Model Of Phonation Research Articles

Characterization of raised phonation in an evoked rabbit phonation model

Our laboratory has developed an in vivo rabbit model to investigate the effects of phonation on expression and turnover of the vocal fold extracellular matrix. As a logical outgrowth of this research to include phonotrauma in the present study, we investigated the hypothesis that an increase in airflow rate delivered to the glottis produces a change in glottal configuration and an increase in mean phonation intensity. Prospective animal study. Six New Zealand white breeder rabbits weighing 3 to 5 kg were used in this study. A rigid endoscope and camera were used to document glottal configuration. Acoustic signals of modal and raised phonation were recorded and digitized. Two separate one-way repeated measures analysis of variance (ANOVA) tests were used to investigate within subject differences in phonation intensity and fundamental frequency between modal and raised phonation. Phonation intensity was 54.19 dB SPL (6.21 standard deviations [SD]) during modal phonation, and 60.31 dB SPL (5.68 SD) during raised phonation. Endoscopic images revealed a convergent glottis, with greater separation of the vocal folds during raised phonation. Results of ANOVA revealed a significant within subjects effect for phonation intensity (P = .011). Pairwise comparisons revealed that phonation intensity increased significantly during raised phonation, compared to modal phonation (P = .008). No differences in mean fundamental frequency were observed between phonation conditions. Improved understanding of factors that control phonation output in the in vivo rabbit model will result in improved capabilities to match phonation dose across animals and provide immediate direction to future biochemical studies.

A Computational Study of the Effect of False Vocal Folds on Glottal Flow and Vocal Fold Vibration During Phonation

The false vocal folds are believed to be components of the acoustic filter that is responsible for shaping the voice. However, the effects of false vocal folds on the vocal fold vibration and the glottal aerodynamic during phonation remain unclear. This effect has implications for computational modeling of phonation as well as for understanding laryngeal pathologies such as glottal incompetence resulting from unilateral vocal fold paralysis. In this study, a high fidelity, two-dimensional computational model, which combines an immersed boundary method for the airflow and a continuum, finite-element method for the vocal folds, is used to examine the effect of the false vocal folds on flow-induced vibration (FIV) of the true vocal folds and the dynamics of the glottal jet. The model is notionally based on a laryngeal CT scan and employs realistic flow conditions and tissue properties. Results show that the false vocal folds potentially have a significant impact on phonation. The false vocal folds reduce the glottal flow impedance and increase the amplitude as well as the mean glottal jet velocity. The false vocal folds also enhance the intensity of the monopole acoustic sources in the glottis. A mechanism for reduction in flow impedance due to the false vocal folds is proposed.

Biomechanics of fundamental frequency regulation: Constitutive modeling of the vocal fold lamina propria

Accurate characterization of biomechanical characteristics of the vocal fold is critical for understanding the regulation of vocal fundamental frequency (F0), which depends on the active control of the intrinsic laryngeal muscles as well as the passive biomechanical response of the vocal fold lamina propria. Specifically, the tissue stress-strain response and viscoelastic properties under cyclic tensile deformation are relevant, when the vocal folds are subjected to length and tension changes due to posturing. This paper describes a constitutive modeling approach quantifying the relationship between vocal fold stress and strain (or stretch), and establishes predictions of F0 with the string model of phonation based on the constitutive parameters. Results indicated that transient and time-dependent changes in F0, including global declinations in declarative sentences, as well as local F0 overshoots and undershoots, can be partially attributed to the time-dependent viscoplastic response of the vocal fold cover.

Influence of flow separation location on phonation onset

The influence of flow separation location on eigenmode synchronization and phonation onset was investigated in a two-dimensional, aeroelastic, continuum model of phonation. A linear stability analysis showed that flow separation played a critical role in initiating eigenmode synchronization and phonation. For a given glottal configuration, a small variation in the flow separation location along the vocal fold surface may lead to a qualitatively different eigenmode-synchronization pattern, and different phonation threshold pressure and frequency. This high sensitivity suggests a need for phonation models to be capable of accurate prediction of the flow separation location. Analysis with different glottal channel geometries showed that a minimum phonation threshold pressure existed for a rectangular glottal channel, consistent with previous experiments. However, in contrast to previous theoretical analyses, this study showed that phonation was facilitated, rather than prohibited, by the upstream movement of the flow separation point within a divergent glottis.

