Publications by authors named "Fariborz Alipour"

27 Publications

  • Page 1 of 1

Comparison of a fiber-gel finite element model of vocal fold vibration to a transversely isotropic stiffness model.

J Acoust Soc Am 2017 09;142(3):1376

National Center for Voice and Speech, 136 South Main Street, Suite 320, Salt Lake City, Utah 84101, USA.

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 the anterior-posterior dimension. No vibrational displacement in the fiber-length direction is allowed, resulting in a plane strain state. This is consistent with the assumption of transverse displacement of a simple string, offering a wide range of natural frequencies (well into the kHz region) with variable tension. For low frequencies, the results compare favorably with the natural frequencies of a transversely isotropic elastic stiffness model (TISM) in which the shear modulus in the longitudinal plane is used to approximate the effect of fiber tension. For high frequencies, however, the natural frequencies do not approach the string mode frequencies unless plane strain is imposed on the TISM model. The simplifying assumption of plane strain, as well as the use of analytical closed-form shape functions, allow for substantial savings in computational time, which is important in clinical and exploratory applications of the FG-FEM model.
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http://dx.doi.org/10.1121/1.5001055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5595586PMC
September 2017

Time-Dependent Pressure and Flow Behavior of a Self-oscillating Laryngeal Model With Ventricular Folds.

J Voice 2015 Nov 11;29(6):649-59. Epub 2015 Apr 11.

Department of Communication Sciences and Disorders, Bowling Green State University, Bowling Green, Ohio.

Objective: 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.

Methods: 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 (including the true vocal folds [TVFs] and FVFs). Vocal fold vibration was modeled with a finite element method, laryngeal flow was simulated with the solution of unsteady Navier-Stokes equations, and the acoustics of the vocal tract was modeled with a wave reflection method.

Results: The results demonstrate realistic phonatory behaviors and therefore may be considered as a pedagogical tool for showing detailed aerodynamic, kinematic, and acoustic characteristics. The TVFs self-oscillated regularly with reasonable amplitude and mucosal waves. There were large pressure gradients in the glottal region. The centerline velocity was highest during glottal closing and sharply dropped near the center of the flow vortex. The average centerline velocity was about 25 m/second in the glottal region. The transglottal pressure was higher during glottal closing when the glottal shape was divergent and pressure recovery was present within the glottis. The centerline velocity increased as expected throughout the convergent glottis, tended to decrease throughout the divergent glottis, and decreased past the TVFs within the ventricle-FVF region.

Conclusions: This model produces realistic results and demonstrates interactions among phonation variables of a highly instructive nature, including the influence of the FVFs.
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http://dx.doi.org/10.1016/j.jvoice.2014.10.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4600634PMC
November 2015

Aerodynamic and acoustic effects of ventricular gap.

J Voice 2014 Mar 8;28(2):154-60. Epub 2013 Dec 8.

Department of Otolaryngology Head Neck Surgery, University of Iowa Healthcare, Iowa City, Iowa.

Purpose: 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.

Methods: Subglottal air pressure, glottal airflow, electroglottograph, acoustic signals, and high-speed video images were recorded in seven excised canine larynges mounted in vitro for laryngeal vibratory experimentation. The degree of gap between the ventricular folds was adjusted and measured using sutures and weights. Data were recorded during phonation when the ventricular gap was narrow, neutral, and large. Glottal resistance was estimated by measures of subglottal pressure and glottal flow.

Results: Glottal resistance increased systematically as ventricular gap became smaller. Wide ventricular gaps were associated with increases in fundamental frequency and decreases in glottal resistance. Sound pressure level did not appear to be impacted by the adjustments in ventricular gap used in this research.

