Computational modeling of phonatory dynamics in a tubular three-dimensional model of the human larynx.

Simulation of the phonatory flow-structure interaction has been conducted in a three-dimensional, tubular shaped laryngeal model that has been designed with a high level of realism with respect to the human laryngeal anatomy. A non-linear spring-based contact force model is also implemented for the purpose of representing contact in more general conditions, especially those associated with three-dimensional modeling of phonation in the presence of vocal fold pathologies. The model is used to study the effects of a moderate (20%) vocal-fold tension imbalance on the phonatory dynamics. The characteristic features of phonation for normal as well as tension-imbalanced vocal folds, such as glottal waveform, glottal jet evolution, mucosal wave-type vocal-fold motion, modal entrainment, and asymmetric glottal jet deflection have been discussed in detail and compared to established data. It is found that while a moderate level of tension asymmetry does not change the vibratory dynamics significantly, it can potentially lead to measurable deterioration in voice quality.

Sensitivity of vocal fold vibratory modes to their three-layer structure: implications for computational modeling of phonation.

The sensitivity of the eigenmodes and eigenfrequencies of the human vocal fold to its three-layer structure is studied using finite-element modeling. The study covers a variety of three-dimensional vocal fold models ranging from an idealized, longitudinally uniform structure to a physiologically more realistic, longitudinally varying structure. Geometric parameters including the thickness of the ligament and cover layers as well as the ligament length are varied systematically. The results indicate that vocal fold vibratory modes are quite insensitive to the longitudinal variation in the thickness of the three layers as well as the variation in ligament length. However, significant overall changes in thickness of each layer can produce noticeable changes in these modes. The implications of these findings on computational modeling of phonation are discussed.

Direct-numerical simulation of the glottal jet and vocal-fold dynamics in a three-dimensional laryngeal model.

An immersed-boundary method based flow solver coupled with a finite-element solid dynamics solver is employed in order to conduct direct-numerical simulations of phonatory dynamics in a three-dimensional model of the human larynx. The computed features of the glottal flow including mean and peak flow rates, and the open and skewness quotients are found to be within the normal physiological range. The flow-induced vibration pattern shows the classical "convergent-divergent" glottal shape, and the vibration amplitude is also found to be typical for human phonation. The vocal fold motion is analyzed through the method of empirical eigenfunctions and this analysis indicates a 1:1 modal entrainment between the "adduction-abduction" mode and the "mucosal wave" mode. The glottal jet is found to exhibit noticeable cycle-to-cycle asymmetric deflections and the mechanism underlying this phenomenon is examined.

A computational study of asymmetric glottal jet deflection during phonation.

Two-dimensional numerical simulations are used to explore the mechanism for asymmetric deflection of the glottal jet during phonation. The model employs the full Navier-Stokes equations for the flow but a simple laryngeal geometry and vocal-fold motion. The study focuses on the effect of Reynolds number and glottal opening angle with a particular emphasis on examining the importance of the so-called "Coanda effect" in jet deflection. The study indicates that the glottal opening angle has no substantial effect on glottal jet deflection. Deflection in the glottal jet is always preceded by large-scale asymmetry in the downstream portion of the glottal jet. A detailed analysis of the velocity and vorticity fields shows that these downstream asymmetric vortex structures induce a flow at the glottal exit which is the primary driver for glottal jet deflection.

A computational study of the effect of vocal-fold asymmetry on phonation.

Unilateral laryngeal paralysis leads to tension imbalance and hence to asynchronous movements between the two vocal folds during phonation. In the current study, a computational model of phonation that couples a two-mass model of the vocal folds with a Navier-Stokes model of the glottal airflow, has been used to examine the dynamics of vocal fold configurations with tension imbalance and its implications for phonation. The simulations show that tension imbalance influences phonation onset, intensity as well as the fundamental phonation frequency. Distinct non-linear effects such as period-doubling bifurcation and preferential frequency selection are also observed.

Assessment of posterior cricoarytenoid botulinum toxin injections in patients with abductor spasmodic dysphonia.

