Characterization of Ethyl Butyrate-Induced Cough Before and After Breath Control Techniques in Healthy Adults.

PURPOSE: Methods for cough elicitation frequently involve aerosolized tussive agents. Here, we sought to determine whether healthy individuals demonstrate a quantifiable cough response after inhaling a volatile ester and if breath control techniques modify this chemically induced cough response. METHOD: Sixty adult male and female participants inhaled prepared liquid dilutions of ethyl butyrate dissolved in paraffin oil at 20%, 40%, and 60% v/v concentrations in triplicate, with presentation order randomized. We delivered stimuli through a face mask connected to an olfactometer and respiratory pneumotachograph. Participants rated sensations of their urge to cough and pleasantness of the odor while cough airflow was measured. Following baseline testing, participants were randomized to implement pursed-lip breathing or slow-paced breathing after inhaling ethyl butyrate to determine the effects of breath control on cough measures. RESULTS: Inhaled ethyl butyrate elicited cough in 70% of participants. Higher concentrations of ethyl butyrate resulted in significantly greater sensation of the urge to cough, F(2, 80) = 10.72, p < .001, and significantly more generated coughs, F(2, 63) = 13.14, p < .001. Compared to baseline, participants rated significantly decreased urge to cough during breath control techniques, F(1, 40) = 11.01, p = .0019. No significant changes were observed in the number of generated coughs between baseline and breath control techniques, F(1, 31) = 7.23, p = .01. CONCLUSIONS: Airborne ethyl butyrate is a tussigenic agent in humans. Our findings provide opportunities for future research directions in normal and disordered cough responses to volatile compounds.

Examining the Influence of Chemosensation on Laryngeal Health and Disorders.

Inhaled airborne stimuli are associated with laryngeal disorders affecting respiration. Clinically, several themes emerged from the literature that point to specific gaps in the understanding and management of these disorders. There is wide variation in the types of airborne stimuli that trigger symptoms, lack of standardization in provocation challenge testing using airborne stimuli, and vague reporting of laryngeal symptoms. Scientifically, evidence exists outside the field of voice science that could prove useful to implement among patients with impaired laryngeal-respiration. To expand this area of expertise, here we provide a thematic overview of relevant evidence and methodological tools from the discipline of chemosensory sciences. This review provides distinctions across the three chemosensory systems of olfaction, trigeminal chemesthesis, and gustation, guidance on selecting and delivering common chemosensory stimuli for clinical testing, and methods of quantifying sensory experiences using principles of human psychophysics. Investigating the science of chemosensation reveals that laryngeal responses to inhaled airborne stimuli have explanations involving physiological mechanisms as well as higher cognitive processing. Fortunately, these findings are consistent with current pharmacological and nonpharmacological interventions for impaired laryngeal-respiration. Based on the close relationships among inhaled airborne stimuli, respiration, and laryngeal function, we propose that new perspectives from chemosensory sciences offer opportunities to improve patient care and target areas of future research.

Voice Handicap Index Changes After Microflap Surgery for Benign Vocal Fold Lesions Are Not Associated With Recommended Absolute Voice Rest Duration.

PURPOSE: Voice rest is frequently prescribed after phonosurgery, but optimal type and duration for voice outcomes have not been demonstrated. Studies to date have been characterized by heterogeneity in surgical procedures and laryngeal diagnoses. We sought to analyze the effect of recommended absolute voice rest duration on outcomes of microflap surgery for benign vocal fold lesions. A secondary purpose was to identify patient factors associated with postoperative voice outcomes. METHOD: Forty-three patients were included in this retrospective review of patients aged 18 years and above who underwent direct microlaryngoscopy with microflap for vocal fold polyp or cyst over a 5-year period at a multidisciplinary voice center. Duration of recommended postoperative absolute voice rest was classified as less than 7 days, 7 days, and more than 7 days. Demographic and vocal hygiene data and voice treatment history were collected. Outcome measures consisted of one pre- and two postoperative Voice Handicap Index (VHI) scores. Effects of recommended voice rest on outcomes were analyzed using mixed models for repeated measures. Effects of patient factors on outcomes were analyzed as exploratory measures. Stroboscopy ratings were analyzed descriptively. RESULTS: Thirteen patients were recommended 7 days of absolute voice rest, 15 were recommended less than 7 days, and 15 were recommended more than 7 days. Postoperatively, VHI scores significantly improved for all patients. Voice rest as a continuous variable was associated with the Functional subscale score in the short term, but there was no effect on VHI total score and no longer term effect of voice rest on any outcome. Age, sex, and preoperative voice therapy were associated with at least one VHI subscale score on at least one time point. CONCLUSION: VHI outcomes of microflap surgery for polyps and cysts do not differ by duration of recommended absolute postoperative voice rest. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.19178459.

