Fariborz Alipour

University of Iowa | UI · Department of Communication Sciences and Disorders

A fiber-gel vocal fold model is compared to a transversely isotropic stiffness model in terms of normal mode vibration. The fiber-gel finite element model (FG-FEM) consists of a series of gel slices, each with a two-dimensional finite element mesh, in a plane transverse to the tissue fibers. The gel slices are coupled with fibers under tension in t...

The purpose of the study was to better understand the pressure-flow behavior of a self-oscillating vocal fold model at various stages of the glottal cycle. An established self-oscillating vocal fold model was extended to include the false vocal folds (FVFs) and was used to study time-dependent pressure and velocity distributions through the larynx...

Supraglottic compression is frequently observed in individuals with dysphonia. It is commonly interpreted as an indication of excessive circumlaryngeal muscular tension and ventricular medialization. The purpose of this study was to describe the aerodynamic and acoustic impact of varying ventricular medialization in a canine model. Subglottal air p...

The false vocal folds are hypothesized to affect the laryngeal flow during speech phonation. This hypothesis is tested both computationally and experimentally using rigid models of the human larynges. The computations are performed using an incompressible Navier-Stokes solver with a second order sharp immersed-boundary formulation, while the experi...

Objective: The purpose of this study was to better understand the muscular anatomy of the ventricular folds (VF) to help improve biomechanical modeling of phonation and to better understand the role of these muscles during phonatory and non-phonatory tasks. Method: Four human larynges were decalcified and sectioned coronally from the posterior to...

The purpose of this study was to determine the conditions needed to elicit phonation from excised human larynges and the resultant range of phonations produced; compare that with similar information previously obtained from canine, pig, sheep, and cow; and relate those findings to previously reported information about viscoelastic properties of the...

The acoustic effects of the supraglottic laryngeal structures (SGSs), including the false vocal folds (FVFs) laryngeal ventricle, and the epiglottis were investigated in an excised canine larynx model with and without these anatomical structures. The purpose of this study was to better understand the acoustic contributions of these structures to ph...

The purpose of this study was to examine the aerodynamic and acoustic effects due to supraglottic compressions, which may be seen in some dysphonic patients. Canine larynges were prepared and mounted and vocal fold oscillations were generated and controlled by the flow of air through the glottis. Glottal adduction was accomplished by rotating the a...

Objective: This study aimed to quantify the major elastic properties of human vocal fold's lamina propria, including longitudinal and transverse Young's modulus, shear modulus, and Poisson's ratio. Methods: Samples were obtained from cadaveric human larynges that were snap frozen within 48 hours postmortem and kept at -82°F and thawed overnight...

Pressure in the laryngeal ventricle was measured with a beveled needle connected to a pressure transducer in excised canine larynges. Air pressures within the ventricle were obtained for different adduction levels of the true vocal folds (TVFs), false vocal folds (FVFs), and subglottal pressures (Ps). Results indicated that the air pressures in the...

Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

Skeletal muscle atrophy is a common and debilitating condition that lacks a pharmacologic therapy. To develop a potential therapy, we identified 63 mRNAs that were regulated by fasting in both human and mouse muscle, and 29 mRNAs that were regulated by both fasting and spinal cord injury in human muscle. We used these two unbiased mRNA expression s...

Spectral measures of the glottal source were investigated using an excised canine larynx (CL) model for various aerodynamic and phonatory conditions. These measures included spectral harmonic difference H1-H2 and spectral slope that are highly correlated with voice quality but not reported in a systematic manner using an excised larynx model. It wa...

Acoustic data has long been harvested in fundamental voice investigations since it is easily obtained using a microphone. However, acoustic signals alone do not reveal much about the complex interplay between sound waves, structural surface waves, mechanical vibrations, and fluid flow involved in phonation. Available high speed imaging techniques h...

In spite of several recent studies, a firm understanding about aerodynamic effects associated with presence of false vocal fold in the larynx is lacking. Of interest is the pressure distribution and formation of laryngeal vortex inceptions. In order to find pressure distribution, two synthetic life-size rigid larynxes were mounted in a wind tunnel...

