The Effect of an Increasing Subglottal Stenosis Constriction That Extends From the Vocal Folds to the Inferior Border of the Cricoid Cartilage.

Acquired subglottal stenosis is an unpredicted complication that can occur in some patients who have undergone prolonged endotracheal intubation. It is a narrowing of the airway at the level of the cricoid cartilage that can restrict airflow and cause breathing difficulty. Stenosis is typically treated with endoscopic airway dilation, with some patients experiencing multiple recurrences. The study highlights the potential of computational fluid dynamics as a noninvasive method for monitoring subglottic stenosis, which can aid in early diagnosis and surgical planning. An anatomically accurate human laryngeal airway model was constructed from computerized tomography (CT) scans. The subglottis cross-sectional area was narrowed systematically using ≈10% decrements. A quadratic profile was used to interpolate the transformation of the airway geometry from its modified shape to the baseline geometry. The numerical results were validated by static pressure measurements conducted in a physical model. The results show that airway resistance follows a squared ratio that is inversely proportional to the size of the subglottal opening (R∝A-2). The study found that critical constriction occurs in the subglottal region at 70% stenosis (upper end of grade 2). Moreover, removing airway tissue below 40% stenosis during surgical intervention does not significantly decrease airway resistance.

Acoustics and aerodynamic effects following glottal and infraglottal medialization in an excised larynx model.

OBJECTIVE: This study aimed to investigate the impact of the implant's vertical location during Type 1 Thyroplasty (T1T) on acoustics and glottal aerodynamics using excised canine larynx model, providing insights into the optimal technique for treating unilateral vocal fold paralysis (UVFP). METHODS: Measurements were conducted in six excised canine larynges using Silastic implants. Two implant locations, glottal and infraglottal, were tested for each larynx at low and high subglottal pressure levels. Acoustic and intraglottal flow velocity field measurements were taken to assess vocal efficiency (VE), cepstral peak prominence (CPP), and the development of intraglottal vortices. RESULTS: The results indicated that the implant's vertical location significantly influenced vocal efficiency (p = 0.045), with the infraglottal implant generally yielding higher VE values. The effect on CPP was not statistically significant (p = 0.234). Intraglottal velocity field measurements demonstrated larger glottal divergence angles and stronger vortices with the infraglottal implant. CONCLUSION: The findings suggest that medializing the paralyzed fold at the infraglottal level rather than the glottal level can lead to improved vocal efficiency. The observed larger divergence angles and stronger intraglottal vortices with infraglottal medialization may enhance voice outcomes in UVFP patients. These findings have important implications for optimizing T1T procedures and improving voice quality in individuals with UVFP. Further research is warranted to validate these results in clinical settings.

Method for Fabricating Transparent Patient-Specific Vocal Tract Replicas.

INTRODUCTION: Transparent, patient-specific vocal tract replicas are helpful in research and educational endeavors but challenging to procure. An accessible method for fabricating these models, improving on previously suggested processes, would make them more widely available. METHOD: Detailed instructions for fabricating a transparent, patient-specific vocal tract model were addressed. The broad steps were (1) digitally reconstructing (patient-specific) vocal tract geometry, (2) producing a vocal tract mold (using methods such as three-dimensional [3D] printing), and (3) casting transparent material (such as silicone) around the vocal tract mold and removing the mold. The cavities remaining within the cast represented the exact geometry of the vocal tract. DISCUSSION: A combination of 3D printing and silicone casting can produce useful vocal tract replicas. Several simple changes to previous methods can improve consistency and reduce the labor and cost of production. Limitations and potential modifications to expand the applications of this method are discussed.

Computational Modeling of Voice Production Using Excised Canine Larynx.

