Abstract
MotivationHuman voice is generated in the larynx by the two oscillating vocal folds. Owing to the limited space and accessibility of the larynx, endoscopic investigation of the actual phonatory process in detail is challenging. Hence the biomechanics of the human phonatory process are still not yet fully understood. Therefore, we adapt a mathematical model of the vocal folds towards vocal fold oscillations to quantify gender and age related differences expressed by computed biomechanical model parameters.MethodsThe vocal fold dynamics are visualized by laryngeal high-speed videoendoscopy (4000 fps). A total of 33 healthy young subjects (16 females, 17 males) and 11 elderly subjects (5 females, 6 males) were recorded. A numerical two-mass model is adapted to the recorded vocal fold oscillations by varying model masses, stiffness and subglottal pressure. For adapting the model towards the recorded vocal fold dynamics, three different optimization algorithms (Nelder–Mead, Particle Swarm Optimization and Simulated Bee Colony) in combination with three cost functions were considered for applicability. Gender differences and age-related kinematic differences reflected by the model parameters were analyzed.Results and conclusionThe biomechanical model in combination with numerical optimization techniques allowed phonatory behavior to be simulated and laryngeal parameters involved to be quantified. All three optimization algorithms showed promising results. However, only one cost function seems to be suitable for this optimization task. The gained model parameters reflect the phonatory biomechanics for men and women well and show quantitative age- and gender-specific differences. The model parameters for younger females and males showed lower subglottal pressures, lower stiffness and higher masses than the corresponding elderly groups. Females exhibited higher subglottal pressures, smaller oscillation masses and larger stiffness than the corresponding similar aged male groups.Optimizing numerical models towards vocal fold oscillations is useful to identify underlying laryngeal components controlling the phonatory process.
Highlights
The human voice represents an essential aspect of oral communication between human beings
The vocal fold dynamics are visualized by laryngeal high-speed videoendoscopy (4000 fps)
A numerical two-mass model is adapted to the recorded vocal fold oscillations by varying model masses, stiffness and subglottal pressure
Summary
The human voice represents an essential aspect of oral communication between human beings. The acoustic voice signal originates in the larynx where the two opposing vocal folds are excited by an airflow generated by the lungs (Fig 1). When starting the voice production process (i.e., phonation), the vocal folds are positioned close to each other. Airflow produced from the lungs streams upwards and increases the subglottal pressure below the vocal folds. After exceeding a certain subglottal pressure level, the vocal folds first start to produce small oscillatory motions that result in a steady-state oscillation (i.e., periodic opening and closing of the vocal folds). A healthy voice signal is normally produced by periodic and symmetric vocal fold oscillations. The closure of the glottis, where the vocal folds almost or entirely close, is considered to be an important part of the normal phonation process [2]
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