Conclusions: Increases in supraglottic compression and associated reduced ventricular width may be observed in a variety of disorders that affect voice quality. Ventricular compression may interact with true vocal fold posture and vibration resulting in predictable changes in aerodynamic, physiological, acoustic, and perceptual measures of phonation. The data from this report supports the theory that narrow ventricular gaps may be associated with disordered phonation. In vitro and in vivo human data are needed to further test this association.
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http://dx.doi.org/10.1016/j.jvoice.2013.10.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943580PMC
March 2014

Muscular anatomy of the human ventricular folds.

Ann Otol Rhinol Laryngol 2013 Sep;122(9):561-7

Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa 52242-1012, USA.

Objectives: Our purpose in this study was to better understand the muscular anatomy of the ventricular folds in order to help improve biomechanical modeling of phonation and to better understand the role of these muscles during phonatory and nonphonatory tasks.

Methods: Four human larynges were decalcified, sectioned coronally from posterior to anterior by a CryoJane tape transfer system, and stained with Masson's trichrome. The total and relative areas of muscles observed in each section were calculated and used for characterizing the muscle distribution within the ventricular folds.

Results: The ventricular folds contained anteriorly coursing thyroarytenoid and ventricularis muscle fibers that were in the lower half of the ventricular fold posteriorly, and some ventricularis muscle was evident in the upper and lateral portions of the fold more anteriorly. Very little muscle tissue was observed in the medial half of the fold, and the anterior half of the ventricular fold was largely devoid of any muscle tissue. All 4 larynges contained muscle bundles that coursed superiorly and medially through the upper half of the fold, toward the lateral margin of the epiglottis.

Conclusions: Although variability of expression was evident, a well-defined thyroarytenoid muscle was readily apparent lateral to the arytenoid cartilage in all specimens.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3831168PMC
http://dx.doi.org/10.1177/000348941312200905DOI Listing
September 2013

A numerical and experimental investigation of the effect of false vocal fold geometry on glottal flow.

J Biomech Eng 2013 Dec;135(12):121006

The false vocal folds are hypothesized to affect the laryngeal flow during 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 experiments are carried out in a wind tunnel with physiologic speeds and dimensions. The computational flow structures are compared with available glottal flow visualizations and are employed to study the vortex dynamics of the glottal flow. Furthermore, pressure data are collected on the surface of the laryngeal models experimentally and computationally. The investigation focuses on three geometric features: the size of the false vocal fold gap; the height between the true and false vocal folds; and the width of the laryngeal ventricle. It is shown that the false vocal fold gap has a significant effect on glottal flow aerodynamics, whereas the second and the third geometric parameters are of lesser importance. The link between pressure distribution on the surface of the larynx and false vocal fold geometry is discussed in the context of vortex evolution in the supraglottal region. It was found that the formation of the starting vortex considerably affects the pressure distribution on the surface of the larynx. The interaction of this vortex structure with false vocal folds creates rebound vortices in the laryngeal ventricle. In the cases of small false vocal fold gap, these rebound vortices are able to reach the true vocal folds during a time period comparable with one cycle of the phonation. Moreover, they can create complex vorticity patterns, which result in significant pressure fluctuations on the surface of the larynx.
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http://dx.doi.org/10.1115/1.4025324DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3815039PMC
December 2013

Phonatory characteristics of the excised human larynx in comparison to other species.

J Voice 2013 Jul;27(4):441-7

Department of Communication Sciences & Disorders, The University of Iowa, Iowa City, Iowa 52242, USA.

Objective: 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 vocal fold tissue (ie, stress-strain curves and Young's modulus).

Methods: Six human larynges of the geriatric group (age range, 70-89) were mounted on the bench without supraglottic structures, and phonation was achieved with the flow of heated and humidified air through the tracheal tube. Using various sutures to mimic the function of the laryngeal muscles, the larynges were put through a series of sustained oscillations with adduction as a control parameter.

Results: The human larynges oscillated with an average frequency that was close to the canine larynges, but the oscillation behavior and wide frequency range were similar to those of pig larynges. The similarity of the wide vibration frequency ranges of human and pig larynges may be because of the nonlinear behavior of their elasticity, which is related to the high collagen content of the vocal folds. On the contrary, other species with limited frequency ranges showed almost linear stress-strain curves because of the higher elastin and lower collagen contents.

