Histologic investigation of hyperphonated canine vocal cords

The Comparison of Narrow Band Imaging, White Light Laryngoscopy and Videolaryngostroboscopy in the Evaluation of Benign Vocal Fold Lesions

BACKGROUND

The aim of the study was comparing the diagnostic role of the white light (WL) endoscopy, video laryngostroboscopy (VLS), and narrow-band imaging (NBI) in the evaluation of the benign vocal fold lesions.

MATERIAL AND METHODS

From March 2018 to June 2019, a total of 118 cases were enrolled in this study. Ninety-eight patients were suspected with vocal fold nodules, cysts, polyps, and sulcus vocalis and 20 patients without a history of dysphonia. Each patient was examined by WL, VLS, and NBI endoscopy. Recorded images and videos were analyzed and scored by three otorhinolaryngologists who had at least 3 years of experience in phoniatrics field. The evaluation results were compared between the methods and the physicians.

RESULTS

A total of 118 cases were grouped by their confirmed diagnosis, vocal fold nodules (n = 28), vocal fold cyst (n = 24), vocal fold polyp (n = 9), and sulcus vocalis (n = 37). When the correct diagnosis rates of the physicians were compared, the statistical significance was found between the physicians in the WL and VLS method (P= 0.014, P= 0.027). No statistically significant difference was found among physicians in NBI method (P = 0.368). The difference between the diagnostic methods was found to be statistically significant in reaching the accurate diagnosis for benign vocal fold lesions (P< 0.001). While the difference between NBI-WL and VLS-WL was statistically significant (P< 0.001 and P< 0.001). The difference between NBI-VLS was not statistically significant while evaluating the vocal fold nodules, cysts, and sulcus vocalis separately (P= 0.102, P = 0.026, P = 0.157). Otherwise, it was statistically significant (P= 0.002) while evaluating total benign lesions in the study. The difference between NBI-VLS combination and VLS, NBI-VLS combination and VLS-WL combination were statistically significant (P< 0.001 and P= 0.001).

CONCLUSION

This study showed that NBI assessments have similar accuracy and sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) to VLS and have a higher value than WL endoscopy in reaching the diagnosis for benign vocal fold lesions. Therefore, NBI can be accepted as a promising approach to identify benign laryngeal lesions due to its optical properties.

Effect of nodule size and stiffness on phonation threshold and collision pressures in a synthetic hemilaryngeal vocal fold model

Synthetic vocal fold (VF) replicas were used to explore the role of nodule size and stiffness on kinematic, aerodynamic, and acoustic measures of voiced speech production. Emphasis was placed on determining how changes in collision pressure may contribute to the development of phonotrauma. This was performed by adding spherical beads with different sizes and moduli of elasticity at the middle of the medial surface of synthetic silicone VF models, representing nodules of varying size and stiffness. The VF models were incorporated into a hemilaryngeal flow facility. For each case, self-sustained oscillations were investigated at the phonation threshold pressure. It was found that increasing the nodule diameter increased the open quotient, phonation threshold pressure, and phonation threshold flow rate. However, these values did not change considerably as a function of the modulus of elasticity of the nodule. Nevertheless, the ratio of collision pressure to subglottal pressure increased significantly for both increasing nodule size and stiffness. This suggests that over time, both growth in size and fibrosis of nodules will lead to an increasing cycle of compensatory vocal hyperfunction that accelerates phonotrauma.

Effects of Different Voice Rest on Vocal Function After Microlaryngeal Surgery: A Systematic Review and Meta-Analysis

OBJECTIVES

To compare the results of a voice handicap index (VHI) scale and acoustic parameters in patients who underwent microlaryngeal surgery followed by either short-duration (voice rest for <7 days) or long-duration (≥7 days) voice rest.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

The PubMed, Embase, and Cochrane Library databases were systematically searched for articles published before March 1, 2021. Randomized controlled trials (RCTs) that measured the voice outcomes of patients after different durations and extents of postoperative voice restriction were included in the meta-analysis.

RESULTS

Four RCTs comprising 112 patients were included in the quantitative meta-analysis. Compared with the long-duration voice rest group, the short-duration group exhibited comparable VHI scores (mean difference [MD], -7.01; 95% CI, -16.12 to 2.09; p = 0.13), maximum phonation time (MD, -2.58; 95% CI, -5.42 to 0.26; p = 0.07), and acoustic variables of jitter (MD, -1.25; 95% CI, -3.43 to 0.94; p = 0.26) and shimmer (MD, -0.79; 95% CI, -2.08 to 0.51; p = 0.24). Subgroup analysis for benign pathology and cold instruments studies demonstrated significantly better VHI scores (MD, -14.45; 95% CI, -26.19 to -2.72; p = 0.02 and MD, -15.98; 95% CI, -28.52 to -3.44; p = 0.01, respectively) in the short-duration group.

CONCLUSIONS

The limited evidence does not demonstrate benefit in voice outcomes from long-duration voice rest and suggests potential unfavorable effects on compliance and quality of life, providing a rationale for short-duration voice rest after microlaryngeal surgery. More studies are required to determine the optimal duration and extent of postoperative voice rest.