A combined experimental-numerical work was conducted to comprehensively validate a subject-specific continuum model of voice production in larynx using excised canine laryngeal experiments. The computational model is a coupling of the Navier-Stokes equations for glottal flow dynamics and a finite element model of vocal fold dynamics. The numerical simulations employed a cover-body vocal fold structure with the geometry reconstructed from magnetic resonance imaging scans and the material properties determined through an optimization-based inverse process of experimental indentation measurement. The results showed that the simulations predicted key features of the dynamics observed in the experiments, including the skewing of the glottal flow waveform, mucosal wave propagation, continuous increase of the divergent angle and intraglottal swirl strength during glottal closing, and flow recirculation between glottal jet and vocal fold. The simulations also predicted the increase of the divergent angle, glottal jet speed, and intraglottal flow swirl strength with the subglottal pressure, same as in the experiments. Quantitatively, the simulations over-predicted the frequency and jet speed and under-predicted the flow rate and divergent angle for the larynx under study. The limitations of the model and their implications were discussed.

Understanding Nasal Emission During Speech Production: A Review of Types, Terminology, and Causality.

There are several different types of nasal emission that can occur during speech due to either velopharyngeal dysfunction or abnormal articulation in the pharynx. Nasal emission can be inaudible or very loud and distracting, depending on the size of the velopharyngeal opening and the physics of the flow. Nasal emission can be obligatory and/or compensatory (due to abnormal structure) or it can be caused by a misarticulation that results in a substitution of a pharyngeal sound for an oral sound, despite normal velopharyngeal structure. Nasal emission can occur on all pressure-sensitive phonemes or it can be phoneme-specific. Although it is generally recognized that the loud and distracting form of nasal emission (called nasal turbulence or nasal rustle) is due to a small velopharyngeal opening, the causality of the distracted sound is debated. This article provides a brief review of the types of nasal emission, the terms used to describe it, and the potential causes. This article also stresses the need for further research to clarify the causality of the sound generated by a small velopharyngeal opening.

Using High-Speed Nasopharyngoscopy to Quantify the Bubbling Above the Velopharyngeal Valve in Cases of Nasal Rustle.

OBJECTIVE: The loud and severely distorting form of audible nasal emission (commonly known as nasal turbulence or nasal rustle) typically occurs with a small velopharyngeal opening during production of pressure-sensitive consonants. The purpose of this study was to determine whether bubbling of the secretions, which commonly occurs on the superior aspect of the velopharyngeal port when there is a small opening, is a periodic process that can generate sound in the nasal cavity. PARTICIPANTS: Ten pediatric patients were included in the study. All participants had normal articulation and resonance but exhibited audible nasal emission characterized as nasal rustle. MEASURES: For each participant, high-speed video (HSV) nasopharyngoscopy and acoustic signals were recorded simultaneously. The acoustic recordings were captured in a manner similar to nasometry using nasal and oral microphones connected to a separation plate. Spectral analysis of the audio recordings and the HSV images was used to determine correlation between the acoustic and visual measurements. RESULTS: This study showed that secretion bubbling is a periodic process and its frequency, measured from the HSV data, was also captured by the acoustic measurements. The nasal acoustic signal correlated more strongly with the video of bubbling than the oral acoustic signal in the majority of the cases where bubbling occurred. CONCLUSION: These findings are strong evidence that secretion bubbling plays a significant role in the mechanism that generates undesired sound in the nasal cavity. Further work is needed to determine whether this sound is perceived as nasal rustle.

Sound production mechanisms of audible nasal emission during the sibilant /s/.

Audible nasal emission is a speech disorder that involves undesired sound generated by airflow into the nasal cavity during production of oral sounds. This disorder is associated with small-to-medium sized velopharyngeal openings. These openings induce turbulence in the nasal cavity, which in turn produces sound. The purpose of this study is to examine the aeroacoustic mechanisms that generate turbulent sound during production of a sibilant /s/ with and without a small opening of the velopharyngeal valve. The models are based on two pediatric subjects who were diagnosed with severe audible nasal emission. The geometries were delineated from computed tomography scans taken while the subjects were sustaining a sibilant sound. Large eddy simulation with the Ffowcs Williams and Hawkings analogy was used to predict the flow behavior and its acoustic characterization. It shows that the majority of the acoustic energy is produced by surface loading, which is related to dipole sources that resonate in the nasal cavity. The quadrupole source term that is associated with the unsteady shear layers is seen to be less significant. It also shows that closure of the velopharyngeal valve changes the far-field spectrum significantly because aeroacoustic mechanisms in the nasal cavity are eliminated.

