Regulation of vocal fold transepithelial water fluxes

In vitro model to evaluate effect of acidic pepsin on vocal fold barrier function

The pathophysiology of laryngopharyngeal reflux (LPR) and its impact on the vocal fold is not well understood, but may involve acid damage to vocal fold barrier functions. Two different components encompass vocal fold barrier function: the mucus barrier and tight junctions. Mucus retained on epithelial microprojections protects the inside of the vocal fold by neutralizing acidic damage. Tight junctions control permeability between cells. Here we developed an in vitro experimental system to evaluate acidic injury and repair of vocal fold barrier functions. We first established an in vitro model of rat vocal fold epithelium that could survive at least one week after barrier function maturation. The model enabled repeated evaluation of the course of vocal fold repair processes. Then, an injury experiment was conducted in which vocal fold cells were exposed to a 5-min treatment with acidic pepsin that injured tight junctions and cell surface microprojections. Both of them healed within one day of injury. Comparing vocal fold cells treated with acid alone with cells treated with acidic pepsin showed that acidic pepsin had a stronger effect on intercellular permeability than acid alone, whereas pepsin had little effect on microprojections. This result suggests that the proteolytic action of pepsin has a larger effect on protein-based tight junctions than on phospholipids in microprojections. This experimental system could contribute to a better understanding of vocal fold repair processes after chemical or physical injuries, as well as voice problems due to LPR pathogenesis.

Is It Hot or Cold? Which Humid Air Is Better for Vocal Hygiene?

OBJECTIVES

The purpose of this research is to determine which type of humid air should be suggested for vocal hygiene by demonstrating the effects of hot humid air and cold humid air on the vocal cord mucosa using different histological methods.

STUDY DESIGN

Randomized controlled study.

METHODS

Cold or hot humid air was applied to the rats for 30 minutes/day for 10 days using a humid air machine placed in a closed glass cage. The control group did not receive any treatment and were kept in their cages under normal laboratory conditions. The animals were sacrificed and their larynxes were removed on the 11th day. Histologically, lamina propria (LP) thickness was measured by Crossman's three stain and the number of mast cells in 1 square millimeter of lamina propria was measured by toluidine blue. In immunohistochemical staining, the intensity of zonula occludens-1 (ZO-1) staining was measured using a rabbit polyclonal antibody and scored from 0 (no staining) to 3 (intense staining). One-way ANOVA and Kruskal-Wallis tests were used to compare groups.

RESULTS

The mean LP thickness was thinner in rats exposed to cold humid air (CHA) than in the control group (P = 0.012). In terms of LP thickness, other intergroup comparisons (cold vs hot and control vs hot) showed no statistically significant difference between groups (P > 0.05). The mean mast cell count did not differ between groups. The hot humid air (HHA) group had more intense ZO-1 staining than the other groups (P < 0.001). There was no difference in ZO-1 staining intensity between the control group and CHA group.

CONCLUSION

HHA and CHA administration had no negative effects on inflammatory findings in the vocal cords (mast cell count or LP thickness). While HHA appears to strengthen the epithelial barrier (denser ZO-1 staining), the physiologic outcomes, such as bronchoconstriction, should be cautiously assessed.

Sensory Innervation of the Larynx and the Search for Mucosal Mechanoreceptors

Purpose The larynx is a uniquely situated organ, juxtaposed between the gastrointestinal and respiratory tracts, and endures considerable immunological challenges while providing reflexogenic responses via putative mucosal mechanoreceptor afferents. Laryngeal afferents mediate precise monitoring of sensory events by relay to the internal branch of the superior laryngeal nerve (iSLN). Exposure to a variety of stimuli (e.g., mechanical, chemical, thermal) at the mucosa-airway interface has likely evolved a diverse array of specialized sensory afferents for rapid laryngeal control. Accordingly, mucosal mechanoreceptors in demarcated laryngeal territories have been hypothesized as primary sources of sensory input. The purpose of this article is to provide a tutorial on current evidence for laryngeal afferent receptors in mucosa, the role of mechano-gated ion channels within airway epithelia and mechanisms for mechanoreceptors implicated in laryngeal health and disease. Method An overview was conducted on the distribution and identity of iSLN-mediated afferent receptors in the larynx, with specific focus on mechanoreceptors and their functional roles in airway mucosa. Results/Conclusions Laryngeal somatosensation at the cell and molecular level is still largely unexplored. This tutorial consolidates various animal and human researches, with translational emphasis provided for the importance of mucosal mechanoreceptors to normal and abnormal laryngeal function. Information presented in this tutorial has relevance to both clinical and research arenas. Improved understanding of iSLN innervation and corresponding mechanotransduction events will help shed light upon a variety of pathological reflex responses, including persistent cough, dysphonia, and laryngospasm.

A Comparison of the Localization of Integral Membrane Proteins in Human and Rabbit Vocal Folds

OBJECTIVES

This study's objective was to identify and compare the localization of Aquaporin (AQP) 1, 4, 7, Na+/K + -ATPase, E-cadherin, zona occludin (ZO)-1, and occludin in human and rabbit vocal folds (VF)s to inform the design of future studies to explore the function of these proteins in the regulation of VF homeostasis.

METHODS

Four human larynges and five New Zealand white rabbit larynges were used. Samples were immunolabeled for primary antibodies against AQP1, AQP4, AQP7, the alpha subunit of Na+/K + -ATPase, E-cadherin, and ZO-1 and occludin and then captured digitally using a Nikon Eclipse 90i microscope and Hamamatsu C10600 Camera. Two raters familiar with human and rabbit VF histology identified positive labeling in tissue structures, including the apical epithelium, basal epithelium/basement membrane, and lamina propria (LP).

RESULTS

Samples from both species showed positive labeling for AQP1 in the basal epithelium/basement membrane, superficial LP, and deep/intermediate LP. Aquaporin 4, Aquaporin 7, Na+/K + -ATPase, and E-cadherin were primarily localized to the epithelium of both species. Zona occludin-1 was primarily localized apical epithelium and the superficial LP of both species. Occludin was primarily present in the apical epithelium in rabbit samples but not human.

CONCLUSION

These data provide evidence of the presence of key ion transport channels and cell adhesion proteins in human and rabbit VFs. Aquaporin 1, 4, 7, Na+/K + -ATPase, E-cadherin, and ZO-1 were similarly localized in both species. These findings will be useful to investigators interested in the exploration of VF homeostasis and barrier integrity in future studies.

LEVEL OF EVIDENCE

N/A Laryngoscope, 131:E1265-E1271, 2021.

Unraveling the molecular pathobiology of vocal fold systemic dehydration using an in vivo rabbit model

Vocal folds are a viscoelastic multilayered structure responsible for voice production. Vocal fold epithelial damage may weaken the protection of deeper layers of lamina propria and thyroarytenoid muscle and impair voice production. Systemic dehydration can adversely affect vocal function by creating suboptimal biomechanical conditions for vocal fold vibration. However, the molecular pathobiology of systemically dehydrated vocal folds is poorly understood. We used an in vivo rabbit model to investigate the complete gene expression profile of systemically dehydrated vocal folds. The RNA-Seq based transcriptome revealed 203 differentially expressed (DE) vocal fold genes due to systemic dehydration. Interestingly, function enrichment analysis showed downregulation of genes involved in cell adhesion, cell junction, inflammation, and upregulation of genes involved in cell proliferation. RT-qPCR validation was performed for a subset of DE genes and confirmed the downregulation of DSG1, CDH3, NECTIN1, SDC1, S100A9, SPINK5, ECM1, IL1A, and IL36A genes. In addition, the upregulation of the transcription factor NR4A3 gene involved in epithelial cell proliferation was validated. Taken together, these results suggest an alteration of the vocal fold epithelial barrier independent of inflammation, which could indicate a disruption and remodeling of the epithelial barrier integrity. This transcriptome provides a first global picture of the molecular changes in vocal fold tissue in response to systemic dehydration. The alterations observed at the transcriptional level help to understand the pathobiology of dehydration in voice function and highlight the benefits of hydration in voice therapy.