LEVEL OF EVIDENCE

1 Laryngoscope, 133:154-161, 2023.

Potential Biophysiological Mechanisms Underlying Vocal Demands and Vocal Fatigue

Patients with complaint of vocal fatigue have perceptual, acoustic, and aerodynamic outcomes that are heterogeneous in nature. One reason may be due to different underlying biophysiological mechanisms that lead to these heterogeneous clinical presentations. Five potential mechanisms are proposed: neuromuscular, metabolic, vocal tissue, afferent, and central neural. Analytical frameworks and study designs to study these mechanisms are also addressed. A better understanding of biophysiological mechanisms of vocal fatigue can improve precision of therapeutic approaches. It can also help shift management from symptom-based to etiology-focused approaches for vocal fatigue.

Collision Pressure and Dissipated Power Dose in a Self-Oscillating Silicone Vocal Fold Model With a Posterior Glottal Opening

PURPOSE

The goal of this study was to experimentally evaluate how compensating for the adverse acoustic effects of a posterior glottal opening (PGO) by increasing subglottal pressure and changing supraglottal compression, as have been associated with vocal hyperfunction, influences the risk of vocal fold (VF) trauma.

METHOD

A self-oscillating synthetic silicone model of the VFs with an airflow bypass that modeled a PGO was investigated in a hemilaryngeal flow facility. The influence of compensatory mechanisms on collision pressure and dissipated collision power was investigated for different PGO areas and supraglottal compression. Compensatory behaviors were mimicked by increasing the subglottal pressure to achieve a target sound pressure level (SPL).

RESULTS

Increasing the subglottal pressure to compensate for decreased SPL due to a PGO produced higher values for both collision pressure and dissipated collision power. Whereas a 10-mm² PGO area produced a 12% increase in the peak collision pressure, the dissipated collision power increased by 122%, mainly due to an increase in the magnitude of the collision velocity. This suggests that the value of peak collision pressure may not fully capture the mechanisms by which phonotrauma occurs. It was also found that an optimal value of supraglottal compression exists that maximizes the radiated SPL, indicating the potential utility of supraglottal compression as a compensatory mechanism.

CONCLUSIONS

Larger PGO areas are expected to increase the risk of phonotrauma due to the concomitant increase in dissipated collision power associated with maintaining SPL. Furthermore, the risk of VF damage may not be fully characterized by only the peak collision pressure.

H2O2 Concentration in Exhaled Breath Condensate Increases After Phonotrauma: A Promise of Noninvasive Monitoring?

PURPOSE

The present study was designed to observe the concentration of hydrogen peroxide (H2O2) in exhaled breath condensate (EBC) after induced phonotrauma.

METHODS

Thirty-five participants were randomly assigned to one of two conditions (1) Vocal demand and (2) Control. Participants in the experimental group (vocal demand) were asked to read aloud some texts during 1 hour, at 85-90 dB. Inflammation (H2O2 from exhaled breath condensate), acoustic, aerodynamic, and subjective measures were obtained at four time points: before vocal demand (baseline), immediately after baseline, 4-hour after baseline, and 24 hours after baseline. The same acquisition process was implemented for subjects in control group, except that they were not asked to engage in any vocal demand tasks at all.

RESULTS

As for biological samples, a significant effect for group was observed. Higher values were found for participants in experimental condition. Significant differences were observed for within contrasts in the experimental group, namely 4 hours against baseline, 4 hours against immediately post, and 24 hours against 4 hours. Instrumental outcomes did not show significant differences across the different conditions at any time points. Self-reported measures (vocal fatigue and sensation of muscle tension) showed a significant main effect for group and main effect for condition.

CONCLUSIONS

Intense vocal demand causes an increase in the concentration of H2O2 obtained from EBC at four hours after baseline, which is compatible with the generation of an inflammatory process in the vocal folds (phonotrauma). Moreover, the increase in the sensation of vocal fatigue and muscle tension after demand tasks seems to be an immediate reaction that did not match in time with the increment of H2O2 concentration.

Restoration Strategies Following Short-Term Vocal Exertion in Healthy Young Adults

Purpose This study aims to investigate the effects of a 10-min vocal exertion task on voice and respiratory measures, to determine whether restorative strategies can mitigate these effects after cessation of exertion, and to assess whether these strategies continue to reduce these detrimental effects when vocal exertion is resumed. Method A prospective, repeated-measures design was used. On consecutive days, 20 participants (equal men and women) completed two vocal exertion tasks separated by 10 min of restoration strategies: vocal rest or controlled phonation (low-level tissue mobilization using straw phonation). Voice and respiratory data were collected at baseline, following the first exertion task, after restoration strategies, and after the second exertion task. Outcome measures included (a) vocal effort, (b) phonation threshold pressure, (c) maximum and minimum fundamental frequencies, (d) cepstral peak prominence of connected speech, (e) lung volume initiation and termination, (f) percent vital capacity expended per syllable, and (g) number of syllables per breath group. Results A worsening of phonation threshold pressure (p < .001), vocal effort (p < .001), and increase of minimum fundamental frequency (p = .007) were observed after vocal exertion. Lung volume initiation (p < .001) and lung volume termination (p < .001) increased. These changes were largely reversed by restoration strategies, but only controlled phonation prevented exertion-induced changes in respiratory kinematic measures on a subsequent vocal exertion task. Conclusions Exertion-induced voice changes occur rapidly and may be mitigated by either controlled phonation or vocal rest. Controlled phonation is recommended as a superior strategy due to evidence of a protective effect on a successive vocal exertion task.

