Intrinsic Laryngeal Muscle Activity Research Articles

Control of Pre-phonatory Glottal Shape by Intrinsic Laryngeal Muscles.

Surgical manipulations to treat glottic insufficiency aim to restore the physiologic pre-phonatory glottal shape. However, the physiologic pre-phonatory glottal shape as a function of interactions between all intrinsic laryngeal muscles (ILMs) has not been described. Vocal fold posture and medial surface shape were investigated across concurrent activation and interactions of thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid/interarytenoid (LCA/IA) muscles. In vivo canine hemilarynx model. The ILMs were stimulated across combinations of four graded levels each from low-to-high activation. A total of 64 distinct medial surface postures (4 TA × 4 CT × 4 LCA/IA levels) were captured using high-speed video. Using a custom 3D interpolation algorithm, the medial surface shape was reconstructed. Combined activation of ILMs yielded a range of unique pre-phonatory postures. Both LCA/IA and TA activation adducted the vocal fold but with greater contribution from TA. The transition from a convergent to a rectangular glottal shape was primarily mediated by TA muscle activation but LCA/IA and TA together resulted in a smooth rectangular glottis compared to TA alone, which caused rectangular glottis with inferomedial bulging. CT activation resulted in a lengthened but slightly abducted glottis. TA was primarily responsible for the rectangular shape of the adducted glottis with synergistic contribution from the LCA/IA. CT contributed minimally to vocal fold medial shape but elongated the glottis. These findings further refine laryngeal posture goals in surgical correction of glottic insufficiency. N/A, Basic science Laryngoscope, 2022.

Assessment of Changes in Laryngeal Configuration and Voice Parameters Among Different Frequencies of Neuromuscular Electrical Stimulation (NMES) and Cumulative Effects of NMES in a Normophonic Subject: A Pilot Study

Neuromuscular electrical stimulation (NMES) is a complementary resource to voice therapy that can be used for the treatment of hypofunctional voice disorders. Although positive clinical studies have been reported, neutral and even potentially harmful effects of NMES are also described in the literature. Furthermore, in the studies examined by the authors, the use of different methods of NMES have been identified, which further contributes to the inconsistent results found among studies. Moreover, limited rationale is provided for the chosen NMES parameters such as electrode placement, frequency of NMES and length of treatment. The aims of this pilot study were to investigate the a) impact of different frequencies of NMES on glottal configuration and vocal fold vibration patterns and b) changes in laryngeal configuration and vocal output across 12 minutes of NMES. Three experiments were carried out looking at changes in laryngeal configuration and voice output using different imaging techniques (fibreoptic nasolaryngoscopy and high-speed video), acoustical analysis (F0, formant analysis, SPL, CPPS and LHSR values), electroglottography (EGG) and Relative Fundamental Frequency (RFF) analyses. Glottal parameters and acoustical measures were recorded before, during, and after stimulation. Data was collected at rest and during phonation. Overall the results showed global changes in laryngeal configuration from normal to hyperfunctional (ie, increased RFF, SPL, CQ, and stiffness). Changes were more pronounced for lower frequencies of NMES and were significant within less than three minutes of application. NMES is an effective resource for the activation of intrinsic laryngeal muscles producing significant levels of adduction within few minutes of application. Lower NMES frequencies produced greater muscle activation when compared to higher frequencies.

Neurophysiological Muscle Activation Scheme for Controlling Vocal Fold Models.