Skeletal muscle atrophy is a common and debilitating condition that lacks a pharmacologic therapy. To develop a potential therapy, we identified 63 mRNAs that were regulated by fasting in both human and mouse muscle, and 29 mRNAs that were regulated by both fasting and spinal cord injury in human muscle. We used these two unbiased mRNA expression s...

Elastic characteristics of the pig, sheep, and cow vocal folds were investigated through a series of in vitro experiments. Sample strips of the vocal-fold tissue were dissected from pig, sheep, and cow vocal folds and mounted inside a saline-filled ergometer chamber that was maintained at 37°C ± 1°C. Sinusoidal elongation was applied on the samples...

The acoustic effects of the supraglottic (SG) structure were investigated through the FFT spectrum analysis of the generated sounds of the excised canine larynx model with and wit hout false vocal folds (FVF). Oscillation was generated by controlling the flow of air through the glottis. The SG structure was kept intact in the first part of the expe...

Despite the functional importance of loud, low-pitched vocalizations in big cats of the genus Panthera, little is known about the physics and physiology of the mechanisms producing such calls. We investigated laryngeal sound production in the laboratory using an excised-larynx setup combined with sound-level measurements and pressure-flow instrumen...

Stress relaxation behavior of the human true and false vocal folds were measured in vitro and modeled for viscoelastic parameter determination. Vibrations of the vocal folds are greatly influenced by the elasticity and viscosity of its mucosal layer. When there is a change in the viscoelastic properties of vocal fold tissue due to disease or trauma...

The aim of this study is to determine how phonation is affected by the presence and by alteration in the position of the supraglottic structures. The study used three excised canine larynges. A series of pressure-flow experiments were completed first on the excised larynx with false folds and epiglottis intact, then with the epiglottis removed, and...

To determine the aerodynamic and acoustic effects due to a sudden change from chest to falsetto register or vice versa. It was hypothesized that the continuous change in subglottal pressure and flow rate alone (pressure-flow sweep [PFS]) can trigger a mode change in the canine larynx. Ten canine larynges were each mounted over a tapered tube that s...

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...

This study was to investigate glottal flow resistance in excised pig, sheep, and cow larynges during phonation at different oscillation ranges and to examine the relation of the glottal flow resistance to the laryngeal geometry and vocal fold vibration. Several pig, sheep, and cow larynges were prepared, mounted on an excised larynx bench, and set...

This paper discusses the effects of measurement uncertainties when calculating elastic moduli of laryngeal tissue. Small dimensions coupled with highly nonlinear elastic properties exacerbate the uncertainties. The sensitivity of both tangent and secant Young's Modulus was quantified in terms of the coefficient of variation, which depended on measu...

The purpose of this study was to find relationships between subglottal pressure (P(s)) and fundamental frequency (F(0)) of phonation in excised larynx models. This included also the relation between F(0) and its rate of change with pressure (dFdP). Canine larynges were prepared and mounted over a tapered tube that supplied pressurized, heated, and...

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 glottalpressure and air particle velocity in narrow passages that pose many technical difficulties. In this paper, to elucidate these challenges, measurement of...

The purpose of this study was to examine the aerodynamic and acoustic effects of the false vocal folds and the epiglottis on excised larynx phonation. Several canine larynges were prepared and mounted over a tapered tube that supplied pressurized, heated, and humidified air. Glottal adduction was accomplished either by using two-pronged probes to p...

The excised larynx of a Siberian tiger, which died of natural causes, was studied on a laboratory bench. Pressure‐flow relations were determined, as well as modes of vibration of the vocal pads. In addition, CT scans of the animal were made available (from previous health examinations), which allowed the vocal‐tract airway to be quantified. The lar...

Squirrel monkey larynges were dissected, mounted on a pseudotracheal tube, and phonated via the flow of compressed heated and humidified air. Synchronized audio and video signals were digitized and analyzed with a signal processing workstation. Image analysis algorithms measured the change in glottal area due to the movement of the left and right v...