Conclusions: The physiological differences in the linearity and ranges of oscillation of excised larynges reported in this study and previous studies are reflective of the tissue composition and mechanics.
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http://dx.doi.org/10.1016/j.jvoice.2013.03.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3701163PMC
July 2013

On the acoustic effects of the supraglottic structures in excised larynges.

J Acoust Soc Am 2013 May;133(5):2984-92

Department of Communication Sciences and Disorders, The University of Iowa, 334E WJSHC, Iowa City, Iowa 52242-1012, USA.

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 phonation. Canine larynges were prepared and mounted over a 3/4 in. tube, which supplied pressurized, heated, and humidified air. Glottal adduction was accomplished by rotating the arytenoids with a suture passed behind the vocal folds to simulate the lateral cricoarytenoid muscle action. The SGSs were kept intact in the first part of the experiment and were removed in the second part. Results indicated that when the FVFs vibrated, a low frequency component was observed in the spectral data. The excised larynx with a SGS had a limited range of frequency with subglottal pressure, while the larynx without a SGS had a larger frequency range. The excised canine larynx with a SGS oscillated with a higher phonation threshold pressure and significantly louder.
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http://dx.doi.org/10.1121/1.4796109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3663863PMC
May 2013

Measurement of vocal folds elastic properties for continuum modeling.

J Voice 2012 Nov 24;26(6):816.e21-9. Epub 2012 Aug 24.

Department of Communication Sciences & Disorders, The University of Iowa, Iowa City, Iowa 52242-1012, USA.

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 in saline solution. Once the sample was tested in the longitudinal direction, two special brackets were glued to the side of each sample and the sample was mounted with brackets in the transverse direction. The shear modulus was obtained from samples mounted between two parallel plates applying shear forces. The Poisson ratio was obtained using high-speed video imaging of two-dimensional samples with markers for longitudinal and transverse strain measurements.

Results: Results indicate that human vocal fold elasticity is very nonlinear with slope that increases 10-15 times from low- to high-strain values. Its average low-strain Young's modulus is approximately 30 kPa in the longitudinal direction and 1 kPa in the transverse direction. The vocal fold longitudinal shear modulus is in the same order of magnitude of its transverse shear modulus (less than 1 kPa). The average Poisson ratio is approximately 0.57.

Conclusions: The present study provides quantitative data for the longitudinal and transverse elastic properties of the human vocal fold tissue and indicates that nonlinear behavior and relative difference of these properties may lead to wide ranges of oscillation frequency and amplitude in human larynges.
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http://dx.doi.org/10.1016/j.jvoice.2012.04.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3508138PMC
November 2012

Ventricular pressures in phonating excised larynges.

J Acoust Soc Am 2012 Aug;132(2):1017-26

Department of Communication Sciences & Disorders, The University of Iowa, 334E WJSHC, Iowa City, Iowa 52242-1012, USA.

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 ventricle appear to be strongly related to the motion of the FVFs rather than to the effects of TVF vibration. Both dc and ac pressures depend on FVF adduction, amplitude of motion of the FVFs, and whether the FVFs touch each other during the vibratory cycle. Mean and peak-to-peak pressures in the ventricle were as high as 65% of the mean and peak-to-peak Ps, respectively, when the FVFs vibrated with large amplitude and contact each cycle. If the glottis was not closed, a medial movement of the FVFs appeared to create a positive pressure pulse on the Ps signal due to an increase in the laryngeal flow resistance. The electroglottograph signal showed evidence of tissue contact for both the TVFs and the FVFs. The study suggests that the laryngeal ventricle acts as a relatively independent aero-acoustic chamber that depends primarily upon the motion of the FVFs.
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http://dx.doi.org/10.1121/1.4730880DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427366PMC
August 2012

Measures of spectral slope using an excised larynx model.

