During vocal fold vibration, the medial surface of both folds forms a convergent shape during ope... more During vocal fold vibration, the medial surface of both folds forms a convergent shape during opening and a divergent shape during closing. A greater maximum divergence angle is associated with greater closing forces which will increase the closing speed of the glottis. An increased closing speed results in a greater acoustic intensity and greater vocal efficiency. Indentation testing showed that as the strain increases, the inferior aspect of the folds becomes stiffer than the superior aspect, resulting in the vertical stiffness gradient (VSG). We hypothesize that a reduction of the vertical stiffness gradient will reduce the maximum divergence angle.
Introduction Accurate characterization of the elastic properties of vocal fold tissue is importan... more Introduction Accurate characterization of the elastic properties of vocal fold tissue is important in phonosurgical correction of vocal fold pathology and development of physiologic phonation models. This paper examines the work to date attempting to characterize the elastic response of the vocal fold tissue, focusing on three commonly used biomechanical testing modalities in the field: longitudinal elongation, linear skin rheometry, and microindentation. It is hoped that a thorough review of current literature in the field will identify strengths and weaknesses associated with each testing technique and suggest directions for future work. Conclusion While much progress has been made in the characterization of vocal fold elasticity, there is still work to be done to make elasticity measurements practical for clinical applications.
We present a noninvasive method for estimating critical closing pressure (Pcrit) using fluid-stru... more We present a noninvasive method for estimating critical closing pressure (Pcrit) using fluid-structure interaction (FSI) simulations and magnetic resonance imaging (MRI) scans in patients with obstructive sleep apnea (OSA). We used patient-specific stiffness measures in our FSI model to account for any individual variability in the elasticity of soft tissues surrounding the upper airway. We validated this model by measuring the degree of agreement between measured and estimated Pcrit.
A combined experimental–numerical work was conducted to comprehensively validate a subject-specif... more A combined experimental–numerical work was conducted to comprehensively validate a subject-specific continuum model of voice production in larynx using excised canine laryngeal experiments. The computational model is a coupling of the Navier–Stokes equations for glottal flow dynamics and a finite element model of vocal fold dynamics. The numerical simulations employed a cover-body vocal fold structure with the geometry reconstructed from magnetic resonance imaging scans and the material properties determined through an optimization-based inverse process of experimental indentation measurement. The results showed that the simulations predicted key features of the dynamics observed in the experiments, including the skewing of the glottal flow waveform, mucosal wave propagation, continuous increase of the divergent angle and intraglottal swirl strength during glottal closing, and flow recirculation between glottal jet and vocal fold. The simulations also predicted the increase of the d...
The Journal of the Acoustical Society of America, 2018
False vocal folds (FVF) or ventricular folds have been shown to impact the vibration of the true ... more False vocal folds (FVF) or ventricular folds have been shown to impact the vibration of the true folds. Using computational and experimental models to examine the aerodynamic and acoustic effects the FVF, previous studies have shown that the presence of FVF lowers the phonation threshold pressure, the overall intraglottal pressure distribution, and enhances intraglottal vortical structures. However, the full effect of the FVF on the glottal flow waveform has never been measured in a tissue model of the larynx. Therefore, the objective of this study was to evaluate the impact of FVF on the glottal flow waveform in an excised canine model. A vocal tract model was placed over the larynx, and direct velocity measurements were taken at the glottal exit using tomographic particle image velocimetry. Measurements were taken with a systematic change of the FVF constriction and integrated to calculate the air flow waveform. The results show that a restriction above the folds increased the overall flow rate (dQ/dt) ...
The Journal of the Acoustical Society of America, 2016
Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. One... more Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. One static model of the canine larynx with a divergent glottis is considered, with the presence of false vocal folds (FVFs). This computational model is developed from empirical data, and compared to similar configurations that do not involve the subject-specific geometrical features. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closure of the TVFs. Models with and without divergent vocal folds are investigated and linked to the existence of vortices. The direct link between the FVFs geometry and the motion of the TVFs, and by...
The Journal of the Acoustical Society of America, 2015
In a recent computational model, Farahani and Zhang [J. Acoust. Soc. Am. 136, EL369-EL375 (2014)]... more In a recent computational model, Farahani and Zhang [J. Acoust. Soc. Am. 136, EL369-EL375 (2014)] concluded that intraglottal vortices did not affect the closing mechanism of the folds. In order to determine the validity of any model that addresses the issue of vortex significance, it is important that the results of the computational model are comparable to experimental results. The results of Farahani and Zhang's model are inconsistent with data published for experimental models, which may challenge the validity of their conclusions.
