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Roger W Chan - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear viscoelastic characterization of human Vocal fold tissues under large-amplitude oscillatory shear (LAOS).
Journal of rheology, 2018Co-Authors: Roger W ChanAbstract:Viscoelastic shear properties of human Vocal fold tissues were previously quantified by the shear moduli (G' and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the Vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach. Human Vocal fold cover and Vocal Ligament specimens from eight subjects were subjected to LAOS rheometric testing with a simple-shear rheometer. The empirical total stress response was decomposed into elastic and viscous stress components, based on odd-integer harmonic decomposition approach with Fourier transform. Nonlinear viscoelastic measures derived from the decomposition were plotted in Pipkin space and as rheological fingerprints to observe the onset of nonlinearity and the type of nonlinear behavior. Results showed that both the Vocal fold cover and the Vocal Ligament experienced intercycle strain softening, intracycle strain stiffening, as well as shear thinning both intercycle and intracycle. The Vocal Ligament appeared to demonstrate an earlier onset of nonlinearity at phonatory frequencies, and higher sensitivity to changes in frequency and strain. In summary, the stress decomposition approach provided much better insights into the nonlinear viscoelastic behavior of the Vocal fold lamina propria than the traditional linear measures.
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Collagen microstructure in the Vocal Ligament: initial results on the potential effects of smoking.
The Laryngoscope, 2014Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Roger W ChanAbstract:Objectives/Hypothesis This investigation quantitatively characterizes the collagenous microstructure of human Vocal Ligament specimens excised postmortem from nonsmokers and smokers. Study Design Retrospective cohort study. Methods Second harmonic generation (SHG) imaging was performed at three anatomical locations of Vocal Ligament specimens: anterior, mid-membranous, and posterior regions. Two microstructural parameters were extracted from the SHG images: (1) normalized fiber density, and (2) fiber dispersion coefficient, quantifying the degree of collagen fiber dispersion about a preferred direction. Results For both the nonsmoker and smoker subjects, the fiber dispersion coefficient was heterogeneous. Differences in the collagenous structure of nonsmokers and smoker subjects were pronounced at the mid-membranous location. However, the directionality of the heterogeneity in the smoker subjects was opposite to that in the nonsmoker subjects. Specifically, the fiber dispersion coefficient in the nonsmoker subjects was lower in the mid-membranous region (indicating more fiber alignment) than at the anterior/posterior regions, but for the smoker subjects the fiber dispersion coefficient was higher at the mid-membranous region. The normalized fiber density was near constant in the nonsmoker subjects, but the smoker subjects had fewer fibers in the mid-membranous region than at the anterior/posterior regions. Conclusion Spatial microstructural variations may exist in the Vocal fold Ligament both in nonsmokers and smokers. Smoking appears to influence the degree and direction of microstructure heterogeneity in the Vocal fold Ligament. Level of Evidence N/A. Laryngoscope, 124:E361–E367, 2014
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An illustrative result of simulated stress resulting from a modulated strain (e.g., Fig. 2b).
2014Co-Authors: Eric J Hunter, Thomas Siegmund, Roger W ChanAbstract:Left: cover refers to the combination of epithelium and a superficial layer of lamina propria. Middle: Ligament refers to the Vocal Ligament, which consists of the intermediate and deep layer of the lamina propria. Right: the cover and Ligament responses summed together to suggest a combined tissue.
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Empirical measurements of biomechanical anisotropy of the human Vocal fold lamina propria
Biomechanics and Modeling in Mechanobiology, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:The Vocal folds are known to be mechanically anisotropic due to the microstructural arrangement of fibrous proteins such as collagen and elastin in the lamina propria. Even though this has been known for many years, the biomechanical anisotropic properties have rarely been experimentally studied. We propose that an indentation procedure can be used with uniaxial tension in order to obtain an estimate of the biomechanical anisotropy within a single specimen. Experiments were performed on the lamina propria of three male and three female human Vocal folds dissected from excised larynges. Two experiments were conducted: each specimen was subjected to cyclic uniaxial tensile loading in the longitudinal (i.e., anterior–posterior) direction, and then to cyclic indentation loading in the transverse (i.e., medial–lateral) direction. The indentation experiment was modeled as contact on a transversely isotropic half-space using the Barnett–Lothe tensors. The longitudinal elastic modulus E _ L was computed from the tensile test, and the transverse elastic modulus E _ T and longitudinal shear modulus G _ L were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of E _ L / E _ T was 14 for the Vocal Ligament and 39 for the Vocal fold cover specimens. Also, the average of E _ L / G _ L , a parameter important for models of phonation, was 28 for the Vocal Ligament and 54 for the Vocal fold cover specimens. These measurements of anisotropy could contribute to more accurate models of fundamental frequency regulation and provide potentially better insights into the mechanics of Vocal fold vibration.
