Computational modeling of vibration‐induced systemic hydration of vocal folds over a range of phonation conditions

Abstract

Predicting phonation conditions that are benign to voice health remains a biomechanically relevant problem. Our objective is to provide insight into vocal fold (VF) hydration based on continuum-based VF models that are able to compute VF stresses during phonation and a scheme for the extraction and generalization of such computational data based on the principle of linear superposition. Because VF tissue is poroelastic, spatial gradients of VF hydrostatic stresses computed for a given phonation condition determine VF interstitial fluid flow. The present approach transforms, based on linear superposition principles, the computed interstitial fluid velocities at the particular phonation to those at an arbitrary phonation condition. Intersititial fluid flow characteristics for a range of phonation conditions are compared. For phonation conditions with no or moderate collision, no dehydration per vibration cycle is predicted throughout the VF. For more severe collision conditions, tissue dehydration is restricted to a region close to the glottal surface. Interstitial fluid displacement in the VF is found to be heterogeneous and strongly dependent on the phonation condition. A phonation condition is found to exist for which dehydration peaks. The proposed method significantly expands the scope and relevance of conducting isolated numerical simulations of VF vibration.

Role of gradients in vocal fold elastic modulus on phonation

“…These conditions impose significant computational modeling challenges. Bhattacharya and Siegmund (2014b) demonstrate the use of commercially available dedicated solvers for flow and structural domains to solve problems of VF FSI including vibration and contact, VF dehydration (Bhattacharya and Siegmund, 2014a) and surface adhesion (Bhattacharya and Siegmund, 2015). Bhattacharya and Siegmund (2014c) validated this framework against experiments on physical replicas.…”

A numerical strategy for finite element modeling of frictionless asymmetric vocal fold collision

“…Note the spurious non-smooth behavior that arises at collision in the Lagrange multiplier solution. It may be argued that the abrupt changes in nodal contact force calculation are a consequence of the non-smoothness introduced by the contact conditions in Equation (11). Regularization of the exact impact solution is a common practice in numerical mechanics, which can be performed by several techniques.…”

“…Furthermore, fully coupled numerical fluid‐structure solvers may present topological limitations in relation to the flow solver. Hence, a minimum glottal gap is typically enforced to model the contact interaction between the two vocal folds , or the collision phenomenon is simply disregarded .…”

“…Furthermore, it is hypothesized that non‐physical vocal fold interpenetration or minimum glottal gap enforcement affects the predicted dynamical and mechanical behavior of the system. Hence, the effect on vocal fold dynamics of simplifications in the contact model with regard to position‐based constraints (e.g., ) are investigated via the penalty solution algorithm. The results are compared with the proposed Lagrange multiplier formulation for exact contact constraint enforcement.…”

“…Furthermore, fully coupled numerical fluid-structure solvers may present topological limitations in relation to the flow solver. Hence, a minimum glottal gap is typically enforced to model the contact interaction between the two vocal folds [11], or the collision phenomenon is simply disregarded [2].The asymmetric contact problem in self-sustained vibrations of the vocal folds is typically disregarded in continuum models of the tissue [12] or formulated in simple lumped-mass models [6,13]. As pointed out in [9], sophisticated contact detection algorithms are required for asymmetric oscillations and intricate vocal folds geometries, especially at the upper vocal fold edges where convex contacting surfaces are present [14].…”