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
The paper presents an efficient method for computational aeroacoustics applied to simulate the fl... more The paper presents an efficient method for computational aeroacoustics applied to simulate the flow and the acoustics for a static laryngeal model considering the vocal folds widely open. The work analyses the whisper-like process defined as the sound generated by the turbulent glottal airflow in the absence of vocal fold vibration. A decomposition of the flow variables is used that allows separation of flow and acoustic computations. The approach consists in solving the low Mach number flow field by incompressible Large Eddy Simulation. This provides the possibility to compute the acoustic sources. The inhomogeneous wave equation derived from the fundamental equations of motion for a compressible fluid is employed to compute the acoustic field. The purpose of the study is to provide realistic numerical predictions of the flow patterns and the generated acoustic field in the glottis and the vocal tract regions.
Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Sym... more Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of false vocal folds (FVFs). The compressible study agrees well with that of the incompressible study. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The glottal jet curvature decreases with the presence of FVFs or the ventricular folds. The gap between the FVFs stretches the flow structure and reduces the jet curvature. The presence of FVFs has a significant effect on the laryngeal flow resistance. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closu...
The Journal of the Acoustical Society of America, 2015
Determining the mechanisms of self-sustained oscillation of the vocal folds requires characteriza... more Determining the mechanisms of self-sustained oscillation of the vocal folds requires characterization of the pressures produced by intraglottal aerodynamics. Because most of the intraglottal aerodynamic forces cannot be measured in a tissue model of the larynx, current understanding of vocal fold vibration mechanism is derived from mechanical, analytical, and computational models. Previous studies have computed intraglottal pressures from measured intraglottal velocity fields and intraglottal geometry; however, this technique for determining pressures is not yet validated. In this study, intraglottal pressure measurements taken in a hemilarynx model are compared with pressure values that are computed from simultaneous velocity measurements. The results showed that significant negative pressure formed near the superior aspect of the folds during closing, which agrees with previous measurements in other hemilarynx models. Intraglottal velocity measurements show that the flow near the ...
During phonation, skewing of the glottal flow waveform (Q) refers to a phenomenon that occurs whe... more During phonation, skewing of the glottal flow waveform (Q) refers to a phenomenon that occurs when the flow decelerates more rapidly than it accelerates. This skewing is clinically important because it increases the glottal efficiency, which is defined by the acoustic intensity (sound pressure level) divided by the subglottal pressure. Current theoretical models predict that the only mechanism to cause skewing of Q involves changes in the vocal tract inertance. The purpose of the current work is to show that other factors at the vocal fold level can also cause skewing of Q and to determine if the acoustic intensity is correlated with maximum flow declination rate. Basic science. Intraglottal geometry and velocity measurements were taken in five canine larynges at the mid-membranous plane using 2-dimensional particle imaging velocimetry (PIV). The flow rate at the glottal exit was computed from the PIV measurements for low, medium, and high subglottal pressures. Vortices form in the ...
The Journal of the Acoustical Society of America, 2014
ABSTRACT A majority of patients with dysphonia report reduced intelligibility in their daily comm... more ABSTRACT A majority of patients with dysphonia report reduced intelligibility in their daily communication environments. Laryngeal pathology often causes abnormal vibration and incomplete closure of the vocal folds, resulting in increased noise and decreased harmonic power in the speech signal. These acoustic consequences likely make dysphonic speech more difficult to understand, particularly in the presence of background noise. The study tested two hypotheses: (1) intelligibility of dysphonic speech is more negatively affected by background noise than that of normal speech, and (2) listener ratings of intelligibility will correlate with clinical measures of dysphonia. One hundred twenty speech samples were collected from 6 adults and 4 children with normal voice and 6 adults and 4 children with varying degrees of dysphonia. Each sample consisted of a short phrase or sentence and was characterized by two acoustic measures commonly associated with degree of dysphonia: cepstral peak prominence (CPP) and harmonic to noise ratio (HNR). Samples were combined with three levels of "cafeteria" noise ( + 0 dB SNR, + 5 dB SNR, and no noise) and then subjected to a speech perception experiment with 60 normal listeners. This project is ongoing. Preliminary results support hypothesis 1; additional findings related to hypothesis 2 will also be discussed.