Lack of respiratory and ocular effects following acute propylene glycol exposure in healthy humans.

OBJECTIVE: Propylene glycol (PG) is a widely used solvent, chemical intermediate and carrier substance for foods, pharmaceutical and cosmetic products. Professional and occupational exposure to PG aerosol and vapor may occur from theatrical smoke generators and during application of deicing products to airplanes. While PG is considered to have low toxicity, the results of one study suggested that brief (1-min) exposure to PG mist elicited ocular and respiratory effects in humans. Because the high concentrations and brief exposure duration in that study were not representative of most occupational exposures, a controlled experimental exposure study was conducted to clarify or confirm the earlier findings. MATERIALS AND METHODS: Ten males and 10 females were exposed to PG aerosol for 4 hrs at 20 and 100 mg/m3 and 30 min at 200 mg/m3. Total PG exposure concentrations (droplets plus gas phase) were 95.6, 442.4 and 871 mg/m3 for the three conditions, respectively. Participants rode a stationary bicycle to simulate physical effort at regular intervals during exposure. Objective measures evaluated in this study included ocular irritation via eye blink task and eye photography and pulmonary function via spirometry, while subjective measures included health symptoms ratings, irritation and dryness ratings of eyes, nose, throat and mouth. RESULTS: Objective measures of pulmonary function and ocular irritation did not reveal any exposure-related changes. Exposure-related changes in symptom reporting were observed; however, the highest symptom ratings did not exceed "slight" on the scale. CONCLUSIONS: The results indicate at the concentrations and acute durations tested, PG does not affect human respiratory function or produce ocular irritation.

Recovery of Vocal Fold Epithelium after Acute Phonotrauma.

We investigated the timeline of tissue repair of vocal fold epithelium after acute vibration exposure using an in vivo rabbit model. Sixty-five New Zealand white breeder rabbits were randomized to 120 min of modal- or raised-intensity phonation. After the larynges were harvested at 0, 4, 8, and 24 h, and at 3 and 7 days, the vocal fold tissue was evaluated using electron microscopy and quantitative real-time polymerase chain reaction. There was an immediate decrease in the microprojection depth and height following raised-intensity phonation, paired with upregulation of cyclooxygenase-2. This initial 24-h period was also characterized by the significant downregulation of junction proteins. Interleukin 1ß and transforming growth factor ß1 were upregulated for 3 and 7 days, respectively, followed by an increase in epithelial cell surface depth at 3 and 7 days. These data appear to demonstrate a shift from inflammatory response to the initiation of a restorative process in the vocal fold epithelium between 24 h and 3 days. Despite the initial damage from raised-intensity phonation, the vocal fold epithelium demonstrates a remarkable capacity for the expeditious recovery of structural changes from transient episodes of acute phonotrauma. While structurally intact, the return of functional barrier integrity may be delayed by repeated episodes of phonotrauma and may also play an important role in the pathophysiology of vocal fold lesions.

Apoptosis and Vocal Fold Disease: Clinically Relevant Implications of Epithelial Cell Death.

Purpose: Vocal fold diseases affecting the epithelium have a detrimental impact on vocal function. This review article provides an overview of apoptosis, the most commonly studied type of programmed cell death. Because apoptosis can damage epithelial cells, this article examines the implications of apoptosis on diseases affecting the vocal fold cover. Method: A review of the extant literature was performed. We summarized the topics of epithelial tissue properties and apoptotic cell death, described what is currently understood about apoptosis in the vocal fold, and proposed several possible explanations for how the role of abnormal apoptosis during wound healing may be involved in vocal pathology. Results and Conclusions: Apoptosis plays an important role in maintaining normal epithelial tissue function. The biological mechanisms responsible for vocal fold diseases of epithelial origin are only beginning to emerge. This article discusses speculations to explain the potential role of deficient versus excessive rates of apoptosis and how disorganized apoptosis may contribute to the development of common diseases of the vocal folds.

Acute exposure to vibration is an apoptosis-inducing stimulus in the vocal fold epithelium.