J Voice 2012 Jul 6;26(4):403-11. Epub 2011 Nov 6.

Department of Communication Sciences & Disorders, The University of Iowa, Iowa City, Iowa 52242-1012, USA.

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 was hypothesized that the acoustic spectra of the glottal source were significantly influenced by the subglottal pressure, glottal adduction, and vocal fold elongation, as well as the resulting vibration pattern. CLs were prepared, mounted on the bench with and without false vocal folds, and made to oscillate with a flow of heated and humidified air. Major control parameters were subglottal pressure, adduction, and elongation. Electroglottograph, subglottal pressure, flow rate, and audio signals were analyzed using custom software. Results suggest that an increase in subglottal pressure and glottal adduction may change the energy balance between harmonics by increasing the spectral energy of the first few harmonics in an unpredictable manner. It is suggested that changes in the dynamics of vocal fold motion may be responsible for different spectral patterns. The finding that the spectral harmonics do not conform to previous findings was demonstrated through various cases. Results of this study may shed light on phonatory spectral control when the larynx is part of a complete vocal tract system.
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http://dx.doi.org/10.1016/j.jvoice.2011.07.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276723PMC
July 2012

mRNA expression signatures of human skeletal muscle atrophy identify a natural compound that increases muscle mass.

Cell Metab 2011 Jun;13(6):627-38

Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, IA 52242, USA.

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 signatures of muscle atrophy to query the Connectivity Map, which singled out ursolic acid as a compound whose signature was opposite to those of atrophy-inducing stresses. A natural compound enriched in apples, ursolic acid reduced muscle atrophy and stimulated muscle hypertrophy in mice. It did so by enhancing skeletal muscle insulin/IGF-I signaling and inhibiting atrophy-associated skeletal muscle mRNA expression. Importantly, ursolic acid's effects on muscle were accompanied by reductions in adiposity, fasting blood glucose, and plasma cholesterol and triglycerides. These findings identify a potential therapy for muscle atrophy and perhaps other metabolic diseases.
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http://dx.doi.org/10.1016/j.cmet.2011.03.020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3120768PMC
June 2011

Vocal power and pressure-flow relationships in excised tiger larynges.

J Exp Biol 2010 Nov;213(Pt 22):3866-73

Department of Communication Sciences and Disorders, The University of Iowa, Iowa City, IA 52242, USA.

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 instrumentation. The larynges of five tigers (three Siberian or Amur, one generic non-pedigreed tiger with Bengal ancestry and one Sumatran), which had died of natural causes, were provided by Omaha's Henry Doorly Zoo over a five-year period. Anatomical investigation indicated the presence of both a rigid cartilaginous plate in the arytenoid portion of the glottis, and a vocal fold fused with a ventricular fold. Both of these features have been confusingly termed 'vocal pads' in the previous literature. We successfully induced phonation in all of these larynges. Our results showed that aerodynamic power in the glottis was of the order of 1.0 W for all specimens, acoustic power radiated (without a vocal tract) was of the order of 0.1 mW, and fundamental frequency ranged between 20 and 100 Hz when a lung pressure in the range of 0-2.0 kPa was applied. The mean glottal airflow increased to the order of 1.0 l s(-1) per 1.0 kPa of pressure, which is predictable from scaling human and canine larynges by glottal length and vibrational amplitude. Phonation threshold pressure was remarkably low, on the order of 0.3 kPa, which is lower than for human and canine larynges phonated without a vocal tract. Our results indicate that a vocal fold length approximately three times greater than that of humans is predictive of the low fundamental frequency, and the extraordinarily flat and broad medial surface of the vocal folds is predictive of the low phonation threshold pressure.
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http://dx.doi.org/10.1242/jeb.044982DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2966350PMC
November 2010

Vocal fold elasticity in the pig, sheep, and cow larynges.

J Voice 2011 Mar 4;25(2):130-6. Epub 2010 Feb 4.