Impact of Vocal Fold Dehydration on Vocal Function and Its Treatment

The change of vocal function after vocal fold dehydration due to dryness was discussed along with the treatment effect of different atomizing agents. Forty-eight staffs from The Central Hospital of Wuhan were recruited. All volunteers breathed dry air for vocal fold dehydration. After dry air inhalation, the subjects were randomly divided into four groups, with 12 cases each. Three groups were treatment groups, receiving 0.9% normal saline (IS), 5% hypertonic saline (HS) and double-distilled water (SW) atomizing inhalation therapy, respectively, and the last group was the control group without treatment. Voice data were collected for all subjects before and immediately after dry air inhalation using the Multi-Dimensional Voice Program (MDVP) system. Atomizing inhalation therapy was given 10 min after dry air inhalation, and voice data were collected using MDVP system at the following time points after atomizing inhalation treatment: 5 min, 20 min, 35 min, 50 min, 65 min, 80 min, 95 min, 110 min. In the control group, voice data were collected at the same time points and compared with those of treatment groups. The vocal function parameters collected before and after dry air inhalation as well as after treatment were subjected to test using SPSS 16.0 software. In the four groups, jitter (fundamental frequency perturbation), shimmer (amplitude perturbation), and amplitude perturbation quotient (APQ) were significantly increased after dry air inhalation (P<0.05). In IS, HS and SW groups, after atomizing inhalation treatment, there was an obvious reduction in jitter, shimmer and APQ, showing significant differences as compared with those after dry air inhalation (P<0.05). Moreover, these parameters were significantly lower than those in the control group (P<0.05). The jitter, shimmer and APQ in the IS group were significantly lower than those in the HS and SW groups (P<0.05). We are led to a conclusion: Vocal fold dehydration induced by dryness can reduce the stability of voice; such decreased voice stability can be improved by atomizing inhalation therapy; without proper treatment, voice stability caused by vocal fold dehydration cannot heal spontaneously; of three atomizing agents namely, IS, HS and SW, IS had the best treatment effect for decreased voice stability caused by vocal fold dehydration.

Magnetic resonance imaging quantification of dehydration and rehydration in vocal fold tissue layers

Clinicians commonly recommend increased hydration to patients with voice disorders. However, effects on clinical voice outcome measures have been inconsistent. Hydration-induced change within different layers of vocal fold tissue is currently unknown. Magnetic Resonance Imaging (MRI) is a promising method of noninvasively measuring water content in vocal folds. We sought to image and quantify changes in water content within vocal fold mucosa and thyroarytenoid muscle after dehydration and rehydration. Excised porcine larynges were imaged using proton density (PD) weighted MRI (1) at baseline and (2) after immersion in one of five hypertonic, isotonic, or hypotonic solutions or in dry air. Larynges dehydrated in hypertonic solutions or dry air were rehydrated and imaged a third time. Scans revealed fluid-rich vocal fold mucosa that was distinct from muscle at baseline. Baseline normalized signal intensity in mucosa and muscle varied by left vs. right vocal fold (p < 0.01) and by anterior, middle, or posterior location (p < 0.0001). Intensity changes in the middle third of vocal fold mucosa differed by solution after immersion (p < 0.01). Hypertonic solutions dehydrated the middle third of mucosa by over 30% (p < 0.001). No difference from baseline was found in anterior or posterior mucosa or in muscle after immersion. No association was found between intensity change in mucosa and muscle after immersion. After rehydration, intensity did not differ by solution in any tissue, and was not different from baseline, but post-rehydration intensity was correlated with post-immersion intensity in both mucosa and muscle (p < 0.05), suggesting that degree of change in vocal fold water content induced by hypertonic solutions ex vivo persists after rehydration. These results indicate that PD-MRI can be used to visualize large mammalian vocal fold tissue layers and to quantify changes in water content within vocal fold mucosa and thyroarytenoid muscle independently.

The effect of electrolyte balance on the voice in hemodialysis patients

OBJECTIVE

The aim of the study was to demonstrate the effect of blood electrolytes on the voice in chronic hemodialysis patients.

METHODS

The study included a total of 59 hemodialysis patients. Pre- and post-dialysis voice recordings were performed. In the analysis of vocal acoustic parameters, fundamental frequency (F0), jitter, shimmer, the noise-to-harmonics ratio (NHR), and F0 minimum and F0 maximum were measured. The Voice Handicap Index-10 (VHI-10), and maximum phonation time (MPT) were evaluated. For perceptual evaluation, the GRBAS scale was used. The duration of dialysis (years) and changes in weight during dialysis were recorded for each patient. From venous blood samples, measurements were taken of hemoglobin (Hb), albumin, Na+, K+, creatinine, uric acid, phosphorus, Ca++, and parathormone.

RESULTS

The difference in the pre and post-dialysis values of F0, shimmer, NHR and MPT were found to be statistically significant (p = 0.001). The only variable determined to have an effect on the change in F0 values was uric acid, and the change in the F0 values was statistically significant (p = 0.009). The only variable determined to have an effect on the change in shimmer values was sodium, and the change was statistically significant (p = 0.034). The only variable determined to have an effect on the change in NHR values was creatinine, and the change in the NHR values was statistically significant (p = 0.028). Hb and the duration of dialysis were determined to have a statistically significant effect on the change in MPT values (p = 0.001).

CONCLUSIONS

The results showed that uric acid was the agent creating a reduction in vocal cord vibration, the agent increasing the difference between vibration waves was Na+, and creatinine increased the NHR rate. The effect of these variables can be considered important in the understanding of vocal cord physiology.

In vivo measurement of vocal fold surface resistance

OBJECTIVES/HYPOTHESIS

A custom-designed probe was developed to measure vocal fold surface resistance in vivo. The purpose of this study was to demonstrate proof of concept of using vocal fold surface resistance as a proxy of functional tissue integrity after acute phonotrauma using an animal model.

STUDY DESIGN

Prospective animal study.

METHODS

New Zealand White breeder rabbits received 120 minutes of airflow without vocal fold approximation (control) or 120 minutes of raised intensity phonation (experimental). The probe was inserted via laryngoscope and placed on the left vocal fold under endoscopic visualization. Vocal fold surface resistance of the middle one-third of the vocal fold was measured after 0 (baseline), 60, and 120 minutes of phonation. After the phonation procedure, the larynx was harvested and prepared for transmission electron microscopy.

RESULTS

In the control group, vocal fold surface resistance values remained stable across time points. In the experimental group, surface resistance (X% ± Y% relative to baseline) was significantly decreased after 120 minutes of raised intensity phonation. This was associated with structural changes using transmission electron microscopy, which revealed damage to the vocal fold epithelium after phonotrauma, including disruption of the epithelium and basement membrane, dilated paracellular spaces, and alterations to epithelial microprojections. In contrast, control vocal fold specimens showed well-preserved stratified squamous epithelia.

CONCLUSIONS

These data demonstrate the feasibility of measuring vocal fold surface resistance in vivo as a means of evaluating functional vocal fold epithelial barrier integrity. Device prototypes are in development for additional testing, validation, and for clinical applications in laryngology.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:E364-E370, 2017.