In this study, we compared 2 techniques for injection of botulinum toxin type A (Botox) into the posterior cricoarytenoid (PCA) muscle for the treatment of abductor spasmodic dysphonia (ABSD). Fifteen patients with ABSD were enrolled in a prospective randomized crossover treatment trial comparing the 2 injection techniques. The PCA muscle was injected with 5 units on each side, with the injections staged 2 weeks apart, via either a percutaneous posterior-lateral approach or a transnasal fiberoptic approach. Eleven patients reported some benefit with the injections; however, the patient-perceived benefits were not related to changes in symptoms on blinded counts by speech pathologists. No significant reductions in the numbers of breathy breaks occurred with either technique, and no differences were found between techniques. Although patients perceived a benefit, blinded symptom counts did not substantiate these benefits. Thus, PCA muscle injections of Botox provided limited benefits to patients with ABSD, demonstrating the need for a more effective therapy for these patients.

Adductor muscle activity abnormalities in abductor spasmodic dysphonia.

OBJECTIVE: To determine laryngeal muscle activation abnormalities associated with speech symptoms in abductor spasmodic dysphonia (ABSD). STUDY DESIGN: Bilateral laryngeal muscle recordings from the posterior cricoarytenoid, thyroarytenoid, and cricothyroid muscles were conducted in 12 ABSD patients. Patients' measures were compared during speech breaks and during speech without breaks and with 10 normal controls. RESULTS: Significant group differences were found in the thyroarytenoid muscle; the patients had significantly greater activity on the right side both during speech breaks and nonbreaks in comparison with the controls. Cricothyroid muscle levels were also increased on the right in the patients. CONCLUSION: An asymmetry in adductor muscle tone between the 2 sides in ABSD may account for difficulties with maintaining phonation and voice onset after voiceless consonants. SIGNIFICANCE: These abnormalities may indicate why PCA BOTOX injections have not been as effective in ABSD as thyroarytenoid injections have been in adductor spasmodic dysphonia.

Endoscopic inferior turbinate reduction: an outcomes analysis.

OBJECTIVES/HYPOTHESIS: In a previous publication, we introduced an endoscopic technique for the treatment of nasal obstruction caused by inferior turbinate hypertrophy. The technique, a modification of the procedure popularized by Mabry, involves resecting the inferior and lateral aspects of the inferior turbinate with a microdebrider under endoscopic guidance. Our preliminary postoperative results were favorable. All 20 patients experienced improvement by postoperative day 5 and the incidence of complications over the first 6 months after surgery was low. The objective of this study is to perform a long-term outcomes analysis of patients undergoing the procedure. STUDY DESIGN: Follow-up survey questionnaire and analysis. METHODS: We sent questionnaires to 60 patients, ranging from 6 to 40 months after surgery, inquiring about continued use of nasal medications, need for further surgery, presence of adverse effects, and improvement in symptoms. Nasal airway obstruction was assessed on a subjective scoring scale from 1 (no obstruction) to 6 (complete obstruction). RESULTS: Of the 28 (47%) patients who returned questionnaires, the severity of daytime nasal obstruction was rated as 2.3 and nighttime nasal obstruction as 2.7. The use of nasal steroids and oral decongestants was 25% and 21%, respectively. Adverse effects were minimal and all but one patient (96%) experienced improvement in their nasal airway. CONCLUSION: These results confirm the long-term effectiveness of this procedure for the relief of nasal obstruction.

Quantification of static and dynamic supraglottic activity.

For estimating supraglottic compression in disordered voice production, categorical rating scales of true vocal fold coverage by supraglottic structures are the current standard. Quantification of change in the position of supraglottic structures compared to no supraglottic activity would be a better method for distinguishing between and within voice-disordered groups. This study developed a method for quantifying static supraglottic activity and extent of false vocal fold (FVF) motion during dynamic supraglottic activity. Twelve control participants and 12 individuals with voice disorders (6 with complaints of vocal fatigue and 6 with vocal fold nodules) were enrolled in the study. These individuals participated in a transnasal fiberoptic laryngeal examination in which various speech tasks were recorded. Single-frame images were selected to represent the positions of minimum and maximum supraglottic compression for each speech task. Two individuals rated these single-frame images using a categorical rating scale. Two other individuals measured the anterior-to-posterior (A-P) distance, vocal fold length, and vocal fold area. A-P and FVF compression were derived from these three measures. Reliability was demonstrated between judges for the ratings and between and within judges for the measures. Significant differences in normalized static supraglottic compression measures corresponded to the rating scale categories. Significant differences in normalized dynamic supraglottic compression measures corresponded to the differences in category ratings between minimum and maximum compression. Using the normalized measures, the voice-disordered groups demonstrated significantly greater static A-P compression (t test, p < .03) than did the control participants. These results suggest that static supraglottic activity may be diagnostic of voice disorder. Normalized dynamic FVF compression ratios were not significantly different between groups. This supports a previous hypothesis that dynamic supraglottic activity serves as an articulatory function at the level of the larynx and is part of the linguistic/phonemic system, rather than evidence of disordered laryngeal function.