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The anisotropic hyperelastic biomechanical response of the Vocal Ligament and implications for frequency regulation: A case study
The Journal of the Acoustical Society of America, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:One of the primary mechanisms to vary one's Vocal frequency is through Vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the Vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during Vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the Vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the Vocal Ligament. Continuum models of vibration were constructed based upon Euler–Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a Vocal Ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human Vocal Ligament specimen.
Ingo R Titze - One of the best experts on this subject based on the ideXlab platform.
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Vocal Tradeoffs in Anterior Glottoplasty for Voice Feminization
The Laryngoscope, 2020Co-Authors: Ingo R Titze, Anil Palaparthi, Ted MauAbstract:OBJECTIVES/HYPOTHESIS Anterior (Wendler) glottoplasty has become a popular surgery for voice feminization. However, there has been some discrepancy between its theoretical pitch-raising potential and what is actually achievable, and downsides to shortening the glottis have not been fully explored. In addition, descriptions of the surgery are inconsistent in their treatment of the Vocal Ligament. This study aimed to determine 1) how fundamental frequency (fo ) is expected to vary with length of anterior glottic fixation, 2) the impact of glottic shortening on sound pressure level (SPL), and 3) the effect of including the Ligament in fixation. STUDY DESIGN Computational simulation. METHODS Voice production was simulated in a fiber-gel finite element computational model using canonical male Vocal fold geometry incorporating a three-layer Vocal fold composition (superficial lamina propria, Vocal Ligament, and thyroarytenoid muscle). Progressive anterior glottic fixation (0, 1/8, 2/8, 3/8, etc. up to 7/8 of membranous Vocal fold length) was simulated. Outcome measures were fo , SPL, and glottal flow waveforms. RESULTS fo increased from 110 Hz to 164 Hz when the anterior one-half Vocal fold was fixed and continued to progressively rise with further fixation. SPL progressively decreased beyond 1/8 to 1/4 fixation. Inclusion of the Vocal Ligament in fixation did not further increase fo . Any fixation increased aperiodicity in the acoustic signal. CONCLUSIONS The optimal length of fixation is a compromise between pitch elevation and reduction in output acoustic power. The simulation also provided a potential explanation for Vocal roughness that is sometimes noted after anterior glottoplasty. LEVEL OF EVIDENCE NA Laryngoscope, 2020.
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Effect of resection depth of early glottic cancer on Vocal outcome: an optimized finite element simulation.
The Laryngoscope, 2015Co-Authors: Ted Mau, Tobias Riede, Anil Palaparthi, Ingo R TitzeAbstract:Objectives/Hypothesis To test the hypothesis that subLigamental cordectomy produces superior acoustic outcome than subepithelial cordectomy for early (T1–2) glottic cancer that requires complete removal of the superficial lamina propria but does not involve the Vocal Ligament. Study Design Computer simulation. Methods A computational tool for Vocal fold surgical planning and simulation (the National Center for Voice and Speech Phonosurgery Optimizer-Simulator) was used to evaluate the acoustic output of alternative Vocal fold morphologies. Four morphologies were simulated: normal, subepithelial cordectomy, subLigamental cordectomy, and transLigamental cordectomy (partial Ligament resection). The primary outcome measure was the range of fundamental frequency (F0) and sound pressure level (SPL). A more restricted F0-SPL range was considered less favorable because of reduced acoustic possibilities given the same range of driving subglottic pressure and identical Vocal fold posturing. Results SubLigamental cordectomy generated solutions covering an F0-SPL range 82% of normal for a rectangular Vocal fold. In contrast, transLigamental and subepithelial cordectomies produced significantly smaller F0-SPL ranges, 57% and 19% of normal, respectively. Conclusion This study illustrates the use of the Phonosurgery Optimizer-Simulator to test a specific hypothesis regarding the merits of two surgical alternatives. These simulation results provide theoretical support for Vocal Ligament excision with maximum muscle preservation when superficial lamina propria resection is necessary but the Vocal Ligament can be spared on oncological grounds. The resection of more tissue may paradoxically allow the eventual recovery of a better speaking voice, assuming glottal width is restored. Application of this conclusion to surgical practice will require confirmatory clinical data. Level of Evidence N/A. Laryngoscope, 125:1892–1899, 2015
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Vocal fold elasticity of the Rocky Mountain elk (Cervus elaphus nelsoni) - producing high fundamental frequency Vocalization with a very long Vocal fold.