Pharyngeal flow simulations during sibilant sound in a patient-specific model with velopharyngeal insufficiency.

Dysfunction of the velopharyngeal valve in the human airway causes speech disorders because there is no separation between the oral and nasal cavities during normal oral speech. The speech literature hypothesizes that undesired sound is formed by turbulent flow in the nasal cavity in cases of small velopharyngeal openings. The aim is to determine the flow behavior and the sound-generating mechanism in the vocal tract using computational fluid dynamics in two patient-specific models with small and large velopharyngeal openings and contrast it with cases of complete velopharyngeal closure. The geometry for the models was reconstructed from computed tomography scans that were taken while the patients were sustaining a sibilant sound. The results for the turbulence are correlated with the broadband acoustic models of Proudman and Curle. The models show that turbulence in the vocal tract increases downstream of a constriction and that sound may be generated from it. Furthermore, most of the sound due to turbulence in the nasal cavity is governed by a dipole source where turbulence interacts with the nasal cavity walls. The generated sound power by turbulence itself in the nasal cavity (the quadrupole source) is two orders of magnitude less than the dipole source.

Comparison of glottal flow rate characteristics based on experimental and computational data.

In a recent computational model, Farahani and Zhang [J. Acoust. Soc. Am. 136, EL369-EL375 (2014)] concluded that intraglottal vortices did not affect the closing mechanism of the folds. In order to determine the validity of any model that addresses the issue of vortex significance, it is important that the results of the computational model are comparable to experimental results. The results of Farahani and Zhang's model are inconsistent with data published for experimental models, which may challenge the validity of their conclusions.

Intraglottal velocity and pressure measurements in a hemilarynx model.

Determining the mechanisms of self-sustained oscillation of the vocal folds requires characterization of the pressures produced by intraglottal aerodynamics. Because most of the intraglottal aerodynamic forces cannot be measured in a tissue model of the larynx, current understanding of vocal fold vibration mechanism is derived from mechanical, analytical, and computational models. Previous studies have computed intraglottal pressures from measured intraglottal velocity fields and intraglottal geometry; however, this technique for determining pressures is not yet validated. In this study, intraglottal pressure measurements taken in a hemilarynx model are compared with pressure values that are computed from simultaneous velocity measurements. The results showed that significant negative pressure formed near the superior aspect of the folds during closing, which agrees with previous measurements in other hemilarynx models. Intraglottal velocity measurements show that the flow near the superior aspect separates from the glottal wall during closing and may develop into a vortex, which further augments the magnitude of negative pressure. Intraglottal pressure distributions, computed by solving the pressure Poisson equation, showed good agreement with pressure measurements. The match between the pressure computations and its measurements validates the current technique, which was previously used to estimate intraglottal pressure distribution in a full larynx model.

Intraglottal geometry and velocity measurements in canine larynges.

Previous flow velocity measurements during phonation in canine larynges were done above the glottal exit. These studies found that vortical structures are present in the flow above the glottis at different phases of the glottal cycle. Some vortices were observed to leave the glottis during the closing phase and assumptions were proposed regarding their formation mechanism. In the current study, intraglottal velocity measurements are performed using PIV, and the intraglottal flow characteristics are determined. Results from five canine larynges show that at low subglottal pressure the glottis assumes a minimal divergence angle during closing and the flow separates at the glottal exit. Vortical structures are observed above the glottis but not inside. As the subglottal pressure is increased, the divergence angle between the folds during closing increases and the location of the flow separation moves upstream into the glottis. Entrainment flow enters the glottis to fill the void that is formed between the glottal jet and the fold. Vortical structures develop near the superior edge at medium and high subglottal pressures from the flow separation. The magnitude of their swirling strength changes as a function of the wall dynamics.