Clinical voice disorders pose significant communication-related challenges to patients. The purpose of this study was to quantify the rate of apoptosis and tumor necrosis factor-alpha (TNF-α) signaling in vocal fold epithelial cells in response to increasing time-doses and cycle-doses of vibration. 20 New Zealand white breeder rabbits were randomized to three groups of time-doses of vibration exposure (30, 60, 120min) or a control group (120min of vocal fold adduction and abduction). Estimated cycle-doses of vocal fold vibration were extrapolated based on mean fundamental frequency. Laryngeal tissue specimens were evaluated for apoptosis and gene transcript and protein levels of TNF-α. Results revealed that terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was significantly higher after 120min of vibration compared to the control. Transmission electron microscopy (TEM) revealed no significant effect of time-dose on the mean area of epithelial cell nuclei. Extrapolated cycle-doses of vibration exposure were closely related to experimental time-dose conditions, although no significant correlations were observed with TUNEL staining or mean area of epithelial cell nuclei. TUNEL staining was positively correlated with TNF-α protein expression. Our findings suggest that apoptosis can be induced in the vocal fold epithelium after 120min of modal intensity phonation. In contrast, shorter durations of vibration exposure do not result in apoptosis signaling. However, morphological features of apoptosis are not observed using TEM. Future studies are necessary to examine the contribution of abnormal apoptosis to vocal fold diseases.

Evaluation of Dying Vocal Fold Epithelial Cells by Ultrastructural Features and TUNEL Method.

Cell death is a regulated mechanism of eliminating cells to maintain tissue homeostasis. This study described 2 methodological procedures for evaluating cell death in the epithelium of immobilized, approximated and vibrated vocal folds from 12 New Zealand white breeder rabbits. The gold standard technique of transmission electron microscopy evaluated high-quality ultrastructural criteria of cell death and a common immunohistochemical marker, the terminal deoxynucleotidyl transferase dUTP nick end labeling method, to confirm cell death signaling. Results revealed that ultrastructural characteristics of apoptotic cell death, specifically condensed chromatin and apoptotic bodies, were observed after vocal fold vibration and approximation. Although episodes of necrosis were rare, few enlarged cell nuclei were present after vibration and approximation. The vocal fold expresses an immunohistochemical marker for apoptosis along the apical surface of the epithelium. This study provides a solid foundation for future investigations regarding the role of cell death in vocal fold health and disease.

Nonstimulated rabbit phonation model: Cricothyroid approximation.

OBJECTIVES/HYPOTHESIS: To describe a nonstimulated in vivo rabbit phonation model using an Isshiki type IV thyroplasty and uninterrupted humidified glottal airflow to produce sustained audible phonation. STUDY DESIGN: Prospective animal study. METHODS: Six New Zealand white breeder rabbits underwent a surgical procedure involving an Isshiki type IV thyroplasty and continuous airflow delivered to the glottis. Phonatory parameters were examined using high-speed laryngeal imaging and acoustic and aerodynamic analysis. Following the procedure, airflow was discontinued, and sutures remained in place to maintain the phonatory glottal configuration for microimaging using a 9.4 Tesla imaging system. RESULTS: High-speed laryngeal imaging revealed sustained vocal fold oscillation throughout the experimental procedure. Analysis of acoustic signals revealed a mean vocal intensity of 61 dB and fundamental frequency of 590 Hz. Aerodynamic analysis revealed a mean airflow rate of 85.91 mL/s and subglottal pressure of 9 cm H2 O. Following the procedure, microimaging revealed that the in vivo phonatory glottal configuration was maintained, providing consistency between the experimental and postexperimental laryngeal geometry. The latter provides a significant milestone that is necessary for geometric reconstruction and to allow for validation of computational simulations against the in vivo rabbit preparation. CONCLUSION: We demonstrate a nonstimulated in vivo phonation preparation using an Isshiki type IV thyroplasty and continuous humidified glottal airflow in a rabbit animal model. This preparation elicits sustained vocal fold vibration and phonatory measures that are consistent with our laboratory's prior work using direct neuromuscular stimulation for evoked phonation. LEVEL OF EVIDENCE: N/A. Laryngoscope, 126:1589-1594, 2016.

Subject-Specific Computational Modeling of Evoked Rabbit Phonation.

