerve and muscle functioning. The purpose of the study was to determine electrode insertion angle and insertion depth for the various laryngeal muscles. Twenty-three cadaver larynges were examined with magnetic resonance tomography (MRT) and Materialize Interactive Medical Image Control System (Leuven, Belgium) 3-dimensional (3D) imaging software. Geometrical analysis was used to calculate the electrode insertion angles. All laryngeal muscles could be identified and 3D visualized on MRT scans. Although the insertion angles were the same in male and female larynges, the insertion depth was significantly larger in male than in female larynges (P<0.05). Of particular clinical importance is the fact that the electrode has to be directed lateral and upward for the thyroarytenoid muscle but lateral and downward for the lateral cricoarytenoid muscle (insertion point=midline lower border of the thyroid). This is the first study that analyzes electrode insertion angles and insertion depths for each laryngeal muscle using 3D imaging. We hope that the information gained from this study will help clinicians performing LEMG to localize the individual laryngeal muscles.

Differential Vibratory Characteristics of Adductor Spasmodic Dysphonia and Muscle Tension Dysphonia on High-Speed Digital Imaging

The purpose of this study was to quantify disorder-specific signature kinematic disturbances of vibratory motion in adductor spasmodic dysphonia (AdSD) and muscle tension dysphonia (MTD), in voice disturbances of a severe nature, with the use of high-speed digital imaging (HSDI). A secondary hypothesis of the study was to investigate the sensitivity and specificity of the signature kinematic features obtained from HSDI, in differentiating between AdSD and MTD. We used vibratory features from automated extraction of vocal fold motion waveforms and glottal cycle montage analysis from HSDI for differential kinematic profiling of AdSD and MTD. Novel features of motion irregularities and micromotions (as small as 27 ms) were greater in number for AdSD, whereas reduced motion irregularities, absence of oscillatory breaks, absence of micromotions, and increased hyperfunction characterized the MTD group. Oscillatory breaks (as small as 8 ms), although present only in the AdSD group, were not statistically significant because of their reduced number of occurrences compared to the other features. Further montage analysis of successive glottal cycles of oscillatory breaks in the AdSD group revealed 3 different kinematic patterns within the AdSD group, indicative of likely AdSD with: 1) possible predominant thyroarytenoid muscle involvement, 2) possible predominant cricothyroid muscle involvement, and 3) possible combined involvements of the thyroarytenoid and lateral cricoarytenoid muscles. Four consistent but unique kinematic patterns were identified within the MTD group: 1) diplophonia, 2) vocal fry, 3) breathy phonation, and 4) pressed phonation. Sensitivity and specificity analysis revealed that only motion irregularity was a significant predictor of the presence of AdSD. Fine kinematic analysis from HSDI can be used to aid detailed clinical profiling of the source characteristics of AdSD and MTD.