Tracheal Anastomosis Leaks Across Suture Techniques and Tensions: A Biomechanical Ex Vivo Study.

BACKGROUND: Anastomotic leak after tracheal resection may occur while coughing in the early postoperative period. We investigated the varying effects of suturing technique, stretch, and tension on anastomotic leaks during simulated coughs. METHODS: End-to-end anastomoses were performed using continuous or interrupted sutures on excised porcine larynges. Tracheas were secured to a pressurized system simulating cough forces, submerged in a water bath, and stretched to 1, 2, and 3 cm above baseline. Peak pressure, incomplete cough generation, and observed leakages were recorded. Parameters were analyzed using Analysis of Variance (ANOVA), multiple linear regression, and logistic regression modeling. RESULTS: Peak tension (B = -0.660, p < 0.001) and stretch lengths (B = -0.329, p = 0.006) were associated with variance in peak pressure (R2 = 0.77, F(3,294) = 8.182, p < 0.001). Incomplete coughs increased with higher peak tension (odds ratio [OR] = 15.627, p < 0.001) and stretching to 3 cm above baseline (OR = 4.335, p < 0.007). Similarly, leak occurrences, primarily from the posterior tracheal wall, increased with higher peak tension (OR = 1.787, p < 0.001) and stretching to 3 cm (OR = 2.613, p = 0.017). No significance was identified with suturing technique. CONCLUSION: Interrupted and continuous suture techniques do not differ in anastomotic strength during simulated coughs. Increased peak tracheal tension is associated with a weaker anastomosis, and tracheal stretch to 3 cm was associated with a weaker anastomosis. Our study supports the commonly held clinical belief that, to create a stronger anastomosis, tension should be minimized, and particular attention should be placed at the posterior tracheal wall during closure. LEVEL OF EVIDENCE: N/A, Benchtop study Laryngoscope, 2024.

How Face Masks Affect Acoustic and Auditory Perceptual Characteristics of the Singing Voice.

Wearing a face mask has been accepted as one of the most effective ways for slowing the spread of COVID-19. Yet information regarding the degree to which masks affect acoustics and perception associated with voice performers is scarce. This study examines these effects with common face masks, namely a neck gaiter, disposable surgical mask, and N95 mask, as well as a novel material that could be used as a mask (acoustic foam). A recorded excerpt from the "Star-Spangled Banner" was played through a miniature speaker placed inside the mouth of a masked manikin. Experienced listeners were asked to rate perceptual qualities of these singing stimuli by blindly comparing them with the same recording captured without a mask. Acoustic analysis showed that face masks affected the sound by enhancing or suppressing different frequency bands compared to no mask. Acoustic energy around the singer's formant was reduced when using surgical and N95 masks, which matches observations that these masks are more detrimental to the perceptions of singing voice compared with neck gaiter or acoustic foam. It suggests that singers can benefit from masks designed for minimal impact on auditory perception of the singing voice while maintaining reasonable efficacy of filtering efficiency.

An Ex-vivo Model Examining Acoustics and Aerodynamic Effects Following Medialization With and Without Arytenoid Adduction.

OBJECTIVES/HYPOTHESIS: Quantify differences in acoustics and intraglottal flow fields between Thyroplasty Type 1 (TT1) with and without arytenoid adduction (AA) using excised canine larynx model. STUDY DESIGN: Basic science experiments using excised larynges. METHODS: Surgical procedures were implemented in eight excised canine larynges. Acoustics and intraglottal flow measurements were taken at low and high subglottal pressures in each experimental setup. RESULTS: In all larynges, vocal efficiency (VE) and cepstrum peak prominence (CPP) were higher, and the mean phonatory flow rate was lower in TT1 with AA than without AA. The glottal asymmetry is reduced with AA and promotes the formation of stronger vortices in the glottal flow during the closing phase of the vibrating folds. CONCLUSIONS: Findings suggest a clear acoustic and aerodynamic benefit to the addition of AA when performing TT1. It shows significant improvement in CPP, translating to decreased breathiness and dysphonia and increased VE, leading to easier and more sustainable phonation. Stronger intraglottal vortices are known to be correlated with the loudness of voice produced by phonation. LEVEL OF EVIDENCE: N/A Laryngoscope, 133:621-627, 2023.

