The movement and control of the vocal folds within the laryngeal cavity enables three crucial physiological functions: 1) allowing respiration by opening, 2) aiding in airway protection by closing, and 3) regulating sound production during phonation. Although treatment options have improved, many of the estimated 7.5 million individuals in the United States who are annually affected by voice-related disorders still face serious challenges related to dysphonia and dysphagia. The need for improved voice-disorder treatments has motivated the work presented in this dissertation which focuses on modeling and manufacturing the vocal folds and aims to answer three main questions: 1) what are the mechanical properties of the vocal folds and how do they change across the full vocal range? 2) how do those properties influence the dynamic behavior of the tissue? and 3) can we manufacture a synthetic vocal fold model that exhibits a desired and controllable dynamic behavior? First, the elastic properties of sixteen porcine vocal folds were evaluated through uniaxial tensile tests on a custom built experimental setup. Stress-strain data was analyzed using an optimization method to yield continuous model parameters which described the linear and nonlinear elastic regions as well as transition points between those regions. Next, the impact of the vocal fold elastic properties on the frequencies of vibration was evaluated through dynamic tests on excised porcine larynges. Sound data was analyzed via a spectrogram and through the use of fast Fourier transforms to study changes in the frequency of vibration while the vocal folds were stretched. Additionally, a mathematical aeroelastic model of phonation was implemented to further evaluate the changing elastic properties on vocal fold dynamics. Next, eight synthetic vocal fold models were created, each with varying mechanical properties and a geometry based on reported anatomical measurements of porcine vocal folds. The synthetic models were then dynamically tested to further study the impact of changes in mechanical properties on the dynamic behavior of the synthetic vocal folds. / Doctor of Philosophy / The movement and control of the vocal folds within the voice-box enables three crucial physiological functions: 1) allowing respiration by opening, 2) aiding in airway protection and swallowing by closing, and 3) regulating sound production during vocalization. Although treatment options have improved, many of the estimated 7.5 million individuals in the United States who are annually affected by voice-related disorders still face serious challenges related to speech production and swallowing which often results in significant detrimental impacts to quality of life. The need for improved treatments is most easily observed in the evaluation of treatment options following a total laryngectomy, which is a procedure where the entire voice-box is removed often due to cancer. Following a laryngectomy, all three of the vital functions of the vocal folds are immediately impacted as patients adjust to breathing through and protecting a redirected airway and are forced to use alternative methods of speech production which often result in monotone or robotic-sounding speech. The need for improved voice-disorder treatments has motivated the work presented in this dissertation which focuses on modeling and manufacturing the vocal folds and aims to answer three main questions: 1) what are the mechanical properties of the vocal folds? 2) how do those properties influence the dynamic behavior of the tissue during sound production? and 3) can we manufacture synthetic vocal folds that produce a desired and controllable dynamic behavior? Sixteen porcine vocal fold samples were mechanical tested to evaluate the elastic properties of the tissue. Next, porcine voice-box samples were experimentally tested in a way that simulated sound production by subjecting the samples to a heated and humidified air flow, similar to the air flow conditions coming out of the lungs. In this way, the relationship between the tissue properties and the frequencies of sound was investigated. Lastly, the synthetic vocal fold samples were evaluated using a similar experimental protocol to further investigate the impact of changing structural properties on the dynamics of the vocal folds during sound production.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96557 |
| Date | 22 January 2020 |
| Creators | Burks, William Garret |
| Contributors | Mechanical Engineering, Leonessa, Alexander, De Vita, Raffaella, Mueller, Rolf, Johnson, Blake, Tarazaga, Pablo Alberto |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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