Excised larynx research usually excludes the false folds in an effort to reveal the true vocal folds. The purpose of this study was to examine the aerodynamic and acoustic effects of the false folds and epiglottis on excised larynxphonation. Canine larynges were mounted over a tapered tube on the excised larynx bench that supplied pressurized, heat...

Air pressure associated with airflow from the lungs drives the vocal folds into oscillation and allows the air to exit the glottis as a turbulent jet, even though laminar flow may enter the glottis from the trachea. The separation of the turbulence from the deterministic portion of the glottal jet was investigated in the excised canine larynx model...

A systematic study of the influence of vocal fold scarring on phonation was conducted. In particular, phonatory variables such as fundamental frequency, oral acoustic intensity, and phonation threshold pressure (PTP) were investigated as a function of the size and position of the laryngeal scar. By means of a finite element model of vocal fold vibr...

Active and passive characteristics of the canine adductor- abductor muscles were investigated through a series of experiments conducted in vitro. Samples of canine posterior cricoarytenoid muscle (PCA), lateral cricoarytenoid muscle (LCA), and interarytenoid muscle (IA) were dissected from dog larynges excised a few minutes before death and kept in...

Tension asymmetries in a finite element model of the vocal folds were examined as a function of lungpressure. The vocal fold model had an asymmetry in the tension ratio ranging from 1.1 to 2.0, corresponding to a 10%–100% increase in tension of the left fold compared to the right, and lungpressure was increased over the range 5–40 cm H2O. For tensi...

An excised larynx model and a latex physical model were used to study acoustic spectra of the phonatory source as a function of subglottal pressure, glottal adduction, and vocal‐fold length. A supraglottal vocal tract was not used, indicating that the acoustic signal corresponded to the output glottal flow. Each model was mounted over an ‐inch trac...

A finite-volume computational model that solves the time-dependent glottal airflow within a forced-oscillation model of the glottis was employed to study glottal flow separation. Tracheal input velocity was independently controlled with a sinusoidally varying parabolic velocity profile. Control parameters included flow rate (Reynolds number), oscil...

A three-dimensional biomechanical model of tissue deformation was developed to simulate dynamic vocal fold abduction and adduction. The model was made of 1721 nearly incompressible finite elements. The cricoarytenoid joint was modeled as a rocking-sliding motion, similar to two concentric cylinders. The vocal ligament and the thyroarytenoid muscle'...

Viscoelastic properties of canine laryngeal muscles were measured in a series of in vitro experiments. Laryngeal posturing that controls vocal fold length and adduction/abduction is an essential component of the voice production. The dynamics of posturing depends on the viscoelastic and physiological properties of the laryngeal muscles. The time-de...

The larynges of eight squirrel monkeys were harvested, dissected, mounted on a pseudotracheal tube, and phonated using compressed air. Patterns of vocal fold oscillation were compared with sound spectrograms of calls recorded from monkeys in our colony. Four different regimes of vocal fold activation were identified. Regime 1 resembled typical huma...

This study examined pressure and velocity profiles in a hemilarynx mechanical model of phonation. The glottal section had parallel walls and was fabricated from hard plastic. Twelve pressure taps were created in the vocal fold surface and connected to a differential pressure transducer through a pressure switch. The glottal gap was measured with fe...

This study examined pressure and velocity profiles in a hemilarynx mechanical model of phonation. The glottal section was fabricated from hard plastic. Twelve pressure taps were mounted in the vocal-fold surface and connected to a differential pressure transducer through a pressure switch. The glottal gap was measured with a filter gauge and the gl...

Flow separation was investigated in pulsatile flow within a computational fluid dynamics (CFD) model of glottis motion. Two‐dimensional time‐dependent laminar flow was calculated for given dynamic wall geometries and flow boundary conditions. A Lagrangian–Eulerian method with a multiblock mesh was employed to allow grid points to move in space to c...

This study introduces a mechanical model of the larynx for investigating dynamic aerodynamic effects of phonation. The model mimics the hemilarynx. The tracheal inlet section was rectangular (25-mm width, 20-mm height). The vocal fold was fabricated with precision machinery from hard plastic with an attached oscillating plunger. A speaker assembly...