The Effects of Negative Pressure Induced by Flow Separation Vortices on Vocal Fold Dynamics during Voice Production.

This study used a two-dimensional flow-structure-interaction computer model to investigate the effects of flow-separation-vortex-induced negative pressure on vocal fold vibration and flow dynamics during vocal fold vibration. The study found that negative pressure induced by flow separation vortices enhances vocal fold vibration by increasing aeroelastic energy transfer during vibration. The result showed that the intraglottal pressure was predominantly negative after flow separation before gradually recovering to zero at the glottis exit. When the negative pressure was removed, the vibration amplitude and flow rate were reduced by up to 20%, and the closing speed, flow skewness quotient, and maximum flow declination rate were reduced by up to 40%. The study provides insights into the complex interactions between flow dynamics, vocal fold vibration, and energy transfer during voice production.

Secretion Bubbling as the Sound Mechanism for Nasal Rustle: A Perceptual Study.

PURPOSE: Secretion bubbling on the superior aspect of the velopharyngeal (VP) valve typically occurs with a small VP opening during production of oral pressure consonants. The use of high-speed nasopharyngoscopy has shown correlation between the bubbling frequency and the acoustics captured with the nasal microphone of the nasometer. The purpose of this study was to investigate if the sound generated by the bubbling process is perceived as nasal rustle (also known as nasal turbulence). METHOD: Speech samples were extracted from the data of patients who were diagnosed with nasal rustle (five boys and five girls, ranging in age from 5 to 10 years old). A customized filter was used to remove the sound generated by the secretion bubbling. Six experienced listeners were asked to rate the perception of nasal rustle in each speech stimuli before and after the filtering process. RESULTS: Rating values for the perception of nasal rustle were overall reduced in all cases after the filtering process. Furthermore, the perception of nasal rustle was eliminated in 40% of the cases. Rating reliability was excellent before the filtering process and moderate to good after filtering. CONCLUSION: Reducing the perception of nasal rustle using spectral filtering based on the bubbling frequencies supports the hypothesis that undesired sound in the nasal cavity is generated from the interaction of the turbulent airflow with the secretion bubbling. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.19111544.

Computational Modeling of Nasal Drug Delivery Using Different Intranasal Corticosteroid Sprays for the Treatment of Eustachian Tube Dysfunction.

Eustachian tube dysfunction (ETD) is a common otolaryngologic condition associated with decreased quality of life. The first-line treatment of ETD is intranasal corticosteroid sprays (INCS). Computational fluid dynamics (CFD) was used to study particle deposition on the Eustachian tube (ET) using two commercial INCS (Flonase and Sensimist). Simulations also considered the effects of nostril side, insertion depth, insertion angle, cone spray angle, inhaling rates, wall impingement treatment, and fluid film. Flonase and Sensimist produced different particle size distributions and sizes. Sensimist droplets are smaller, less sensitive to asymmetry in nostrils anatomy and variation in insertion angle, and therefore can reach the posterior nasopharynx more readily. Flonase produces larger particles with greater inertia. Its particles deposition is more sensitive to intrasubject variation in nasal anatomy and insertion angles. The particle deposition on the ET was sensitive to the wall impingement model. The deposition on the ET was insignificant with adherence only <0.15% but increased up to 1-4% when including additional outcomes rebound and splash effects when droplets impact with the wall. The dose redistribution with the fluid film is significant but plays a secondary effect on the ET deposition. Flonase aligned parallel with the hard palate produced 4% deposition efficiency on the ET, but this decreased <0.14% at the higher insertion angle. INCS with larger droplet sizes with a small insertion angle may be more effective at targeting droplet deposition on the ET opening.

Fluid-Structure Interaction Analysis of Aerodynamic and Elasticity Forces During Vocal Fold Vibration.