Surgical therapy of T1 and selected cases of T2 glottic carcinoma: cordectomy, horizontal glottectomy and CO2 laser endoscopic resection.

AIMS AND BACKGROUND: Among the different laryngeal neoplasms, glottic carcinoma is known to be one of the most suitable for functional management. Nevertheless, the best treatment for T1 and T2 glottic carcinoma, whether an open neck procedure, endoscopy or radiotherapy, with reference to recurrence, survival, and functional results, has long been debated. STUDY DESIGN: From February 1983 to September 1997, 83 patients with well to undifferentiated glottic carcinoma (48 pT1a, 14 pT1b, and 21 selected cases of pT2 with impairment of vocal cord mobility) were submitted to surgery at the Otorhinolaryngologic Section of the Department of Surgical Sciences and Organ Transplantations of Cagliari University. Surgical treatment included 30 laryngofissures with simple or enlarged cordectomy, 22 horizontal glottectomies and 31 endoscopic laser resections. A retrospective review of the records of the patients was performed in order to obtain a better understanding of the outcome of the three different surgical procedures in our institution. RESULTS: According to the Kaplan-Meier method, the probability of remaining free of local recurrence 3 years after primary surgery was 0.90 for the T1 group and 0.85 for the T2 group. The distribution of recurrences for cordectomy, glottectomy and CO2 laser at 3 years showed a cumulative probability of remaining free of disease after primary surgery of 0.86, 0.85 and 0.88. The probability of remaining free of local recurrence 3 years after salvage surgery was 0.96 for the T1 group and 0.95 for the T2 group. Analyzing the phenomena for type of surgical procedure, local control at 3 years after salvage surgery for cordectomy, glottectomy and exclusive CO2 laser was 0.93, 0.90 and 0.92, respectively. In the endoscopic group, local control rate after any type of salvage therapy modified the percentage at 3 years to 100%. Anterior commissure spread (AC1-AC2) resulted in a difference (not statistically significant) in local control between the group of patients without and with anterior commissure involvement. Laryngeal preservation was achieved in 93.7% (45/48) of patients who survived after salvage surgery following open neck procedures and in 100% of patients originally submitted to the endoscopic approach. CONCLUSIONS: In our experience, although open laryngeal procedures can be still considered a valid option in the treatment of T1 and selected cases of T2 glottic carcinoma, endoscopic laser excision offered an oncologically adequate alternative to the traditional techniques, with minimum discomfort for the patient and satisfactory preliminary functional results.

Endoscopic revision of failed external dacryocystorhinostomy.

Obstruction of the lacrimal pathways is a relatively frequent problem usually corrected by external dacryocystorhinostomy. Failure of the external approach may be due to an inadequate rhinostomy, excessive scar tissue production, anatomical anomalies or concomitant paranasal sinus infectious. The introduction of direct and angled endoscopes for paranasal sinus surgery and the refinement of endoscopic surgical procedures allows a complete intranasal exposure and surgical management of the lacrimal sac, even in cases of recurrent obstruction. The present work offers a retrospective review of the records of seven patients who underwent a revision endoscopic dacriocystorhinostomy (ENDCR) between January 1994 and June 1997 for failed external dacryocystorhinostomy. The preoperative evaluation of the patients, the surgical technique and the postoperative management are examined in detail. A permanent dacryocystorhinostomy was obtained in six patients. One patient underwent a successful bilateral procedure. One patient experienced a persistent stenosis. There were no complications related to the surgical procedure. In our experience the revision endoscopic dacryocystorhinostomy offered several advantages, including a complete exposure of those anatomical anomalies or inflammatory changes of the normal structures that commonly hinder conventional external surgery. Although a larger series will further elucidate the efficacy of this procedure in failed external dacryocystorhinostomy, we recommend considering revision ENDCR as an alternative to the external revision technique.

Modulation of laryngeal responses to superior laryngeal nerve stimulation by volitional swallowing in awake humans.