The pressure-flow relationship was examined in excised canine and human larynges with and without a vocal tract. Canine and human larynges were prepared and cut in the midsagittal plane from the top to about 10 mm below the vocal folds. The right half was removed and replaced with an acrylic plate. The vocal tract was simulated initially with a 15-...

A finite‐element model of the passive properties of laryngeal muscles was created, based on nonlinear stress–strain responses of laryngeal muscular tissue [E. J. Hunter and I. Titze, J. Acoust. Soc. Am. 108, 2531 (2000)]. Using this finite‐element muscle model as a building block, groups of muscles are used to construct a 3‐D tissue model of vocal...

Airflow from the lungs drives the vocal folds into oscillation and exits the glottis as a turbulent jet, even though laminar flow is documented entering the glottis. Incomplete glottal closure may result in air leakage that becomes turbulent. This turbulence is thought to be the main source of breathiness in the voice. Few studies have measured deg...

Asymmetric vibrations of a finite‐element model of the vocal folds were analyzed using the method of empirical eigenfunctions. In a previous study of symmetric vibrations from the model, periodic vibrations yielded two dominant eigenfunctions, which were related to the theoretical normal modes of the model. In a more recent study, the method of emp...

During phonation, air pressures act upon the vocal folds to help maintain their oscillation. The air pressures vary dynamically along the medial surface of the vocal folds, although no live human or excised studies have shown how those pressure profiles vary in time. The purpose of this study was to examine time-dependent glottal pressure profiles...

Glottal adduction is a primary laryngeal variable that helps to determine glottal configuration and phonatory output. Greater adduction of the vocal folds can be produced by narrowing the gap between the vocal processes or by bulging the medial surface of the vocal folds. This study examined phonatory effects due to changing the degree of bulging u...

A finite-element model of the vocal fold is developed from basic laws of continuum mechanics to obtain the oscillatory characteristics of the vocal folds. The model is capable of accommodating inhomogeneous, anisotropic material properties and irregular geometry of the boundaries. It has provisions for asymmetry across the midplane, both from the g...

Airflow patterns of a hemilarynx were simulated numerically by the method of computational fluid dynamics (CFD) and were investigated experimentally with a flow visualization method. In the numerical model, vocal fold motion was simulated by sinusoidal variations of the inferior and superior glottal widths at different phase conditions. The straigh...

This study introduces a mechanical model of the larynx for investigating the aerodynamics of phonation. The model mimics the hemilarynx. The tracheal inlet section was rectangular (2.5 cm by 2 cm). The vocal fold was fabricated from hard plastic with an attached oscillating plunger. A speaker assembly and audio amplifier drove the plunger, mimickin...

This article discusses the molecular composition of the vocal fold and the relationship of fibrous molecules to the biomechanical and physiological performance of the tissue. The components of the extracellular matrix may be divided into fibrous proteins and interstitial proteins. The fibrous proteins, consisting of collagens and elastins, are the...

The geometric structure of the cricothyroid (CT) muscle and thyroarytenoid (TA) muscle was quantified in 6 human and 3 canine larynges. Each muscle was divided into a series of fiber bundles. With a 3-dimensional micrometer probe, the coordinates of the origin and insertion of each bundle were measured before dissection. It was found that the mass...

Pressure‐flow relationship was examined in the excised canine and human larynges with and without vocal tract. Canine and human larynges were prepared and cut in the midsaggital plane from the top to about 10 mm below the vocal folds. The right half was removed and replaced with a Plexiglas plate with imbedded pressure taps along the medial surface...

Active and passive characteristics of the canine cricothyroid muscle were investigated through a series of experiments conducted in vitro and compared with their counterparts in the thyroarytenoid muscle. Samples from separate portions of canine cricothyroid muscle, namely, the pars recta and pars obliqua, were dissected from dog larynges excised a...

Human phonation is the flow?induced oscillation of the vocal folds, producing pulsatile jet through the glottis, which may become turbulent. This turbulent jet was investigated in an excised canine larynx model with simultaneous recordings of air particle velocity, subglottal pressure, airflow rate, and EGG signal for various conditions of phonatio...