A physiologically-based scheme that incorporates inherent neurological fluctuations in the activation of intrinsic laryngeal muscles into a lumped-element vocal fold model is proposed. Herein, muscles are activated through a combination of neural firing rate and recruitment of additional motor units, both of which have stochastic components. The mathematical framework and underlying physiological assumptions are described, and the effects of the fluctuations are tested via a parametric analysis using a body-cover model of the vocal folds for steady-state sustained vowels. The inherent muscle activation fluctuations have a bandwidth that varies with the firing rate, yielding both low and high-frequency components. When applying the proposed fluctuation scheme to the voice production model, changes in the dynamics of the system can be observed, ranging from fluctuations in the fundamental frequency to unstable behavior near bifurcation regions. The resulting coefficient of variation of the model parameters is not uniform with muscle activation. The stochastic components of muscle activation influence both the fine structure variability and the ability to achieve a target value for pitch control. These components can have a significant impact on the vocal fold parameters, as well as the outputs of the voice production model. Good agreement was found when contrasting the proposed scheme with prior experimental studies accounting for variability in vocal fold posturing and spectral characteristics of the muscle activation signal. The proposed scheme constitutes a novel and physiologically-based approach for controlling lumped-element models for normal voice production and can be extended to explore neuropathological conditions.

Laryngeal Electromyography and Acoustic Voice Analysis in Parkinson's Disease: a comparative study

SummaryParkinson's disease (PD) involves a progressive depletion of dopamine in the basal ganglia leading to motor alterations. Oral communication impairment occurs in 75% to 90% of patients and has been poorly studied.Aimto asses laryngeal electromyography (LEMG) patterns and correlate them to vocal analysis in patients with Parkinson's disease.Materials and MethodsThis is a prospective study. Twenty six adults with PD underwent laryngeal electromyography. Rest and phonation potentials were analyzed. VOXMETRIA® and GRAM 5.1.6. ® were used in acoustic analysis.ResultsThe main electromyographic pattern observed in the PD group was rest hypertonicity meaning that patients with PD presented with spontaneous intrinsic laryngeal muscle activity during voice rest, which occurred in 73% of the individuals. Not a case of laryngeal tremor was detected by electromyography, although vocal tremor was detected by VOXMETRIA in 69.5% of the individuals and in 61% of them by perceptive-auditive analysis.ConclusionVocal tremor was the main acoustic change in the PD group, with no correlation to LEMG findings.

Laryngeal electromyography as a diagnostic tool for Parkinson's disease

To study the laryngeal electromyography pattern in patients with Parkinson's disease (PD) and vocal complaints at different stages of the disease. Cross-sectional cohort study. Ninety-four adults with PD and vocal complaints at different stages of the disease (according to the Hoehn and Yahr scale) underwent laryngeal electromyography. Tremors were not detected on laryngeal electromyography of the cricothyroid and thyroarytenoid muscles even in patients with clinical tremor. Laryngeal electromyography hypercontractility during voice rest was the typical result observed in 91.5% of patients regardless of disease severity. Gender and age of subjects did not correlate with laryngeal electromyography results. Patients with PD presented spontaneous intrinsic laryngeal muscle activity during voice rest, regardless of disease severity. This study was significant because it reported on the use of laryngeal electromyography in a large number of patients with PD and vocal complaints grouped according to PD severity. The patterns observed suggest that laryngeal electromyography is a valuable diagnostic tool for PD even at early phases of the disease.

Intrinsic laryngeal muscle activity in response to autonomic nervous system activation

To determine whether the intrinsic laryngeal muscles exhibit a response to induced autonomic nervous system (ANS) activation, and to characterize responses that may occur. Prospective within-subjects study. A cold pressor (CP) task was used to trigger a whole-body ANS response in eight vocally normal adult females. Surface electromyography of the trapezius muscle and bipolar hook-wire electromyography of intrinsic laryngeal muscles, as well as cardiovascular measures of heart rate (HR) and blood pressure (systolic [SBP] and diastolic [DBP]), were used to characterize participants' response to CP exposure compared to at-rest baseline. Cardiovascular response to the CP task was confirmed for subjects via HR or blood pressure measures. Post hoc Bonferroni analysis confirmed statistically significant increases in HR (P = .027), SBP (P < .001), and DBP (P < .001) during the CP task as compared to baseline. Concurrent increases in muscle activity were generally observed in trapezius, posterior cricoarytenoid, bilateral thyroarytenoid/lateral cricoarytenoid muscle complex, and bilateral cricothyroid muscles for each subject. Three individuals elected to repeat the CP task and displayed the same pattern of laryngeal response as observed in their first exposure. Results for repeated baseline measures obtained after the cessation of the CP task were compared to pre-CP baseline. Overall laryngeal activation remained even after the cardiovascular response was attenuated. Results are consistent with the suggestion that human laryngeal muscles exhibit an elevated level of activation concurrent with ANS activation, and endorse the putative link between laryngeal muscle tension and acute stress. Findings are replicable within a subset of three individuals.