Department of Communication Sciences and Disorders, The University of Iowa, Iowa City, Iowa, USA.

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 to obtain the passive force measurements. Force and elongation data from the samples were recorded electronically with a dual-servo system (ergometer). Stress-Strain data were compared to characterize the interspecies differences in the elastic properties of vocal folds. Pig vocal folds exhibited the most nonlinear stress-strain relationship, indicating the presence of a high level of collagen fibers. Cow vocal folds had the highest Young's modulus, but the tissue displayed a nearly linear stress-strain profile. Previous studies of phonation in these three species have indicated that pig larynges have the highest range of phonation frequencies, making them a good candidate for animal studies. The current study provides quantitative data for the elastic properties of the oscillating laryngeal tissue in these species and indicates that nonlinear behavior of these tissues may lead to wider oscillation ranges.
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http://dx.doi.org/10.1016/j.jvoice.2009.09.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2888685PMC
March 2011

Aerodynamic and acoustic effects of abrupt frequency changes in excised larynges.

J Speech Lang Hear Res 2009 Apr 11;52(2):465-81. Epub 2008 Aug 11.

The University of Iowa, Iowa City, IA 52242-1012, USA.

Purpose: 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.

Method: Ten canine larynges were each mounted over a tapered tube that supplied pressurized, heated, and humidified air. Glottographic signals were recorded during each PFS experiment, during which airflow was increased in a gradual manner for a period of 20-30 s.

Results: Abrupt changes in fundamental frequency (F(0)) and mode of vibration occurred during the PFS in the passive larynx without any change in adduction or elongation. The lower frequency mode of oscillation of the vocal folds, perceptually identified as the chest register, had relatively large amplitude oscillation, significant vocal fold contact, a rich spectral content, and a relatively loud audio signal. The higher frequency mode of oscillation, perceptually identified as falsetto, had little or no vocal fold contact and a dominant first partial. Relatively abrupt F(0) changes also occurred for gradual adduction changes, with the chest register corresponding to greater adduction, falsetto to less adduction.
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http://dx.doi.org/10.1044/1092-4388(2008/07-0212)DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2665729PMC
April 2009

Phonatory characteristics of excised pig, sheep, and cow larynges.

J Acoust Soc Am 2008 Jun;123(6):4572-81

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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.
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http://dx.doi.org/10.1121/1.2908289DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2468220PMC
June 2008

Glottal airflow resistance in excised pig, sheep, and cow larynges.

J Voice 2009 Jan 19;23(1):40-50. Epub 2007 Nov 19.

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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 into oscillation with pressurized, heated, and humidified air. Glottal adduction was controlled by either using two-pronged probes to press the arytenoids together, or by passing a suture to simulate the lateral cricoarytenoid muscle action. Each excised larynx was subjected to a series of pressure-flow experiments, with adduction and flow rate as independent variables. The subglottal pressure, fundamental frequency, and glottal flow resistance were treated as dependent variables. The subglottal pressure, electroglottograph (EGG), and flow rate signals were recorded during each experiment. Glottal flow resistance was calculated from the pressure and flow signals, whereas the EGG signal was used to extract fundamental frequency. Preliminary data indicated a nonlinear behavior in the pressure-flow relations of these larynges with increasing glottal resistance due to increases in adduction. The average glottal flow resistance was 35.3+/-14.8 cmH(2)O/(L/s) for the pig, 30.8+/-17.5 cmH(2)O/(L/s) for the sheep, and 26.9+/-14.9 cmH(2)O/(L/s) for the cow.
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http://dx.doi.org/10.1016/j.jvoice.2007.03.007DOI Listing
January 2009

On pressure-frequency relations in the excised larynx.