Laryngeal sensori-motor closure reflexes are important for the protection of the airway and prevent the entry of foreign substances into the trachea and lungs. The purpose of this study was to determine how such reflexes might be modulated during volitional swallowing in awake humans, when persons are at risk of entry of food or liquids into the airway. The frequency and the amplitude of laryngeal adductor responses evoked by electrical stimulation of the internal branch of the superior laryngeal nerve (ISLN) were studied during different phases of volitional swallowing. Subjects swallowed water on command while electrical stimuli were presented to the ISLN at various intervals from 500 ms to 5 s following the command. Laryngeal adductor responses to unilateral ISLN stimulation were recorded bilaterally in the thyroarytenoid muscles using hooked wire electrodes. Early ipsilateral R1 responses occurred at 17 ms, and later bilateral R2 began around 65 ms. The muscle responses to stimuli occurring during expiration without swallowing were quantified as control trials. Responses to stimulation presented before swallowing, during the swallow, within 3 s after swallowing, and between 3 and 5 s after a swallow were measured. The frequency and amplitude of three responses (ipsilateral R1 and bilateral R2) relative to the control responses were compared across the different phases relative to the occurrence of swallowing. Results demonstrated that a reduction occurred in both the frequency and amplitude of the later bilateral R2 laryngeal responses to electrical stimulation for up to 3 s after swallowing (P = 0.005). The amplitude and frequency of ipsilateral R1 laryngeal responses, however, did not show a significant main effect following the swallow (P = 0.28), although there was a significant time by measure interaction (P = 0.006) related to reduced R1 response amplitude up to 3 s after swallowing (P = 0.021). Therefore, the more rapid and shorter unilateral R1 responses continued to provide some, albeit reduced, laryngeal protective functions after swallowing, whereas the later bilateral R2 responses were suppressed both in occurrence and amplitude for up to 3 s after swallowing. The results suggest that R2 laryngeal adductor responses are suppressed following swallowing when residues may remain in the laryngeal vestibule putting persons at increased risk for the entry of foreign substances into the airway.

Early arytenoid adduction for vagal paralysis after skull base surgery.

OBJECTIVES: To evaluate the efficacy of early arytenoid adduction in the management of vagal paralysis after skull base surgery. STUDY DESIGN: Retrospective evaluation at a tertiary care skull base center. METHODS: Aggressive surgical management of skull base lesions has become increasingly popular owing to advances in surgical technique and intraoperative monitoring. Temporary and permanent lower cranial neuropathies occur frequently, especially after the surgical management of lesions involving the vertebrobasilar system and the jugular foramen. An injury to the proximal vagus nerve is usually associated with dysphonia and swallowing dysfunction. An early arytenoid adduction has been employed in 26 patients with a vagal paralysis after skull base surgery. Most commonly, the neurosurgical patient underwent an arytenoid adduction under general anesthesia on postoperative day 2. RESULTS: Videostroboscopy after arytenoid adduction demonstrated 76% of patients had complete glottic closure. Of those with inadequate glottic closure, all demonstrated a well-medialized posterior glottis with a persistent anterior glottal gap. These patients were easily treated with a secondary type I thyroplasty under local anesthesia with sedation resulting in complete glottic closure. Despite excellent voice outcomes, 66% of these patients had dysphagia requiring enteral feedings for nutritional support. CONCLUSIONS: An early arytenoid adduction is an excellent medialization technique that can be performed safely in the early postoperative period under general anesthesia after skull base surgery.

Effects of botulinum toxin on pathophysiology in spasmodic dysphonia.

To determine the mechanism of symptom relief with treatment by botulinum toxin injection in persons with adductor spasmodic dysphonia (ADSD), we evaluated the effects of unilateral thyroarytenoid muscle injections on both injected and noninjected muscles in 10 subjects with ADSD, using electromyography on both sides of the larynx before and after treatment. The subjects' speech symptoms were reduced (p = .005) 2 weeks following injection, when the electromyographic study occurred. Muscle activation levels and the numbers of spasmodic muscle bursts decreased significantly (p < or = .03) postinjection in both the injected and noninjected muscles. The reductions in laryngeal muscle bursts correlated with symptom reduction (r > or = .7) in all muscles. Reductions in laryngeal muscle bursts did not relate to either absolute or normalized levels of muscle activity before or after botulinum toxin injection. The results suggest that changes in the central pathophysiology are responsible for changes in speech symptoms following treatment.