Stereotypic laryngeal and respiratory motor patterns generate different call types in rat ultrasound vocalization.

Rodents produce highly variable ultrasound whistles as communication signals unlike many other mammals, who employ flow-induced vocal fold oscillations to produce sound. The role of larynx muscles in controlling sound features across different call types in ultrasound vocalization (USV) was investigated using laryngeal muscle electromyographic (EMG) activity, subglottal pressure measurements and vocal sound output in awake and spontaneously behaving Sprague-Dawley rats. Results support the hypothesis that glottal shape determines fundamental frequency. EMG activities of thyroarytenoid and cricothyroid muscles were aligned with call duration. EMG intensity increased with fundamental frequency. Phasic activities of both muscles were aligned with fast changing fundamental frequency contours, for example in trills. Activities of the sternothyroid and sternohyoid muscles, two muscles involved in vocal production in other mammals, are not critical for the production of rat USV. To test how stereotypic laryngeal and respiratory activity are across call types and individuals, sets of ten EMG and subglottal pressure parameters were measured in six different call types from six rats. Using discriminant function analysis, on average 80% of parameter sets were correctly assigned to their respective call type. This was significantly higher than the chance level. Since fundamental frequency features of USV are tightly associated with stereotypic activity of intrinsic laryngeal muscles and muscles contributing to build-up of subglottal pressure, USV provide insight into the neurophysiological control of peripheral vocal motor patterns.

Subglottal pressure, tracheal airflow, and intrinsic laryngeal muscle activity during rat ultrasound vocalization

Vocal production requires complex planning and coordination of respiratory, laryngeal, and vocal tract movements, which are incompletely understood in most mammals. Rats produce a variety of whistles in the ultrasonic range that are of communicative relevance and of importance as a model system, but the sources of acoustic variability were mostly unknown. The goal was to identify sources of fundamental frequency variability. Subglottal pressure, tracheal airflow, and electromyographic (EMG) data from two intrinsic laryngeal muscles were measured during 22-kHz and 50-kHz call production in awake, spontaneously behaving adult male rats. During ultrasound vocalization, subglottal pressure ranged between 0.8 and 1.9 kPa. Pressure differences between call types were not significant. The relation between fundamental frequency and subglottal pressure within call types was inconsistent. Experimental manipulations of subglottal pressure had only small effects on fundamental frequency. Tracheal airflow patterns were also inconsistently associated with frequency. Pressure and flow seem to play a small role in regulation of fundamental frequency. Muscle activity, however, is precisely regulated and very sensitive to alterations, presumably because of effects on resonance properties in the vocal tract. EMG activity of cricothyroid and thyroarytenoid muscle was tonic in calls with slow or no fundamental frequency modulations, like 22-kHz and flat 50-kHz calls. Both muscles showed brief high-amplitude, alternating bursts at rates up to 150 Hz during production of frequency-modulated 50-kHz calls. A differentiated and fine regulation of intrinsic laryngeal muscles is critical for normal ultrasound vocalization. Many features of the laryngeal muscle activation pattern during ultrasound vocalization in rats are shared with other mammals.