The Journal of experimental biology, 2008Co-Authors: Tobias Riede, Ingo R TitzeAbstract:The Vocal folds of male Rocky Mountain elk (Cervus elaphus nelsoni) are about 3 cm long. If fundamental frequency were to be predicted by a simple vibrating string formula, as is often done for the human larynx, such long Vocal folds would bear enormous stress to produce the species-specific mating call with an average fundamental frequency of 1 kHz. Predictions would be closer to 50 Hz. Vocal fold histology revealed the presence of a large Vocal Ligament between the Vocal fold epithelium and the thyroarytenoid muscle. In tensile tests, the stress-strain response of Vocal fold epithelium and the Vocal Ligament were determined. Elasticity of both tissue structures reached quantitative values similar to human tissue. It seems unlikely that the longitudinal stress in elk Vocal folds can exceed that in human Vocal folds by an order of magnitude to overcome the drop in fundamental frequency due to a 3:1 increase in Vocal fold length. Alternative hypotheses of how the elk produces high fundamental frequency utterances, despite its very long Vocal fold, include a reduced effective Vocal fold length in vibration, either due to bending properties along the Vocal fold, or by actively moving the boundary point with muscle stiffening. The relationships between an individual's average fundamental frequency, Vocal fold length and body size are discussed.
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Refinements in modeling the passive properties of laryngeal soft tissue
Journal of applied physiology (Bethesda Md. : 1985), 2007Co-Authors: Eric J Hunter, Ingo R TitzeAbstract:The nonlinear viscoelastic passive properties of three canine intrinsic laryngeal muscles, the lateral cricoarytenoid (LCA), the posterior cricoarytenoid (PCA), and the interarytenoid (IA), were fit to the parameters of a modified Kelvin model. These properties were compared with those of the thyroarytenoid (TA) and cricothyroid (CT) muscles, as well as previously unpublished viscoelastic characteristics of the human Vocal Ligament. Passive parameters of the modified Kelvin model were summarized for the Vocal Ligament, mucosa, and all five laryngeal muscles. Results suggest that the LCA, PCA, and IA muscles are functionally different from the TA and CT muscles in their load-bearing capacity. Furthermore, the LCA, PCA, and IA have a much larger stress-strain hysteresis effect than has been previously reported for the TA and CT or the Vocal Ligament. The variation in this effect suggests that the connective tissue within the TA and CT muscles is somehow similar to the Vocal Ligament but different from the LCA, PCA, or IA muscles. Further demonstrating the potential significance of grouping tissues in the laryngeal system by functional groups in the laryngeal system was the unique finding that, over their working elongation range, the LCA and PCA were nearly as exponentially stiff as the Vocal Ligament. This paper was written in conjunction with an online technical report (http://www.ncvs.org/ncvs/library/tech) in which comprehensive muscle data and sensitivity analysis, as well as downloadable data files and computer scripts, are made available.
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a three dimensional model of Vocal fold abduction adduction
Journal of the Acoustical Society of America, 2004Co-Authors: Eric J Hunter, Ingo R Titze, Fariborz AlipourAbstract: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°. Using the posterior-cricoarytenoid muscle, the model produced an angular abduction speed of 405° 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.
