There are many conditions and diseases that affect voice production. One of these, subglottic stenosis (SGS), is characterized by a narrowing of the trachea near the cricotracheal junction. SGS causes dyspnea (labored breathing) and frequently surgery is necessary to eliminate the airway obstruction. SGS is also believed to adversely affect voice quality. While significant research has been conducted to study the effect of SGS on breathing, relatively few studies concerning its effect on voice production have been performed. The purpose of this research was to provide quantitative results concerning the predicted effects of SGS on vocal fold (VF) vibration and resulting sound production, and to provide tools for more extensive research involving synthetic VF models in the future. This was achieved through an experimental procedure in which a device simulating SGS was coupled with synthetic VF models and acoustic, aerodynamic, and vibratory measurements were acquired. Additionally, a device was developed and tested to study the effects of VF posturing using synthetic VF models. The design of the device is anticipated to serve as a useful tool in future experiments.The device simulating SGS was capable of creating an artificial stenosis of adjustable severity. The device was designed so that synthetic VF models inserted into rigid plates could be placed on top of the device, downstream of the stenosis. An experiment was conducted with the SGS device in conjunction with synthetic four-layer VF models in which flow and pressure were measured, radiated sound data were recorded, and visual data from a high-speed camera were captured as the percent obstruction was changed. The effects of subglottic stenosis were quantified using metrics such as onset pressure, glottal area, smoothed cepstral peak prominence (CPPS), harmonic-to-noise ratio (HNR), acoustic spectra, air flow, and pressure below and above the stenosis. The results show that the glottal area was not noticeably affected by the stenosis until 80% or 90% obstruction, and flow resistance through the stenosis was not significantly affected until 85% obstruction. However, changes in acoustics occurred as low as 65% or 70% obstruction.An MRI-compatible posturing device was developed which was capable of causing abduction/adduction and elongation in synthetic VF models. The device was used to adduct synthetic VF models from an abducted position into a pre-determined final phonatory posture as high-speed video and pressure data were collected. The device adducted to final phonatory posture in 500 ms, and phonation was initiated 680 ms later. In addition, the elongation of the synthetic models was varied as high-speed data were collected. The frequency of vibration of the four-layer models was found to not vary significantly when the models were elongated.

One of the primary objectives of voice research is to better understand the biomechanics of voice production and how changes in properties of the vocal folds (VFs) affect voice ability and quality. Synthetic VF models provide a way to observe how changes in geometry and material property affect voice biomechanics. This thesis seeks to evaluate an approach of using a genetic algorithm to design synthetic VF models in three ways: first, through the development of a computationally cost-effective 3D vocal fold model; second, by creating and optimizing a variation of this model; and third, by validating the approach. To reduce computation times, a user-defined function (UDF) was implemented in low-fidelity 2D and 3D computational VF models. The UDF replaced the conventional meshed fluid domain with the mechanical energy equation. The UDF was implemented in the commercial finite element code ADINA and verified to produce results that were similar to those of 2D and 3D VF models with meshed fluid domains. Computation times were reduced by 86% for 2D VF models and 74% for 3D VF models while core vibratory characteristic changes were less than 5%. The results from using the UDF demonstrate that computation times could be reduced while still producing acceptable results. A genetic algorithm optimizer was developed to study the effects of altering geometry and material elasticity on frequency, closed quotient (CQ), and maximum flow declination rate (MFDR). The objective was to achieve frequency and CQ values within the normal human physiological range while maximizing MFDR. The resulting models enabled an exploration of trends between objective and design variables. Significant trends and aspects of model variability are discussed. The results demonstrate the benefit of using a structured model exploration method to create models with desirable characteristics. Two synthetic VF models were fabricated to validate predictions made by models produced by the genetic algorithm. Fabricated models were subjected to tests where frequency, CQ, and sound pressure level were measured. Trends between computational and synthetic VF model responses are discussed. The results show that predicted frequency trends between computational and synthetic models were similar, trends for closed quotient were inconclusive, and relationships between MFDR and sound pressure level remained consistent. Overall, while discrepancies between computational and synthetic VF model results were observed and areas in need of further study are noted, the study results provide evidence of potential for using the present optimization method to design synthetic VF models.