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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Evaluating the biomechanical characteristics of cuffed-tracheostomy tubes using finite element analysis.

The objective of this study was to perform finite element analysis (FEA) of cuff inflation within an anatomically accurate model of an adult trachea in four different cuffed-tracheostomy tube designs. The leakage quantified by the distance between the cuff and trachea was largest for the Tracoe cuff and smallest for the Portex cuff. The smooth muscle stresses were greatest for the Portex and least for the Distal cuff, respectively. The proposed FEA model offers a promising approach to virtually evaluate the sealing efficacy of cuffed-tracheostomy tubes and the tracheal wall stresses induced by cuff inflation, prior to application.

Medial Surface Dynamics as a Function of Subglottal Pressure in a Canine Larynx Model.

During vocal fold vibration, there may be a mucosal wave in the superior-inferior (vertical) direction, resulting in a convergent shape during opening and a divergent shape during closing. Most of our understanding of the converging/diverging shape of the glottis has come from studies in a hemilarynx model. Previous work has shown that vibratory patterns in the full excised larynx are different than the hemilarynx. This study characterized the dynamics of the medial glottal wall geometry during vibrations in the full excised canine larynx model. Using particle image velocimetry, the intraglottal geometry was measured at the midmembranous coronal plane in an excised canine larynx model. Measurements of the glottal area were taken simultaneously using high-speed imaging. The results show that skewing of the glottal area waveform occurs without the presence of a vocal tract and that the phase-lag of the superior edge relative to the inferior edge is smaller than reported and depends on the subglottal pressure. In addition, it shows that the glottal divergence angle during closing is proportional to the magnitude of the acoustic intensity and the intraglottal negative pressure. This preliminary data suggests that more studies are needed to determine the important mechanisms determining the relationship between intraglottal flow, intraglottal geometry, and acoustics.

Quantification of the Intraglottal Pressure Induced by Flow Separation Vortices Using Large Eddy Simulation.

The greatest rate of change in the glottal flow rate during phonation is a rapid decrease that occurs during the latter part of the glottal closing. Previous works showed that intraglottal flow separation vortices form in a divergent glottis, produce negative gauge pressures (below atmospheric) during closing. It is hypothesized here that flow separation vortices contribute to the rapid closing mechanism of the true vocal folds during phonation. Four idealized static models (M5) of the human larynx were investigated using large eddy simulation: 2 models featured parallel folds that did not enable flow separation in the glottis and 2 models involved a divergent glottis. The influence of the ventricular gap (narrow/wide) is evaluated. An unsteady pressure inlet representing a voicing cycle was applied to the sub-glottal region to mimic the time-varying glottal flow. Intraglottal vortex structures formed downstream of the separation point in a divergent glottis. Their existence caused a higher closing force that was applied onto the vocal folds. A narrow ventricular gap strengthens this effect. Strength of the intraglottal vortices increased with the maximum flow declination rate. Therefore, a more divergent shape of the glottis during glottal closing will be one of the main contributors to the voice quality.

Effects of False Vocal Folds on Intraglottal Velocity Fields.

Previous models have theorized that, during phonation, skewing of the glottal waveform (which is correlated with acoustic intensity) occurred because of inertance of the vocal tract. Later, we reported that skewing of the flow rate waveform can occur without the presence of a vocal tract in an excised canine larynx. We hypothesized that in the absence of a vocal tract, the skewing formed when dynamic pressures acted on the glottal wall during the closing phase; such pressures were greatly affected by formation of intraglottal vortices. In this study, we aim to identify how changes in false vocal folds constriction can affect the acoustics and intraglottal flow dynamics. The intraglottal flow measurements were made using particle image velocimetry in an excised canine larynx where a vocal tract model was placed above the larynx and the constriction between the false vocal folds was varied. Our results show that for similar values of subglottal pressures, the skewing of the glottal waveform, strength of the intraglottal vortices, and acoustic energy increased as the constriction between the false vocal folds was increased. These preliminary findings suggest that acoustic intensity during phonation can be increased by the addition of a vocal tract with false fold constriction.