J Acoust Soc Am 2007 Oct;122(4):2296-305

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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 humidified air. Glottal adduction was accomplished either by using two-pronged probes to press the arytenoids together or by passing a suture to simulate lateral cricoarytenoid muscle activation. The pressure-frequency relation was obtained through a series of pressure-flow sweep experiments that were conducted for eight excised canine larynges. It was found that, at set adduction and elongation levels, the pressure-frequency relation is nonlinear, and is highly influenced by the adduction and elongation. The results indicated that for the lower phonation mode, the average rate of change of frequency with pressure was 2.9+/-0.7 Hzcm H(2)O, and for the higher mode was 5.3+/-0.5 Hzcm H(2)O for adduction changes and 8.2+/-4.4 Hzcm H(2)O for elongation changes. The results suggest that during speech and singing, the dFdP relationships are taken into account.
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http://dx.doi.org/10.1121/1.2772230DOI Listing
October 2007

Phonatory effects of supraglottic structures in excised canine larynges.

J Voice 2009 Jan 2;23(1):51-61. Epub 2007 Apr 2.

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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 finally with the false folds removed. Aerodynamic and acoustic effects were quantified with the analysis of the pressure, flow, and audio signals. The results of the study indicated that (1) elevation of the epiglottis to upright position from a horizontal position decreased subglottal pressure, increased flow (decreased laryngeal resistance), and slightly decreased fundamental frequency; (2) vibration of the false vocal folds induced some irregularity into the acoustic output of the larynx; (3) the presence of the epiglottis and the false vocal folds enhanced the second partial of the acoustic signal; and (4) the absence of the epiglottis and false folds increased low-frequency noise (between 0 and 300 Hz). Alteration in the position of the supraglottic structures affects laryngeal aerodynamics and acoustics, possibly due to biomechanical linkage with true vocal folds. When the supraglottic structures are present they act as resonators, enhancing the second partial and when they are absent (as in persons with supraglottic laryngectomy), low-frequency noise is increased perhaps due to the loss of boundary conditions or due to the presence of loose tissue.
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http://dx.doi.org/10.1016/j.jvoice.2007.01.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2641024PMC
January 2009

Aerodynamic and acoustic effects of false vocal folds and epiglottis in excised larynx models.

Ann Otol Rhinol Laryngol 2007 Feb;116(2):135-44

From the Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242-1012, USA.

Objectives: 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.

Methods: 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 press the arytenoids together or by passing a suture to simulate lateral cricoarytenoid muscle activation. First, the excised larynx with false vocal folds and epiglottis intact was subjected to a series of pressure-flow experiments with longitudinal tension and adduction as major control parameters. Then, the epiglottis and finally the false vocal folds were removed and the experiment was repeated. The subglottal pressure and the electroglottographic, flow rate, audio, and sound pressure signals were recorded during each experiment. Glottal flow resistance was calculated from the pressure and flow signals. The electroglottographic signal was used to extract the fundamental frequency.

Results: It was found that the false vocal folds and the epiglottis offer a positive contribution to the glottal resistance and sound intensity of the larynx. Also, vocal fold elongation and glottal medial compression caused an increase in glottal resistance. The pressure-flow relationships were approximately linear regardless of the structure.

Conclusions: The addition of the supraglottic laryngeal structures has a significant impact on both aerodynamic and acoustic characteristics of excised larynges.
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http://dx.doi.org/10.1177/000348940711600210DOI Listing
February 2007

Sensitivity of elastic properties to measurement uncertainties in laryngeal muscles with implications for voice fundamental frequency prediction.

J Voice 2007 Nov 10;21(6):641-50. Epub 2006 Aug 10.

National Center for Voice and Speech, The Denver Center for the Performing Arts, Denver, Colorado 80204, USA.

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 measurement of reference length and cross-sectional area. Uncertainties in the measurement of mass, used to calculate cross-sectional area of a small tissue sample, affected Young's Modulus calculations when tissue absorption of the hydrating solution was not accounted for. Uncertainty in reference length had twice the effect on elasticity than other measures. The implication of these measurement errors on predicted fundamental frequency of vocalization is discussed. Refinements on isolated muscle experimental protocols are proposed that pay greatest attention to measures of highest sensitivity.
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http://dx.doi.org/10.1016/j.jvoice.2006.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4778974PMC
November 2007

Characterizing glottal jet turbulence.

