Developing lifelike vocal fold models is challenging due to various associatedbiomechanical complexities. Nevertheless, the development and analysis of improved vocal foldmodels is worthwhile since they are valuable tools for gaining insight into human vocal foldvibratory, aerodynamic, and acoustic response characteristics. This thesis seeks to contribute tothe development of computational and physical vocal fold modeling in two ways. First is byintroducing a method of obtaining internal deformation fields within vibrating synthetic vocal foldmodels; second is by presenting an optimization algorithm coupled with a computational vocalfold model to optimize geometry and stiffness of a synthetic vocal fold model to achieve morerealistic vibration patterns.The method for tracking the internal deformation of self-oscillating vocal fold models isbased on MR imaging. Silicone models scaled to four times life-size to lower the flow-inducedvibration frequency were imbedded with fiducial markers in a coronal plane. Candidate markermaterials were tested using static specimens, and two materials, cupric sulfate and glass, werechosen for testing in the vibrating VF models. The vibrating models were imaged using a gatedMRI protocol wherein MRI acquisition was triggered using the subglottal pressure signal. Twodimensionalimage slices at different phases during self-oscillation were captured, and in eachphase the fiducial markers were clearly visible. The process was also demonstrated using a threedimensionalscan at two phases. The benefit of averaging to increase signal-to-noise ratio wasexplored. The results demonstrate the ability to use MRI to acquire quantitative deformation datathat could be used, for example, to validate computational models of flow-induced VF vibrationand quantify deformation fields encountered by cells in bioreactor studies.A low fidelity, two-dimensional, finite element model of VF flow-induced vibration wascoupled with a custom MATLAB-based genetic algorithm optimizer. The objective was to achievea closed quotient within the normal human physiological range. The results showed that changesin geometry and stiffness would lead to a model that exhibited the desired characteristics. Aphysical model based on optimized parameters was then fabricated and the closed quotient wastested. The physical model successfully vibrated with nonzero closed quotient as predicted by thecomputational model.

Vocal fold models are valuable for studying voice production. They provide an alternative method of studying the mechanics of the voice that does not require in vivo experimentation or the use of excised human or animal tissue. In this thesis, a new method of creating vocal fold models through additive manufacturing is described. The purpose of this research was to reduce model fabrication time, to decrease the number of model failures during manufacturing, and to lay the foundation for creating models with more lifelike geometric and material properties. This research was conducted in four stages. First, a suitable silicone additive manufacturing technique using a UV-curable silicone was chosen. The technique chosen was called freeform reversible embedding (FRE) and involved embedding liquid silicone material into a gel-like medium named organogel. The UV-curable silicone's material properties were identified to confirm its utility in vocal fold model design. Second, an open-source, fused deposition modeling slicing software was selected to create g-code for the printer. Applicable software settings were tuned through qualitative printing tests to find their optimal values for use in FRE printing. Third, 3D-printed cubes were used in tensile tests to characterize the material properties of FRE-printed, silicone material. The cubes were found to be anisotropic, exhibiting different modulus values corresponding to the layer orientation of the printed material. Fourth, vocal fold models were FRE-printed in two different layer orientations and were used in phonation tests to gather data for onset pressure, vibratory frequency, amplitude, and flow rate. The printed models self-oscillated and withstood the strains induced by phonation. These tests showed that layer direction affects the phonation properties of the models, demonstrating that models with layers in the coronal plane had slightly lower frequencies and onset pressures than models with layers in the sagittal plane. The models' onset pressures were higher than what is found in human vocal folds. However, their frequencies were within a comparable range. These tests showed the effectiveness of additive manufacturing in the application of vocal fold fabrication, reducing production effort by allowing researchers to go directly from model design to fabrication in a single manufacturing step. It is anticipated that this method will be modified to incorporate printing of multiple stiffnesses of silicone to better mimic the material properties of vocal fold tissue, and that the anisotropy of 3D-printed material will be leveraged to model the anisotropy of human vocal folds. This work also has potential application areas outside of voice research.

Final publication is available at http://onlinelibrary.wiley.com/doi/10.1002/term.2060/abstract;jsessionid=F0849D98381EEF9E83401A02B9042F4D.f04t02 / 京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19602号 / 医博第4109号 / 新制||医||1014(附属図書館) / 32638 / 京都大学大学院医学研究科医学専攻 / (主査)教授 別所 和久, 教授 伊佐 正, 教授 川口 義弥 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20235号 / 医博第4194号 / 新制||医||1019(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 別所 和久, 教授 鈴木 茂彦, 教授 渡邊 直樹 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Purpose: This study examined voice onset time (VOT) in children with and without vocal fold nodules (VFN). The purpose of this study was to provide further evidence regarding the need for individualized research and treatment dedicated to the pediatric population. The pediatric population has a distinctly different laryngeal mechanism than adults, as they are still developing. Although the pediatric system is anatomically different from that of a fully mature adult system, treatment for children with VFN is largely based on adult research. This study examined the VOTs of voiceless consonants, as the transition from the voiceless consonant to the subsequent vowel requires significant vocal and articulatory control and coordination. Measures of VOT change throughout the maturation as VOT follows a significant developmental pattern. Children with and without VFN were enlisted in order to examine the effects VFN have on VOT. Hypotheses: We hypothesize that children with VFN would have differences in 1) average VOT values compared to the control group, with no prediction for direction of difference (shorter and longer), and 2) between-word variability of VOT values compared to the control group, with no prediction for direction of difference (more variable and less variable). Methods: Participant data were retrospectively collected and included children between 6 and 12 years old with VFN and age- and sex-matched controls. Participants were recorded producing the six CAPE-V sentences. Four voiceless consonants were selected for VOT analysis. Praat was utilized to manually mark the vocal onset of the stop consonant by the current researcher. A previous researcher identified the vocal offset, and each placement was confirmed by the current researcher. VOT was calculated as the time between the stop consonant burst and the vocal onset of the vowel. Results: There was no significant difference between the VFN and the control groups in average VOT or VOT variability. Within the VFN group, participants who were more dysphonic (lower cepstral peak prominence (CPP) values) had more variable VOT values. Participants in the VFN group had lower CPP values than the control group, suggesting that CPP measures are a reliable indicator of dysphonia. Additionally, within the VFN group, male children had lower CPP values than female children. Conclusion: Although no group difference was found, the within-group analyses indicated that VFNs impacted productions. Children with VFN who were more dysphonic had increased VOT variability. This may suggest that VFN impact a child’s ability to phonate therefore causing more variability within productions. Future research is needed to study the impact dysphonia treatment for children with VFN may have on VOT values. Additionally, a longitudinal study of the impact of VFNs on VOT values during developmental stages may be warranted. / Public Health