Predominant Vertical Location of Benign Vocal Fold Lesions by Sex and Music Genre: Implication for Pathogenesis

OBJECTIVES/HYPOTHESIS

Vertical locations of vocal fold mucosal lesions (VFMLs) vary along the free edge. As the vertical contact area of vocal folds (VFs) depends on the vocal register, lesions may occur in the contact area of more frequently used vocal registers. This study investigated the cause of location variations by comparing the vertical sites of VFMLs in singers of both sexes with different music genres.

STUDY DESIGN

Retrospective review.

METHODS

Sixty professional classical and rock singers (11 male classical [M-classical], 22 male rock [M-rock], 13 female classical [F-classical], and 14 female rock [F-rock] singers) who underwent microlaryngeal surgery for VF polyps and nodules and their 108 lesions were enrolled. The VF free edge was vertically divided into three equal parts and classified into the following four lesion sites: upper, middle, lower, and multiple sites.

RESULTS

Upper lesions were most common among F-classical singers (73.9%), whereas lower lesions were most common among M-classical (90.0%) and M-rock (60.6%) singers. Among lesions localized to a single site, lower lesions were most common among F-rock singers (37.0%). F-classical singers had significantly more upper lesions than the other groups (P < .001). M-classical singers had significantly more lower lesions than female singers of any genre (P < .001).

CONCLUSION

Upper lesions were most common among F-classical singers who mostly used the head voice. Lower lesions were most common among singers who mainly used the modal voice. This study suggests that sex, the dominant vocal register used for singing, and mechanical stress on VFs influence the vertical site of VFMLs.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E2284-E2291, 2021.

Consecuencias laringoscópicas, electroglotográficas, acústicas y sintomatológicas producidas por la sobrecarga vocal en mujeres con voces sanas y no entrenadas

La sobrecarga es una de las etapas del continuo de carga vocal. Actualmente, se considera que su investigación permite una mejor comprensión de la patología y sintomatología funcional de la voz. El objetivo de este trabajo fue analizar las consecuencias laringoscópicas, electroglotográficas, acústicas y sintomatológicas producidas por la sobrecarga vocal en mujeres con voces sanas y no entrenadas. Se examinó el comportamiento acústico, laringoscópico, electroglotográfico y sintomatológico de 30 mujeres que se sometieron a una tarea de sobrecarga vocal caracterizada por la lectura ininterrumpida de un texto durante 60 minutos, cuya intensidad fluctuó entre los 75 y 85 dB. A nivel laringoscópico, se observó mayor vascularización, aumento de la compresión supraglótica y cambios en la amplitud, simetría y onda mucosa. Acústicamente, se evidenció incremento significativo en la frecuencia fundamental e intensidad vocal. En la electroglotografía, el cociente de cierre y la fase abierta y cerrada disminuyeron significativamente, mientras que a nivel sintomatológico, la totalidad de la muestra expresó al menos un síntoma de fatiga vocal. En conclusión, los hallazgos observados son expresiones de la fatiga del mecanismo tiroaritenoideo y de la inflamación aguda de la cubierta cordal. 

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.

Ovine Vocal Fold Tissue Fatigue Response to Accumulated, Large-Amplitude Vibration Exposure at Phonatory Frequencies

Purpose The contribution of tissue mechanical response to vocal fatigue is poorly understood. This study investigated the fatigue response of vocal fold tissues to large-amplitude vibration exposure at phonatory frequencies, using an ex vivo ovine model. Method Twelve sheep vocal fold mucosal specimens were subjected to sinusoidal, simple-shear deformation for prolonged cycles, under a large but physiological shear strain (46%) in a frequency range of 100-230 Hz. The duration of shear varied from a critical vibration exposure limit of 1,040 s to 4 times the limit (4,160 s). Tissue viscoelastic response was quantified by the elastic shear modulus (G'), viscous shear modulus (G″), and damping ratio (G″/G'). Results Distinct response patterns were observed at different frequencies. G' and G″ generally decreased with vibration exposure at 100 Hz, whereas they generally increased with vibration exposure at 200 and 230 Hz. Statistically significant differences were found for G″ increasing with vibration exposure at 200 Hz and damping ratio decreasing with vibration exposure at 200 Hz. Significant increases with frequency were also found for all viscoelastic functions. Results suggested that the contribution of tissue viscoelastic response to vocal fatigue could be highly frequency dependent. In particular, increases in G″ with vibration exposure could lead to high phonation threshold pressures and difficulty sustaining phonation at higher frequencies following prolonged vocalization. Conclusion These preliminary findings may help us better understand vocal fatigue and recovery and should be corroborated by studies with human vocal fold tissues.

Prolonged phonation impairs the integrity and barrier function of porcine vocal fold epithelium: a preliminary study

PURPOSE

Voice abuse is known to be a common risk factor of voice disorders and prolonged; high-intensity phonation has been shown to damage the vocal fold epithelium. We aim to evaluate the effects of phonation on the integrity and barrier function of vocal fold epithelium using a porcine laryngeal model.

