Asymmetric triangular body-cover model of the vocal folds with bilateral intrinsic muscle activation

Abstract

Many voice disorders are linked to imbalanced muscle activity and known to exhibit asymmetric vocal fold vibration. However, the relation between imbalanced muscle activation and asymmetric vocal fold vibration is not well understood. This study introduces an asymmetric triangular body-cover model of the vocal folds, controlled by the activation of bilateral intrinsic laryngeal muscles, to investigate the effects of muscle imbalance on vocal fold oscillation. Various scenarios were considered, encompassing imbalance in individual muscles and muscle pairs, as well as accounting for asymmetry in lumped element parameters. Measurements of amplitude and phase asymmetries were employed to match the oscillatory behavior of two pathological cases: unilateral paralysis and muscle tension dysphonia. The resulting simulations exhibit muscle imbalance consistent with expectations in the composition of these voice disorders, yielding asymmetries exceeding 30% for paralysis and below 5% for dysphonia. This underscores the relevance of muscle imbalance in representing phonatory scenarios and its potential for characterizing asymmetry in vocal fold vibration.

FIG. 1.

(Color online) Effects of the five intrinsic muscle in glottal posture. Adapted from Titze and Hunter (2007) J. Acoust. Soc. Am. 121(4), 2254, with permission of Acoustical Society of America. Copyright 2007 Acoustical Society of America.

FIG. 2.

(Color online) Schematic diagram of the VF configuration according to the a-TBCM for an abducted glottal configuration and asymmetrical muscle activation. The scheme shows the following: The vocal process (VP) defined by its position on the x and y axes ( $x_{02}, y_{02}$). The position of the posterior wall ( $x_{p2}, y_{p2}$). The posterior (PGO) and membranous (MGO) portions of glottal opening. Lumped mechanical components of mass (m), spring (k) and damper (d); for the upper (u), lower (l) and body (b) blocks; for the left (L) and right (R) vocal fold.

FIG. 3.

(Color online) Kymogram parametrization: x_L, x_R displacement of left/right VF; t_L, t_R time of maximal left/right VF displacement; x_c, x_o mediolateral position of VFs at the glottal closure/opening; A_L, A_R maximum displacement of left/right VF; W peak-to-peak glottal width; P glottal period; and OP open phase. Adapted from Mehta et al. (2011) J. Acoust. Soc. Am. 130(6), 3999–4009, with permission of Acoustical Society of America. Copyright 2011 Acoustical Society of America.

FIG. 4.

(Color online) Effects on normalized (pointed line) masses and (solid line) springs when varying the joint asymmetry factor q for LCA/IA (a), CT/TA (b) configurations, and single asymmetry in CT (c) and TA muscle (d). The legend represents the nomenclature in a-TBCM scheme (see Fig. 2, and Table III) for mass m, and spring k: upper u, lower l, and body b blocks. The gray color describes the effects due to the asymmetry mechanism introduced in SH95.

FIG. 5.

(Color online) Effects on PGO (a) and f_o (b) when varying q for muscle imbalance configurations. SH95 results shown for comparison.

FIG. 6.

(Color online) Comparison of kymograms and airflows from a-TBCM simulations for asymmetry scenarios and two imbalance conditions: hypofunction (q = 0.5) and hyperfunction (q = 1.5.).

FIG. 7.

(Color online) Effect of changing q on asymmetry metrics; AA (a) and PA (b), for the different imbalance approaches.

FIG. 8.

(Color online) Comparison of clínical (HSV and DKG) data and the corresponding simulated responses using a-TBCM: (left) Unilateral VF paralysis and (right) muscle tension dysphonia.

FIG. 9.

(Color online) Top view: 2D diagram describing the abducted VFs positioning for the cover blocks in the a-TBCM.

FIG. 10.

(Color online) Glottal area scheme for VF blocks: (top) no collision, (bottom) collision.

FIG. 11.

(Color online) The three collision scenarios in the a-TBCM determined by the left/right posterior displacements: (Top) case $\Delta x_{\mathrm{R}},\Delta x_{\mathrm{L}}>0$, (middle) $\Delta x_{\mathrm{R}}>0$ and $\Delta x_{\mathrm{L}}=0$ (and vice versa), and (bottom) $\Delta x_{\mathrm{R}},\Delta x_{\mathrm{L}}=0$.