J Acoust Soc Am 2006 Feb;119(2):1063-73

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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. The present study is methodological in that the main goal was to examine three methods of obtaining reasonable representations of both the deterministic signal and the residual turbulence portion: (a) smoothing, (b) wavelet denoising, and (c) ensemble averaging. Ensemble averaging resulted in a deterministic signal that disregarded gross cyclic alterations while exaggerating the turbulence intensity. Wavelet denoising can perform an excellent analysis and synthesis of the glottal velocity, but was problematic in determining which levels of analysis to choose to represent both the deterministic and turbulence appropriately. Smoothing appeared to be the most appropriate for phonation velocities because it preserved gross cyclic variations important to perturbations and modulations, while extracting turbulence at what appears to be reasonable levels.
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http://dx.doi.org/10.1121/1.2151809DOI Listing
February 2006

Influence of vocal fold scarring on phonation: predictions from a finite element model.

Ann Otol Rhinol Laryngol 2005 Nov;114(11):847-52

Laryngeal Dynamics Laboratory, Division of Head and Neck Surgery, David Geffen School of Medicine, The University of California, Los Angeles, Los Angeles, California, USA.

Objectives: 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.

Methods: By means of a finite element model of vocal fold vibration, the viscoelastic properties of both normal and scarred vocal fold mucosae were simulated on the basis of recent rheological data obtained from rabbit and canine models.

Results: The study showed that an increase in the viscoelasticity of the scarred mucosa resulted in an increase in fundamental frequency, an increase in PTP, and a decrease in oral acoustic intensity. With regard to positioning of the scar, the PTP increased most significantly when the scar was within +/-2 mm of the superior-medial junction of the vocal folds.

Conclusions: The systematic data obtained in this investigation agree with the general clinical experience. In the future, these findings may be further validated on human subjects as newly emerging technologies such as linear skin rheometry and optical coherence tomography allow the histologic and viscoelastic properties of the normal and scarred vocal fold mucosae to be measured in the clinic.
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http://dx.doi.org/10.1177/000348940511401107DOI Listing
November 2005

Active and passive properties of canine abduction/adduction laryngeal muscles.

J Voice 2005 Sep;19(3):350-9

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, 52242, USA.

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 Krebs-Ringer solution at a temperature of 37 degrees C +/- 1 degree C and a pH of 7.4 +/- 0.05. Active twitch and tetanic force was obtained in an isometric condition by applying field stimulation to the muscle samples through a pair of parallel-plate platinum electrodes. Force and elongation of the samples were obtained electronically with a dual-servo system (ergometer). The results indicate that the twitch contraction times of the three muscles are very similar, with the average of 32 +/- 1.9 ms for PCA, 29 +/- 1.6 ms for LCA, and 32 +/- 2.4 ms for IA across all elongations. Thus, PCA, LCA, and IA muscles are all faster than the cricothyroid (CT) muscles but slower than the thyroarytenoid (TA) muscles. The tetanic force response times of these muscles are also similar, with a maximum rate of force increase of 0.14 N/ms.
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http://dx.doi.org/10.1016/j.jvoice.2004.04.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1552101PMC
September 2005

Flow separation in a computational oscillating vocal fold model.

J Acoust Soc Am 2004 Sep;116(3):1710-9

Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa 52242, USA.

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), oscillation frequency and amplitude of the vocal folds, and the phase difference between the superior and inferior glottal margins. Results for static divergent glottal shapes suggest that velocity increase caused glottal separation to move downstream, but reduction in velocity increase and velocity decrease moved the separation upstream. At the fixed frequency, an increase of amplitude of the glottal walls moved the separation further downstream during glottal closing. Increase of Reynolds number caused the flow separation to move upstream in the glottis. The flow separation cross-sectional ratio ranged from approximately 1.1 to 1.9 (average of 1.47) for the divergent shapes. Results suggest that there may be a strong interaction of rate of change of airflow, inertia, and wall movement. Flow separation appeared to be "delayed" during the vibratory cycle, leading to movement of the separation point upstream of the glottal end only after a significant divergent angle was reached, and to persist upstream into the convergent phase of the cycle.
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http://dx.doi.org/10.1121/1.1779274DOI Listing
September 2004

A three-dimensional model of vocal fold abduction/adduction.