METHODS

Ex vivo porcine larynges were phonated at low intensity or high intensity for 15, 30, or 60 min within 4 h after harvest. Vocal fold epithelium was visualized using transmission electron microscopy (TEM). The barrier function of vocal fold epithelium was evaluated by measuring the permeability to model molecules, fluorescein (376 Da), and fluorescein isothiocyanate (FITC)-dextrans of 4000 and 10,000 Da (FD4, FD10), in a Franz diffusing cell.

RESULTS

Cell death and dilated intercellular space after phonation were observed using TEM. Thickness of vocal fold epithelium was significantly reduced after low-intensity phonation for 30 and 60 min and high-intensity phonation for 15, 30, and 60 min. Epithelial permeability to fluorescein was significantly increased after low-intensity phonation for 30 and 60 min, and high-intensity phonation. Permeability to FD4 was significantly increased after high-intensity phonation for 30 and 60 min. Phonation did not alter the permeability to FD10 significantly.

CONCLUSION

Long-duration phonation destroys the integrity and barrier function of vocal fold epithelium. These effects likely make vocal folds more vulnerable to other environmental irritants, such as tobacco smoke, reflux components, allergens, and inhaled pollutants. Destroyed barrier function may be an important factor in the pathogenesis of voice lesions related to voice abuse.

Survival in Vivo Canine Phonation Model Without Stimulation

OBJECTIVES

We describe a survival nonstimulated in vivo canine phonation model using distending laryngoscope, cramp frame, and constant humidified glottal airflow to elicit phonation.

METHODS

Five beagle dogs were involved in this study. One cuffed endotracheal tube was placed below the glottis through the tracheotomy and delivered humidified airflow to the glottis. Arytenoids approximation was maintained using a clamp under the distending laryngoscope. Acoustic and aerodynamic parameters were measured using synchronous signal collection system and analysis software. Vocal oscillation also was examined using stroboscope laryngeal imaging.

RESULTS

For the nonstimulated in vivo phonation animal, the sound intensity and fundamental frequency were 78.3 ± 6.8 dB and 127.6 ± 29.2 Hz in the first experiment and 82.9 ± 6.6 dB and 175.2 ± 4.4 Hz 4 weeks later. The aerodynamic analysis revealed the mean subglottal phonation threshold pressure (PTP) and phonation threshold flow (PTF) were 8.5 ± 4.0 cmH₂0 and 683.0 ± 356.4 mL/s in the first experiment and 16.1 ± 8.6 cmH₂0 and 384.8.0 ± 230.6 mL/s in the second experiment 4 weeks later. Stroboscope image revealed sustained vocal vibration during great airflow delivery to glottis in the phonation animal model.

CONCLUSIONS

We developed a survival nonstimulated in vivo phonation canine model that allows the study of long-term animal phonation study as its own control.

Quantifying Vocal Fatigue Recovery: Dynamic Vocal Recovery Trajectories after a Vocal Loading Exercise

Objectives

We quantified the recovery of voice following a 2-hour vocal loading exercise (oral reading).

Methods

Eighty-six adult participants tracked their voice recovery using short vocal tasks and perceptual ratings after an initial vocal loading exercise and for the following 2 days.

Results

Short-term recovery was apparent, with 90% recovery within 4 to 6 hours and full recovery at 12 to 18 hours. Recovery was shown to be similar to a dermal wound healing trajectory.

Conclusions

The new recovery trajectory highlighted by the vocal loading exercise in the current study is called a vocal recovery trajectory. By comparing vocal fatigue to dermal wound healing, this trajectory is parallel to a chronic wound healing trajectory (as opposed to an acute wound healing trajectory). This parallel suggests that vocal fatigue from the daily use of the voice could be treated as a chronic wound, with the healing and repair mechanisms in a state of constant repair. In addition, there is likely a vocal fatigue threshold at which point the level of tissue damage would shift the chronic healing trajectory to an acute healing trajectory.

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.

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.

Physiologic and Acoustic Effects of Opera Performance

INTRODUCTION/HYPOTHESIS

Opera performance is physiological and emotional, and singing performers utilize their larynges in often strenuous ways. Historically, the training of a classical voice has been considered the paragon of healthy singing. However, the natural history of a performing larynx has not been studied systematically. There is paucity of scientific studies to guide practice patterns, particularly with regard to the course and extent of post-performance physiologic and acoustic changes.

STUDY DESIGN

A prospective case series was carried out.

METHODS

Principal singers in the Houston Grand Opera's 2012-2013 repertory were enlisted, for a total of seven singers. Stroboscopy was performed prior to the start of rehearsals, and at the completion of the opera's run. Data points included erythema, edema, masses or lesions, mucosal waveform, supraglottic posture; acoustic measurements were also performed.

RESULTS

There were statistically significant differences (P < 0.05) in the mucosal wave on pre- and postperformance stroboscopic examinations. Acoustical measures did not achieve statistical significance, but there was a trend toward increased harmonic-to-noise ratio in postperformance measures, as well as decreased frequency range and reading F₀. Measures of intra- and inter-rater reliability indicated varying levels of intra-rater reliability, and generally poor inter-rater reliability.

CONCLUSIONS

This pilot study describes physiologic and acoustic changes that may occur over the course of a series of rehearsals and performances in the operatic larynx. In so doing, it highlights a need for larger studies with increased frequency of serial examinations to study in a systematized way what may be natural reactive changes that occur during performance.