Robert H Ossoff - One of the best experts on this subject based on the ideXlab platform.
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LATERAL LARYNGOTOMY FOR THE REMOVAL OF TEFLON GRANULOMA
2016Co-Authors: James L. Netterville, John R. Coleman, Cheryl L. Rainey, Lou Reinisch, Robert H OssoffAbstract:Teflon injection has been used for Vocal fold medialization following paralysis. Recently, numerous articles have discussed the complications of Teflon injection, including overinjection, airway obstruction, Teflon granuloma, and an abnormal mass effect creating a decreased vibratory character of the true Vocal fold. Multiple techniques for Teflon removal have been described. This report details our experience with complete Teflon granuloma removal via a lateral laryngotomy under local anesthesia. Micro-scopic dissection of the entire granuloma and the paraglottic space was accomplished in all patients. Due to extensive destruction caused by the granuloma, the Vocal Ligament was resected in 3 patients; it was partially resected and reanastomosed in 1 case, and spared in 6 patients. Laryngeal reconstruction was accomplished with an inferiorly based sternohyoid muscle rotation flap and ary-tenoid adduction. Effortful speech secondary to pressed Vocal quality resolved in all patients. Near-normal to normal Vocal quality was obtained in 4 patients, with the average "voice desirability " improving 60 % and the effective glottic width increasing 29%. Factors that contributed to a successful outcome included noninvolvement of the Vocal Ligament and sparing of the mucosal cover. KEY WORDS- granuloma, laryngotomy. Teflon
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PHONOMICROSURGERY II: SURGICAL TECHNIQUES
Otolaryngologic clinics of North America, 2000Co-Authors: C. Gaelyn Garrett, Robert H OssoffAbstract:Optimal Vocal outcome is the major goal of treatment of benign non-neoplastic Vocal fold lesions. Current phonomicrosurgery techniques are based on a complete understanding of Vocal fold anatomy and the physiology of Vocal fold vibration. With the knowledge that these lesions typically involve the superficial layer of the lamina propria and not the overlying epithelium, dissection and excision should be limited to this layer. Vocal fold microflap techniques leave the overlying epithelium and the mucosal cover intact to minimize postoperative scarring and possible tethering to the underlying Vocal Ligament. Surgical excision is followed by a program of Vocal rehabilitation.
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Current Endoscopic Treatment of Dysphonia
Diagnostic and therapeutic endoscopy, 2000Co-Authors: John M. Schweinfurth, Robert H OssoffAbstract:Benign laryngeal disorders result in dysphonia because of effects on glottic closure and the vibratory characteristics of the true Vocal fold. Treatment is initially directed at reversing medical conditions and patterns of abuse with surgery reserved for unresolving lesions resulting in troublesome dysphonia. Benign lesions that require surgery are excised as precisely as possible sparing overlying mucosa and the underlying Vocal Ligament. Vocal fold scarring is currently best treated by augmentation procedures, and atrophy may be compensated for by medialization thyroplasty or by adding bulk to the affected folds. Application of current knowledge of laryngeal histology and physiology is prerequisite to endoscopic surgical intervention.
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Lateral laryngotomy for the removal of Teflon granuloma.
Annals of Otology Rhinology and Laryngology, 1998Co-Authors: James L. Netterville, John R. Coleman, Cheryl L. Rainey, Susan Chang, Lou Reinisch, Robert H OssoffAbstract:Teflon injection has been used for Vocal fold medialization following paralysis. Recently, numerous articles have discussed the complications of Teflon injection, including overinjection, airway obstruction, Teflon granuloma, and an abnormal mass effect creating a decreased vibratory character of the true Vocal fold. Multiple techniques for Teflon removal have been described. This report details our experience with complete Teflon granuloma removal via a lateral laryngotomy under local anesthesia. Microscopic dissection of the entire granuloma and the paraglottic space was accomplished in all patients. Due to extensive destruction caused by the granuloma, the Vocal Ligament was resected in 3 patients; it was partially resected and reanastomosed in 1 case, and spared in 6 patients. Laryngeal reconstruction was accomplished with an inferiorly based sternohyoid muscle rotation flap and arytenoid adduction. Effortful speech secondary to pressed Vocal quality resolved in all patients. Near-normal to normal voc...