Carbachol injection into the pontine reticular formation depresses laryngeal muscle activities and airway reflexes in decerebrate cats

To understand the role of cholinoceptive, medial pontine reticular formation (mPRF) neurons in the control of upper airway, pharyngolaryngeal reflexes, we measured activities of intrinsic laryngeal muscles (posterior cricoarytenoid, PCA; thyroarytenoid, TA), diaphragm (DIA), genioglossus (GG) and a neck muscle (trapezius) in unanesthetized, decerebrated, spontaneously breathing cats with and without mPRF carbachol injections. The ethimoidal nerve was electrically stimulated to evoke sneezing, and the superior laryngeal nerve to evoke the laryngeal reflex, swallowing, and coughing. Carbachol reduced the amplitudes of the spontaneous electromyographic activities in the neck, TA, PCA, GG, and DIA to 7%, 30%, 54%, 45% and 71% of control, respectively, reduced the respiratory rate to 53% without changes in expiratory CO 2 concentration; the magnitude of the laryngeal reflex in the TA muscle to 56%; increased its latency by 13%; and reduced the probability of stimulus-induced sneezing, swallowing, and coughing to less than 40%. These changes lasted more than 1 h. These data demonstrate that important upper airway reflexes are suppressed by increasing cholinergic neurotransmission in the mPRF. Because acetylcholine release in the mPRF changes in accordance with sleep–wake cycles, the present findings are relevant to the control of upper airway reflexes during various vigilance states.

Intra-Oral Pressure–Based Voicing Control of Electrolaryngeal Speech with Intra-Oral Vibrator

In normal speech, coordinated activities of intrinsic laryngeal muscles suspend a glottal sound at utterance of voiceless consonants, automatically realizing a voicing control. In electrolaryngeal speech, however, the lack of voicing control is one of the causes of unclear voice, voiceless consonants tending to be misheard as the corresponding voiced consonants. In the present work, we developed an intra-oral vibrator with an intra-oral pressure sensor that detected utterance of voiceless phonemes during the intra-oral electrolaryngeal speech, and demonstrated that an intra-oral pressure-based voicing control could improve the intelligibility of the speech. The test voices were obtained from one electrolaryngeal speaker and one normal speaker. We first investigated on the speech analysis software how a voice onset time (VOT) and first formant (F1) transition of the test consonant-vowel syllables contributed to voiceless/voiced contrasts, and developed an adequate voicing control strategy. We then compared the intelligibility of consonant-vowel syllables among the intra-oral electrolaryngeal speech with and without online voicing control. The increase of intra-oral pressure, typically with a peak ranging from 10 to 50 gf/cm2, could reliably identify utterance of voiceless consonants. The speech analysis and intelligibility test then demonstrated that a short VOT caused the misidentification of the voiced consonants due to a clear F1 transition. Finally, taking these results together, the online voicing control, which suspended the prosthetic tone while the intra-oral pressure exceeded 2.5 gf/cm2 and during the 35 milliseconds that followed, proved efficient to improve the voiceless/voiced contrast.

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.

Quasi-trapezoidal pulses to selectively block the activation of intrinsic laryngeal muscles during vagal nerve stimulation

The stimulation of the vagus nerve has been used as an anti-epileptic treatment for over a decade, and its use for depression and chronic heart failure is currently under investigation. Co-activation of the intrinsic laryngeal muscles may limit the clinical use of vagal stimulation, especially in the case of prolonged activation. To prevent this, the use of a selective stimulation paradigm has been tested in seven acute pig experiments. Quasi-trapezoidal pulses successfully blocked the population of the largest and fastest vagal myelinated fibers being responsible for the co-activation. The first response in the vagus compound action potential was reduced by 75 ± 22% (mean ± SD) and the co-activated muscle action potential by 67 ± 25%. The vagal bradycardic effects remained unchanged during the selective block, confirming the leading role of thin nerve fibers for the vagal control of the heart. Quasi-trapezoidal pulses may be an alternative to rectangular pulses in clinical vagal stimulation when the co-activation of laryngeal muscles must be avoided.

