The influence of asymmetric vocal fold stiffness on voice production was evaluated using life-sized, self-oscillating vocal fold models with an idealized geometry based on the human vocal folds. The models were fabricated using flexible, materially-linear silicone compounds with Young’s modulus values comparable to that of vocal fold tissue. The models included a two-layer design to simulate the vocal fold layered structure. The respective Young’s moduli of elasticity of the “left” and “right” vocal fold models were varied to create asymmetric conditions. High-speed videokymography was used to measure maximum vocal fold excursion, vibration frequency, and left-right phase shift, all of which were significantly influenced by asymmetry. Onset pressure, a measure of vocal effort, increased with asymmetry. Particle image velocimetry (PIV) analysis showed significantly greater skewing of the glottal jet in the direction of the stiffer vocal fold model. Potential applications to various clinical conditions are mentioned, and suggestions for future related studies are presented.

Recent vocal fold vibration studies have used models defined using idealized geometry. Although these models exhibit important similarities with human vocal fold vibration, some aspects of their motion are less than realistic. In this report it is demonstrated that more realistic motion may be obtained when using geometry derived from magnetic resonance imaging (MRI) data. The dynamic response of both idealized and MRI-based synthetic vocal fold models are presented. MRI-based model improvements include evidence of mucosal wave-like motion and less vertical movement. Limitations of the MRI-based model are discussed and suggestions for further synthetic model development are offered.

Simplified models have been used to simulate and study the flow-induced vibrations of the human vocal folds. While it is clear that the models' responses are sensitive to geometry, it is not clear how and to what extent specific geometric features influence model motion. In this study geometric features that played significant roles in governing the motion of a two-layer (body-cover), two-dimensional, finite element vocal fold model were identified. The model was defined using a flow solver based on the viscous, unsteady, Navier-Stokes equations and a solid solver that allowed for large strain and deformation. A screening-type design-of-experiments approach was used to identify the relative importance of 13 geometric parameters. Five output measures were analyzed to assess the magnitude of each geometric parameter's effect on the model's motion. The measures related to frequency, glottal width, flow rate, intraglottal angle, and intraglottal phase delay. The most significant geometric parameters were those associated with the cover--primarily the pre-phonatory intraglottal angle--as well as the body inferior angle. Some models exhibited evidence of improved model motion, including mucosal wave-like motion and alternating convergent-divergent glottal profiles, although further improvements are still needed to more closely mimic human vocal fold motion.

Numerous synthetic and computational models have been and are currently being used in research studies of human vocal fold vibration. Model geometry plays an integral role in governing dynamic response. However, the various model geometry definitions have typically been idealized and often exhibit wide variability with each other. The present research compares the response of synthetic vocal fold models of different geometries. One model is based on idealized geometry, while the other is based on geometry obtained from the National Library of Medicine’s visible human project (VHP). The process for image extraction, model definition, and model fabrication is described, including: (1) image conversion from 2-D VHP image sequences to 3-D stereolithography (STL) format, (2) conversion to 3-D computer model format in which model geometric manipulations can be performed, and (3) fabrication of synthetic models using rapid prototyping. Results of measurements to characterize the dynamic response of self-oscillating synthetic vocal fold models, including onset and offset pressure, instantaneous glottal width using high-speed imaging, and glottal jet velocity profiles using particle image velocimetry (PIV), are presented for models based on both VHP data and idealized geometries. The sensitivity of the models to geometry changes is also reported.

Synthetic continuum models of the vocal folds, though only relatively recently developed, have found significant use in studying the flow-induced vibrations of the vocal folds. The advantages of these models include long lifetime and reasonable comparison with human vocal fold characteristics. However, the geometry typically employed is highly idealized, with uniformly shaped cross section and rigid mounting to rectangular plates. In this presentation, the development and characterization of a multi-component model of the human larynx is presented. The model includes the following synthetic components: multi-layer vocal folds consisting of materials with nonlinear stress-strain properties, cartilaginous and soft tissue framework, and posture control. The fabrication process, including extraction of geometric information from medical images, is summarized. Various aspects of the model are characterized to compare the model behavior with that of the human larynx. Measurements of the synthetic vocal fold material properties, including stress-strain dependence, tangent modulus, and Poissons ratio, are presented. Dependence on subglottal pressure of the model vibration frequency, flow rate, vibration amplitude, and other flow field and jet characteristics are quantified using high-speed imaging, flow visualization, and particle image velocimetry.