The Annals of otology, rhinology, and laryngology, 2010
Our previous work has shown that the symmetric, smooth, convergent shape of the subglottis reduce... more Our previous work has shown that the symmetric, smooth, convergent shape of the subglottis reduces turbulent airflow at the glottal entrance. Medialization thyroplasty may alter the glottal shape and is very likely to introduce some degree of glottal asymmetry, which could result in increased turbulence and a reduction in voice quality. This study reports the effects of medializing and not medializing the subglottis in silicone models of human cadaveric larynges. In experiment 1, silicone models of 4 human cadaveric larynges were created. The subglottis was then completely medialized in all 4 models. Hot-wire anemometry was used to measure velocity and turbulence profiles at the entrance and exit of the subglottis. In experiment 2, 1 model was created to accommodate incremental medialization of the glottis without any medialization of the subglottis. Airflow characteristics were likewise measured. In experiment 1, the average maximum turbulence intensity (TI) at the exit of the lary...
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
Page 1. American Institute of Aeronautics and Astronautics 092407 1 Flow analysis of a jet emanat... more Page 1. American Institute of Aeronautics and Astronautics 092407 1 Flow analysis of a jet emanating from a flexible membrane nozzle using particle image velocimetry RR Lakhamraju1*, S. Murugappan2 , EJ Gutmark1 , and S. Khosla2 ...
We performed flow computations on an accurate upper airway model in a patient with obstructive sl... more We performed flow computations on an accurate upper airway model in a patient with obstructive sleep apnea and computed the velocity, static pressure, and wall shear stress distribution in the model. Cartesian coordinates for airway boundaries were determined from cross-sectional magnetic resonance images, and a 3-dimensional computational model of the upper airway was constructed. Flow simulations were then performed within a FLUENT commercial software framework. Four different flow conditions were simulated during inspiration, assuming the steady-state condition. The results were analyzed from the perspectives of velocity, static pressure, and wall shear stress distribution. We observed that the highest axial velocity was at the site of minimum cross-sectional area (retropalatal pharynx) resulting in the lowest level of wall static pressure. The highest wall shear stresses were at the same location. The pressure drop was significantly larger for higher flow rates than for lower flow rates. Our results indicate that the presence of airway narrowing, through change in the flow characteristics that result in increased flow velocity and reduced static pressure, can itself increase airway collapsibility. Additionally, the effects of wall shear stress on airway walls may be an important factor in the progression over time of the severity of obstructive sleep apnea.
During vocal fold vibration, the medial surface of both folds forms a convergent shape during ope... more During vocal fold vibration, the medial surface of both folds forms a convergent shape during opening and a divergent shape during closing. A greater maximum divergence angle is associated with greater closing forces which will increase the closing speed of the glottis. An increased closing speed results in a greater acoustic intensity and greater vocal efficiency. Indentation testing showed that as the strain increases, the inferior aspect of the folds becomes stiffer than the superior aspect, resulting in the vertical stiffness gradient (VSG). We hypothesize that a reduction of the vertical stiffness gradient will reduce the maximum divergence angle.
Introduction Accurate characterization of the elastic properties of vocal fold tissue is importan... more Introduction Accurate characterization of the elastic properties of vocal fold tissue is important in phonosurgical correction of vocal fold pathology and development of physiologic phonation models. This paper examines the work to date attempting to characterize the elastic response of the vocal fold tissue, focusing on three commonly used biomechanical testing modalities in the field: longitudinal elongation, linear skin rheometry, and microindentation. It is hoped that a thorough review of current literature in the field will identify strengths and weaknesses associated with each testing technique and suggest directions for future work. Conclusion While much progress has been made in the characterization of vocal fold elasticity, there is still work to be done to make elasticity measurements practical for clinical applications.
We present a noninvasive method for estimating critical closing pressure (Pcrit) using fluid-stru... more We present a noninvasive method for estimating critical closing pressure (Pcrit) using fluid-structure interaction (FSI) simulations and magnetic resonance imaging (MRI) scans in patients with obstructive sleep apnea (OSA). We used patient-specific stiffness measures in our FSI model to account for any individual variability in the elasticity of soft tissues surrounding the upper airway. We validated this model by measuring the degree of agreement between measured and estimated Pcrit.
A combined experimental–numerical work was conducted to comprehensively validate a subject-specif... more A combined experimental–numerical work was conducted to comprehensively validate a subject-specific continuum model of voice production in larynx using excised canine laryngeal experiments. The computational model is a coupling of the Navier–Stokes equations for glottal flow dynamics and a finite element model of vocal fold dynamics. The numerical simulations employed a cover-body vocal fold structure with the geometry reconstructed from magnetic resonance imaging scans and the material properties determined through an optimization-based inverse process of experimental indentation measurement. The results showed that the simulations predicted key features of the dynamics observed in the experiments, including the skewing of the glottal flow waveform, mucosal wave propagation, continuous increase of the divergent angle and intraglottal swirl strength during glottal closing, and flow recirculation between glottal jet and vocal fold. The simulations also predicted the increase of the d...