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Lateral laryngotomy for the removal of teflon granuloma
Annals of Otology Rhinology and Laryngology, 1998Co-Authors: James L. Netterville, John R. Coleman, Cheryl L. Rainey, Susan Chang, Lou Reinisch, Robert H OssoffAbstract:Teflon injection has been used for Vocal fold medialization following paralysis. Recently, numerous articles have discussed the complications of Teflon injection, including overinjection, airway obstruction, Teflon granuloma, and an abnormal mass effect creating a decreased vibratory character of the true Vocal fold. Multiple techniques for Teflon removal have been described. This report details our experience with complete Teflon granuloma removal via a lateral laryngotomy under local anesthesia. Microscopic dissection of the entire granuloma and the paraglottic space was accomplished in all patients. Due to extensive destruction caused by the granuloma, the Vocal Ligament was resected in 3 patients; it was partially resected and reanastomosed in 1 case, and spared in 6 patients. Laryngeal reconstruction was accomplished with an inferiorly based sternohyoid muscle rotation flap and arytenoid adduction. Effortful speech secondary to pressed Vocal quality resolved in all patients. Near-normal to normal Vocal quality was obtained in 4 patients, with the average "voice desirability" improving 60% and the effective glottic width increasing 29%. Factors that contributed to a successful outcome included noninvolvement of the Vocal Ligament and sparing of the mucosal cover.
Thomas Siegmund - One of the best experts on this subject based on the ideXlab platform.
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Collagen microstructure in the Vocal Ligament: initial results on the potential effects of smoking.
The Laryngoscope, 2014Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Roger W ChanAbstract:Objectives/Hypothesis This investigation quantitatively characterizes the collagenous microstructure of human Vocal Ligament specimens excised postmortem from nonsmokers and smokers. Study Design Retrospective cohort study. Methods Second harmonic generation (SHG) imaging was performed at three anatomical locations of Vocal Ligament specimens: anterior, mid-membranous, and posterior regions. Two microstructural parameters were extracted from the SHG images: (1) normalized fiber density, and (2) fiber dispersion coefficient, quantifying the degree of collagen fiber dispersion about a preferred direction. Results For both the nonsmoker and smoker subjects, the fiber dispersion coefficient was heterogeneous. Differences in the collagenous structure of nonsmokers and smoker subjects were pronounced at the mid-membranous location. However, the directionality of the heterogeneity in the smoker subjects was opposite to that in the nonsmoker subjects. Specifically, the fiber dispersion coefficient in the nonsmoker subjects was lower in the mid-membranous region (indicating more fiber alignment) than at the anterior/posterior regions, but for the smoker subjects the fiber dispersion coefficient was higher at the mid-membranous region. The normalized fiber density was near constant in the nonsmoker subjects, but the smoker subjects had fewer fibers in the mid-membranous region than at the anterior/posterior regions. Conclusion Spatial microstructural variations may exist in the Vocal fold Ligament both in nonsmokers and smokers. Smoking appears to influence the degree and direction of microstructure heterogeneity in the Vocal fold Ligament. Level of Evidence N/A. Laryngoscope, 124:E361–E367, 2014
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An illustrative result of simulated stress resulting from a modulated strain (e.g., Fig. 2b).
2014Co-Authors: Eric J Hunter, Thomas Siegmund, Roger W ChanAbstract:Left: cover refers to the combination of epithelium and a superficial layer of lamina propria. Middle: Ligament refers to the Vocal Ligament, which consists of the intermediate and deep layer of the lamina propria. Right: the cover and Ligament responses summed together to suggest a combined tissue.
