An excised animal larynx model has been used in many studies to better understand the physiological and anatomical properties of the human larynx. One difference between an ex vivo model and an in vivo model is that ion loss occurs postmortem. To compensate for this in the excised model, researchers most commonly use a preservation method that includes completely submerging the specimen in isotonic saline (0.9% Na+Cl-) and then flash freezing it in liquid nitrogen. The flash freezing method allows researchers to maintain the integrity of the structures while also being able to gather specimens as they become available. Not enough research has been done to understand the effects of a preservation method on the outcomes of the study. Additionally, no common method has been established for preservation across studies to ensure that results are not being influenced by this variable. This prospective, mixed experimental design study includes three groups, a control group and two experimental groups. The control group consisted of 10 bench-mounted porcine larynges that were soaked in isotonic saline and flash frozen with liquid nitrogen. Prior to the experiment, the frozen larynges were thawed overnight before trials. The other two groups consisted of 10 bench-mounted porcine larynges each; these larynges were soaked in either isotonic saline or Ringer’s solution, a balanced fluid used in vivo to counteract dehydration. Larynges from these two groups were kept fresh and stored in a refrigerator overnight before trials. On the day of experimentation, each larynx was mounted on a bench top setup including three micropositioners to stabilize, adduct, and elongate the vocal folds. All the larynges were connected to a pseudolung via the trachea and humidified air was passed through to the vocal folds until phonation was achieved. Phonatory trials consisted of brief phonation followed by 5-minute desiccation intervals until phonation was no longer achieved. Phonation threshold flow (PTF), defined as the flow observed at the onset of phonation, was observed during each phonation trial; and flow values were compared within and between groups. Statistically significant differences were found between the Ringer’s group and the fresh saline group as well as between the Ringer’s group and the frozen saline group, indicating that PTF is influenced by the larynx preservation method.

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.

An excised animal larynx model has been used in many studies to better understand the physiological and anatomical properties of the human larynx. One difference between an ex vivo model and an in vivo model is that ion loss occurs postmortem. To compensate for this in the excised model, researchers most commonly use a preservation method that includes completely submerging the specimen in isotonic saline (0.9% Na+Cl-) and then flash freezing it in liquid nitrogen. The flash freezing method allows researchers to maintain the integrity of the structures while also being able to gather specimens as they become available. Not enough research has been done to understand the effects of a preservation method on the outcomes of the study. Additionally, no common method has been established for preservation across studies to ensure that results are not being influenced by this variable. This prospective, mixed experimental design study includes three groups, a control group and two experimental groups. The control group consisted of 10 bench-mounted porcine larynges that were soaked in isotonic saline and flash frozen with liquid nitrogen. Prior to the experiment, the frozen larynges were thawed overnight before trials. The other two groups consisted of 10 bench-mounted porcine larynges each; these larynges were soaked in either isotonic saline or Ringers solution, a balanced fluid used in vivo to counteract dehydration. Larynges from these two groups were kept fresh and stored in a refrigerator overnight before trials. On the day of experimentation, each larynx was mounted on a bench top setup including three micropositioners to stabilize, adduct, and elongate the vocal folds. All the larynges were connected to a pseudolung via the trachea and humidified air was passed through to the vocal folds until phonation was achieved. Phonatory trials consisted of brief phonation followed by 5-minute desiccation intervals until phonation was no longer achieved. Phonation threshold flow (PTF), defined as the flow observed at the onset of phonation, was observed during each phonation trial; and flow values were compared within and between groups. Statistically significant differences were found between the Ringers group and the fresh saline group as well as between the Ringers group and the frozen saline group, indicating that PTF is influenced by the larynx preservation method.

Subglottic stenosis (SGS) is an abnormal narrowing of the airway at the level of the cricoid cartilage, above the first tracheal ring and immediately beneath the vocal folds. Individuals with SGS experience a reduction in their ability to breathe as well as adverse effects on voice function. SGS can result from a variety of causes with the type of treatment depending on stenosis severity. Surgical techniques such as laryngotracheal and cricotracheal reconstruction are beneficial for airway maintenance; however, these procedures have resulted in negative effects on voice production. On the other hand, there are patients with SGS who do not require surgery and still experience voice problems. The purpose of this study was to quantify the effects of SGS on vocal fold vibration using an excised larynx benchtop mechanical model. Using a within-subjects repeated measures design, nine porcine larynges underwent experimental conditions including 0% (i.e., normal airway), 50% and 75% stenosed. The primary outcome measure was phonation threshold flow (PTF), which is the rate of flow observed at the onset of phonation. For all larynges, the normal and stenosed conditions were sampled three times each and averaged. Analysis of the results revealed no statistically significant differences in PTF; however, descriptive data showed decreases in PTF and increased variability in PTF values as percent stenosis increased. These findings lay important groundwork for future research in SGS, specifically those that employ ex vivo methodologies. PTF has emerged as a promising means of quantifying voice function in addition to the traditional onset pressure measures. Future studies should examine a broader range of stenosis conditions with a larger sample size to promote generalization to clinical populations including individuals with 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.

Previous studies have found vocal fold hydration to be crucial for healthy function of the vocal mechanism. Surface tissue hydration facilitates efficient vocal fold oscillation. The composition of vocal fold surface fluid includes protective water and mucus layers, similar to the fluid that covers the mucosa and epithelia of the upper airway. Laryngeal dehydration has been linked to several factors such as mouth breathing, obstructive sleep apnea, dry air exposure, upper airway hypersensitivity, and certain diseases or behavioral voice use factors. Laryngeal dehydration affects phonation threshold pressure (PTP) and phonation threshold flow (PTF), defined as the pressure and flow observed at the onset of phonation, respectively. The application of topical nebulized isotonic saline (0.9% Na+Cl-) has been shown in previous work to decrease PTP. However, there are no studies examining the effects of aerosolized saline, administered supraglottally, on dehydrated excised porcine larynges. Examining the effects of aerosolized saline in an excised model is essential to determine any independent effects of this treatment in the absence of other physiologic mechanisms such as mucus secretion. This study sought to investigate the effects of aerosolized saline on dehydrated animal vocal folds to determine if the administration of supraglottic aerosolized saline, via a nebulizer, could reverse the adverse effects of laryngeal dehydration. The study included a prospective, mixed experimental design with two groups, one desiccation/aerosolization (A/B) group and a control (A) group, each comprised of five bench-mounted porcine larynges. Larynges in both groups received desiccated air (<1% relative humidity) supraglottally via custom tubing for 1-min doses until the vocal folds ceased audible phonation. Following the desiccation challenge, the A/B group received 2-min doses of aerosolized isotonic saline until phonation began again. The PTP and PTF were measured during phonation trials following each dose of the desiccation or aerosolization treatment. Significant changes in PTP and PTF were observed following both the dehydration and aerosolization treatment. The PTP increased significantly following the dehydration challenge and returned near baseline following the aerosolization treatment. The results of this investigation supported the hypothesis that the administration of aerosolized saline may reverse the adverse effects of vocal fold dehydration. Moreover, in a more physiologically realistic excised model, applying the mechanics of respiration, this study advanced the development of innovative theories related to the reversal of the adverse effects of dehydration, which may prevent the development of voice disorders.