J Acoust Soc Am 2004 Apr;115(4):1747-59

National Center for Voice and Speech, The Denver Center for the Performing Arts, Denver, Colorado 80204, USA.

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's fiber characteristics were implemented as a fiber-gel composite made of an isotropic ground substance imbedded with fibers. These fibers had contractile and/or passive nonlinear stress-strain characteristics. The verification of the model was made by comparing the range and speed of motion to published vocal fold kinematic data. The model simulated abduction to a maximum glottal angle of about 31 degrees. Using the posterior-cricoarytenoid muscle, the model produced an angular abduction speed of 405 degrees per second. The system mechanics seemed to favor abduction over adduction in both peak speed and response time, even when all intrinsic muscle properties were kept identical. The model also verified the notion that the vocalis and muscularis portions of the thyroarytenoid muscle play significantly different roles in posturing, with the muscularis portion having the larger effect on arytenoid movement. Other insights into the mechanisms of abduction/adduction were given.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1550351PMC
http://dx.doi.org/10.1121/1.1652033DOI Listing
April 2004

Laryngeal biomechanics and vocal communication in the squirrel monkey (Saimiri boliviensis).

J Acoust Soc Am 2003 Apr;113(4 Pt 1):2114-26

Department of Psychology, University of South Alabama, Mobile, Alabama 36688, USA.

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 human vowel production, with regular vocal-fold vibration, a prominent fundamental frequency, and an accompanying series of harmonic overtones. This regime is likely to give rise to squirrel monkey "cackles," as well as a variety of other harmonically structured calls. In regime 2, the pattern of vibrations exhibited the presence of two or more unrelated frequencies (biphonation). This regime of glottal activity resembled the biphonation observed in many exemplars of "twitter" and "kecker" calls. The vocal folds oscillated continuously in regime 3, but produced glottal pulses whose amplitudes waxed and waned rhythmically. This phenomenon resulted in the percept of a series of discrete pulses, and may give rise to "errs," "churrs," and other calls composed of a rapid sequence of acoustic elements. In regime 4, the period of each oscillation was quasi-irregular. Shrieks and other broadband calls or call elements that lack an apparent fundamental frequency may be produced in this manner.
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http://dx.doi.org/10.1121/1.1528930DOI Listing
April 2003

Pressure and velocity profiles in a static mechanical hemilarynx model.

J Acoust Soc Am 2002 Dec;112(6):2996-3003

Department of Speech Pathology and Audiology, The University of Iowa, 334 WJSHC, Iowa City, Iowa 52242, USA.

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 feeler gauges and the uniform glottal duct was verified by use of a laser system. Eight pressure transducers were placed in the flat wall opposite the vocal fold. Hot-wire anemometry was used to obtain velocity profiles upstream and downstream of the glottis. The results indicate that the pressure distribution on the vocal fold surface was consistent with pressure change along a parallel duct, whereas the pressures on the opposite flat wall typically were lower (by 8%-40% of the transglottal pressure just past mid-glottis). The upstream velocity profiles were symmetric regardless of the constriction shape and size. The jet flow downstream of the glottis was turbulent even for laminar upstream conditions. The front of the jet was consistently approximately 1.5 mm from the flat wall for glottal gaps of 0.4, 0.8 and 1.2 mm. The turbulence intensity also remained approximately at the same location of about 4 mm from the flat wall for the two larger gaps.
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http://dx.doi.org/10.1121/1.1519540DOI Listing
December 2002