The effect of the intraglottal vortices on the glottal flow waveform was explored using flow-structure-interaction (FSI) modeling. These vortices form near the superior aspect of the vocal folds during the closing phase of the folds' vibration. The geometry of the vocal fold was based on the well-known M5 model. The model did not include a vocal tract to remove its inertance effect on the glottal flow. Material properties for the cover and body layers of the folds were set using curve fit to experimental data of tissue elasticity. A commercially available FSI solver was used to perform simulations at low and high values of subglottal input pressure. Validation of the FSI results showed a good agreement for the glottal flow and the vocal fold displacement data with measurements taken in the excised canine larynx model. The simulations result further support the hypothesis that intraglottal vortices can affect the glottal flow waveform, specifically its maximum flow declination rate (MFDR). It showed that MFDR occurs at the same phase when the highest intraglottal vortical strength and the negative pressure occur. It also showed that when MFDR occurs, the magnitude of the aerodynamic force acting on the glottal wall is greater than the elastic recoil force predicted in the tissue. These findings are significant because nearly all theoretical and computational models that study the vocal fold vibrations mechanism do not consider the intraglottal negative pressure caused by the vortices as an additional closing force acting on the folds.

Surgical Treatment of Acquired Velopharyngeal Insufficiency in Adults With Dysphagia and Dysphonia.

OBJECTIVES: Velopharyngeal insufficiency (VPI) is a form of velopharyngeal dysfunction caused by abnormal or insufficient anatomy. This process is known to be associated with dysphagia and dysphonia but surgical interventions for these complex patients have not been well studied. The current study characterized a small cohort of adult patients with acquired VPI, dysphonia, and dysphagia, as well as associated surgical interventions. METHODS: A retrospective descriptive case series of 22 (N = 22) adult patients over a 6-year period with acquired VPI and varying degrees of dysphagia and dysphonia was described from a multi-disciplinary voice and swallowing clinic. Perceptual assessment, nasopharyngoscopy, fluoroscopic swallowing assessment, and patient reported outcomes were reviewed to characterize the cohort. RESULTS: VPI etiologies included: stroke (n = 4), head and neck cancer (n = 5), brainstem lesions (n = 5), trauma (n = 5), and other/unknown (n = 3). All 22 patients underwent nasopharyngoscopy and were categorized as having unilateral (n = 13), central (n = 4), or no (n = 5) velopharyngeal deficits. Seventeen patients (77.2%) underwent modified barium swallow studies, revealing that soft palate elevation scored least impaired among patients with no VPI, and most impaired among patients with unilateral VPI deficits. All 22 patients underwent some form of surgical intervention for VPI, with 14 (63.6%) of those patients requiring additional surgical revision. CONCLUSION: This series is one of the first to the authors' knowledge to characterize a cohort of individuals with VPI, dysphagia, and dysphonia and associated surgical interventions.

Change in aeroacoustic sound mechanism during sibilant sound with different velopharyngeal opening sizes.

The velopharyngeal valve regulates the opening between the nasal and oral cavities. The lack of complete closure is especially problematic in speech because inappropriate leakage of airflow and/or sound into the nasal cavity causes abnormal sound production and increased nasality. The purpose of this study is to use the large eddy simulation approach to examine changes in sound source mechanisms as the size of the opening changes during the production of a sibilant sound. The baseline geometry of the model is based on the pharyngeal airway of a subject having a small velopharyngeal opening while sustaining a sibilant sound. Modifications to the model are done by systematically widening or narrowing the opening (all else being equal). Results show that acoustic energy in the nasal cavity is directly related to the size of the velopharyngeal opening and that there is a critical size where the magnitude of Lighthill's acoustics source in the nasal cavity is maximized. The far-field acoustic energy and its correlation with the sound source mechanisms are also dependent on the size of the velopharyngeal opening. Patient-specific geometry with a velopharyngeal opening during a normal sibilant /s/ sound is shown to the left. Lighthill's acoustic source term is displayed on the right and varies depending on the size of the velopharyngeal opening.