Simulation data are presented from a computer model that combines vocal fold tissue mechanics, laryngeal aerodynamics, and vocal tract acoustics. These simulations are based upon the laws of physics that govern airflow, vibration of the vocal folds, and wave propagation in the vocal tract. The tissue mechanics was modeled with the finite element me...

Self‐sustained oscillation of the vocal folds was simulated by combining two‐dimensional laryngeal airflow with multidimensional tissue movement. A finite‐element model was used for the solution of viscoelastic waves in the tissue and a finite‐volume method was used in the solution of Navier–Stokes equations for the airflow. A so‐called ‘‘shadow me...

The membranous contact quotient (MCQ) is introduced as a measure of dynamic glottal competence. It is defined as the ratio of the membranous contact glottis (the anterior-posterior length of contact between the two membranous vocal folds) and the membranous vocal fold length. An elliptical approximation to the vocal fold contour during phonation wa...

Pressure-flow relationships were obtained for five excised canine larynges. Simultaneous recordings were made of average subglottal pressure, average air flow, and the electroglottograph at various levels of adduction and vocal fold lengths. The level of adduction was controlled by positioning the arytenoid cartilages via laterally imbedded three-p...

Computational fluid dynamics(CFD) was used to obtain numerical solutions to laryngeal flow between simulated vibrating vocal folds. The unsteady Navier?Stokes equations were solved with a finite volume method using a nonuniform staggered grid. Vocal fold motion was simulated by sinusoidal variation of the inferior and superior glottal widths. The s...

Relationships among average subglottal pressure, average glottal airflow, and glottal adduction (vocal process gap), variables related to glottal competence, were obtained for one human subject. The data define the pressure‐flow‐adduction space. Results are similar to those of a study using excised canine larynges [Alipour et al., ‘‘Pressure‐flow r...

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and p...

A numerical simulation of laryngeal flow was developed to study flow patterns and pressure and velocity waveforms in a model of the oscillating glottis. The unsteady Navier–Stokes equations were solved with a finite volume method using a nonuniform staggered grid. The numerical method was tested against published experimental data. In this study of...

Pulsatile flow in an excised canine larynx was investigated with simultaneous recordings of air velocity, subglottal pressure, volume pow rate, and the signal from an electro-glottograph (EGG)for various conditions of phonation. Canine larynges were mounted on a pseudotrachea and sustained oscillations were established and maintained with sutures a...

The wave equation was solved in a cylindrical coordinate system for models of the vocal tract corresponding to vowels, /a/, /i/, and /u/. A straight cylindrical model of vocal tract was built upon area function data for each vowel. Using boundary fitted coordinates, the vocal tract shape and its boundary conditions were simplified to a straight tub...

The longitudinal elastic properties of the human vocal ligament were quantified by stress-strain measurements and by modeling the response mathematically. Human ligaments were obtained from surgery and autopsy cases. They were dissected, mounted, and stretched with a dual-servo ergometer to measure force versus elongation and to convert the results...

Pulsatile airflow in the excised larynx was investigated with simultaneous recordings of air velocity, subglottal pressure, volume flow, and the electroglottograph signal for various conditions of the larynx. Canine larynges were mounted on a bench with sutures attached to cartilages to mimic the function of laryngeal muscles. Sustained oscillation...

Dynamic modeling of vocal fold tissue movement and laryngeal airflow was combined in a computer simulations for the purpose of voice production. A finite‐element model was used for the solution of tissue mechanics and a finite volume method was used in the solution of Navier–Stokes equations for the airflow. A so‐called ‘‘shadow method’’ simulated...

The longitudinal elastic properties of the human vocal ligament were quantified by stress‐strain measurements and by modeling the response mathematically. Human ligaments were obtained from surgery and autopsy cases. They were dissected, mounted, and stretched with a dual‐servo ergometer to measure force versus elongation and to convert the results...

The pulsatile airflow in the excised larynx was investigated with the simultaneous measurements of glottalpressure, volume flow, EGG, and particle velocity at various dynamic conditions of the larynx. Canine larynges were mounted in a bench with some sutures attached to cartilages to mimic the function of laryngealmuscles. The sustained oscillation...