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Empirical measurements of biomechanical anisotropy of the human Vocal fold lamina propria
Biomechanics and Modeling in Mechanobiology, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:The Vocal folds are known to be mechanically anisotropic due to the microstructural arrangement of fibrous proteins such as collagen and elastin in the lamina propria. Even though this has been known for many years, the biomechanical anisotropic properties have rarely been experimentally studied. We propose that an indentation procedure can be used with uniaxial tension in order to obtain an estimate of the biomechanical anisotropy within a single specimen. Experiments were performed on the lamina propria of three male and three female human Vocal folds dissected from excised larynges. Two experiments were conducted: each specimen was subjected to cyclic uniaxial tensile loading in the longitudinal (i.e., anterior–posterior) direction, and then to cyclic indentation loading in the transverse (i.e., medial–lateral) direction. The indentation experiment was modeled as contact on a transversely isotropic half-space using the Barnett–Lothe tensors. The longitudinal elastic modulus E _ L was computed from the tensile test, and the transverse elastic modulus E _ T and longitudinal shear modulus G _ L were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of E _ L / E _ T was 14 for the Vocal Ligament and 39 for the Vocal fold cover specimens. Also, the average of E _ L / G _ L , a parameter important for models of phonation, was 28 for the Vocal Ligament and 54 for the Vocal fold cover specimens. These measurements of anisotropy could contribute to more accurate models of fundamental frequency regulation and provide potentially better insights into the mechanics of Vocal fold vibration.
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The anisotropic hyperelastic biomechanical response of the Vocal Ligament and implications for frequency regulation: A case study
The Journal of the Acoustical Society of America, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:One of the primary mechanisms to vary one's Vocal frequency is through Vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the Vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during Vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the Vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the Vocal Ligament. Continuum models of vibration were constructed based upon Euler–Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a Vocal Ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human Vocal Ligament specimen.
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Spatially varying properties of the Vocal Ligament contribute to its eigenfrequency response.
Journal of the mechanical behavior of biomedical materials, 2010Co-Authors: Jordan E. Kelleher, Kai Zhang, Thomas Siegmund, Roger W ChanAbstract:The Vocal Ligament is known to have nonlinear variation in geometry, yet this is rarely considered in empirical or computational studies. This paper investigates the effects of a nonlinear variation of the anterior-to-posterior geometry and the corresponding spatial variation in elastic modulus on the fundamental frequency of vibration for the Vocal Ligament. Uniaxial tensile tests were performed on a Vocal Ligament specimen dissected from an excised 60-year-old male larynx. Digital image correlation (DIC) was used to obtain the spatial deformation field for the entire Ligament specimen. DIC results revealed that the tensile deformation was very heterogeneous, with the least amount of deformation occurring in the region of smallest cross-sectional area. The elastic modulus was calculated locally and was found to be approximately 10 times higher at the midpoint of the Vocal Ligament than in the anterior and posterior macula flavae regions. Based on the spatially varying material properties obtained, finite element models (isotropic and transversely isotropic) were created to investigate how the effects of varying cross-section, heterogeneous stiffness, and anisotropy could affect the fundamental frequency of vibration. It was found that the spatial cross-section variation and the spatially varying anisotropy (i.e. modulus ratio) are significant to predictions of the vibration characteristics. Fundamental frequencies predicted with a finite element model are discussed in view of rotatory inertia and contribution of transverse shear deformation.
Jordan E. Kelleher - One of the best experts on this subject based on the ideXlab platform.
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Collagen microstructure in the Vocal Ligament: initial results on the potential effects of smoking.
