Constitutive model of human vocal fold tissue for fundamental frequency regulation

Kai Zhang, Purdue University

Abstract

Human voice is produced by flow-induced self-sustained oscillation of the vocal fold lamina propria. The mechanical properties of the vocal fold lamina propria, including the vocal fold cover and the vocal ligament, play an important role in regulating the fundamental frequency of human phonation. This study examines the hyperelastic and time-dependent tensile deformation behavior of cover and ligament specimens isolated from excised human larynges. Results show that the vocal fold lamina propria exhibits both elastic and viscous behavior. Specifically, the transient mechanical responses of cyclic stress relaxation and creep are observed. One of the primary goals of the thesis is to formulate constitutive models that could describe the mechanical behaviors of the vocal fold lamina propria. A two-network constitutive model is capable of describing the nonlinear elastic and hysteretic aspects of the tissue behavior, but fails to characterize any transient mechanical responses. A three-network constitutive model proves effective in characterizing the cyclic stress relaxation and creep behavior. Several statistically significant differences in the mechanical response differentiating cover and ligament, as well as age and gender, are found and then related to the histological structure of the human vocal fold extracellular matrix (ECM). ^ The constitutive descriptions of the tissue mechanical response are combined with a structural model of beam vibration accounting for the cover and the ligament. Despite the availability of only a small data set, the model predicts an age dependence of F₀ in males and the pitch differences across gender, in agreement with experimental findings. Our findings may also help explain the mechanisms of some widely observed transient phenomena in F ₀ regulation during phonation. Results show that local fluctuations such as F₀ overshoots and undershoots can be characterized by the biomechanical model and might be related to the processes of stress relaxation of vocal fold tissues during length changes. The global changes of F ₀ declination in declarative sentence production can also be characterized by the model. Such F₀ declination is partially attributed to the peak stress decay associated with stress relaxation of the vocal fold lamina propria and partially to neuromuscular control of the vocal fold length.^

Degree

Ph.D.

Advisors

Thomas Siegmund, Purdue University.

Subject Area

Engineering, Mechanical

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