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.

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.

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, β-catenin, interleukin 1β, cyclooxygenase-2, transforming growth factor β-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.

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.

Determination of strain field on the superior surface of excised larynx vocal folds using DIC

OBJECTIVE/HYPOTHESIS

The objective of the present study was to quantify the mechanical strain and stress in excised porcine larynges during self-oscillation using digital image correlation (DIC) method. The use of DIC in the excised larynx setup may yield accurate measurements of the vocal fold displacement field.

STUDY DESIGN

Ex vivo animal larynx.

METHODS

Measurements were performed using excised porcine larynges on a humidified flow bench, equipped with two high-speed cameras and a commercially available DIC software. Surface deformations were calculated from digital images recorded at 3000 frames per second during continuous self-oscillation for four excised porcine larynges. Larynx preparation consisted of removing the supraglottal wall and the false folds. DIC yielded the deformation field on the superior visible surface of the vocal folds. Measurement data for adducted and freely suspended vocal folds were also used to estimate the distribution of the initial prephonatory strain field. An isotropic constitutive law, the polymer eight-chain model, was used to estimate the surface distributions of planar stresses from the strain data.

RESULTS

The Lagrangian normal strain values were between ∼16% and ∼29% along the anterior-posterior direction. The motion of material points on the vocal fold surface described an elliptical trajectory during oscillation. A phase difference was observed between the anterior-posterior and the medial-lateral component of the displacement. The strain data and eight-chain model yielded a maximum stress of ∼4 kPa along the medial-lateral direction on the superior surface.

CONCLUSION

DIC allowed the strain field over the superior surface of an excised porcine larynx to be quantified during self-oscillation. The approach allowed the determination of the trajectory of specific points on the vocal fold surface. The results for the excised larynx were found to be significantly different than previous results obtained using synthetic replicas. The present study provides suggestions for future studies in human subjects.

Clinical practice: vocal nodules in dysphonic children

Common among children, vocal symptoms are a cause of concern for parents who seek elucidation of their diagnosis and treatment. Vocal nodules are the major cause of dysphonias in children and are related to vocal abuse. We conducted a literature review considering clinical, physiopathological, epidemiological, and histological aspects of vocal nodules, as well as diagnostic methods, highlighting the main studies addressing this issue. The controversial points of treatments were also discussed.

Voice rest after vocal fold surgery: current practice and evidence

Objective:

Voice rest is commonly recommended after vocal fold surgery, but there is a lack of evidence base and no standard protocol. The aim of this study was to establish common practice regarding voice rest following vocal fold surgery.

Method:

An online survey was circulated via e-mail invitation to members of the ENT UK Expert Panel between October and November 2011.

Results:

The survey revealed that 86.5 per cent of respondents agreed that ‘complete voice rest’ means no sound production at all, but there was variability in how ‘relative voice rest’ was defined. There was no dominant type of voice rest routinely recommended after surgery for laryngeal papillomatosis or intermediate pathologies. There was considerable variability in the duration of voice rest recommended, with no statistically significant, most popular response (except for malignant lesions). Surgeons with less than 10 years of experience were more likely to recommend fewer days of voice rest.

Conclusion:

There is a lack of consistency in advice given to patients after vocal fold surgery, in terms of both type and length of voice rest. This may arise from an absence of robust evidence on which to base practice.

A computational study of systemic hydration in vocal fold collision

Mechanical stresses develop within vocal fold (VF) soft tissues due to phonation-associated vibration and collision. These stresses in turn affect the hydration of VF tissue and thus influence voice health. In this paper, high-fidelity numerical computations are described, taking into account fully 3D geometry, realistic tissue and air properties, and high-amplitude vibration and collision. A segregated solver approach is employed, using sophisticated commercial solvers for both the VF tissue and glottal airflow domains. The tissue viscoelastic properties were derived from a biphasic formulation. Two cases were considered, whereby the tissue viscoelastic properties corresponded to two different volume fractions of the fluid phase of the VF tissue. For each case, hydrostatic stresses occurring as a result of vibration and collision were investigated. Assuming the VF tissue to be poroelastic, interstitial fluid movement within VF tissue was estimated from the hydrostatic stress gradient. Computed measures of overall VF dynamics (peak airflow velocity, magnitude of VF deformation, frequency of vibration and contact pressure) were well within the range of experimentally observed values. The VF motion leading to mechanical stresses within the VFs and their effect on the interstitial fluid flux is detailed. It is found that average deformation and vibration of VFs tend to increase the state of hydration of the VF tissue, whereas VF collision works to reduce hydration.

Experiments on Analysing Voice Production: Excised (Human, Animal) and In Vivo (Animal) Approaches

Experiments on human and on animal excised specimens as well as in vivo animal preparations are so far the most realistic approaches to simulate the in vivo process of human phonation. These experiments do not have the disadvantage of limited space within the neck and enable studies of the actual organ necessary for phonation, i.e., the larynx. The studies additionally allow the analysis of flow, vocal fold dynamics, and resulting acoustics in relation to well-defined laryngeal alterations.