Theoretical simulation and experimental validation of inverse quasi-one-dimensional steady and unsteady glottal flow models

In physical modeling of phonation, the pressure drop along the glottal constriction is classically assessed with the glottal geometry and the subglottal pressure as known input parameters. Application of physical modeling to study phonation abnormalities and pathologies requires input parameters related to in vivo measurable quantities commonly corresponding to the physical model output parameters. Therefore, the current research presents the inversion of some popular simplified flow models in order to estimate the subglottal pressure, the glottal constriction area, or the separation coefficient inherent to the simplified flow modeling for steady and unsteady flow conditions. The inverse models are firstly validated against direct simulations and secondly against in vitro measurements performed for different configurations of rigid vocal fold replicas mounted in a suitable experimental setup. The influence of the pressure corrections related to viscosity and flow unsteadiness on the flow modeling is quantified. The inversion of one-dimensional glottal flow models including the major viscous effects can predict the main flow quantities with respect to the in vitro measurements. However, the inverse model accuracy is strongly dependent on the pertinence of the direct flow modeling. The choice of the separation coefficient is preponderant to obtain pressure predictions relevant to the experimental data.

Phonatory characteristics of excised pig, sheep, and cow larynges

The purpose of this study was to examine the phonatory characteristics of pig, sheep, and cow excised larynges and to find out which of these animal species is the best model for human phonation. Excised pig, sheep, and cow larynges were prepared and mounted over a tapered tube on the excised bench that supplied pressurized, heated, and humidified air in a manner similar to that for excised canine models. Each excised larynx was subjected to a series of pressure-flow experiments with adduction as major control parameter. The subglottal pressure, electroglottograph (EGG), mean flow rate, audio signal, and sound pressure level were recorded during each experiment. EGG signal was used to extract the fundamental frequency. It was found that pressure-frequency relations were nonlinear for these species with large rate of frequency changes for the pig. The average oscillation frequencies for these species were 220+/-57 Hz for the pig, 102+/-33 Hz for the sheep, and 73+/-10 Hz for the cow. The average phonation threshold pressure for the pig was 7.4+/-2.0 cm H(2)O, 6.9+/-2.9 cm H(2)O for the sheep, and 4.4+/-2.3 cm H(2)O for the cow.

Characterisation of the velocity distribution on rigid in‐vitro upper airway replicas

Qualitative and quantitative characterisation of the velocity distribution is an important aspect in order to study respiration related flow phenomena in the upper airways as well as for human speech production. Classical phonation models exploit one‐dimensional flow descriptions in order to estimate the pressure forces exerted on the vocal folds tissues. In this case, the velocity distribution is expressed as an analytical relationship depending on volume velocity airflow, geometry and pressure distribution. Therefore simplified flow models can be validated by measuring the relevant quantities. However, more detailed and quantitative velocity predictions, aiming e.g. to improve phonation modelling or to study turbulent sound production, require increased precision for both the qualitative and quantitative characterisation of the velocity distribution. The current paper presents preliminary in‐vitro measurements of the velocity distribution obtained by Particle Image Velocimetry combined with hot film ane...

Intraglottal pressures in a static physical model of the converging glottis: entrance loss coefficients, exit coefficients, Bernoulli effects, and viscous effects

Pressure distributions were obtained with a static physical model (M5) at diameters d = 0.005, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 cm for converging angles of 5, 10, 20, and 40 degrees. At each diameter and angle, transglottal pressures typically ranged from 3 to 15 cm H2O. For each angle, diameter, and transglottal pressure, the measured pressure at the glottal entrance was used to calculate an entrance loss coefficient, and the measured pressure near the glottal exit was used to determine an exit coefficient. Previous work with the uniform glottis, where the only important physical effect was viscosity, found linear fits to the intraglottal pressures to be excellent approximations. Since the widening channel of the converging glottis produces Bernoulli effects as well as viscous effects, a parabolic form for intraglottal pressures is explored. Such an analytic form for the intraglottal pressures when accompanied by tables of entrance loss and exit coefficients would be a useful tool for researchers needing expressions easily included in numerical models of phonation. The validity of the new analytic treatment will be assessed by comparing the calculated pressures with the observed M5 pressures. [Work supported by NIH R01DC03577.]