The Journal of the Acoustical Society of America, 2018
False vocal folds (FVF) or ventricular folds have been shown to impact the vibration of the true ... more False vocal folds (FVF) or ventricular folds have been shown to impact the vibration of the true folds. Using computational and experimental models to examine the aerodynamic and acoustic effects the FVF, previous studies have shown that the presence of FVF lowers the phonation threshold pressure, the overall intraglottal pressure distribution, and enhances intraglottal vortical structures. However, the full effect of the FVF on the glottal flow waveform has never been measured in a tissue model of the larynx. Therefore, the objective of this study was to evaluate the impact of FVF on the glottal flow waveform in an excised canine model. A vocal tract model was placed over the larynx, and direct velocity measurements were taken at the glottal exit using tomographic particle image velocimetry. Measurements were taken with a systematic change of the FVF constriction and integrated to calculate the air flow waveform. The results show that a restriction above the folds increased the overall flow rate (dQ/dt) ...
The Journal of the Acoustical Society of America, 2016
Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. One... more Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. One static model of the canine larynx with a divergent glottis is considered, with the presence of false vocal folds (FVFs). This computational model is developed from empirical data, and compared to similar configurations that do not involve the subject-specific geometrical features. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closure of the TVFs. Models with and without divergent vocal folds are investigated and linked to the existence of vortices. The direct link between the FVFs geometry and the motion of the TVFs, and by...
The Journal of the Acoustical Society of America, 2015
In a recent computational model, Farahani and Zhang [J. Acoust. Soc. Am. 136, EL369-EL375 (2014)]... more In a recent computational model, Farahani and Zhang [J. Acoust. Soc. Am. 136, EL369-EL375 (2014)] concluded that intraglottal vortices did not affect the closing mechanism of the folds. In order to determine the validity of any model that addresses the issue of vortex significance, it is important that the results of the computational model are comparable to experimental results. The results of Farahani and Zhang's model are inconsistent with data published for experimental models, which may challenge the validity of their conclusions.
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
The paper presents an efficient method for computational aeroacoustics applied to simulate the fl... more The paper presents an efficient method for computational aeroacoustics applied to simulate the flow and the acoustics for a static laryngeal model considering the vocal folds widely open. The work analyses the whisper-like process defined as the sound generated by the turbulent glottal airflow in the absence of vocal fold vibration. A decomposition of the flow variables is used that allows separation of flow and acoustic computations. The approach consists in solving the low Mach number flow field by incompressible Large Eddy Simulation. This provides the possibility to compute the acoustic sources. The inhomogeneous wave equation derived from the fundamental equations of motion for a compressible fluid is employed to compute the acoustic field. The purpose of the study is to provide realistic numerical predictions of the flow patterns and the generated acoustic field in the glottis and the vocal tract regions.
Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Sym... more Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of false vocal folds (FVFs). The compressible study agrees well with that of the incompressible study. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The glottal jet curvature decreases with the presence of FVFs or the ventricular folds. The gap between the FVFs stretches the flow structure and reduces the jet curvature. The presence of FVFs has a significant effect on the laryngeal flow resistance. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closu...
The Journal of the Acoustical Society of America, 2015
Determining the mechanisms of self-sustained oscillation of the vocal folds requires characteriza... more Determining the mechanisms of self-sustained oscillation of the vocal folds requires characterization of the pressures produced by intraglottal aerodynamics. Because most of the intraglottal aerodynamic forces cannot be measured in a tissue model of the larynx, current understanding of vocal fold vibration mechanism is derived from mechanical, analytical, and computational models. Previous studies have computed intraglottal pressures from measured intraglottal velocity fields and intraglottal geometry; however, this technique for determining pressures is not yet validated. In this study, intraglottal pressure measurements taken in a hemilarynx model are compared with pressure values that are computed from simultaneous velocity measurements. The results showed that significant negative pressure formed near the superior aspect of the folds during closing, which agrees with previous measurements in other hemilarynx models. Intraglottal velocity measurements show that the flow near the ...