Shifts in Biochemical Markers Associated with Wound Healing in Laryngeal Secretions following Phonotrauma: A Preliminary Study

The current study sought to determine whether shifts in key components of the inflammatory process could be detected from laryngeal secretions sampled before and after vocal loading. A healthy 44-year-old woman served as the subject. The vocal folds were swabbed to collect baseline secretions. Ten and 20 minutes after nearly constant loud phonation for 1 hour, the vocal folds were swabbed again. The findings indicated strong shifts in several key inflammatory mediators: interleukin-1beta, tumor necrosis factor alpha, and matrix metalloproteinase 8. The concentrations of those mediators continued to increase from the 10- to 20-minute postloading time-points. Transforming growth factor beta and prostaglandin E2 did not demonstrate clear shifts. In summary, mediators reflecting the acute inflammatory process could be detected from laryngeal secretions in an awake human. The upward slope of the curves at the 20-minute time interval indicates the need for longer follow-up sampling to determine the full biological response of the vocal folds to acute phonotrauma.

Silence and Voicing Accumulations in Italian Primary School Teachers With and Without Voice Disorders

OBJECTIVES

The relationship between the silence and voicing accumulations of primary school teachers and the teachers' clinical status was examined to determine whether more voicing accumulations and fewer silence accumulations were measured for the vocally unhealthy subjects than for the healthy subjects, which would imply more vocal loading and fewer short-term recovery moments.

METHODS

Twenty-six Italian primary school teachers were allocated by clinicians to three groups: (1) with organic voice disorders, (2) with subjectively mild organic alteration or functional voice symptoms, and (3) normal voice quality and physiology. Continuous silence and voicing periods were measured with the APM3200 during the teachers' 4-hour workdays. The accumulations were grouped into seven time intervals, ranging from 0.03-0.9 to 3.16-10 seconds, according to Italian prosody. The effects of group on silence and voicing accumulations were evaluated.

RESULTS

Regarding silence accumulations, Group 1 accumulated higher values in intervals between 0.1 and 3.15 seconds than other groups, whereas Groups 2 and 3 did not differ from each other. Voicing accumulations between 0.17 and 3.15 seconds were higher for subjects with a structural disorder. A higher time dose was accumulated by these subjects (40.6%) than other subjects (Group 2, 31.9%; Group 3, 32.3%).

CONCLUSIONS

Although previous research has suggested that a rest period of a few seconds may produce some vocal fatigue recovery, these results indicate that periods shorter than 3.16 seconds may not have an observable effect on recovery. The results provide insight into how vocal fatigue and vocal recovery may relate to voice disorders in occupational voice users.

Basic Science: The Foundation of Evidence-Based Voice Therapy

Basic science research is part of the circle of translational research that provides the scientific underpinning for evidence-based practice. The translation from bench to bedside, however, is sometimes not obvious. This short review seeks to demonstrate ways in which basic science can inform our clinical practice as voice therapists. From in vitro molecular and cellular studies to in vivo animal models, basic science can investigate biological mechanisms of vocal health, such as vocal fold hydration, and voice use, such as voice rest and vocal exercise, in ways that are impossible in human clinical studies. Knowledge of these mechanisms inform and guide our clinical investigations and help provide evidence for behavioral voice therapy.

In vivo investigation of acidified pepsin exposure to porcine vocal fold epithelia

OBJECTIVES/HYPOTHESIS

The study objective was to investigate epithelial changes in response to direct, repeated, acidified pepsin exposures in an in vivo porcine model. We hypothesized that 12 acidified pepsin applications to simulate reflux would elicit a vocal fold response characterized by inflammation, epithelial proliferation, and increased intercellular space, as well as changes in the gene expression of epithelial junctional proteins, ion transporter proteins, and proinflammatory cytokines.

STUDY DESIGN

Prospective, in vivo study.

METHODS

Pigs received acidified pepsin (pH = 4) or saline (sham) applied directly to vocal folds. Larynges were collected following three exposures per week for 4 weeks. Vocal fold tissue morphology, collagen, and elastin were evaluated histologically. Gene expression of E-cadherin, zona occludens-1, cystic fibrosis transmembrane conductance regulator, epithelial sodium channel, interleukin-1β, tumor necrosis factor-α, and interferon-γ were measured. Ultrastructural alterations, epithelial intercellular space diameter, and microridge height were measured using transmission electron microscopy.

RESULTS

There were no significant differences in histology, gene transcripts, epithelial ultrastructure, intercellular space, and microridge height after acidified pepsin exposure.

CONCLUSIONS

Twelve simulated reflux challenges were insufficient to elicit epithelial changes, demonstrating the resistance of healthy vocal folds to direct, repeated acidified pepsin exposures. These data increase our understanding of healthy vocal fold defenses and lay the groundwork for a prospective, uninjured, nonsurgical, laryngopharyngeal reflux model where pigs can be exposed directly to acidified pepsin.

Utility of cell viability assays for use with ex vivo vocal fold epithelial tissue

OBJECTIVES/HYPOTHESIS

Ex vivo models are routinely used to investigate the barrier function of the vocal fold epithelium. However, there are limited reports on assays that can be used to investigate the effect of clinically relevant challenges on vocal fold epithelial tissue viability. Our objective was to determine the utility of two assays routinely used in cell culture-a cellular metabolic activity assay and a cell membrane integrity assay-to investigate the viability of ex vivo porcine vocal fold epithelium.

STUDY DESIGN

Prospective, ex vivo animal study.

METHODS

Porcine vocal folds were exposed to acrolein, hydrochloric acid, or hydrogen peroxide challenge. An untreated, sham challenge was included as a control. Assays including metabolic activity, cell membrane integrity, and histology were used to determine whether challenges reduced epithelial viability as compared to sham.

RESULTS

Cell membrane integrity and metabolic activity assays detected reductions in viability following hydrochloric acid and hydrogen peroxide challenges but not acrolein challenge as compared to sham. No challenge produced significant changes in epithelial appearance as evidenced by light microscopy.

CONCLUSIONS

Metabolic activity and cell membrane integrity assays are valuable tools that can be used to evaluate the viability of ex vivo vocal fold epithelial tissue following clinically relevant challenges. As viability is reduced, the ability of epithelial tissue to maintain its barrier function is compromised. Accurate assessment of viability may provide us clues into understanding mechanisms underlying vocal fold epithelial injury and disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 125:E180-E185, 2015.

Bicarbonate availability for vocal fold epithelial defense to acidic challenge

OBJECTIVES

Bicarbonate is critical for acid-base tissue homeostasis. In this study we investigated the role of bicarbonate ion transport in vocal fold epithelial defense to acid challenges. Acidic insults to the larynx are common in gastric reflux, carcinogenesis and metastasis, and acute inflammation.

METHODS

Ion transport was measured in viable porcine vocal fold epithelium. First, 18 vocal folds were exposed to either the carbonic anhydrase antagonist acetazolamide or to vehicle. Second, 32 vocal folds were exposed to either a control buffer or a bicarbonate-free buffer on their luminal or basolateral surface or both. Third, 32 vocal folds were challenged with acid in the presence of bicarbonate-free or control buffer.

RESULTS

The vocal fold transepithelial resistance was greater than 300 Ω*cm(2), suggesting robust barrier integrity. Ion transport did not change after exposure to acetazolamide (p > 0.05). Exposure to bicarbonate-free buffer did not compromise vocal fold ion transport (p > 0.05). Ion transport increased after acid challenge. This increase approached statistical significance and was the greatest for the control buffer and for the bicarbonate-free buffer applied to the basolateral surface.

CONCLUSIONS

Bicarbonate secretion may contribute to vocal fold defense against acid challenge. Our data offer a potential novel role for bicarbonate as a therapeutic agent to reduce pH abnormalities in the larynx and prevent associated pathological changes.

Vocal fold epithelial barrier in health and injury: a research review

PURPOSE

Vocal fold epithelium is composed of layers of individual epithelial cells joined by junctional complexes constituting a unique interface with the external environment. This barrier provides structural stability to the vocal folds and protects underlying connective tissue from injury while being nearly continuously exposed to potentially hazardous insults, including environmental or systemic-based irritants such as pollutants and reflux, surgical procedures, and vibratory trauma. Small disruptions in the epithelial barrier may have a large impact on susceptibility to injury and overall vocal health. The purpose of this article is to provide a broad-based review of current knowledge of the vocal fold epithelial barrier.