Supraglottic activity: evidence of vocal hyperfunction or laryngeal articulation?

False vocal fold (FVF) adduction and compression of the arytenoid cartilages to the petiole of the epiglottis in an anterior to posterior (A-P) direction have been thought to characterize voice disorders with abnormally increased muscle tension or effort, often termed hyperfunctional voice disorders. To further evaluate the association between hyperfunctional voice disorders and supraglottic activity, we compared the incidence of static and dynamic supraglottic activity in individuals with normal laryngeal mucosa, normal voice quality, and no voice complaints to two populations: subjects with vocal fold nodules and subjects with complaints of dysphonia without visible vocal fold lesions, glottal incompetence, or impairment of arytenoid cartilage motion ("hyperfunctional" group). Thirty-two subjects were assigned to one of these three groups (10 control, 12 nodule, and 10 hyperfunctional). Laryngeal movements were recorded using flexible videoendoscopy while a subject was performing speech tasks such as sustained phonation, syllable repetitions, sentence imitations, and conversation. Samples were randomized by subject and task and rated for presence or absence of A-P and FVF compression. Statistically significant group differences were found for FVF compression across speech tasks (chi-square, p<0.001). The control group had the smallest incidence (45%), nodule patients the next larger incidence (68%), and hyperfunctional patients the largest incidence (80%). Statistically significant group differences were found for A-P compression across speech tasks (chi-square, p<.05). The control group had the smallest incidence (74%), nodule patients the next larger incidence (78%), and hyperfunctional patients the largest incidence (92%). Statistically significant task differences were found for the presence of FVF compression in control subjects (chi-square, p<.005), hyperfunctional patients (chi-square, p<.025), and nodule patients (chi-square, p<.001), but not for A-P compression for any of the groups. A higher incidence of FVF compression was present for the speech tasks that included glottal stops. This context-specific variation in supraglottic activity suggested a dynamic component to FVF compression and also explained the high proportion of FVF compression in the control group. Each video sample was also rated for consistency of FVF or A-P compression to explore the static and dynamic nature of supraglottic activity. For samples on which raters agreed, A-P compression was typically present consistently, suggesting a static component, and FVF compression inconsistently, suggesting a dynamic component, for all three groups (chi-square, p<.001). These findings do not support previous suggestions that supraglottic activity may be a precursor to developing vocal fold nodules, as the nodule patients did not exhibit a higher incidence or consistency of A-P or FVF compression than patients with hyperfunctional voicing patterns in this study. Subjects in the hyperfunctional voice group were found to have static components of FVF and A-P compression. The presence of FVF compression in speech tasks that included glottal stops in the control group suggests an articulatory function at the laryngeal level.

Chronic intermittent stimulation of the thyroarytenoid muscle maintains dynamic control of glottal adduction.

Patients with laryngeal motor control disorders need improved dynamic glottal closure for speech and swallowing. To evaluate the functional outcome of intermittent chronic thyroarytenoid muscle stimulation in an animal model, 6 canines were implanted with bilateral Medtronic Xtrel systems containing Peterson-type electrodes in the inferior and superior portions of the thyroarytenoid muscle. Stimulation was on one side only at 60 Hz, for 5 s on and 5 s off, over 8 h, 5 days per week, up to 8 months. Monthly videorecordings were done under anesthesia to measure the voltage threshold for detectable movement on each side, and vocal fold displacement and velocity during maximal stimulation of each side. Movement thresholds were lower in the inferior portion of the thyroarytenoid muscle (P

Exit jet particle velocity in the in vivo canine laryngeal model with variable nerve stimulation.

This study extends previous work on exit jet particle velocity in the in vivo canine model of phonation by measuring air particle velocity at multiple locations in the midline of the glottis and across multiple levels of recurrent laryngeal nerve (RLN) and superior laryngeal nerve (SLN) stimulation. In a second experiment, exit jet particle velocity was measured at midline and offmidline positions with constant levels of RLN and SLN stimulation. In this study, peak particle velocity was higher at the anterior commissure than at the posterior commissure in the midline of the glottis, and peak particle velocity was higher at the midline than at offmidline positions. In addition, increasing levels of RLN stimulation resulted in increasing peak particle velocity; however, increasing levels of SLN stimulation failed to produce a uniform effect on peak particle velocity.