PURPOSE OF REVIEW

This paper provides an overview of the applications and usefulness of excised (human/animal) specimen and in vivo animal experiments in voice research. These experiments have enabled visualization and analysis of dehydration effects, vocal fold scarring, bifurcation and chaotic vibrations, three-dimensional vibrations, aerodynamic effects, and mucosal wave propagation along the medial surface. Quantitative data will be shown to give an overview of measured laryngeal parameter values. As yet, a full understanding of all existing interactions in voice production has not been achieved, and thus, where possible, we try to indicate areas needing further study.

RECENT FINDINGS

A further motivation behind this review is to highlight recent findings and technologies related to the study of vocal fold dynamics and its applications. For example, studies of interactions between vocal tract airflow and generation of acoustics have recently shown that airflow superior to the glottis is governed by not only vocal fold dynamics but also by subglottal and supraglottal structures. In addition, promising new methods to investigate kinematics and dynamics have been reported recently, including dynamic optical coherence tomography, X-ray stroboscopy and three-dimensional reconstruction with laser projection systems. Finally, we touch on the relevance of vocal fold dynamics to clinical laryngology and to clinically-oriented research.

Verification of two minimally invasive methods for the estimation of the contact pressure in human vocal folds during phonation

The contact pressure on the vocal fold surface during high pitch or amplitude voice production is believed to be one major source of phonotrauma. Models for the quantitative estimate of the contact pressure may be valuable for prevention and treatment. Various indirect and minimally invasive approaches have been purported to estimate contact pressure. But the accuracy of these methods has not yet been objectively verified in controlled laboratory settings. In the present study, two indirect approaches for the estimation of the contact pressure were investigated. One is based on a Hertzian impact model, and the other on a finite element model. A probe microphone was used for direct measurements of the contact pressure and verifications of the indirect approaches. A silicone replica of human vocal folds was used as a test bed. Consistent contact pressure estimations were obtained using all three methods. The advantages and disadvantages of each approach for eventual clinical applications are described.

The inability to produce soft voice (IPSV): a tool to detect vocal change in school-teachers

PURPOSE

This study investigated whether clinicians could detect voice changes reported by teachers, from self-ratings teachers conducted of their inability to produce soft voice (IPSV).

METHODS

Ten teachers wore a vocal dosimeter and completed daily IPSV ratings approximately every 2 hours for 14 days. Following the 2 weeks of dosimetry, two speech clinicians specialized in voice rated the teachers' IPSV from dosimeter recordings. Teacher and clinician ratings were compared for each participant.

RESULTS

Although agreement between teacher and clinician ratings was not significant, descriptive analyses demonstrated an average difference score of 1.7 (SD 1.4) between teacher and clinician ratings.

CONCLUSIONS

This study supports the potential usefulness of the IPSV as a simple tool to detect voice changes in oneself or others.

Towards a self-rating tool of the inability to produce soft voice based on nonlinear events: a preliminary study

The purpose of this preliminary study was to investigate the feasibility of a tool to compare a severity index of nonlinear events and vocal self-rating over a long period of time. One hundred and ninety-seven phonations were analyzed to quantify the severity of instabilities in the voice attributed to nonlinear dynamic phenomena, including voice breaks, subharmonics, and frequency jumps. Instabilities were first counted; then a severity index was calculated for the instabilities in each phonation. The two quantities were compared to the subject's autoperceptual rating. Generally speaking, the measures derived from nonlinear dynamic analysis of the high-pitched, soft phonations followed the subject's own rating of inability to produce soft voice. These preliminary single subject results provide a foundation for future multi-subject studies to formulate acoustic and autoperceptual measures for the fatiguing effects of prolonged speaking in vocally demanding professions. However, given the number of observations, the results are still useful in showing general relationships. While future work should add additional subjects, a study providing preliminary evidence is useful before attempting to undertake a multi-subject study with complex analysis (i.e., individually selecting the nonlinear events) and with a long observation duration (days, weeks, and months) of subject.

Raised intensity phonation compromises vocal fold epithelial barrier integrity

OBJECTIVES/HYPOTHESIS

We investigated the hypothesis that 30 minutes of raised intensity phonation alters transcript levels of vocal fold intercellular tight junction proteins and disrupts the vocal fold epithelial barrier.

STUDY DESIGN

Prospective animal study.

METHODS

Eighteen New Zealand white breeder rabbits were randomly assigned to receive 30 minutes of raised intensity phonation or approximation of the vocal folds without phonation. Quantitative polymerase chain reaction (qPCR) was used to investigate transcript levels of the epithelial intercellular tight junction proteins, occludin and zonula occludin-1 (ZO-1), and the adherens junction proteins β-catenin and E-cadherin. Structural alterations to the vocal fold epithelium were further examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

Mann-Whitney U revealed significantly decreased occludin (P = .016) and β-catenin (P = .016) gene expression from rabbits undergoing raised intensity phonation compared with control. There were no significant differences in Z0-1 and E-cadherin gene expression between groups (P > .025). SEM revealed significant obliteration, desquamation, and evidence of microhole formation in rabbit vocal folds exposed to raised intensity phonation compared with control, whereas TEM revealed dilated intercellular morphology between groups.

CONCLUSIONS

Results provide support for the hypothesis that a transient episode of raised intensity phonation alters transcript levels of vocal fold intercellular tight junction proteins and disrupts integrity of the epithelial barrier. The loss of barrier integrity may have significant consequences on epithelial defenses and compromise protection of the underlying mucosa from damage secondary to prolonged vibration exposure.

