Effect of Longitudinal Variation of Vocal Fold Inner Layer Thickness on Fluid-Structure Interaction During Voice Production

Abstract

A three-dimensional fluid-structure interaction computational model was used to investigate the effect of the longitudinal variation of vocal fold inner layer thickness on voice production. The computational model coupled a finite element method based continuum vocal fold model and a Navier-Stokes equation based incompressible flow model. Four vocal fold models, one with constant layer thickness and the others with different degrees of layer thickness variation in the longitudinal direction, were studied. It was found that the varied thickness resulted in up to 24% stiffness reduction at the middle and up to 47% stiffness increase near the anterior and posterior ends of the vocal fold; however, the average stiffness was not affected. The fluid-structure interaction simulations on the four models showed that the thickness variation did not affect vibration amplitude, glottal flow rate, and the waveform related parameters. However, it increased glottal angles at the middle of the vocal fold, suggesting that vocal fold vibration amplitude was determined by the average stiffness of the vocal fold, while the glottal angle was determined by the local stiffness. The models with longitudinal variation of layer thickness consumed less energy during the vibrations compared with the constant layer thickness one.

Overview on state-of-the-art numerical modeling of the phonation process

“…Damping was simulated using a Rayleigh damping scheme with coefficients a = 24.1915 and b = 0.000127. The vocal fold tissue was modeled as viscoelastic, transversely isotropic material in the other four studies [67][68][69]. A constant density q = 1043 kg/m 3 , in-plane transversal and longitudinal Poisson ratio (m p = 0.9, m pz = 0) inside the layers is used.…”

“…A pressure inlet and outlet condition drive the flow, and a nopenetration and a no-slip condition are applied to the walls. For the acoustics equation in four studies [67][68][69][70], soundhard wall boundary conditions are applied at the tissue walls. A total reflecting boundary condition models the free field radiation.…”

“…A total reflecting boundary condition models the free field radiation. Towards the lower airways, a Dirichlet boundary condition was described in [67,68] or an anechoic termination was used in [69,70].…”

“…Furthermore, the model verification was performed by refining the grid and time step sizes. The computational models used in [67][68][69] build upon established FSI models from previous years and the experience gained there. In [70], a grid independence study was carried out.…”

Impact of Instructed Laryngeal Manipulation on Acoustic Measures of Voice–Preliminary Results

“…4 Mathematical models and in vivo experiments have suggested that the voice is affected by changes in thickness of both the cover and body of the vocal fold. 29 The cover-body layer thickness ratio significantly affects flow-tissue interactions influencing both fundamental frequency (F0) and vibration pattern. 30 Increased vocal fold thickness (thick TVFM) was believed to result in greater vertical phase difference and longer glottal closure time, leading to stronger harmonic structures.…”