When developing high-fidelity computational model of vocal fold vibration for voice production of individuals, one would run into typical issues of unknown model parameters and model validation of individual-specific characteristics of phonation. In the current study, the evoked rabbit phonation is adopted to explore some of these issues. In particular, the mechanical properties of the rabbit's vocal fold tissue are unknown for individual subjects. In the model, we couple a 3D vocal fold model that is based on the magnetic resonance (MR) scan of the rabbit larynx and a simple one-dimensional (1D) model for the glottal airflow to perform fast simulations of the vocal fold dynamics. This hybrid three-dimensional (3D)/1D model is then used along with the experimental measurement of each individual subject for determination of the vocal fold properties. The vibration frequency and deformation amplitude from the final model are matched reasonably well for individual subjects. The modeling and validation approaches adopted here could be useful for future development of subject-specific computational models of vocal fold vibration.

Randomized controlled trial of supplemental augmentative and alternative communication versus voice rest alone after phonomicrosurgery.

OBJECTIVE: This randomized trial investigated voice rest and supplemental text-to-speech communication versus voice rest alone on visual analog scale measures of communication effectiveness and magnitude of voice use. STUDY DESIGN: Randomized clinical trial. SETTING: Multicenter outpatient voice clinics. SUBJECTS: Thirty-seven patients undergoing phonomicrosurgery. METHODS: Patients undergoing phonomicrosurgery were randomized to voice rest and supplemental text-to-speech communication or voice rest alone. The primary outcome measure was the impact of voice rest on ability to communicate effectively over a 7-day period. Pre- and postoperative magnitude of voice use was also measured as an observational outcome. RESULTS: Patients randomized to voice rest and supplemental text-to-speech communication reported higher median communication effectiveness on each postoperative day compared to those randomized to voice rest alone, with significantly higher median communication effectiveness on postoperative days 3 (P=.03) and 5 (P=.01). Magnitude of voice use did not differ on any preoperative (P>.05) or postoperative day (P>.05), nor did patients significantly decrease voice use as the surgery date approached (P>.05). However, there was a significant reduction in median voice use pre- to postoperatively across patients (P<.001) with median voice use ranging from 0 to 3 throughout the postoperative week. CONCLUSION: Supplemental text-to-speech communication increased patient-perceived communication effectiveness on postoperative days 3 and 5 over voice rest alone. With the prevalence of smartphones and the widespread use of text messaging, supplemental text-to-speech communication may provide an accessible and cost-effective communication option for patients on vocal restrictions.

Effects of phonation time and magnitude dose on vocal fold epithelial genes, barrier integrity, and function.

OBJECTIVES/HYPOTHESIS: To investigate the effects of increasing time and magnitude doses of vibration exposure on transcription of the vocal fold's junctional proteins, structural alterations, and functional tissue outcomes. STUDY DESIGN: Animal study. METHODS: 100 New Zealand White breeder rabbits were studied. Dependent variables were measured in response to increasing time doses (30, 60, or 120 minutes) and magnitude doses (control, modal intensity, and raised intensity) of vibration exposure. Messenger RNA expression of occludin, zonula occluden-1 (ZO-1), E-cadherin, ß-catenin, interleukin 1ß, cyclooxygenase-2, transforming growth factor ß-1, and fibronectin were measured. Tissue structural alterations were assessed using transmission electron microscopy (TEM). Transepithelial resistance was used to measure functional tissue outcomes. RESULTS: Occludin gene expression was downregulated in vocal folds exposed to 120-minute time doses of raised-intensity phonation, relative to control, and modal-intensity phonation. ZO-1 gene expression was upregulated following a 120-minute time dose of modal-intensity phonation, compared to control, and downregulated after a 120-minute time dose of raised-intensity phonation, compared to modal-intensity phonation. E-cadherin gene expression was downregulated after a 120-minute time dose of raised-intensity phonation, compared to control and modal-intensity phonation. TEM revealed extensive desquamation of the stratified squamous epithelial cells with increasing time and magnitude doses of vibration exposure. A general observation of lower transepithelial resistance measures was made in tissues exposed to raised-intensity phonation compared to all other groups. CONCLUSIONS: This study provides evidence of vocal fold tissue responses to varying time and magnitude doses of vibration exposure. LEVEL OF EVIDENCE: NA.

Nonlinear analyses of elicited modal, raised, and pressed rabbit phonation.