The neuronal circuit of augmenting effects on intrinsic laryngeal muscle activities induced by nasal air-jet stimulation in decerebrate cats

We previously demonstrated that during nasal air-jet stimulation, both the activities of intrinsic laryngeal adductor and abductor muscles persistently increase, whereas the respiratory cycle prolongs and the activity of diaphragm decreases [Am. J. Rhinol. 9 (1995) 203–208; Neurosci. Res. 31 (1998) 137–146]. The purpose of this study was to clarify the neuronal circuit underlying the augmentation of intrinsic laryngeal muscles evoked by nasal air-jet stimulation. The immunohistologic analysis of Fos-expression was reported to determine the distribution of activated neurons in cat brainstem evoked by sneeze-inducing air puff stimulation of the nasal mucosa [Brain Res. 687 (1995) 143–154]. In sneezing cats, immunoreactivity was evoked in projection areas of the ethmoidal afferents, e.g. the subnuclei caudalis, interpolaris and in interstitial islands of the trigeminal sensory complex. Immunoreactivity was also enhanced in the solitary complex, the nucleus retroambiguus, the pontine parabrachial area and the lateral aspect of the parvocellular reticular formation [Brain Res. 687 (1995) 143–154]. In the present study, we focussed on the parvocellular reticular nucleus (PRN) as a relay of the neural circuit contributed to the augmentation of intrinsic laryngeal muscles evoked by nasal air-jet stimulation. We recorded the neuronal behavior of PRN during the nasal air-jet stimulation in precollicular-postmammillary decerebrate cats. As the results, 24% (17/71) of recorded neurons which were activated orthodromically by the electrical stimulation to anterior ethmoidal nerve, increased their firing rates in response to the nasal air-jet stimulation. Furthermore, spike-triggered averaging method revealed that four of these 17 PRN neurons activated intrinsic laryngeal muscles, suggesting that such neurons have excitatory projections to the intrinsic laryngeal muscle motoneurons in the nucleus ambiguus. These results suggest that the some of PRN neuron play a role in augmentation of the intrinsic laryngeal muscles activities during nasal air-jet stimulation.

The augmentation of intrinsic laryngeal muscle activity by air-jet stimulation of the nasal cavity in decerebrate cats

The purpose of this study was to examine the functional roles of nasal afferents in modulating the activity of the intrinsic laryngeal muscles. The electromyographic activities of the intrinsic laryngeal muscles and major respiratory muscles were recorded in cats during nasal air-jet stimulation. The activities of brainstem respiratory neurons were also recorded to determine which neurons transmit nasal afferent signals to the intrinsic laryngeal motoneurons. These axonal projections were identified by antidromic activation evoked by stimulation to the spinal cord at C4 level and the laryngeal nerve. The length of the respiratory cycle was prolonged and the diaphragmatic activity was decreased during air-jet stimulation of the nasal cavity. In contrast, the activities of both the intrinsic laryngeal adductor and abductor muscles were increased. Examination of the laryngeal reflexes revealed increase in the activities of intrinsic laryngeal motoneurons during both respiratory phases. Most of the respiratory neurons recorded decreased their peak firing rate during air-jet stimulation, reflecting decreased diaphragmatic activity; however, the peak firing rate of the bulbospinal expiratory neurons in the portion of the ventral respiratory group caudal to the obex did not decrease during stimulation. These findings demonstrate the nasal air-jet stimulation decreases the activities of major inspiratory muscles in order to avoid inspiration of foreign bodies into the nasal cavity and augments the activities of intrinsic laryngeal muscles, enabling prompt elicitation of the laryngeal airway reflex. Our findings also suggest that the nasal afferents suppress the major inspiratory activities by way of brainstem inspiratory neurons, but that the activities of intrinsic laryngeal muscles are controled through undetermined pathway(s) other than the pathway through respiratory neurons.

The dynamics of length change in canine vocal folds

The time courses of vocal fold elongation and contraction have been measured as a function of intrinsic laryngeal muscle activity. The superior and recurrent laryngeal nerves of anesthetized canines were stimulated supramaximally (on-off in all combinations) while the vocal folds were surgically exposed and illuminated for conventional and higher speed (300 frames per second) video recording. Microsutures were placed on various points on the vocal folds to measure elongation and contraction. Vocal fold strain, defined as elongation divided by rest length, ranged from -17% to +45%. The typical time constant for exponential increase or decrease in strain was about 30 ms. This reflects primarily the intrinsic muscle activation times rather than a passive (inertial or viscoelastic) response of cricothyroid joint rotation or translation.

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.