Impact of Vertical Stiffness Gradient on the Maximum Divergence Angle.

INTRODUCTION: During vocal fold vibration, the medial surface of both folds forms a convergent shape during opening and a divergent shape during closing. A greater maximum divergence angle is associated with greater closing forces which will increase the closing speed of the glottis. An increased closing speed results in a greater acoustic intensity and greater vocal efficiency. Indentation testing showed that as the strain increases, the inferior aspect of the folds becomes stiffer than the superior aspect, resulting in the vertical stiffness gradient (VSG). We hypothesize that a reduction of the vertical stiffness gradient will reduce the maximum divergence angle. METHODS: Four excised canine larynges were tested. Stress-strain curves of the superior and inferior aspects of the fold in the mid membranous plane of the baseline larynges were taken using the indentation method. Calcium hydroxylapatite (CaHA) crystals were then injected into the superior aspect of the fold. The stress-strain tests were repeated. Particle imaging velocimetry (PIV) of the intraglottal velocity fields was performed in three larynges at different subglottal pressures in the mid coronal plane for the baseline and CaHA-injected larynges. RESULTS: CaHA injection reduced the inferior-superior stiffness gradient in all larynges. The maximal divergence angle was markedly reduced. In some cases, there was not a divergent angle. DISCUSSION: Marked reduction of the vertical stiffness gradient significantly reduces the maximum divergence angle. Clinical implications will be discussed. LEVEL OF EVIDENCE: NA Laryngoscope, 131:E1934-E1940, 2021.

Effects of velopharyngeal openings on flow characteristics of nasal emission.

Nasal emission is a speech disorder where undesired airflow enters the nasal cavity during speech due to inadequate closure of the velopharyngeal valve. Nasal emission is typically inaudible with large velopharyngeal openings and very distorting with small openings. This study aims to understand how flow characteristics in the nasal cavity change as a function of velopharyngeal opening using computational fluid dynamics. The model is based on a subject who was diagnosed with distorting nasal emission and a small velopharyngeal opening. The baseline geometry was delineated from CT scans that were taken, while the subject was sustaining a sibilant sound. Modifications to the model were done by systematically widening or narrowing the velopharyngeal opening while keeping the geometry constant elsewhere. Results show that if the flow resistance across the velopharyngeal valve is smaller than resistance across the oral constriction, flow characteristics such as velocity and turbulence are inversely proportional to the size of the opening. If flow resistance is higher across the velopharyngeal valve than the oral constriction, turbulence in the nasal cavity will be reduced at a higher rate. These findings can be used to generalize that the area ratio of the velopharyngeal opening to the oral constriction is a factor that determines airflow characteristics and subsequently its sound during production of sibilant sound. It implies that the highest level of turbulence in the nasal cavity, and subsequently the sound that will likely be perceived as the most severe nasal emission is produced when the size of openings is equal.

Volume velocity in a canine larynx model using time­resolved tomographic particle image velocimetry.

In the classic source-filter theory, the source of sound is flow modulation. "Flow" is the flow rate (Q) and flow modulation is dQ/dt. Other investigators have argued, using theoretical, computational, and mechanical models of the larynx, that there are additional sources of sound. To determine the acoustic role of dQ/dt in a tissue model, Q needs to be accurately measured within a few millimeters of the glottal exit; however, no direct measures of Q currently exist. The goal of this study is to obtain this waveform in an excised canine larynx model using time-resolved tomographic particle image velocimetry. The flow rate data are captured simultaneously with acoustic measurements to determine relations with vocal characteristics. The results show that glottal waveform characteristics such as maximum flow declination rate are proportional to the subglottal pressure, fundamental frequency, and acoustic intensity. These findings are important as they use direct measurements of the volume flow at the glottal exit to validate some of the assumptions used in the source-filter theory. In addition, future work will address the accuracy of indirect clinical measurement techniques, such as the Rothenberg mask.

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.