During phonation, skewing of the glottal flow waveform (Q) refers to a phenomenon that occurs whe... more During phonation, skewing of the glottal flow waveform (Q) refers to a phenomenon that occurs when the flow decelerates more rapidly than it accelerates. This skewing is clinically important because it increases the glottal efficiency, which is defined by the acoustic intensity (sound pressure level) divided by the subglottal pressure. Current theoretical models predict that the only mechanism to cause skewing of Q involves changes in the vocal tract inertance. The purpose of the current work is to show that other factors at the vocal fold level can also cause skewing of Q and to determine if the acoustic intensity is correlated with maximum flow declination rate. Basic science. Intraglottal geometry and velocity measurements were taken in five canine larynges at the mid-membranous plane using 2-dimensional particle imaging velocimetry (PIV). The flow rate at the glottal exit was computed from the PIV measurements for low, medium, and high subglottal pressures. Vortices form in the ...
The Journal of the Acoustical Society of America, 2014
ABSTRACT A majority of patients with dysphonia report reduced intelligibility in their daily comm... more ABSTRACT A majority of patients with dysphonia report reduced intelligibility in their daily communication environments. Laryngeal pathology often causes abnormal vibration and incomplete closure of the vocal folds, resulting in increased noise and decreased harmonic power in the speech signal. These acoustic consequences likely make dysphonic speech more difficult to understand, particularly in the presence of background noise. The study tested two hypotheses: (1) intelligibility of dysphonic speech is more negatively affected by background noise than that of normal speech, and (2) listener ratings of intelligibility will correlate with clinical measures of dysphonia. One hundred twenty speech samples were collected from 6 adults and 4 children with normal voice and 6 adults and 4 children with varying degrees of dysphonia. Each sample consisted of a short phrase or sentence and was characterized by two acoustic measures commonly associated with degree of dysphonia: cepstral peak prominence (CPP) and harmonic to noise ratio (HNR). Samples were combined with three levels of "cafeteria" noise ( + 0 dB SNR, + 5 dB SNR, and no noise) and then subjected to a speech perception experiment with 60 normal listeners. This project is ongoing. Preliminary results support hypothesis 1; additional findings related to hypothesis 2 will also be discussed.
The Annals of otology, rhinology, and laryngology, 2010
Our previous work has shown that the symmetric, smooth, convergent shape of the subglottis reduce... more Our previous work has shown that the symmetric, smooth, convergent shape of the subglottis reduces turbulent airflow at the glottal entrance. Medialization thyroplasty may alter the glottal shape and is very likely to introduce some degree of glottal asymmetry, which could result in increased turbulence and a reduction in voice quality. This study reports the effects of medializing and not medializing the subglottis in silicone models of human cadaveric larynges. In experiment 1, silicone models of 4 human cadaveric larynges were created. The subglottis was then completely medialized in all 4 models. Hot-wire anemometry was used to measure velocity and turbulence profiles at the entrance and exit of the subglottis. In experiment 2, 1 model was created to accommodate incremental medialization of the glottis without any medialization of the subglottis. Airflow characteristics were likewise measured. In experiment 1, the average maximum turbulence intensity (TI) at the exit of the lary...
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
Page 1. American Institute of Aeronautics and Astronautics 092407 1 Flow analysis of a jet emanat... more Page 1. American Institute of Aeronautics and Astronautics 092407 1 Flow analysis of a jet emanating from a flexible membrane nozzle using particle image velocimetry RR Lakhamraju1*, S. Murugappan2 , EJ Gutmark1 , and S. Khosla2 ...
We performed flow computations on an accurate upper airway model in a patient with obstructive sl... more We performed flow computations on an accurate upper airway model in a patient with obstructive sleep apnea and computed the velocity, static pressure, and wall shear stress distribution in the model. Cartesian coordinates for airway boundaries were determined from cross-sectional magnetic resonance images, and a 3-dimensional computational model of the upper airway was constructed. Flow simulations were then performed within a FLUENT commercial software framework. Four different flow conditions were simulated during inspiration, assuming the steady-state condition. The results were analyzed from the perspectives of velocity, static pressure, and wall shear stress distribution. We observed that the highest axial velocity was at the site of minimum cross-sectional area (retropalatal pharynx) resulting in the lowest level of wall static pressure. The highest wall shear stresses were at the same location. The pressure drop was significantly larger for higher flow rates than for lower flow rates. Our results indicate that the presence of airway narrowing, through change in the flow characteristics that result in increased flow velocity and reduced static pressure, can itself increase airway collapsibility. Additionally, the effects of wall shear stress on airway walls may be an important factor in the progression over time of the severity of obstructive sleep apnea.
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Papers by Sid Khosla