Adductor Spasmodic Dysphonia – Changes in dosing after prolonged injections

CONTACT OBJECTIVES: Botulinum toxin therapy (BTX) for adductor spasmodic dysphonia (ADSD) requires re-injection. The dosing effects after prolonged treatment are not well reported. We report our ten-year experience in the utilization of BTX in ADSD STUDY DESIGN: Retrospective chart review METHODS: From a database of 182 ADSD patients from 1997-2008 treated with BTX, we pulled a subset of 87 patients receiving BTX for greater than 3 visits (average 10.27 visits, range 3-40). We analyzed duration of effect, dosing effects and changes in administration technique. RESULTS: This study group was predominantly female (3:1), presenting at mean age 60. All BTX was administered with laryngeal electromyographic guidance. The average starting dose was 2.28 units (range 1.25 – 3.75). The average dose per injection was 2.15 units (range 0.25-12.5) with an average time interval of 5.6 months between visits. Patients reached a stable dosing regimen at an average of 1.34 months, with 75% optimized after the first visit. There was a trend towards increased average dosage for patients during their 15th treatment visit and up (p=0.14), with increased variation in effect (SD 0.95 vs 1.36). Average time interval between visits tended to decrease over time. Patients who began treatment at older ages in the 6th and 7th tended to require decreasing dosages over time. 10 out of 87 patients progressed to unilateral injections after an average of 12.5 treatment visits, with 70% efficacy. CONCLUSIONS: Botulinum therapy in ADSD is stable and safe. Prolonged treatment over 15 visits may require changes in dosing and technique. Unilateral injections provide an effective alternative to bilateral injection. Name: Nina Chinosornvatana, MD Organization: Mount Sinai Hospital Email: nchinos@gmail.com •Patient positioned supine with neck slightly extended. Laryngeal electromyography (LEMG) ground and reference electrodes are placed. Neck prepped. •Botulinum toxin diluted to 100 units per 4cc of injectable bacteriostatic saline. 1cc tuberculin syringe fixed to LEMG monopolar electrode injector needle. •Needle inserted through the skin just off of midline at the level of the cricothyroid membrane. Needle advanced superolaterally towards the targeted thyroarytenoid muscle. •LEMG used to verify placement of needle into thyroarytenoid muscle, showing increased muscle action potential complexes with phonation and cough. •Starting dosage administered is 2.5 units to each side. Subsequent dosing is determined dependent on prior dosage and its effectiveness. • Botulinum therapy was shown to have prolonged efficacy, with successful injections administered at upper limits of 80 injections, 40 visits, and 10 years. This is consistent with BTX’s proven record of safety and efficacy in the literature. To date, there are no reports of mortality attributed to BTX treatment in the literature. 7 The most common adverse effect has been temporary excessive breathiness from overinjection. •We recommend 2.5 units to each thyroarytenoid muscle as an effective starting dose with use of laryngeal electromyographic guidance. Reported rates of starting dosage administration vary; our 70% efficacy rate after the first visit compares favorably to other reported series. 6,7 •We saw an increase in dosage variability in patients receiving prolonged treatment beyond 15 visits, with a trend towards increased average dosing. Other series have reported decreases in dosing requirements over time without resistance. 7 We therefore recommend vigilant attention to changes in dosing requirement or technique in patients over 15 visits, with consideration of unilateral injections as an alternative to bilateral injection. •Unilateral injections have been reported to be successful in a wide range of doses, from 2.5u – 30u. 9 Comparisons to bilateral injections have shown similar efficacy, with some reports of decreased side effect profiles. 10 Our experience confirms unilateral administration as a useful and effective alternative to bilateral injection. •Adductor spasmodic dysphonia (ADSD) is an idiopathic focal dystonia of the intrinsic laryngeal adductor musculature. Spasms most frequently affect the thyroarytenoid muscles, but can also involve the lateral cricoarytenoid and interarytenoids, resulting in overforceful vocal fold closure. •Clinically, ADSD presents with strangulated strained vocal quality, and is characterized by repetitive breaks in phonation and pitch, requiring increased effort during speech. ADSD is triggered by speech, in particular, voiced sounds. 1 •Treatment options for ADSD include speech therapy, recurrent laryngeal nerve sectioning2,3 , partial thyroarytenoid myectomy4, anterior commissure release, and botulinum administration. The use of botulinum remains the gold standard treatment due to its effectiveness, reliability, and high safety profile.5 •Chemodenervation with botulinum requires reinjection. Because there is significant variability in patient response and toxin delivery, individualization of treatment is necessary for optimal effect. Adductor Spasmodic Dysphonia

Association of treadmill upper airway endoscopic evaluation with results of ultrasonography and resting upper airway endoscopic evaluation

Assessment of arytenoid movement has traditionally been performed using upper airway (UA) endoscopy. However, recent work suggests that laryngeal ultrasonography may provide additional complementary information. To determine the value of laryngeal ultrasonography for the diagnosis of recurrent laryngeal neuropathy in the horse. Horses with abnormal arytenoid movement (AM) during treadmill UA endoscopy would have increased echogenicity of the left cricoarytenoideus lateralis muscle (CALM) and smaller left CALM and vocalis size while horses with normal AM during treadmill UA endoscopy would have normal echogenicity of the left CALM and similar left and right CALM and vocalis muscle size. Laryngeal ultrasonography would be more accurate than resting endoscopy at predicting abnormal AM. Medical records were examined to identify Thoroughbred racehorses aged ≥2 years that had undergone resting and treadmill UA endoscopy and laryngeal ultrasonography. Resting and treadmill AM was graded using accepted scales. The treadmill examination was used as the criterion standard for AM. Laryngeal ultrasonography was performed and the relative echogenicity of the left and right CALM and the cross-sectional area (CSA) of the CALM and vocalis muscle determined. Data analysis included Chi-squared tests, paired t tests and one-way ANOVA. The presence of abnormal AM was associated with relative hyperechogenicity of the CALM while normal AM was not. Laryngeal ultrasonography had a sensitivity of 90% and specificity of 98% and resting UA endoscopy had a sensitivity of 80% and specificity of 81% for diagnosis of abnormal AM. CSA of the left CALM and vocalis muscle was not different between groups. Laryngeal ultrasonography has high accuracy for diagnosing abnormal AM. Ultrasonography is a valuable addition to the diagnostic evaluation of the equine UA.