METHOD

A comprehensive review of the literature was conducted. Details of the structure of the vocal fold epithelial barrier are presented and evaluated in the context of function in injury and pathology. The importance of the epithelial-associated vocal fold mucus barrier is also introduced.

RESULTS/CONCLUSIONS

Information presented in this review is valuable for clinicians and researchers as it highlights the importance of this understudied portion of the vocal folds to overall vocal health and disease. Prevention and treatment of injury to the epithelial barrier is a significant area awaiting further investigation.

Structural and functional vocal fold epithelial integrity following injury

OBJECTIVES/HYPOTHESIS

An intact epithelium is an important part of vocal fold defense. Damage to the epithelium can compromise vocal fold homeostasis and protection of the host tissue from viral and bacterial invasion. Elucidating the effects of damage on epithelial architectural and barrier integrity provides insight into the role of epithelium in protecting vocal folds. Using an animal model, we evaluated the time course of structural and functional epithelial restoration following injury.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Forty rats underwent surgery to remove vocal fold mucosa unilaterally. Larynges were harvested at five time intervals between 3 to 90 days postinjury and were prepared for histological and permeability analyses.

RESULTS

Rapid restoration of structural integrity was demonstrated by return of a multilayerd epithelium, intercellular junctions, and basement membrane at 5 days postinjury. Atypical epithelial permeability was observed up to 5 weeks postinjury.

CONCLUSION

Restoration of epithelial barrier integrity lags epithelial structural restoration. Consequently, epithelial regeneration cannot be equated with return of functional barrier integrity. Rather, ongoing leakiness of regenerated epithelium indicates that vocal folds remain at risk for damage, pathogen invasion, and remodeling postinjury.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 124:2764-2769, 2014.

Quantification of acute vocal fold epithelial surface damage with increasing time and magnitude doses of vibration exposure

Because the vocal folds undergo repeated trauma during continuous cycles of vibration, the epithelium is routinely susceptible to damage during phonation. Excessive and prolonged vibration exposure is considered a significant predisposing factor in the development of vocal fold pathology. The purpose of the present study was to quantify the extent of epithelial surface damage following increased time and magnitude doses of vibration exposure using an in vivo rabbit phonation model. Forty-five New Zealand white breeder rabbits were randomized to nine groups and received varying phonation time-doses (30, 60, or 120 minutes) and magnitude-doses (control, modal intensity phonation, or raised intensity phonation) of vibration exposure. Scanning electron microscopy and transmission electron microscopy was used to quantify the degree of epithelial surface damage. Results revealed a significant reduction in microprojection density, microprojection height, and depth of the epithelial surface with increasing time and phonation magnitudes doses, signifying increased epithelial surface damage risk with excessive and prolonged vibration exposure. Destruction to the epithelial cell surface may provide significant insight into the disruption of cell function following prolonged vibration exposure. One important goal achieved in the present study was the quantification of epithelial surface damage using objective imaging criteria. These data provide an important foundation for future studies of long-term tissue recovery from excessive and prolonged vibration exposure.

Vocal function and upper airway thermoregulation in five different environmental conditions

PURPOSE

Phonation threshold pressure and perceived phonatory effort were hypothesized to increase and upper airway temperature to decrease following exposure to cold and/or dry air. Greater changes were expected with mouth versus nose breathing.

METHOD

In a within-participant repeated measures design, 15 consented participants (7 men, 8 women) completed 20-min duration trials to allow for adequate thermal equilibration for both nose and mouth breathing in 5 different environments: 3 temperatures (°C) matched for relative humidity (% RH), cold (15 °C, 40% RH), thermally neutral (25 °C, 40% RH), and hot (35 °C, 40% RH); and 2 temperatures with variable relative humidity to match vapor pressure for the neutral environment (25 °C, 40% RH), cold (15 °C, 74% RH) and hot (35 °C, 23% RH). Following each equilibration trial, measures were taken in this order: upper airway temperature (transnasal thermistor probe), phonation threshold pressure, and perceived phonatory effort.

RESULTS

Data were analyzed using repeated measures analysis of variance, and no significant differences were established.

CONCLUSIONS

The study hypotheses were not supported. Findings suggest that the upper airway is tightly regulated for temperature when challenged by a realistic range of temperature and relative humidity environments. This is the first study of its kind to include measurement of upper airway temperature in conjunction with measures of vocal function.

Human embryonic stem cell-derived epithelial cells in a novel in vitro model of vocal mucosa

A satisfactory in vitro model of vocal fold mucosa does not exist, thus precluding a systematic, controlled study of vocal fold biology and biomechanics. We sought to create a valid, reproducible three-dimensional (3D) in vitro model of human origin of vocal fold mucosa of human origin. We hypothesized that coculture of human embryonic stem cell (hESC)-derived simple epithelial cells with primary vocal fold fibroblasts under appropriate conditions would elicit morphogenesis of progenitor cells into vocal fold epithelial-like cells and creation of a basement membrane. Using an in vitro prospective study design, hESCs were differentiated into cells that coexpressed the simple epithelial cell marker, keratin 18 (K18), and the transcription factor, p63. These simple epithelial cells were cocultured with primary vocal fold fibroblasts seeded in a collagen gel scaffold. The cells were cultured for 3 weeks in a keratinocyte medium at an air-liquid interface. After that time, the engineered mucosa demonstrated a stratified, squamous epithelium and a continuous basement membrane recapitulating the key morphologic and phenotypic characteristics of native vocal fold mucosa. hESC-derived epithelial cells exhibited positive staining for vocal fold stratified, squamous epithelial markers, keratin 13 (K13) and 14 (K14), as well as tight junctions, adherens junctions, gap junctions, and desmosomes. Despite the presence of components critical for epithelial structural integrity, the epithelium demonstrated greater permeability than native tissue indicating compromised functional integrity. While further work is warranted to improve functional barrier integrity, this study demonstrates that hESC-derived epithelial progenitor cells can be engineered to create a replicable 3D in vitro model of vocal fold mucosa featuring a multilayered, terminally differentiated epithelium.

Quantifying the effects of altering ambient humidity on ionic composition of vocal fold surface fluid

OBJECTIVES/HYPOTHESIS

Vocal fold surface fluid (VFSF) is important in hydration and defense of underlying epithelial cells. The objective of this study was to quantify changes in the ionic composition of VFSF after altering the humidity of inhaled air. We tested the hypothesis that low humidity exposure would increase the concentration of VFSF sodium (Na(+)) and chloride (Cl(-)) ions but that high humidity exposure would decrease the concentration of VFSF Na(+) and Cl(-) ions as compared to the low humidity challenge.

STUDY DESIGN

Prospective design.

METHODS

Eighteen healthy adults participated in this study. VFSF was collected from each subject at baseline and following exposure to low humidity and high humidity environments. VFSF Na(+) concentration was assessed using inductively coupled plasma mass spectrometry. VFSF Cl(-) concentration was measured with indirect potentiometry. All analyses were completed by personnel blinded to the hypothesis being tested.

RESULTS

The low humidity environment increased Na(+) concentration in the majority of the subjects. Data for changes in Cl(-) concentrations were variable. Overall the data did not reach statistical significance (P > .05). Subjective impressions suggested that VFSF collection was more difficult in low humidity as compared to the high humidity and baseline conditions.

CONCLUSIONS

This study is the first attempt to measure the ionic concentration of VFSF. The results from the current study have important implications for future programmatic research quantifying the effects of pollutants and laryngopharyngeal reflux on VFSF composition, epithelial hydration, and vocal fold defense.

