Combination inhaled corticosteroids (ICs) are the primary treatment prescribed for patients with asthma; however, voice problems are also associated with ICs. In this study, 32 rabbits were assigned randomly to one of five experimental groups: baseline, induction, induction control, reversibility, and reversibility control. The baseline group received no treatment and larynges were obtained following quarantine. Rabbits belonging to experimental groups received IC treatment twice a day until trained raters noted visible vocal fold changes during endoscopy, which was performed every 2 weeks. When changes were observed, animals were euthanized, and the larynges were harvested from the experimental induction group and the corresponding control group. The remaining rabbits entered a withdrawal phase wherein ICs were discontinued, and endoscopy was performed every 2 weeks until visual-perceptual ratings indicated a return to baseline. Subsequently, all excised larynges underwent benchtop phonation trials to acquire aerodynamic data relating to vocal fold functioning at phonation onset. Analysis included 17 rabbits from the previous phase of the study and showed an increase in phonation threshold pressure (PTP) and phonation threshold flow (PTF) following IC use compared to the control groups. Rabbits in the experimental withdrawal group showed lower PTP and PTF compared to the induction group, but still greater values than the control groups. These results indicate IC-related adverse vocal effects may decrease after treatment is withdrawn but might not reverse completely. These findings indicate a trend toward recovery when ICs are withdrawn but lay critical groundwork for future studies involving asthma management and IC-driven voice disorders.

Several studies involving excised animal larynges have been performed to simulate the structural and physiological properties of the human larynx. The most common way to preserve the laryngeal tissue being studied is by immersing it in a 0.9% isotonic saline solution and then flash freezing it. Isotonic saline is used empirically to replenish the potential ion loss that occurs postmortem. Each larynx is flash frozen so it can be used at a more convenient time while still maintaining the integrity of the tissue. However, the preservation methods found in previous studies tend to vary and no consensus had been reached about which method of preservation is ideal. This study sought to investigate the effects of solution and storage on phonation threshold pressure (PTP). Phonation threshold pressure is commonly used to investigate mucosal wave of the vocal folds, prephonatory glottal width, and vocal fold cover. This study involved a prospective, mixed experimental design with three groups, including a control group and two experimental groups. Each group consisted of 10 bench-mounted porcine larynges. The control group was immersed in 0.9% isotonic saline, flash frozen with liquid nitrogen within 24 hours postmortem, and thawed overnight before the experiment. The second group was immersed in 0.9% isotonic saline and the third group was submersed in Ringer's solution. Each of these groups was kept in their solution in a refrigerator for approximately 15 hours and was used for the experiment within 24 hours postmortem. Each larynx was mounted on a bench on a tabletop with three micropositioners to adduct and elongate the vocal folds. A pseudolung connected to the trachea directed humidified air to the vocal folds subglottally until phonation was achieved. The larynges in all three groups underwent these phonatory trials with 5-minute desiccation trials between each until phonation could no longer be achieved. Phonation threshold pressure was then observed and compared within groups and between groups. The signals were obtained using MATLAB. The results indicated that PTP was lowest for the frozen versus fresh groups. PTP values increased slightly for the frozen group, but the frozen group demonstrated less variability across specimens as compared to the fresh groups. Collectively, these results indicate that there are substantial differences between fresh and frozen specimens. These differences should be considered when designing tissue studies for purposes of generalization to human phonation.

The purpose of the present study was to examine the effects of external laryngeal vibration on voice function. The current study was based on a recent pilot study using silicone vocal folds that demonstrated a decrease in phonation threshold pressure (PTP; cmH2O) when an external oscillation was applied to the vocal folds. Using a within-subjects experimental design, a custom external oscillatory device was fitted to the posterior portion of 12 excised pig larynges using a traditional benchtop phonation setup. For each larynx, phonation was elicited during 30 repeated trials, including 15 with and 15 without external oscillation. During the phonation trials, aerodynamic measures were collected. The outcome measure for this study was PTP, which has been established in the literature as being correlated with physiologic and self-perceived vocal effort. Furthermore, PTP is used routinely as an aerodynamic indicator of voice function, vocal efficiency, and the nature and severity of voice disorders. Although the aim was to quantify either positive (i.e., PTP decrease) or negative (i.e., PTP increase) effects of external oscillation on PTP, it was hypothesized that external oscillation would result in a reduction in average PTP values. The results of the study indicate that application of an external oscillatory device results in significantly lower PTP. These findings have important clinical implications for PTP signal acquisition and the potential use of external oscillation as a therapeutic tool to improve voice function.