Effects of raised-intensity phonation on inflammatory mediator gene expression in normal rabbit vocal fold

OBJECTIVE

To investigate the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory messenger RNA (mRNA) expression in vivo.

STUDY DESIGN

Prospective animal study.

SETTING

Laboratory.

SUBJECTS AND METHODS

Ten New Zealand White breeder rabbits received 30 minutes of experimentally induced modal or raised-intensity phonation, followed by a 30-minute recovery period. A separate group of five rabbits served as sham controls. Real-time polymerase chain reaction was performed to investigate the mRNA expression of interleukin 1beta (IL-1beta), transforming growth factor beta-1 (TGFbeta1), and cyclooxygenase-2 (COX-2). Separate one-way analysis of variance (ANOVA) tests were used to investigate differences in gene expression across groups, with an appropriate alpha correction of 0.016 to control for type I error. Significant main effects were further examined using Fisher's least significant difference.

RESULTS

ANOVA revealed that there were differences for IL-1beta, TGFbeta1, and COX-2 between sham control, modal phonation, and raised-intensity phonation (P 0.0001). Pairwise comparisons revealed that the expression of IL-1beta, COX-2, and TGFbeta1 increased significantly during raised-intensity phonation, compared to modal phonation and sham control (P 0.0001).

CONCLUSION

Results provided support for the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory mRNA expression. Future studies will investigate the signal transduction pathways and mechanisms regulating the vocal fold inflammatory response. The long-term goal of these studies is to advance understanding of the molecular and cellular events underlying phonation-related tissue alterations.

Vocal polyps: clinical, morphological, and immunohistochemical aspects

OBJECTIVES

To study the clinical, morphological, and immunohistochemical characteristics of vocal polyps.

STUDY DESIGN

Prospective and retrospective.

METHODS

Clinical study: 76 medical charts from patients with polyps were reviewed. Histology study: in 42 slides from surgical specimens, the following were analyzed: epithelium, basal membrane, and lamina propria. In the transmission and scanning electron microscopy (TEM and SEM) studies, eight new cases of polyps were included. An immunohistochemical study was carried out in the 42 specimens, using antibody antifibronectin, antilaminin, and anticollagen IV.

RESULTS

Genders--43% males and 57% females; age range--between 21 and 40 years (36.85%); and between 41 and 60 years of age (51.31%); smoking and drinking-reported by 39 and 15 patients, respectively; associated symptoms-vocal abuse (61%), gastroesophageal (47%), and nasosinusal symptoms (32%); occupation--teachers (24.0%) and maids (18.0%). Histology--epithelial hyperplasia (31.71%), hyperkeratosis, (14.28%), edema (100%), vessel proliferation (92.86%), and congestion (83.33%). SEM--reduction in mucous lacing and increase in desquamating cells. TEM--hyperplastic epithelium, enlargement of the intercellular junctions, dense subepithelial network of collagen and basal membrane with adhesion loss. Immunohistochemistry--greater immunoexpression of fibronectin, laminin, and collagen IV around the vessels.

CONCLUSIONS

In vocal polyps, the morphological analyses show lamina propria with edema, vessel proliferation and inflammation, basement membrane with adhesion loss in some areas and dense network of subepithelial collagen. Immunohistochemistry techniques identify pigmentation of the antibodies anti-fibronectin, anti-laminin, and anti-collagen IV in the endothelium of blood vessels.

Vocal fold nodules: morphological and immunohistochemical investigations

The objective of this study was to investigate the morphological and immunohistochemical characteristics of vocal fold nodules. The study design was prospective and retrospective. For the histological study, we reviewed 15 slides from the surgical cases of vocal fold nodules, in which we analyzed epithelium, basal membrane (bm), and lamina propria. For the transmission and scanning electron microscopy (TEM, SEM) studies, five new cases on vocal fold nodules were included. Immunohistochemistry study was carried out in the 15 specimens, using antifibronectin, antilaminin, and anticollagen IV antibodies. The main histological alterations were epithelial hyperplasia (73.33%), basement membrane thickening (86.66%), edema, and fibrosis (93.33%). SEM--reduction in mucous lacing and increase in the desquamating cells, without epithelial erosion. TEM--hyperplasia of the epithelium, enlargement of the intercellular junctions, which was filled by fluid, subepithelial thickening of the lamina reticularis, and break points in the basal membrane. Immunohistochemistry--we identified greater immunoexpression of fibronectin on the basal membrane, on the lamina propria, and around the vessels. Antilaminin and anticollagen IV antibodies showed higher pigmentation on the endothelium of the vessels than that on the basal membrane. In vocal fold nodules, combined assessment using light microscopy, electron microscopy, and immunohistochemistry can reveal important morphological details useful in characterizing these lesions.