Localization and regulation of aquaporins in the murine larynx

CONCLUSION

Expression of aquaporins (AQPs) in the vocal folds and the parasympathetic regulation of AQPs in the laryngeal glands may be important for controlling laryngeal secretion and vocal fold hydration. These findings are thought to be an initial step towards understanding potential mechanisms of water flow through the vocal fold surface.

OBJECTIVES

Lubrication of the vocal folds is important for phonation and laryngeal defense. However, the system of water transport in the laryngeal epithelium has not yet been clarified. We investigated the expression of AQP water channnels (AQP1-9) in the murine larynx and examined the neural regulating mechanisms of these subtypes.

METHODS

The distribution of AQPs (AQP1-9) in the murine larynx was examined by immunohistochemistry. Next, the neural mechanism regulating AQPs in the larynx was investigated using unilaterally vagotomized mice.

RESULTS

AQP1, 4, and 5 were expressed in the laryngeal epithelium including the vocal folds. Vocal fold AQP expression was minimal at the vocal process. AQP2, 3, 5, 6, 7, and 8 were localized to the submucosal glands. Expression of AQPs in the vagotomized region was significantly decreased compared with the contralateral intact side. The expression in the laryngeal glands was also decreased in the aged mice.

Tight junction-related barrier contributes to the electrophysiological asymmetry across vocal fold epithelium

Electrophysiological homeostasis is indispensable to vocal fold hydration. We investigate tight junction (TJ)-associated components, occludin and ZO-1, and permeability with or without the challenge of a permeability-augmenting agent, histamine. Freshly excised ovine larynges are obtained from a local abattoir. TJ markers are explored via reverse transcriptase polymerase chain reaction (RT-PCR). Paracellular permeabilities are measured in an Ussing system. The gene expression of both TJ markers is detected in native ovine vocal fold epithelium. Luminal histamine treatment significantly decreases transepithelial resistance (TER) (N = 72, p<0.01) and increases penetration of protein tracer (N = 35, p<0.001), respectively, in a time-, and dose-dependent fashion. The present study demonstrates that histamine compromises TJ-related paracellular barrier across vocal fold epithelium. The detection of TJ markers indicates the existence of typical TJ components in non-keratinized, stratified vocal fold epithelium. The responsiveness of paracellular permeabilities to histamine would highlight the functional significance of this TJ-equivalent system to the electrophysiological homeostasis, which, in turn, regulates the vocal fold superficial hydration.

The effects of cigarette smoke condensate on vocal fold transepithelial resistance and inflammatory signaling in vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

In response to chronic cigarette smoke exposure, a subset of patients present with edematous vocal folds, characteristically referred to as Reinke's edema. This phenotype differs from the tissue changes associated with prolonged smoke exposure in the lower airway, and the mechanism underlying Reinke's edema remains poorly described. We hypothesize that the effects of smoke are diffuse and involve both the epithelium and mucosa.

STUDY DESIGN

In vitro, ex vivo experiment.

METHODS

Transepithelial resistance (R(T) ) was quantified in an ex vivo, viable, porcine vocal fold model. Excised tissue was exposed to cigarette smoke condensate (CSC) and R(T) was computed at baseline and 1 and 4 hours after exposure. In vitro, human vocal fold fibroblasts were exposed to CSC. Cyclooxygenase 2 (COX-2), microsomal prostaglandin E synthase-1, and 15-hydroxyprostaglandin dehydrogenase mRNA expression were assessed at 4 hours. Prostaglandin E2 (PGE2) synthesis was quantified via immunoassay following 24 hours of CSC exposure.

RESULTS

CSC had no effect on R(T) . CSC did, however, induce COX-2 mRNA expression as well as its downstream lipid mediator PGE2. PGE2 metabolism appears to be regulated via both synthetic and degradative enzymes in response to cigarette smoke.

CONCLUSIONS

In vitro, CSC initiates an inflammatory response in vocal fold fibroblasts. However, in isolation, the epithelial resistance is not altered by CSC, at least acutely. These data may suggest a role for the interaction between the inflammatory response in the mucosa and compromised epithelial barrier function, as has been shown in other tissues.

Nebulized isotonic saline versus water following a laryngeal desiccation challenge in classically trained sopranos

PURPOSE

To examine the effects of nebulized isotonic saline (IS) versus sterile water (SW) on self-perceived phonatory effort (PPE) and phonation threshold pressure (PTP) following a surface laryngeal dehydration challenge in classically trained sopranos.

METHOD

In a double-blind, within-subject crossover design, 34 sopranos breathed dry air (relative humidity < 1%) transorally for 15 min and then nebulized 3 mL of IS or SW, or experienced a no-treatment control condition over 3 consecutive weeks. PPE and PTP were measured every 15 min from baseline through 2 hr postdesiccation.

RESULTS

PPE increased significantly following the laryngeal desiccation challenge in all 3 treatment conditions (p < .01). After nebulization, PPE returned to baseline for the IS condition only. For the SW and control conditions, PPE remained above baseline during the 2 hr after desiccation. No statistically significant changes in PTP following laryngeal desiccation were observed, although values for the IS condition remained below baseline for nearly 2 hr after nebulization. PPE and PTP were not significantly correlated.

CONCLUSIONS

Following a laryngeal surface dehydration challenge, classically trained sopranos reported increased vocal effort that persisted for at least 2 hr. Compared with SW, nebulized IS showed promise as an effective way to remediate the adverse, self-perceived effects of laryngeal desiccation.

A meta-analysis of outcomes of hydration intervention on phonation threshold pressure

OBJECTIVES

Vocal fold hydration is purported to promote optimal biomechanical characteristics of vocal fold mucosa, increase efficiency of vocal fold oscillation, and enhance voice quality. The purpose of this work was to determine the magnitude and consistency of the effect of vocal fold hydration on vocal fold function across published clinical studies.

METHODS

We completed a comprehensive meta-analysis of the effects of superficial and systemic vocal fold hydration on phonation threshold pressure (PTP), a measure of efficiency of voice production.

RESULTS

We identified 34 studies that examined the effects of hydration on vocal function. Of these studies, 14 examined the effects of hydration on PTP. Nine of these articles met the criteria for inclusion in this analysis. We observed an average effect size of 0.33, indicating that, overall, hydration treatment demonstrated a tendency to reduce PTP. However, this decrease in phonatory effort did not reach significance at the 95% confidence level. The effects of hydration intervention varied considerably across studies (-0.19 to 3.96). We considered that two factors, pitch level of the task and vocal health of participants, may have contributed to this variability in findings. However, our analysis found that these factors could not account for differences in effect size.

CONCLUSION

To understand the variability in outcomes across studies, the role of factors that may impact the effects of hydration, such as the amount, type, and duration of intervention, must be determined. Only then can we obtain data to guide best clinical practice for protecting and rehabilitating vocal function.

E-cadherin and transglutaminase-1 epithelial barrier restoration precedes type IV collagen basement membrane reconstruction following vocal fold mucosal injury

The vocal fold epithelium is critical to upper airway immunologic defense and water/ion transport; therefore, any form of physical trauma or insult increases the vulnerability of this structure to functional impairment and pathogen invasion/infection. In this study, we examined the reestablishment of epithelial and basement membrane barrier structures in a well-established rat model of vocal fold mucosal injury. We observed active cell recruitment culminating in peak hyperplasia at 3 days postinjury, the establishment of robust E-cadherin+ and transglutaminase-1+ biochemical barrier signals along the epithelial surface by 3 days postinjury, and the persistent absence of a type IV collagen+ basement membrane at 7 days postinjury. The distinct spatial and temporal immunoactivity of these molecules is consistent with a programmed repair process driving the restoration of vocal fold mucosal integrity and permeability. These data may inform future efforts to optimize functional mucosal recovery postinjury and avoid undesirable events such as barrier compromise or epithelial metaplasia.