Coupled 2D‐Fluid‐Structure‐Acoustic Simulation of the Human Voice

The human voice is a key factor in social life. If the phonation process is disturbed due to a disease as e.g. hoarseness, communication and social life are strongly affected. Therefore, it is necessary to enhance therapies in order to minimize affliction caused by a disease. There exist different approaches to improve therapies. Experimental field studies of different physical parameters, like acoustic pressure or vocal fold displacements are one possibility. Another promising approach to advance insight into laryngeal dynamics is given by numerical simulations. Due to the growing computing power the complexity of numerical phonation models is steadily increasing and full fluid‐structure‐acoustic interacting models are now feasible. Therefore, we have developed a two‐dimensional numerical model for the human phonation process, which includes the complete fluid‐structure‐acoustic interaction. As discretization method the finite‐element method was applied for all possible three physical fields. The fluid‐structure and the structure‐acoustic interactions are based on general continuum mechanical principles; the fluid‐acoustic interaction is based on Lighthill's acoustic analogy. Therewith, the analysis of all sound mechanisms, which consist of the eddy‐induced, the volume‐induced, and the mechanical‐induced sound can be performed. First simulation results will be presented and discussed.

Ex Vivo Perfused Larynx Model of Phonation: Preliminary Study

Although excised laryngeal models and physical models of the larynx are important in the study of laryngeal dynamics, they cannot be used to study the influence of neuromuscular contraction on vocal fold vibration, especially with regard to the thyroarytenoid muscle. Our aim was to develop an ex vivo larynx model of phonation, and combine the benefits of the in vivo and excised laryngeal models to the ex vivo situation. Three canine larynges were surgically removed and perfused ex vivo with modified Krebs-Henseleit reperfusion solution. The laryngeal nerves were stimulated, and an assessment of neuromuscular viability, phonation, and vocal fold vibration was made. Neuromuscular stimulation, phonation, and experimental manipulation were possible for several hours after the onset of ex vivo perfusion. Repeatable periodic phonation in short bursts was achieved. Perfusion appears critical to maintain ex vivo viability, as adductory force was almost immediately lost upon cessation of ex vivo perfusion. The ex vivo larynx model has the potential to facilitate the measurement of glottal variables in a neuromuscularly correct model. We propose that the further development of this laryngeal model may be useful in the study of laryngeal dynamics, particularly when invasive measurements, such as that of glottal exit flow, are required.

Sperm whale three-dimensional track, swim orientation, beam pattern, and click levels observed on bottom-mounted hydrophones

In an earlier paper [Nosal and Frazer Appl. Acoust. 61, 1187-1201 (2006)], a sperm whale was tracked in three-dimensions using direct and surface-reflected time differences (DRTD) of clicks recorded on five bottom-mounted hydrophones, a passive method that is robust to timing errors between hydrophones. This paper refines the DRTD method and combines it with a time of (direct) arrival method to improve the accuracy of the track. The position and origin time of each click having been estimated, pitch and yaw are then obtained by assuming the main axis of the whale is tangent to the track. Roll is then found by applying the bent horn model of sperm whale phonation, in which each click is composed of two pulses, p0 and p1, that exit the whale at different points. With instantaneous pitch, roll, and yaw estimated from time differences, amplitudes are then used to estimate the beam patterns of the p0 and p1 pulses. The resulting beam patterns independently confirm those obtained by Zimmer et al. [J. Acoust. Soc. Am. 117, 1473-1485 (2005); 118, 3337-3345 (2005)] with a very different experimental setup. A method for estimating relative click levels is presented and used to find that click levels decrease toward the end of a click series, prior to the "creak" associated with prey capture.