Sternum-hyoid muscle transposition and arytenoid adduction for unilateral vocal cord paralysis

To explore the therapeutic effect of sternum-hyoid muscle transposition and arytenoid adduction for unilateral vocal cord paralysis (UVCP). Included in this study were 19 patients with UVCP lasted for 12 months to 15 years. The surgical technique was as follows. The thyroid cartilage was engaged with a skin hook and gently rotated anteriorly. The lateral-inferior corner of the thyroid cartilage was exposed and the muscular process of the arytenoid was identified. Then, the thyroid lamina on the involved side was parasagittally separated 5 mm off the midline. The inner perichondrium was carefully freed from the overlying thyroid cartilage. The lamina was retracted laterally, and a 3-0 prolene suture was placed through the muscular process and tied to the cricoid cartilage at the origin of the lateral cricoarytenoid muscle. A bipedicled strap muscle flap was then transposed into the space between the lamina and the inner perichondrium. Pre- and postoperative voice evaluations measured mean fundamental frequency, jitter, shimmer, harmonic ratio and maximal phonation time, as well as assessments of voice quality. Vocal improvement was obtained in 100% (19 of 19) of patients. Immediately after the operation, the ingression could be observed in vocal cord membrane and vocal process, vocal cord volume was amplified. There was a significant difference (P < 0.05) in all parameters (fundamental frequency, jitter, shimmer, harmonic ratio and maximal phonation time) between pre- and postoperative voice evaluations measured mean. There was no significant difference (P > 0.05) in voice evaluations measured mean between 2 months and 12 months after operation in all patients. No major complications were noted in any patient. Sternum-hyoid muscle transposition and arytenoid adduction for unilateral vocal cord paralysis is simple and convenient, no immune rejection, and the long-term result is stable.

Transoral laser ventricular fold resection and thyroarytenoid myoneurectomy for adductor spasmodic dysphonia: Long‐term outcome

A transoral approach to laser myoneurectomy of the thyroarytenoid muscles was recently reported as an effective technique for treatment of adductor spasmodic dysphonia (ASD). The short-term results were encouraging. In this study, a long-term surgical outcome of this technique is investigated. A prospective clinical series. Fifty-two patients with ASD underwent transoral laryngomicrosurgery with a CO(2) laser to resect the ventricular folds followed by myoneurectomy of the thyroarytenoid muscles. The nerve fibers of recurrent laryngeal nerve terminating at the thyroarytenoid muscle, which were frequently found branching deeply among the posterior belly of this muscle, were vaporized. Care was taken not to damage the vocal ligaments, lateral cricoarytenoid muscles, or arytenoid cartilages. Pre- and postoperative subjective voice assessments, and acoustic and aerodynamic measurements, were performed and statistically analyzed. Twenty-nine of the 52 patients who were followed up for more than 12 months (range, 12-63 months; mean, 31 months) were studied. Moderate and marked vocal improvement was achieved in 90% (26/29) of the patients. Three patients had 30% improvement, which was reported as unsuccessful. Eight of the 26 patients who were satisfied with their postoperative voice still had a mild strain during phonation. Of the eight patients, seven achieved normal or nearly normal voice quality after revision laser surgery. No significant vocal deficit or paralysis was observed in any patient. After long-term follow-up of 31 months on average, approximately 90% of the ASD patients obtained moderate to marked improvement of vocal performance after transoral laser surgery. The long-lasting outcome is encouraging.