Simulated reflux decreases vocal fold epithelial barrier resistance

OBJECTIVES/HYPOTHESIS

The vocal fold epithelium provides a barrier to the entry of inhaled and systemic challenges. However, the location of the epithelium makes it vulnerable to damage. Past research suggests, but does not directly demonstrate, that exposure to gastric reflux adversely affects the function of the epithelial barrier. Understanding the nature of reflux-induced epithelial barrier dysfunction is necessary to better recognize the mechanisms for vocal fold susceptibility to this disease. Therefore, we examined the effects of physiologically relevant reflux challenges on vocal fold transepithelial resistance and gross epithelial and subepithelial appearance.

STUDY DESIGN

Ex vivo, mixed design with between-group and repeated-measures analyses.

METHODS

Healthy, native porcine vocal folds (N = 52) were exposed to physiologically relevant acidic pepsin, acid-only, or pepsin-only challenges and examined with electrophysiology and light microscopy. For all challenges, vocal folds exposed to a neutral pH served as control.

RESULTS

Acidic pepsin and acid-only challenges, but not pepsin-only or control challenges significantly reduced transepithelial resistance within 30 minutes. Reductions in transepithelial resistance were irreversible. Challenge exposure produced minimal gross changes in vocal fold epithelial or subepithelial appearance as evidenced by light microscopy.

CONCLUSIONS

These findings demonstrate that acidic environments characteristic of gastric reflux compromise epithelial barrier function without gross structural changes. In healthy, native vocal folds, reductions in transepithelial resistance could reflect reflux-related epithelial disruption. These results might guide the development of pharmacologic and therapeutic recommendations for patients with reflux, such as continued acid-suppression therapy and patient antireflux behavioral education.

The role of hydration in vocal fold physiology

PURPOSE OF REVIEW

Increased vocal fold hydration is a popular target in the prevention and management of voice disorders. Current intervention strategies focus on enhancing both systemic (internal) and superficial (surface) hydration. We review relevant bench and human research on the role of hydration in vocal fold physiology.

RECENT FINDINGS

Bench and human studies provide converging evidence that systemic and superficial dehydration are detrimental to vocal fold physiology. Dehydration challenges increase the viscous properties of excised vocal fold tissue. Systemic, superficial, and combined drying challenges increase aerodynamic and acoustic measures of voice production in speakers. Emerging theoretical and clinical data suggest that increasing both systemic and superficial hydration levels may benefit voice production; however, robust evidence for positive outcomes of hydration treatments is lacking.

SUMMARY

Increased systemic and superficial vocal fold hydration as a component of vocal hygiene may improve overall health and efficiency of the vocal apparatus. However, continued exploration of biological mechanisms regulating vocal fold hydration is needed to optimize clinical hydration interventions. Specifically, the development of hydration treatments that maximize positive phonatory outcomes will necessitate understanding of the signaling pathways linking systemic and superficial hydration.

Alteration in cellular morphology, density and distribution in rat vocal fold mucosa following injury

The vocal fold mucosa plays an important role in voice production. Its cellular composition and density frequently change under various pathological conditions, often contributing to altered extracellular matrix production, tissue viscoelasticity, and voice quality. In this study, cellular changes in the rat mucosa following a unilateral stripping injury were investigated and analyzed semi-quantitatively. Distinctive and sequential changes in cellular morphology, composition, and density were observed in the mucosa post-injury. Cellular recruitment was a major event during the early stage of injury and reached its peak level by day 5 post-injury. Several types of cells, including neutrophil-like cells, epithelial cells, and fibroblast-like cells, were sequentially recruited. The sequential emergence of reactive cell populations following injury and subsequent reconstruction of the mucosa suggests their involvement in vocal fold tissue repair and scar formation processes.

Hypertonic challenge to porcine vocal folds: effects on epithelial barrier function

OBJECTIVE

Dehydration challenges can increase the chemical composition of surface fluid overlying vocal fold epithelia (hypertonic surface fluid). The vocal fold epithelium is posited to act as a barrier, shielding the lamina propria from perturbations in the airway lumen. However, the effects of hypertonic surface fluid on the barrier functions of vocal fold epithelia have not been quantified. We, therefore, sought to investigate whether hypertonic surface fluid compromises epithelial barrier function. We examined the effects of hypertonic surface fluid on vocal fold epithelial resistance, paracellular pathway morphology, and tight junction protein integrity.

STUDY DESIGN

Ex vivo, between group design.

SETTING

Laboratory.

METHODS

Porcine vocal folds (n = 24) were exposed to hypertonic or isotonic challenge and examined by electrophysiology, transmission electron microscopy, and Western blot analyses.

RESULTS

Hypertonic, but not isotonic, challenge significantly reduced transepithelial resistance. This decrease in resistance was observed immediately after the challenge and was consistent with the appearance of dilated paracellular pathway morphology. However, hypertonic challenge did not alter protein levels of occludin, zona occludens-1, E-cadherin, or beta-catenin.

CONCLUSION

Hypertonic surface fluid alters epithelial barrier function in the vocal folds. Specifically, exposure to hypertonic challenges increases epithelial permeability. Given the important role of the vocal fold epithelium in shielding the underlying mucosa from inhaled pathogens and pollutants, our data provide the impetus for future studies on pharmacological treatments aimed at restoring the hydration level and chemical composition of vocal fold surface fluid.

Vocal fold surface hydration: a review

Vocal fold surface liquid homeostasis contributes to optimal vocal physiology. In this paper we review emerging evidence that vocal fold surface liquid is maintained in part by salt and water fluxes across the epithelium. Based on recent immunolocalization and electrophysiological findings, we describe a transcellular pathway as one mechanism for regulating superficial vocal fold hydration. We propose that the pathway includes the sodium-potassium pump, sodium-potassium-chloride cotransporter, epithelial sodium channels, cystic fibrosis transmembrane regulator chloride channels, and aquaporin water channels. By integrating knowledge of the regulating mechanisms underlying ion and fluid transport with observations from hydration challenges and treatments using in vitro and in vivo studies, we provide a theoretical basis for understanding how environmental and behavioral challenges and clinical interventions may modify vocal fold surface liquid composition. We present converging evidence that clinical protocols directed at facilitating vocal fold epithelial ion and fluid transport may benefit healthy speakers, those with voice disorders, and those at risk for voice disorders.

The cystic fibrosis transmembrane conductance regulator and chloride-dependent ion fluxes of ovine vocal fold epithelium

PURPOSE

Ion-driven transepithelial water fluxes participate in maintaining superficial vocal fold hydration, which is necessary for normal voice production. The authors hypothesized that Cl(-) channels are present in vocal fold epithelial cells and that transepithelial Cl(-) fluxes can be manipulated pharmacologically.

METHOD

Immunohistochemical assays were used to identify cystic fibrosis transmembrane regulator Cl(-) channels in ovine vocal fold mucosae (n = 2). Electrophysiological responses of vocal fold mucosae (n = 80) to Cl(-) channel inhibitors and secretagogues were evaluated in an ovine model using a randomized controlled experimental design.

RESULTS

Cystic fibrosis transmembrane regulator channels were localized to the plasma membranes of epithelial cells. The Cl(-) transport inhibitor, diphenylamine-2-carboxylate, elicited a 30% decrease in mean short-circuit current (I(sc); n = 10). The secretagogue, isobutylmethylxanthine, yielded a 31.7% increase in mean I(sc) (n = 10). Another secretagogue, uridine triphosphate, elicited a 48.8% immediate and 17.3% sustained increase in mean I(sc) (n = 10). No sustained increases occurred following application of secretagogues to mucosae bathed in a low Cl(-) environment (n = 10), suggesting that responses were Cl(-) dependent.