The unsteady airflow in the larynx with moving boundaries was visualized using numerical simulation. By employing the method of computational fluid dynamics(CFD), a two?dimensional model of laminar flow in the glottal constriction was built considering the changes in the wall geometry with time at a given frequency. The glottal wall was approximate...

Elastic properties of canine vocal fold tissue (muscle and mucosa) were obtained through a series of experiments conducted in vitro and were modeled mathematically. The elastic properties play a significant role in quantitative analysis of vocal fold vibrations and theory of pitch control. Samples of vocalis muscle and mucosa were dissected and pre...

Tetanic response of canine cricothyroid muscle tissue was investigated through a series of experiments conducted in vitro. Two separate portions of the cricothyroid muscle, namely the pars recta and pars oblique, were studied. Samples of the muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution...

Laryngealflow was visualized by numerical simulation. Using computational fluid dynamics, a two‐dimensional model of laryngealflow was built and aerodynamic properties were calculated for steady‐state laminar regime. Three configurations of vocal folds with convergent, rectangular, and divergent glottis were used to study the effects of glottal sha...

Active properties of canine laryngealmuscles were investigated through a series of experiments conducted in vitro. Samples of the thyroarytenoid medial and lateral muscles, also, cricothyroid pars recta and pars oblique, were dissected from dog larynges excised a few minutes before death and kept in Krebs solution at a temperature of 37 ± 1 °C and...

Active properties of canine vocalis muscle tissue were investigated through a series of experiments conducted in vitro. Samples of the vocalis muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degree C and a pH of 7.4 +/- 0.05. Isometric and isotonic tetanic responses...

A computer simulation for vibration of the vocal folds is presented. Free and forced oscillations were studied by imposing an impulse and time varying surface forces. The solution was obtained by a semidiscrete numerical method. A finite-element technique was used for solution of the problem in space and a Crank-Nicholson finite-difference method w...

Viable tissue samples of the vocalis muscle and pars recta portion of the cricothyroid muscle were dissected from the excised larynges of middle-aged, male, mixed breed dogs. The samples were maintained in an aerated Krebs-Ringer solution and curarized. Temperature and pH were controlled. Field stimulation was performed with parallel-plate platinum...

The twitch response of the canine vocalis muscle was investigated through a series of experiments conducted in vitro. Samples of vocalis muscle were dissected and prepared from canine larynges a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degrees C and pH of 7.4 +/- 0.05. Field stimulation with parallel-plate si...

Analysis of vocal fold vibration requires information on the viscoelastic properties of the vocalis muscle. The force response of two canine vocalis muscles was measured in one-dimensional, stepwise elongation of the tissue as a function of time with a computer-controlled ergometer. The viscoelastic behavior of the muscle in its passive state was d...

The peak tension and time course of isometric twitch contraction of vocalis musclein vitro have been measured. Samples of vocalis muscle tissue were dissected and prepared from live dogs in Krebs‐Ringer solution at a temperature of about 37 °C. The samples were stimulated with a single square pulse of amplitude 68 V and 2.5‐ms duration with a Grass...

A computer simulation for two‐dimensional vibration of the vocal folds is presented. Free and forced oscillations are studied by imposing an impulse and time varying surface force. The solution is obtained by a semi‐discrete numerical method. A finite element technique is used for the space‐dependent solution and a Crank‐Nicholson finite difference...

Mechanical analysis of vocal fold vibration requires information on the viscoelasticproperties of vocalis muscle. Force response of a dog's vocalis muscle was measured by one?dimensional stepwise elongation of the tissue with a computer?controlled ergometer in an isometric mode. A quasilinear viscoelastic model as proposed by Fung (Biomechanics: It...

The high temperatures and gaseous products of combustion of hydrocarbon fuels in proposed large scale magnetohydrodynamic generators have resulted in a need to develop accurate models for prediction of gas temperature profiles and wall heat fluxes. At the high temperatures and large sizes, radiative heat transfer in the combustion gases may be a si...