No description available.

The purpose of this study was to examine the effectiveness of relative fundamental frequency (RFF) in quantifying voice disorder severity and possible change with treatment in individuals with Primary Sjögren's Syndrome (SS). Participants completed twice-daily audio recordings during an ABAB within-subjects experimental study investigating the effects of nebulized saline on voice production in this population. Voice samples of the Rainbow Passage from seven of the eight individuals with Primary SS involved in a larger investigation met inclusion criteria for analysis, for a total of 555 tokens. The results indicated that RFF values for this sample were similar to previously reported RFF values for individuals with voice disorders. RFF values improved with nebulized saline treatment but did not fall within the normal range for typical speakers. These findings were similar to other populations of voice disorders who experienced improvement, but not complete normalization, of RFF with treatment. Patient-based factors, such as age and diagnosis as well as measurement and methodological factors, might affect RFF values. The results from this study indicate that RFF is a potentially useful measure in quantifying voice production and disorder severity in individuals with Primary SS.

The voice plays a vital role in human communication. The purpose of voice research is to advance the understanding of voice production physics, with the ultimate goal of leading to improved voice care. In this research computational and synthetic vocal fold models were used to explore the role of subglottal geometry in vocal fold vibration. Three specific studies were performed. First, the effect of the inferior vocal fold surface angle on voice production was investigated using a two-dimensional self-oscillating finite element vocal fold model. Varying the inferior angle resulted in significant changes to model vibratory motion, glottal width, flow rate, and energy transfer. The changes were attributed primarily to changes in structural, rather than aerodynamic, factors. Second, subglottic stenosis (SGS) was introduced and parametrically varied in a similar computational model to determine the influence of SGS on vocal fold vibration. High severities of SGS influenced several factors related to vibration, including glottal width, flow rate, flow resistance, and vibration frequency. Subglottal pressure distributions and flow patterns were also affected. Third, the response of a self-oscillating silicone vocal fold model to varying degrees of SGS in an experimental setup was studied. Consistent with the computational SGS study, SGS had an effect on the synthetic model response at high severities. Changes were seen particularly in subglottal pressure and radiated acoustic sound, and consequently glottal efficiency, which may have important implications regarding the effect of SGS on the human voice.

Self-oscillating synthetic vocal fold (VF) models are often used to study human voice production. In this thesis, a method for fabricating multi-layer self-oscillating synthetic VF models using silicone 3D printing is presented. Multi-material 3D printing enables faster fabrication times with more complex geometries than traditional casting methods and builds a foundation for producing VF models with potentially more life-like geometries, materials, and vibratory characteristics. The printing method in this study used a custom dual extruder and slicing software to print UV-curable liquid silicone into a gel-like support matrix. The extruder was fabricated using high-torque stepper motors with high resolution leadscrews for precise extrusion and retraction. The custom slicing software accounted for challenges with printing a low-viscosity uncured silicone and was capable of allowing the user to visually observe the effects of print settings on print paths before finalizing the g-code. Three validation tests were conducted to demonstrate the 3D printer’s ability to print ultra-soft silicone with the desired range of stiffness, change between materials quickly, and print a material stiffness gradient. Two types of VF models were printed in this study, a previously-designed model with multiple distinct layers (“EPI” model), and the same model but with a vertical stiffness gradient (VSG) in the superficial lamina propria layer. The EPI model was chosen to demonstrate the ability to 3D print a multi-layer model, and the VSG model was chosen to demonstrate the ability to print multi-material VFs with geometric and material properties that are difficult to fabricate using traditional casting methods. Sixteen VFs (i.e., eight pairs) of each model type were printed, and their vibratory responses were recorded, including onset pressure, frequency, and glottal width. A micro-CT scanner was used to evaluate the external geometric accuracy of the models. One-centimeter cubes were 3D printed and tensile tested to characterize the material properties of each set of VF models. The material and phonatory properties of both the EPI and VSG VF models were found to be comparable to human data and to previous data acquired using synthetic VF models fabricated via other methods. In this thesis, the 3D printing methodology is summarized, the setup and results of the validation and VF model tests are reported and discussed, and recommendations for future work are provided.

No description available.