CONCLUSIONS

The authors provide structural and functional evidence for the presence of a transepithelial pathway for Cl(-) fluxes. Pharmacological manipulation of this pathway may offer a mechanism for maintaining superficial vocal fold hydration.

Phonatory effects of airway dehydration: preliminary evidence for impaired compensation to oral breathing in individuals with a history of vocal fatigue

PURPOSE

Airway drying is detrimental to phonation and is posited to exacerbate vocal fatigue. However, limited research has demonstrated the adverse phonatory effects of dehydration in speakers reporting vocal fatigue. We compared the negative phonatory consequences of short-term oral breathing at low, moderate, and high humidity in individuals reporting a history of vocal fatigue and control participants.

METHOD

Females reporting a history of vocal fatigue (N = 8) and matched controls (N = 8) participated in a repeated-measures design over 3 different days.

RESULTS

Oral breathing at low and moderate humidity increased phonation threshold pressure (PTP) to a greater extent in individuals reporting a history of vocal fatigue as compared to controls. Conversely, PTP did not increase in either participant group after oral breathing in a humid environment. Perceived phonatory effort (PPE) ratings were poorly correlated with PTP.

CONCLUSIONS

The emergence of between-group differences in PTP at low and moderate but not high ambient humidity demonstrates that drying challenges might be detrimental to voice production in individuals with a history of vocal fatigue. Based on the phonatory effects of dehydration, we suggest that individuals reporting vocal fatigue may demonstrate impaired compensation to airway drying induced by short-term oral breathing.

Cyclic adenosine monophosphate regulation of ion transport in porcine vocal fold mucosae

OBJECTIVES/HYPOTHESIS

Cyclic adenosine monophosphate (cAMP) is an important biological molecule that regulates ion transport and inflammatory responses in epithelial tissue. The present study examined whether the adenylyl cyclase activator, forskolin, would increase cAMP concentration in porcine vocal fold mucosa and whether the effects of increased cAMP would be manifested as a functional increase in transepithelial ion transport. Additionally, changes in cAMP concentrations following exposure to an inflammatory mediator, tumor necrosis factor-alpha (TNFalpha) were investigated.

STUDY DESIGN

In vitro experimental design with matched treatment and control groups.

METHODS

Porcine vocal fold mucosae (N = 30) and tracheal mucosae (N = 20) were exposed to forskolin, TNFalpha, or vehicle (dimethyl sulfoxide) treatment. cAMP concentrations were determined with enzyme-linked immunosorbent assay. Ion transport was measured using electrophysiological techniques.

RESULTS

Thirty minute exposure to forskolin significantly increased cAMP concentration and ion transport in porcine vocal fold and tracheal mucosae. However, 30-minute and 2-hour exposure to TNFalpha did not significantly alter cAMP concentration.

CONCLUSIONS

We demonstrate that forskolin-sensitive adenylyl cyclase is present in vocal fold mucosa, and further, that the product, cAMP increases vocal fold ion transport. The results presented here contribute to our understanding of the intracellular mechanisms underlying vocal fold ion transport. As ion transport is important for maintaining superficial vocal fold hydration, data demonstrating forskolin-stimulated ion transport in vocal fold mucosa suggest opportunities for developing pharmacological treatments that increase surface hydration.

Preliminary Study on the Quantitative Analysis of Vocal Loading Effects on Vocal Fold Dynamics Using Phonovibrograms

Objectives:

The purpose of the present study was to determine whether high-speed digital imaging with phonovibrogram (PVG) analysis would identify changes in vocal fold vibratory characteristics following prolonged reading (vocal fatigue) in subjects with normal voice to evaluate the voice effects of vocal loading.

Methods:

Three healthy subjects' larynges were examined with an endoscopic high-speed imaging system at 4 different levels of vocal load. Vocal fold dynamics were segmented and processed by PVGs. The PVG images were quantitatively described by a parameter set enabling an individual characterization of vocal fold dynamics. To reveal differences between the subjects, we performed a linear discrimination analysis. Within each subject, the identification of vocal loading effects was performed by statistical analysis (1-way analysis of variance), and 2-tailed paired t-tests were used as a consistency check between left and right vocal fold sides.

Results:

For each subject, the PVG analysis enabled a precise quantification of the entire range of vocal fold dynamics. Independently of the high-speed videos (vocal loads), each subject could be identified by his or her PVG parameters on linear discrimination analysis. In all subjects, the effect of vocal loading was reflected by alterations of PVG parameters representing the posterior opening and closing dynamics. Evaluation within subjects revealed slight asymmetric vibratory behavior between the left and right vocal folds, confirming earlier assumptions.

Conclusions:

Within the investigated subjects, vocal loading does affect the vibratory characteristics of the vocal folds. Left-right vocal fold vibratory asymmetries do occur in healthy voices and can be identified by PVGs. High-speed digital imaging in combination with PVG analysis seems to be a promising tool for investigation of vocal fold fatigue and disorders resulting even from small dynamic changes.

Vocal fold epithelial response to luminal osmotic perturbation

PURPOSE

Dry-air challenges increase the osmolarity of fluid lining the luminal surface of the proximal airway. The homeostasis of surface fluid is thought to be essential for voice production and laryngeal defense. Therefore, the authors hypothesized that viable vocal fold epithelium would generate a water flux to reduce an osmotic challenge (150 mOsm mannitol) on the lumen. Bidirectional transepithelial water fluxes were measured in vocal folds exposed to physiologically realistic luminal osmotic perturbations in vitro.

METHOD

Thirty-six native ovine vocal folds were exposed to either luminal hyperosmotic or isosmotic perturbations. Vocal fold viability and water fluxes toward the lumen and into the mucosa were measured at prechallenge baseline and for 30 min after challenge.

RESULTS

Vocal fold electrophysiological viability was maintained for the duration of osmotic perturbation. Luminal osmotic exposure increased luminally directed transepithelial water fluxes in 60% of vocal folds. This increase was electrically silent, of short duration, and would not negate the osmotic gradient.

CONCLUSION

Ovine vocal fold epithelia detect osmotic perturbations to the luminal surface in vitro. This ability to detect and respond to changes in surface composition may be important in homeostatic regulation of vocal fold surface fluid during osmotic perturbations in respiration and phonation.

The effects of three nebulized osmotic agents in the dry larynx

PURPOSE

This investigation examined the effects of nebulized hypertonic saline, isotonic saline (IS), and sterile (hypotonic) water on phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) following a surface laryngeal dehydration challenge.

METHOD

In a double-blind, randomized experimental trial, 60 vocally healthy women (n = 15 per group) underwent a laryngeal desiccation challenge involving oral breathing for 15 min using medical-grade dry air (RH<1%). Three of the four groups then received nebulized isotonic saline (0.9% NaCl), hypertonic saline (7% NaCl), or sterile (hypotonic) water, respectively; the 4th group served as a nontreatment control. PTP and PPE were estimated for high-pitched productions at baseline, immediately postdesiccation, and at 5, 20, 35, and 50 min postnebulization.

RESULTS

PTP increased significantly for all groups following the desiccation challenge. PTP values were, on average, 0.5 cm H(2)O greater immediately postdesiccation versus baseline. In contrast, PTP values did not change significantly following the administration of nebulized treatments, although a temporary trend toward a reduction in PTP was observed for the IS group. Unexpectedly, PPE ratings decreased significantly after the desiccation challenge. In general, PPE ratings were poorly correlated with PTP measures.

CONCLUSION

A laryngeal desiccation challenge (i.e., temporary exposure to extremely low relative humidity while breathing transorally) significantly increased PTP. Although interesting trends emerged, none of the nebulized treatments significantly enhanced recovery from the negative effects of desiccation on PTP. In light of very low correlations between PTP and PPE, serious questions are raised regarding presumed associations between these measures.