Effects of sepsis on the neuromuscular blocking actions of d-tubocurarine on rat adductor and abductor laryngeal muscles

We evaluated the effects of sepsis on the neuromuscular blocking actions of d-tubocurarine (dTc) in the lateral cricoarytenoid (LCA) and posterior cricoarytenoid (PCA) muscles, an adductor muscle and an abductor muscle of the vocal cords, respectively, in vitro. Sepsis was induced in rats by cecal ligation and puncture (CLP) to elicit panperitonitis. Electromyograms (EMGs) and endplate potentials (EPPs) were recorded from the LCA and PCA muscles of CLP-operated septic rats and sham-operated nonseptic rats, using extracellular and intracellular microelectrodes, respectively. EMG and EPP (amplitude and quantum content) were depressed by dTc, but the dTc-induced neuromuscular blocking effects were attenuated by sepsis. The suppressive effects of dTc on EMG and EPP (amplitude and quantum content) were less intense in the LCA muscle than in the PCA muscle under both sepsis and nonsepsis conditions. Our study shows that sepsis has a depressive effect on dTc-induced neuromuscular blocking actions at both the adductor and abductor muscles of vocal cords in the larynx.

Clinical and Electrophysiological Characteristics of Larynx in Myasthenia Gravis

We investigated the clinical and electrophysiological characteristics of the larynx in patients with myasthenia gravis (MG). Thirty-two cases of MG were analyzed. The laryngeal behaviors and characteristics of laryngeal electromyography were evaluated, and voice assessment and repetitive nerve stimulation (RNS) tests were conducted. The initial symptoms of patients were ptosis and/or diplopia in 28, dysphagia and slurred speech in 3, and limb weakness in 1. Only 8 patients had slight hoarseness and vocal fatigue, and 4 patients had positive laryngeal signs. When compared with normal subjects, the patients with MG had worse results on the acoustic analysis of shimmer, their normalized noise energy was greater, and the harmonics-to-noise ratio and maximum phonation time were significantly lower. The RNS findings were positive in 28 patients and negative in 4 patients. The average (+/-SD) amplitude decrement was 31.9% +/- 19.1%. The mean number of involved laryngeal muscles was 2.22 +/- 1.35. Cricothyroid muscles were involved in 26 cases, thyroarytenoid muscles were involved in 14 cases, posterior cricoarytenoid muscles were involved in 6 cases, and lateral cricoarytenoid muscles were involved in 2 cases. Although few patients presented with laryngeal symptoms as their initial symptoms, most patients with MG exhibited asymmetry and abnormal findings on laryngeal electromyography. The RNS test for laryngeal muscles is a more sensitive indicator for the diagnosis of MG, especially in the cricothyroid muscle.

Vocal Fold Bowing in Elderly Male Monozygotic Twins: A Case Study

This case study examined case histories, diagnostic features, and treatment response in two 79-year-old male monozygotic (identical) twins with vocal fold bowing, exploring both genetic and environmental factors. DNA concordance was examined via cheek swab. Case histories, videostroboscopy, auditory- and visual-perceptual assessment, electromyography, acoustic measures, and Voice Handicap ratings were undertaken. Both twins underwent surgical intervention and subsequent voice therapy. Monozygosity was confirmed for DNA polymorphisms, with 10 of 10 concordance for STR DNA markers. For both twins, auditory- and visual-perceptual assessments indicated severe bowing, hoarseness, and breathiness, although Twin 1 was judged to be extremely severe. Differences in reference to root-mean-square amplitudes were observed for thyroarytenoid and lateral cricoarytenoid muscles, with smaller relative amplitudes observed for the Twin 1 versus Twin 2. No consistent voice improvement was observed after surgical intervention(s), despite improved mid-membranous vocal fold closure. Marked reductions in Voice Handicap Index total scores were observed after behavioral voice therapy, coinciding with increased mid-membranous and posterior laryngeal (interarytenoid) glottal closure. No substantive differences in acoustic measures were observed. Vocal fold bowing was more severe for Twin 1 versus Twin 2 despite identical heritability factors. Overall voice improvement with treatment was greater for Twin 2 than Twin 1. Environmental factors might partially account for the differences observed between the twins, including variability in their responsiveness to behavioral voice therapy. Voice therapy was useful in improving mid-membranous and posterior laryngeal closure, although dysphonia remained severe in both cases.

Laryngeale Schrotschussverletzung

Laryngeal shot injuries are rare. The case of a 65-year-old man who suffered from an injury with lead pellets is reported. After exploration with removal of the pellet from the lateral cricoarytenoid muscle, an immobility of the vocal fold developed, accompanied by impaired vocal function. Despite persisting immobility of the vocal fold, after 12 weeks voice compensation was achieved by voice therapy.

