Could Spatial Heterogeneity in Human Vocal Fold Elastic Properties Improve the Quality of Phonation?

Journal of Biomechanics

2015

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New studies show that the elastic properties of the vocal folds (VFs) vary locally. In particular strong gradients exist in the distribution of elastic modulus along the length of the VF ligament, which is an important load-bearing constituent of the VF tissue. There is further evidence that changes in VF health are associated with alterations in modulus gradients. The role of VF modulus gradation on VF vibration and phonation remains unexplored. In this study the magnitude of the gradient in VF elastic modulus is varied, and sophisticated computational simulations are performed of the self-oscillation of three-dimensional VFs with realistic modeling of airflow physical properties. Results highlight that phonation frequency, characteristic modes of deformation and phase differences, glottal airflow rate, spectral-width of vocal output, and glottal jet dynamics are dependent on the magnitude of VF elastic modulus gradation. The results advance the understanding of how VF functional gradation can lead to perceptible changes in speech quality.

Section: Discussionmentioning

confidence: 87%

“…Kelleher et al (2012) show that gradients in elastic modulus are smaller in cover and ligament specimens excised from subjects associated with tobacco use than specimens excised from non-smokers. Kelleher et al (2010) show that in vacuo eigenmodes of VF tissue are dependent on gradients in elastic modulus.…”

Section: Introductionmentioning

confidence: 81%

Role of gradients in vocal fold elastic modulus on phonation

Bhattacharya

Journal of Biomechanics

2015

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“…Each tissue was mounted in the tensile testing setup in a manner where the specimen's length was near the in situ measurement in order to closely mimic the physiological state. The uniaxial tensile test was conducted for 180 cycles, similar to previous studies on vocal fold elasticity (Kelleher et al, 2011, 2012). …”

Section: Methodsmentioning

confidence: 99%

Empirical measurements of biomechanical anisotropy of the human vocal fold lamina propria

Biomech Model Mechanobiol

et al. 2012

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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 EL was computed from the tensile test, and the transverse elastic modulus ET and longitudinal shear modulus GL were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of EL/ET was 14 for the vocal ligament and 39 for the vocal fold cover specimens. Also, the average of EL/GL, 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.

“…We speculate that the microstructural arrangement likely varies based upon the anterior-posterior location along the vocal ligament as indicated by the heterogeneous elastic response measured in previous studies. 22,30 A more complete analysis should include the fiber dispersion at several locations along the vocal ligament to account for the histological heterogeneity. A recent study has documented the dispersion and density of collagenous fibers of the vocal ligament with more samples and provided a statistical range.…”

Section: Discussionmentioning

confidence: 99%

“…Since vocal fold tissue has been shown to be heterogeneous, it was important that the elastic properties be measured in the same region. 22,30 However, for the constitutive and vibration modeling the elastic properties of the overall tissue (i.e., from the anterior commissure to the vocal process) were used.…”

Section: B Biomechanical Testingmentioning

confidence: 99%

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

et al. 2013

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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.