Physical mechanisms of phonation onset: A linear stability analysis of an aeroelastic continuum model of phonation

In an investigation of phonation onset, a linear stability analysis was performed on a two-dimensional, aeroelastic, continuum model of phonation. The model consisted of a vocal fold-shaped constriction situated in a rigid pipe coupled to a potential flow which separated at the superior edge of the vocal fold. The vocal fold constriction was modeled as a plane-strain linear elastic layer. The dominant eigenvalues and eigenmodes of the fluid-structure-interaction system were investigated as a function of glottal airflow. To investigate specific aerodynamic mechanisms of phonation onset, individual components of the glottal airflow (e.g., flow-induced stiffness, inertia, and damping) were systematically added to the driving force. The investigations suggested that flow-induced stiffness was the primary mechanism of phonation onset, involving the synchronization of two structural eigenmodes. Only under conditions of negligible structural damping and a restricted set of vocal fold geometries did flow-induced damping become the primary mechanism of phonation onset. However, for moderate to high structural damping and a more generalized set of vocal fold geometries, flow-induced stiffness remained the primary mechanism of phonation onset.

On the use of kernel-based methods in sound synthesis by physical modeling

In this paper we discuss an approach to the modeling of acoustic systems that combines prior information, exploited through physical modeling, and nonlinear dynamics reconstruction, exploited through support vector machine regression. We demonstrate our approach on two case studies, both addressing the broad class of acoustic systems for which the sound generation is obtained through the interaction of a linear system (resonator) and a nonlinear system (excitation). The first case is a physically based impact model, where the resonator is described in terms of its normal modes and the nonlinear contact force is modeled through a simplified collision equation and kernel regression. In the second case study, a model of the voice phonation is illustrated in which the vocal folds are represented by a lumped linear mass-spring system and the nonlinear flow component is modeled through simple Bernoulli-based equations and kernel regression.

Physical mechanisms of phonation onset: The role of flow instabilities

Current models of phonation exhibit a series of flow phenomena such as an oscillating flow separation point, the Coanda effect, and vortex shedding downstream of the glottis. While accounting for such phenomena significantly increases the computational load and may influence many aspects of phonation, the influence of such airflow features on phonation onset is still unknown. In a two-dimensional continuum model of phonation with a fixed flow separation point, a recent analysis showed that, in the absence of acoustics, the primary physical mechanism of phonation onset was the matching of the flow stiffness (i.e., the intraglottal airflow pressure) with the elastic stiffness of the vocal folds, resembling common observations of human phonation. Thus, the oscillation of the flow separation point may be merely a consequence of the unsteady motion of the vocal folds, with only a minor influence on phonation onset at low frequencies. With a natural frequency much higher than the phonation frequency, flow instabilities such as vortex shedding may also only play a secondary role in determining the conditions of phonation onset (apart from being responsible for flow separation and the transglottal pressure drop), at least for normal phonation. Further experiments are needed to clarify the relative importance of these flow features on phonation onset.

Fluid dynamics measurements during phonation

Fluid dynamic properties of air within the larynx changes so rapidly during phonation that its measurement could be a challenge for voice research. These measurements included time varying glottal pressure and air particle velocity in narrow passages that pose many technical difficulties. In this paper, to elucidate these challenges, measurement of dynamic pressure acting on the vocal folds in a canine hemilarynx model has been initially examined. Then static and dynamic volume flow measurements and, finally, the particle velocity measurements with hot‐wire anemometry within the glottal jet have been discussed. Canine excised larynges as well as canine hemilarynges were used as phonation models. For dynamic pressure measurements, miniature pressure transducers were embedded in a Plexiglas plate that replaced one vocal fold and recorded the oscillation pressure. All mounted laryngeal models were subjected to increasing pressure‐flow sweeps at various adduction levels and the measured data was processed for dynamic pressure and velocity profiles. Results indicated that pressure within the glottis vary both vertically and longitudinally during each vibratory cycle. The pressure signals close to the superior edge showed large negative values due to the motion of the vocal folds. [Work supported by NIDCD Grant No. DC03566.]

Structural analysis of a three-layered vocal fold model

Although many detailed fluid-structure interaction models of human phonation have been created, structural analysis of the vocal fold structure is uncommon. As a result, the vocal fold structure is not well understood. Structural analysis provides useful information for the creation of efficient fluid-structure interaction and reduced order models. To this end, a detailed model of the human vocal fold was created, and modal analysis was used to determine the model’s sensitivity to boundary conditions, geometric parameters, and material properties.