Control of vocal fold cover stiffness by laryngeal muscles: A preliminary study

To perform preliminary measurements of the shear modulus of the vocal fold cover layer during intrinsic laryngeal muscle contraction. Shear modulus was measured in an in vivo canine larynx and an ex vivo human larynx. Shear stress was applied to the transverse axis of the vocal fold using a modified linear skin rheometer (LSR) via an attached suction probe. The probe displacement in response to the applied force was measured at various levels of laryngeal muscle contraction. The force-displacement data were used to derive the shear modulus using a simple shear model. In the ex vivo human larynx, lateral cricoarytenoid (LCA) muscle and cricothyroid (CT) muscle activity was simulated with arytenoid adduction and cricothyroid approximation sutures, respectively. In the in vivo canine, adductor muscle and CT muscle contraction was induced with graded stimulation of the recurrent laryngeal nerve (RLN) and the superior laryngeal nerves (SLN), respectively. : Baseline shear modulus was between 1,076 and 1,307 Pascals. In the ex vivo human larynx, the shear modulus increased gradually to a maximum of 1.6 times baseline value with graded arytenoid adduction and 3.7 times baseline value with cricothyroid approximation. In the in vivo larynx, the shear modulus increased to a maximum of 1.6 times baseline value with RLN stimulation and 2.5 times baseline value with SLN stimulation. Findings are in agreement with the cover-body model in that cricothyroid muscle activity generates a greater change in cover stiffness than laryngeal adductors. The role of the individual laryngeal adductors (thyroarytenoid [TA] vs. LCA) in control of vocal fold cover stiffness remains to be further elucidated.

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.

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.

Anatomic study of human laryngeal ganglia: Number and distribution

We have studied 12 laryngeal nerves: six internal branches of the superior laryngeal nerve (ILN) and six recurrent laryngeal nerves (RLN) from three human adult larynges (two males and one female). After dissection of each individual laryngeal nerve using a surgical microscope, the nerves were preserved in 10% formalin, embedded in paraffin wax, serially sectioned transversely at a thickness of 10 microm and stained with hematoxylin and eosin. We found 2-4 ganglia associated with the ILN. At least two ganglia were always present (six out of six cases), the largest one being associated with the branch of the nerve innervating the vestibule and the smallest one associated with the branch innervating the aryepiglottic fold. Other ganglia were found associated with the branches for the glosso-epiglottic fold and vallecula (four out of six cases) and interarytenoid muscle (three out of six cases). The RLN showed from two to six ganglia, all of them located in its anterior terminal division. Two of the ganglia were located in the part of the nerve between the origin of the branches for the interarytenoid and lateral cricoarytenoid muscles (three out of six cases). The remaining ganglia were located close to or at the origin of the muscular branches innervating the intrinsic laryngeal muscles. The cytology of the ganglia reported suggests that they were all autonomic in nature, probably parasympathetic.

Glottal Airflow Resistance in Excised Pig, Sheep, and Cow Larynges

This study was to investigate glottal flow resistance in excised pig, sheep, and cow larynges during phonation at different oscillation ranges and to examine the relation of the glottal flow resistance to the laryngeal geometry and vocal fold vibration. Several pig, sheep, and cow larynges were prepared, mounted on an excised larynx bench, and set into oscillation with pressurized, heated, and humidified air. Glottal adduction was controlled by either using two-pronged probes to press the arytenoids together, or by passing a suture to simulate the lateral cricoarytenoid muscle action. Each excised larynx was subjected to a series of pressure-flow experiments, with adduction and flow rate as independent variables. The subglottal pressure, fundamental frequency, and glottal flow resistance were treated as dependent variables. The subglottal pressure, electroglottograph (EGG), and flow rate signals were recorded during each experiment. Glottal flow resistance was calculated from the pressure and flow signals, whereas the EGG signal was used to extract fundamental frequency. Preliminary data indicated a nonlinear behavior in the pressure-flow relations of these larynges with increasing glottal resistance due to increases in adduction. The average glottal flow resistance was 35.3+/-14.8 cmH(2)O/(L/s) for the pig, 30.8+/-17.5 cmH(2)O/(L/s) for the sheep, and 26.9+/-14.9 cmH(2)O/(L/s) for the cow.