The Laryngoscope, 2014Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Roger W ChanAbstract:Objectives/Hypothesis This investigation quantitatively characterizes the collagenous microstructure of human Vocal Ligament specimens excised postmortem from nonsmokers and smokers. Study Design Retrospective cohort study. Methods Second harmonic generation (SHG) imaging was performed at three anatomical locations of Vocal Ligament specimens: anterior, mid-membranous, and posterior regions. Two microstructural parameters were extracted from the SHG images: (1) normalized fiber density, and (2) fiber dispersion coefficient, quantifying the degree of collagen fiber dispersion about a preferred direction. Results For both the nonsmoker and smoker subjects, the fiber dispersion coefficient was heterogeneous. Differences in the collagenous structure of nonsmokers and smoker subjects were pronounced at the mid-membranous location. However, the directionality of the heterogeneity in the smoker subjects was opposite to that in the nonsmoker subjects. Specifically, the fiber dispersion coefficient in the nonsmoker subjects was lower in the mid-membranous region (indicating more fiber alignment) than at the anterior/posterior regions, but for the smoker subjects the fiber dispersion coefficient was higher at the mid-membranous region. The normalized fiber density was near constant in the nonsmoker subjects, but the smoker subjects had fewer fibers in the mid-membranous region than at the anterior/posterior regions. Conclusion Spatial microstructural variations may exist in the Vocal fold Ligament both in nonsmokers and smokers. Smoking appears to influence the degree and direction of microstructure heterogeneity in the Vocal fold Ligament. Level of Evidence N/A. Laryngoscope, 124:E361–E367, 2014
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Empirical measurements of biomechanical anisotropy of the human Vocal fold lamina propria
Biomechanics and Modeling in Mechanobiology, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:The Vocal folds are known to be mechanically anisotropic due to the microstructural arrangement of fibrous proteins such as collagen and elastin in the lamina propria. Even though this has been known for many years, the biomechanical anisotropic properties have rarely been experimentally studied. We propose that an indentation procedure can be used with uniaxial tension in order to obtain an estimate of the biomechanical anisotropy within a single specimen. Experiments were performed on the lamina propria of three male and three female human Vocal folds dissected from excised larynges. Two experiments were conducted: each specimen was subjected to cyclic uniaxial tensile loading in the longitudinal (i.e., anterior–posterior) direction, and then to cyclic indentation loading in the transverse (i.e., medial–lateral) direction. The indentation experiment was modeled as contact on a transversely isotropic half-space using the Barnett–Lothe tensors. The longitudinal elastic modulus E _ L was computed from the tensile test, and the transverse elastic modulus E _ T and longitudinal shear modulus G _ L were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of E _ L / E _ T was 14 for the Vocal Ligament and 39 for the Vocal fold cover specimens. Also, the average of E _ L / G _ L , a parameter important for models of phonation, was 28 for the Vocal Ligament and 54 for the Vocal fold cover specimens. These measurements of anisotropy could contribute to more accurate models of fundamental frequency regulation and provide potentially better insights into the mechanics of Vocal fold vibration.
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The anisotropic hyperelastic biomechanical response of the Vocal Ligament and implications for frequency regulation: A case study
The Journal of the Acoustical Society of America, 2013Co-Authors: Jordan E. Kelleher, Thomas Siegmund, Elhum Naseri, Roger W ChanAbstract:One of the primary mechanisms to vary one's Vocal frequency is through Vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the Vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during Vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the Vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the Vocal Ligament. Continuum models of vibration were constructed based upon Euler–Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a Vocal Ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human Vocal Ligament specimen.
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Spatially varying properties of the Vocal Ligament contribute to its eigenfrequency response.
Journal of the mechanical behavior of biomedical materials, 2010Co-Authors: Jordan E. Kelleher, Kai Zhang, Thomas Siegmund, Roger W ChanAbstract:The Vocal Ligament is known to have nonlinear variation in geometry, yet this is rarely considered in empirical or computational studies. This paper investigates the effects of a nonlinear variation of the anterior-to-posterior geometry and the corresponding spatial variation in elastic modulus on the fundamental frequency of vibration for the Vocal Ligament. Uniaxial tensile tests were performed on a Vocal Ligament specimen dissected from an excised 60-year-old male larynx. Digital image correlation (DIC) was used to obtain the spatial deformation field for the entire Ligament specimen. DIC results revealed that the tensile deformation was very heterogeneous, with the least amount of deformation occurring in the region of smallest cross-sectional area. The elastic modulus was calculated locally and was found to be approximately 10 times higher at the midpoint of the Vocal Ligament than in the anterior and posterior macula flavae regions. Based on the spatially varying material properties obtained, finite element models (isotropic and transversely isotropic) were created to investigate how the effects of varying cross-section, heterogeneous stiffness, and anisotropy could affect the fundamental frequency of vibration. It was found that the spatial cross-section variation and the spatially varying anisotropy (i.e. modulus ratio) are significant to predictions of the vibration characteristics. Fundamental frequencies predicted with a finite element model are discussed in view of rotatory inertia and contribution of transverse shear deformation.