Single motor unit activity of human intrinsic laryngeal muscles during respiration.

Individual motor units in the thyroarytenoid (TA) and cricothyroid (CT) muscles were studied in 10 normal human volunteers during quiet respiration. Both tonic and phasic firing patterns were found in both TA and CT units. The rate of firing was higher during inhalation than during exhalation in phasic TA units and in tonic CT units. Tonically active units had a higher firing frequency than phasically active units in both TA and CT muscles. Phasically active units corresponded with the respiratory cycle, with firing associated with inhalation in both the TA and CT muscles. A variety of firing patterns were found between units in both the TA and CT muscles, and in one subject, units recorded from the same muscle had very different firing patterns. The results suggest that although laryngeal motoneurons are modulated by the respiratory cycle, they do not respond uniformly to respiration.

Study of Vibratory Pattern of the Vocal Folds in the Excised Canine Larynx

The effect of simulated thyroarytenoid and cricothyroid muscle contraction on the vibratory pattern of the vocal folds was studied in the excised canine larynx. To simulate the action of the thyroarytenoid muscle, small balloons were inflated in the paraglottic space at the level of the vocal folds. To simulate the action of the cricothyroid muscle, longitudinal tension was applied to the anterior commissure of the vocal folds. The photoglottographic and electroglottographic signals, sound intensity, and airflow rate were measured. This study showed that balloon inflation simulating thyroarytenoid muscle contraction produced an elevation of frequency of vibration with a decrease in open quotient, and that an increase in longitudinal tension simulating cricothyroid muscle contraction produced an elevation of frequency with an increase in open quotient. Vocal resistance decreased with increasing open quotient, amplitude of the photoglottographic waveform, and the frequency of vibration. Vocal efficiency increased with increasing photoglottographic amplitude and decreased with increasing frequency. The vocal efficiency peaked when the open quotient was approximately 0.5. This study suggests that glottographic parameters may be useful in assessing the effect of intrinsic laryngeal muscle activity on vocal efficiency and glottic resistance.

Laryngeal Electromyographic Activity in Adductor and Abductor Spasmodic Dysphonia

Vocal symptoms in spasmodic dysphonia (SD) range from strain-strangle phonation and glottal-stop phonatory breaks of adductor SD to breathy phonation and aspirate phonatory breaks of abductor SD. Many SD subjects show both symptom types. Heterogeneity in vocal symptoms contributes to controversy surrounding the etiology(s) of SD. Acoustic/perceptual analyses of vocal symptoms are inconclusive in resolving this controversy. This investigation moves the search for distinguishing features of adductor and abductor SD to the level of neuromuscular control and analysis of intrinsic laryngeal muscle (adductor and abductor) activity. Subjects rated perceptually as primarily adductor or abductor SD sustained production of vegetative gestures and isolated speech sounds (/i/ and /s/). Qualitative and quantitative analyses of electromyographic signals recorded from thyroarytenoid (TA) failed to differentiate SD subjects by symptom type. Analysis of TA and posterior cricoarytenoid (PCA) activity in one abductor SD revealed high levels in both muscles during production of the voiced vowel. Data suggest that a possible explanation for symptom heterogeneity in SD is the relation between disrupted neuromotor input to laryngeal muscles and reflexive or conscious compensations constrained by laryngeal biomechanics.

Use of flexible fiberoptic laryngoscopy to assess patients with spasmodic dysphonia

<h2>Summary</h2> Flexible videolaryngoscopy was used to study 38 patients with spasmodic dysphonia, rating excessive activation of intrinsic laryngeal muscles, extrinsic muscle hyperfunction, tremor, and dystonic movements. Seventeen patients were also studied after unilateral botulinum toxin injection. Dysfunction varied greatly; however, discrete patterns could not be identified. Functional status correlated significantly with the total score of all pathologic indicators, but not with any single parameter. Botulinum toxin was highly effective in reducing intrinsic laryngeal muscle activation, but did not always improve tremor. Extrinsic laryngeal muscle hyperfunction was not significantly affected by the toxin