OBJECTIVES/HYPOTHESIS: The purpose of this study was to use nonlinear dynamic analysis methods such as phase space portraits and correlation dimension (D2) as well as descriptive spectrographic analyses to characterize acoustic signals produced during evoked rabbit phonation. METHODS: Seventeen New Zealand white breeder rabbits were used to perform the study. A Grass S-88 stimulator (SA Instrumentation, Encinitas, CA) and constant current isolation unit (Grass Telefactor, model PSIU6; West Warwick, RI) were used to provide electrical stimulation to laryngeal musculature, and transglottal airflow rate and stimulation current (mA) were manipulated to elicit modal, raised intensity, and pressed phonations. Central 1 second portions of the most stable portion of the acoustic waveform for modal, raised intensity, and pressed phonations were edited and then analyzed via phase space portraits, Poincaré sections, and the estimation of the D2. In an attempt to limit the effects of the highly variable and nonstationary characteristics of some of the signals being analyzed, D2 analysis was also performed on the most stable central 200-millisecond portion of the acoustic waveform. Descriptive analysis of each phonation was also conducted using sound spectrograms. RESULTS: Results showed that the complexity of phonation and the subsequent acoustic waveform is increased as transglottal airflow rate and degree of glottal adduction are manipulated in the evoked rabbit phonation model. In particular, phonatory complexity, as quantified via D2 analyses and demonstrated via spectrographic characteristics, increases from "modal" (ie, phonation elicited at just above the phonation threshold pressure) to raised intensity (phonation elicited by increasing transglottal airflow rate) to pressed (phonation elicited by increasing the stimulation current delivered to the larynx). Variations in a single dynamic dimension (airflow rate or adductory force) resulted in significantly increased productions of nonlinear phenomenon, including bifurcations from periodicity to regions of subharmonic content, fundamental frequency, and harmonic jumps, and evidence of periodicity within aperiodic regions ("chaos"). CONCLUSIONS: The evoked rabbit phonation model described in this study allows for the elicitation of various types of phonations under controlled conditions and, therefore, has the potential to provide insight regarding important variables that may elicit examples of nonlinear phenomena such as subharmonics and deterministic chaos.

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.

Test-retest reliability for aerodynamic measures of voice.

OBJECTIVES/HYPOTHESIS: The purpose of this study was to investigate the intrasubject reliability of aerodynamic characteristics of the voice within typical/normal speakers across testing sessions using the Phonatory Aerodynamic System (PAS 6600; KayPENTAX, Montvale, NJ). METHODS: Participants were 60 healthy young adults (30 males and 30 females) between the ages 18 and 31 years with perceptually typical voice. Participants were tested using the PAS 6600 (Phonatory Aerodynamic System) on two separate days with approximately 1 week between each session at approximately the same time of day. Four PAS protocols were conducted (vital capacity, maximum sustained phonation, comfortable sustained phonation, and voicing efficiency) and measures of expiratory volume, maximum phonation time, mean expiratory airflow (during vowel production) and target airflow (obtained via syllable repetition), peak air pressure, aerodynamic power, aerodynamic resistance, and aerodynamic efficiency were obtained during each testing session. Associated acoustic measures of vocal intensity and frequency were also collected. All phonations were elicited at comfortable pitch and loudness. RESULTS: All aerodynamic and associated variables evaluated in this study showed useable test-retest reliability (ie, intraclass correlation coefficients [ICCs] ≥ 0.60). A high degree of mean test-retest reliability was found across all subjects for aerodynamic and associated acoustic measurements of vital capacity, maximum sustained phonation, glottal resistance, and vocal intensity (all with ICCs > 0.75). Although strong ICCs were observed for measures of glottal power and mean expiratory airflow in males, weaker overall results for these measures (ICC range: 0.60-0.67) were observed in females subjects and sizable coefficients of variation were observed for measures of power, resistance, and efficiency in both men and women. Differences in degree of reliability from measure to measure were revealed in greater detail using methods such as ICCs and coefficients of variation than with means comparison testing. The results of this study also show that reliable aerodynamic and associated measures may be elicited using comfortable pitch and loudness. CONCLUSIONS: The 1-week test-retest reliability for the majority of aerodynamic and associated acoustic measures assessed in this study is considered good-to-excellent. Clinicians and researchers using aerodynamic and associated measures should be aware of possible significant gender effects that influence both normative expectations as well as the standard error of measurement (ie, typical error) and estimates of minimum difference that may be used to differentiate typical from disordered voice.