Animal models are used extensively in voice research to study aspects of phonation, including physiology, kinematics, structure, and histology. Animals such as dog, cow, pig, sheep, deer, monkey, ferret, and rabbit have been used in voice research, with pig being one of the most common models. It is thought that the pig larynx is highly similar to the human larynx and one of the best models used in animal translational research. As with any model, however, the pig larynx does have some limitations. Perhaps a limitation most important to the rationale of this investigation is that pigs are difficult animals to study in vivo. Maintenance for a pig is challenging due to its large size and the variability of phonation use in the animal. Therefore, viable and practical alternatives are needed for in vivo voice research. The current study collected preliminary normative data from an alternate animal model, the rabbit, which has been used more recently in studies to model human phonation. The rabbit model was chosen due to its histological similarities to humans, in vivo phonation patterns, size, and practicality. The rabbit represents a more practical model for some longitudinal designs, as well as ex vivo phonatory models with aerodynamic measures as the primary variables. The current study involved a comparison of two aerodynamic measures, specifically phonation threshold pressure (PTP) and phonation threshold flow (PTF) between two groups, pig and rabbit larynges. The purpose of this study was to determine normative aerodynamic values for rabbits and to compare these with normative values for pigs during excised larynx benchtop phonation. Each group consisted of 15 larynges that were finely dissected to reveal the true vocal folds. Each larynx was then connected to a pseudolung and humidified air was passed through it. Fifteen phonation trials were elicited and the results averaged for each larynx. The results indicated that PTP and PTF were significantly different between the two groups, with PTP and PTF being lower for the rabbit group. Additionally, PTP values for rabbits were closer than pigs to the typical human value; however, some methodological challenges to rabbit benchtop models, including size and structural integrity, also exist. But the results from this study indicate that rabbits should be considered a viable option for voice research that would be more feasible with a small animal option that translates well to humans than a large animal option.

This thesis is part of a larger series of studies being conducted by Kristine Tanner, PhD, Associate Professor in the Department of Communication Disorders at Brigham Young University (BYU). The larger project is funded by the National Institute on Deafness and Other Communication Disorders at the National Institutes of Health. This thesis primarily investigated the effects of combination inhaled corticosteroids (ICs) on aerodynamic measures of the voice. In recent years, an increase in the localized laryngeal side effects from IC treatment, including dysphonia, have been reported. This study employed a between-groups experimental design, with two groups of rabbit larynges having been exposed to either ICs or nebulized isotonic saline two times each day for eight weeks at The University of Utah. For this study, the independent variable is group condition (i.e., IC versus saline) and the dependent variables are two aerodynamic measurements made at the onset of phonation using a benchtop experimental setup, namely phonation threshold pressure (PTP; cmH2O) and phonation threshold flow (PTF; L/min). The results of this study indicate a significant difference in PTP and PTF between vocal folds treated with IC as compared to vocal folds treated with nebulized isotonic saline solution. Implications of this study suggest negative changes in the voice due to IC treatment.

Hydration of the vocal folds is important for the production of normal voice. Dehydration makes voice production more difficult and increases vocal effort. Laryngeal desiccation has been shown to increase phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. Nebulized saline may reverse or offset this effect. However, few data exist regarding the effects of laryngeal desiccation and nebulized treatments in males. Further, the dose-response relationship between laryngeal desiccation and nebulized hydration treatments is unknown. This study examined the effects of two doses of nebulized isotonic saline following a laryngeal desiccation challenge in healthy male speakers. In a double-blinded, within-subjects design, 10 male college students (age range 18-26 years) attended two data collection sessions involving a 30-minute desiccation challenge followed by 3 mL or 9 mL of nebulized isotonic saline. PTP for the 10th and 80th fundamental frequency (F0) percentiles and PPE were collected before and after the desiccation challenge and at 5, 35, and 65 minutes after the nebulized treatment. PPE increased significantly following the laryngeal desiccation challenge (p < .01). Following nebulization, PPE decreased toward baseline for both doses of isotonic saline (p < .01), but failed to reverse the desiccation effect completely. No statistically significant changes in PTP occurred following the laryngeal desiccation challenge or subsequent treatments. Compared with previous research involving females, these results suggest males may respond differently to laryngeal desiccation and nebulized hydration treatments.

Vocal fold hydration is important for healthy function of the vocal mechanism. Vocal fold surface fluid protects the mucosa and facilitates efficient vocal fold oscillation. Dry air exposure, mouth breathing, insufficient intake of liquids, and behavioral factors may contribute to laryngeal dehydration. Singers are believed to be particularly at risk for voice problems related to dehydration due to environmental and voice use factors. Laryngeal desiccation and nebulized hydration treatments have been shown to influence phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. However, little research exists exploring the effects of hydration in males. Additionally, few studies have examined the dose-response relationship of hydration treatments. This investigation examined the effects of a laryngeal desiccation challenge and two different doses of nebulized isotonic saline on voice production in trained male singers. In a double-blind, within-subjects repeated measures crossover investigation, 10 male singers (ages 18 to 24) received a 30 minute laryngeal desiccation challenge followed by either 3 mL or 9 mL of nebulized isotonic saline on two consecutive weeks. PTP, PPE, and self-perceived mouth and throat dryness were sampled during the following observations: predesiccation, post-desiccation, and at 5, 35, and 65 minutes post-nebulization. No differences in PTP were observed after desiccation or nebulized treatment. PPE, however, rose significantly after desiccation and returned near baseline after treatment. No significant differences between dosages were observed.