Voicing and silence periods in daily and weekly vocalizations of teachers

The National Center for Voice and Speech (NCVS) data bank on voice dosimetry was used to study the distributions of continuous voicing periods and silence periods in 31 teachers over the duration of two weeks. Recordings were made during all awake hours of the day. Voicing periods were grouped into half decades, ranging from 0.0316 to 0.10 s for the shortest periods of phonation to 31.6-100 s for the longest periods of phonation. Silence periods were grouped into similar half decades, but ranged up to periods of several hours. On average, the teachers had 1800 occurrences of voicing (onset followed by offset) per hour at work and 1200 occurrences per hour while not at work. Voicing occurred 23% of the total time at work, dropping to 13% during off-work hours and 12% on weekends. The greatest accumulation of voicing occurred in the 0.316-1.0 s voicing periods, whereas the greatest accumulation of silence occurred in the 3-10 s silence periods. The study begins to lay the groundwork for understanding vocal fatigue in terms of repetitive motion and collision of tissue, as well as recovery from such mechanical stress.

Effect of Hemodialysis on the Thickness of Vocal Folds: A Possible Explanation for Postdialysis Hoarseness

BACKGROUND

Determining the dry weight of chronically hemodialysed patients is a common problem. Patients on intermittent hemodialysis often experience transient hoarseness at the end of dialysis. The vocal folds may be affected by the hydration state.

AIM

To test the hypothesis that postdialysis hoarseness may be related to changes in the thickness of the vocal folds.

METHODS

Twenty-five stable chronic hemodialysis patients underwent endoscopic nasopharyngeal laryngoscopy before and after dialysis. Pictures of the vocal folds were taken and the folds were measured using computer software. Eighteen vocal folds from 16 patients were technically adequate for analysis. The change in the width/length ratio of the vocal folds (W/L) was used as a measurement of the folds' thickness.

RESULTS

W/L decreased from 0.175 +/- 0.011 before dialysis to 0.152 +/- 0.009 after dialysis (p < 0.01, mean reduction 10.9 +/- 3.8%). Patients' weight decreased by 4.7 +/- 0.3% (p < 0.0001), systolic blood pressure decreased by 15.0 +/- 3.1% (p < 0.001), diastolic blood pressure decreased by 13.0 +/- 3.6% (p < 0.01), and mean blood pressure decreased by 14.1 +/- 3.1% (p < 0.001). Sixty percent of the patients had postdialysis hoarseness, and in 72% of the patients a decrease in the vocal folds' thickness was observed.

CONCLUSIONS

Chronic hemodialysis patients may experience transient postdialysis hoarseness, and a decrease in the vocal folds' thickness. The latter may result from dehydration.

[Vocal fold superficial layer of lamina propria histology after the position of mucosa pediculated flap: canine experimental study]

Many techniques were applied to treat patients with sulcus vocalis and scarred vocal folds. Their results were not good enough. In the Technique of Vocal Fold Pediculated Mucosa Flap, an anterior pediculated flap of vocal fold is positioned on the superficial layer of the lamina propria, below the free margin.

AIM

To describe histological postoperative findings on the superficial layer of lamina propria during the application of the technique Vocal Fold Pediculated Mucosa Flap. The following parameters were compared between tested and control groups: total, type I and type III collagen and number of cellular nucleus.

STUDY DESIGN

experimental.

MATERIAL AND METHOD

Fifteen dogs were used. One vocal fold was submitted to the intervention and the other was left as control. Each group of three dogs was sacrificed on 10, 30, 90, 180 and 360 days after the experimental surgery. Hematoxylin and eosin (H.E.) and Syrius Red were the staining techniques used.

RESULTS

Type I and total collagen suggested increased results in the tested group on postoperative days 90 and 180, nevertheless there was statistical significance only on postoperative day 180 (p<0.05). Type III collagen group area was less significant than the control group on postoperative day 180 (p<0.05). The number of cellular nucleus was increased on the 10th postoperative day, but decreased after the 30th day.

DISCUSSION

The findings about total and type I collagen and the amount of cellular nucleus on the superficial layer of lamina propria were similar to laryngeal postoperative studies in dogs. More complex studies would contribute with new data about the present subject.

Markers of wound healing in vocal fold secretions from patients with laryngeal pathology

This study seeks to determine the ability of enzyme-linked immunosorbent assays of vocal fold secretions to detect and describe the inflammatory response in the vocal folds. Vocal fold and palatal secretions were collected during operation from patients with a range of vocal fold disorders and from control patients. The secretions were subjected to assays for interleukin-1beta, prostaglandin E2, and transforming growth factor beta. The results indicate a differential expression of mediators associated with the wound healing cascade in the vocal folds. The prostaglandin E2 levels clearly differentiated vocal fold secretions associated with laryngeal disease versus control sites. Furthermore, the interleukin-1beta concentrations were significantly elevated in subjects with epithelial lesions of the vocal folds as opposed to lesions of the lamina propria. Although still in its infancy, such analysis may ultimately hold scientific and clinical utility in the study and management of patients with vocal fold disease.

Oral breathing challenge in participants with vocal attrition

Vocal folds undergo osmotic challenge by mouth breathing during singing, exercising, and loud speaking. Just 15 min of obligatory oral breathing, to dry the vocal folds, increases phonation threshold pressure (Pth) and expiratory vocal effort in healthy speakers (M. Sivasankar & K. Fisher, 2002). We questioned whether oral breathing is more detrimental to phonation in healthy participants with a history of temporary vocal attrition. The effects of a 15-min oral or nasal breathing challenge on Pth and perceived expiratory vocal effort were compared for participants reporting symptoms of vocal attrition (N = 18, ages 19-38 years) and normal controls (N = 20, ages 19-33 years). Post-challenge-prechallenge differences in Pth (deltaPth) and effort (deltaEffort) revealed that oral breathing, but not nasal breathing, increased Pth (p < .001 ) and effort (p < .001) at low, comfortable, and high pitch. deltaPth was significantly greater in participants with vocal attrition than in normal controls (p < .001). Nasal breathing reduced Pth for all controls but not for all participants reporting vocal attrition. deltaPth was significantly and linearly correlated with deltaEffort (rvocal attrition = .81, p < .001; rcontrol = .84, p < .001). We speculate that the greater increases in Pth in participants reporting vocal attrition may result from delayed or inadequate compensatory response to superficial laryngeal dehydration. Obligatory oral breathing may place voice users at risk for exacerbating vocal attrition. That sol layer depletion by obligatory oral breathing increased Pth and vocal effort provides support for the role of superficial hydration in maintaining ease of phonation.

Oral breathing increases Pth and vocal effort by superficial drying of vocal fold mucosa

Oral breathing superficially dehydrates the airway lumen by decreasing the depth of the sol layer in humans and animals. Conversely, nasal breathing can increase the humidity of inspired air. We compared the effects of short-term oral and nasal breathing on Pth and perceived vocal effort in 20 female subjects randomly assigned to two groups: oral breathing (N = 10, age 21-32 years); nasal breathing (N = 10, age 20-36 years). We hypothesized that short-term oral breathing, but not nasal breathing, would increase Pth, and that subjects would perceive this change as an increase in vocal effort. Following 15 minutes of oral breathing, Pth increased at comfortable and low pitch (p < 0.01) with 6 of 10 subjects reporting increased vocal effort. Nasal breathing reduced Pth at all three pitches (p < 0.01), and 7 of 10 subjects reported decreased vocal effort. Over all subjects, 49% of the variance in treatment-induced change in Pth was accounted for by change in vocal effort (R = 0.70). We posit that obligatory oral breathing places healthy subjects at risk for symptoms of increased vocal effort. The facilitatory role of superficial hydration on vocal fold oscillation should be considered in biomechanical models of phonation and in the clinical prevention of laryngeal dryness.