Simulations of vocal fold movement and aerodynamics using the Uintah Computational Framework

This study applies a tightly coupled fluid-structure interaction algorithm to the modeling of phonation. The Uintah Computational Framework models vocal fold material using the Material Point Method (MPM), which permits arbitrarily large material displacements and multiple materials characterizing the vocal fold properties. The air is modeled using a compressible Navier-Stokes solver, the Implicit Continuous-fluid Eulerian (ICE) method developed at Los Alamos National Laboratory by B. A. Kashiwa. The MPM and ICE methods are coupled together to generate a unique simulation tool. Preliminary simulations are shown of 2-D model vocal folds interacting with prescribed transglottal pressures between 100 Pa and 800 Pa illustrating the intrinsic coupling between the vocal folds and the air. Results are presented showing how the new simulation scheme characterizes the materials and how the aerodynamics that results displays the essential characteristics of glottal flow. The next steps of incorporating three-dimensionality and acoustics will be discussed. The present simulations set the stage for a realistic computational glottis and for eventual modeling of the effects of vocal fold pathologies on the acoustical output. [Work supported at Bowling Green State University in part by the National Institutes of Health and at the University of Utah by the Department of Energy.]

Strobokymographic and Videostroboscopic Analysis of Vocal Fold Motion in Unilateral Superior Laryngeal Nerve Paralysis

The clinical diagnosis of superior laryngeal nerve paralysis (SLNp) is infrequently made, because of the heterogeneity of clinical presentations and laryngoscopic findings. Laryngeal electromyography (LEMG) can provide the definitive diagnosis of this abnormality. With increasing use of LEMG in clinical practice, this condition is now more frequently appreciated by otolaryngologists. A characteristic, but infrequently reported, videostroboscopic vocal fold motion termed Gegenschlagen ("dashing-against-each-other") has previously been described to occur in unilateral SLNp. We encountered such motion in a clinical case, which we subsequently verified as unilateral SLNp by means of LEMG. This characteristic glottic motion was then verified in an in vivo canine model of phonation after unilateral SLNp. Videostrobokymography was performed to generate kymograms that illustrated this vocal fold motion clearly. Kymograms of both human and canine subjects with SLNp demonstrated an undulating motion of the horizontally shifting glottic space as the medial edges of the vocal folds chased each other 90 degrees out of phase. As one vocal fold mucosal edge was opening, the other was closing, and this repeated motion appeared as vocal folds chasing or dashing against each other. Although not uniformly seen in all cases, this vocal fold motion appears to be unique to SLNp.

Linear stability analysis of an aeroelastic model of phonation

This study presents a linear stability analysis of a two‐dimensional aeroelastic model of phonation, which incorporates the interaction between the glottal flow and the vocal folds. The model consists of a wall constriction (shaped by the medial surface of vocal the folds), which is situated in a rigid pipe with an applied potential flow. The vocal‐fold constriction is modeled as a plane‐strain linear elastic layer. An eigenvalue problem is formulated and the eigenvalues of the coupled system and the eigenshape of the vocal fold surface are calculated. Both linear divergence and flutter instabilities are possible. Phonation onset frequency and pressure are investigated as a function of glottal channel width, vocal fold geometry, and vocal fold material properties. Based on aeroelasticity theory, this model allows the prediction of the effects of changing geometric and viscoelastic properties of the vocal folds on phonation onset.

The influence of subglottal acoustics on laboratory models of phonation

Many previous laboratory investigations of phonation involving physical models, excised larynges, and in vivo canine larynges have failed to fully specify the subglottal system. Many of these same studies have reported a variety of nonlinear phenomena, including bifurcations (e.g., various classes of phonation onset and offset, register changes, frequency jumps), subharmonics, and chaos, and attributed such phenomena to the biomechanical properties of the larynx. However, such nonlinear phenomena may also be indicative of strong coupling between the voice source and the subglottal tract. Consequently, in such studies, it has not been clear whether the underlying mechanisms of such nonlinear phenomena were acoustical, biomechanical, or a coupling of the acoustical and biomechanical systems. Using a physical model of vocal fold vibration, and tracheal tube lengths which have been commonly reported in the literature, it is hypothesized and subsequently shown that such nonlinear phenomena may be replicated solely on the basis of laryngeal interactions with the acoustical resonances of the subglottal system. Recommendations are given for ruling out acoustical resonances as the source of nonlinear phenomena in future laboratory studies of phonation.