The purpose of this study was to examine external laryngeal oscillation and its potential effects on phonation threshold pressure (PTP; cm H2O) and phonation threshold flow (PTF; L/sec). Measures of PTP and PTF have inherent limitations due to the nonlinear nature of phonation, influencing their clinical and experimental utility. This is true particularly for tracking relatively small changes in voice function because variability in the measure itself can be larger than that resulting from voice change. Elevated PTP and PTF are associated with a variety of voice disorders and correlate with self-reported vocal effort and fatigue. Prior studies involving silicone and excised animal larynges have demonstrated PTP reduction in response to external oscillation. In an extension of this work, this thesis examined external laryngeal oscillation and aerodynamic voice measures in two experiments including a translational benchtop to human approach. Experiment 1 used a within-subjects counterbalanced design to examine PTF in 12 porcine larynges. Larynges were fitted with a custom oscillation device and 30 phonation trials were conducted for each larynx, 15 with external oscillation and 15 without. Although summary statistics indicated that PTF was lower with external oscillation, differences were not significant. Experiment 2 applied a within-subjects counterbalanced design to examine PTP in four healthy adult females and one healthy adult male. Individuals produced repeated syllable strings of /pi/ productions at comfortable pitch with and without external oscillation using an electrolarynx and the second and third syllables were averaged. Descriptive analysis indicated that PTP was lowered for female participants but not the male participant. Taken together, the results of these studies offer preliminary evidence that external oscillation influences voice onset aerodynamic measures. The effects of external oscillation seem to be more evident in PTP. These findings have important clinical and research applications for PTP measurement and the potential positive influence on voice function. These preliminary results indicate the need for further research in this area.

Subglottic stenosis (SGS) is a narrowing of the airway below the vocal folds and above the trachea. This narrowing may be idiopathic or caused by scarring in the airway due to prolonged endotracheal intubation, radiation therapy, trauma, or gastroesophageal reflux disease. People who present with SGS often experience respiratory difficulty both at rest and during exertion. Breathing difficulty increases with stenosis severity. SGS is also associated with voice problems. Research has identified relationships among stenosis severity, voice function and certain types of surgical management; however, many aspects of these relationships are not fully understood due to the complexities of studying human phonation in this population. The purpose of the present study was to examine the effects of SGS on aerodynamic features of voice function using an excised larynx benchtop mechanical model. Specifically, this research involved the comparison of excised porcine vocal fold vibration at baseline and under experimental conditions of 50% and 75% stenosed. The dependent variable was phonation threshold pressure (PTP), the minimum pressure needed to initiate and maintain vocal fold vibration. PTP was analyzed for nine excised porcine larynges, sampled three times each, at baseline and the two stenosis conditions. The results of this study revealed no differences in PTP based on within-subjects comparisons. Because airflow changes with airway narrowing, this finding might indicate that other factors are responsible for the voice problems associated with SGS that were not accounted for in the current mechanical model. Vocal fold tone is not easily simulated in a benchtop setup and might be an important consideration for future studies. The quantification and manipulation of vocal fold adduction, as well as the study of high-speed imaging, could be useful in future work involving excised larynx mechanical models for the study of SGS. The results from this pilot work represent an important step toward optimizing the experimental setup for studying aerodynamic features of SGS.

Vocal fold hydration is important for efficient oscillation during voice production. Dehydration of the vocal fold surface is believed to produce adverse effects on the voice. Specifically, low environmental humidity, mouth breathing, and certain medical conditions may contribute to laryngeal and vocal fold dehydration. This dehydration effect may be quantified using the observed pressure and flow at the onset of phonation, operationally defined as phonation threshold pressure (PTP) and phonation threshold flow (PTF), respectively. Previous research has documented that nebulized isotonic saline (0.9% Na+Cl-) can reduce PTP. Additionally, the topical application of liquid saline increases vocal fold hydration in excised larynx studies. However, no studies have examined the prevention of vocal fold dehydration using aerosolized saline in an excised larynx mechanical model. The purpose of the current investigation was to determine the preventive effects of aerosolized isotonic saline in a physiologically realistic excised larynx model. Using a prospective, mixed experimental design with a control group, five bench-mounted, excised porcine larynges received 4-min doses of aerosolized saline delivered supraglottally for a total of 24 min. Subsequently, larynges received 1-min doses of desiccated air (<1% relative humidity) delivered supraglottally. A control group of five porcine larynges received only desiccated air. Phonation was attempted following each dose of aerosolized saline or desiccated air. The desiccation doses were repeated for both groups until the larynges were no longer able to phonate. The PTP and PTF were measured at baseline and following each dose of aerosolized saline or desiccated air. Analysis of the results indicated that aerosolized saline significantly delayed the adverse effects of vocal fold dehydration based on the total number of desiccation doses required to cease phonation for experimental versus control groups (p = .002). Trends demonstrated that PTP decreased after aerosolized saline and increased during desiccation trials. The PTF trends were similar during desiccation. The results from this study indicate that aerosolized saline may be used prophylactically to prevent vocal fold dehydration. These findings offer important advances in vocal fold hydration theory and dehydration prevention in a physiologically realistic excised mechanical model.