Voice rest versus exercise: a review of the literature

Voice rest is commonly prescribed after vocal fold surgery to promote wound healing of the vocal fold. Currently, there is no standard protocol that is established based on biological evidence. In orthopedic rehabilitation, long-term rest is found to be less effective for connective tissue healing than exercise. Connective tissue healing is also an important factor for successful voice rehabilitation; however, whether this concept can be extrapolated to voice rehabilitation is unknown. The purpose of this article is to review current clinical and basic science literature to examine the effect of voice rest in postsurgical rehabilitation. First, we present a summary of clinical literature that pertains to voice rest. Second, we present description of connective tissues that are involved in orthopedic and voice rehabilitation, specifically, ligament and lamina propria, respectively, and their wound healing process. Third, a summary of the literature from orthopedic research on the effect of rest versus exercise is presented. Lastly, it summarizes in vitro and in vivo studies that examined the effect of mechanical stress on vocal fold tissue. Current literature suggests that there is a lack of clinical evidence that supports a specific type and duration of voice rest, and extrapolation of the findings from orthopedic research may be unreasonable due to the morphological and biochemical difference between the tissues. To determine the effect of voice rest, further elucidation of vocal fold wound healing process and the effect of mechanical stress on vocal fold tissue remodeling are needed.

Liquid accumulation in vibrating vocal fold tissue: a simplified model based on a fluid-saturated porous solid theory

The human vocal fold is treated as a continuous, transversally isotropic, porous solid saturated with liquid. A set of mathematical equations, based on the theory of fluid-saturated porous solids, is developed to formulate the vibration of the vocal fold tissue. As the fluid-saturated porous tissue model degenerates to the continuous elastic tissue model when the relative movement of liquid in the porous tissue is ignored, it can be considered a more general description of vocal fold tissue than the continuous, elastic model. Using the fluid-saturated porous tissue model, the vibration of a bunch of one-dimensional fibers in the vocal fold is analytically solved based on the small-amplitude assumption. It is found that the vibration of the tissue will lead to the accumulation of excess liquid in the midmembranous vocal fold. The degree of liquid accumulation is positively proportional to the vibratory amplitude and frequency. The correspondence between the liquid distribution predicted by the porous tissue theory and the location of vocal nodules observed in clinical practice, provides theoretical evidence for the liquid accumulation hypothesis of vocal nodule formation (Jiang, Ph.D., dissertation, 1991, University of Iowa).

Model of evoked rabbit phonation

OBJECTIVES

We describe a method for eliciting phonation in an in vivo rabbit preparation using low-frequency, bipolar pulsed stimulation of the cricothyroid muscles with airflow delivered to the glottis.

METHODS

Ten New Zealand White breeder rabbits weighing 3 to 5 kg were used in this study. The cricothyroid muscles were isolated bilaterally, and separate pairs of anode-cathode hooked-wire electrodes were inserted into each muscle. A Grass S-88 stimulator and 2 constant-current PSIU6 isolation units were used to deliver bipolar square wave pulses to each cricothyroid muscle, with airflow delivered to the glottis through a cuffed endotracheal tube.

RESULTS

Phonation was evoked with a 50-Hz, 4-mA stimulus train of 1-ms pulses delivered to each cricothyroid muscle. The pulse trains were on for 2 seconds and were repeated every 5 seconds over a period of 180 minutes. Airflow was delivered at 143 cm3/s, producing phonation measuring 71 to 85 dB sound pressure level.

CONCLUSIONS

Evoked phonation is feasible in rabbits by use of bipolar stimulation of the cricothyroid muscles with airflow delivered to the glottis. The in vivo rabbit preparation described may provide a useful small animal option for studies of evoked phonation. From the level and consistency of the adduction observed, we hypothesize that current spreading to the underlying adductor muscles and nerves resulted in neural pathway involvement beyond discrete activation of the cricothyroid muscle, providing sufficient approximation of the vocal folds for phonation.

A patient-specific in silico model of inflammation and healing tested in acute vocal fold injury

The development of personalized medicine is a primary objective of the medical community and increasingly also of funding and registration agencies. Modeling is generally perceived as a key enabling tool to target this goal. Agent-Based Models (ABMs) have previously been used to simulate inflammation at various scales up to the whole-organism level. We extended this approach to the case of a novel, patient-specific ABM that we generated for vocal fold inflammation, with the ultimate goal of identifying individually optimized treatments. ABM simulations reproduced trajectories of inflammatory mediators in laryngeal secretions of individuals subjected to experimental phonotrauma up to 4 hrs post-injury, and predicted the levels of inflammatory mediators 24 hrs post-injury. Subject-specific simulations also predicted different outcomes from behavioral treatment regimens to which subjects had not been exposed. We propose that this translational application of computational modeling could be used to design patient-specific therapies for the larynx, and will serve as a paradigm for future extension to other clinical domains.

Vocal nodules and edema may be due to vibration-induced rises in capillary pressure

HYPOTHESIS

Vocal fold vibration may physically raise intravascular pressure to levels high enough to damage capillaries and result in leakage of erythrocytes. This type of injury is commonly seen in benign vocal fold lesions and is not well explained.

STUDY DESIGN

Theoretical, retrospective.

METHODS

The relationship of intravascular pressure to vibration frequency and amplitude is derived and confirmed with a physical blood vessel model, then applied to published human measurements to estimate human intravascular pressures.

RESULTS

Vocal fold intravascular pressure is predicted to have a quadratic dependence on both frequency and amplitude. During speaking, the pressure may rise to over 20 cmH2O, and may reach levels far higher for screaming and singing. Such pressure magnitudes are known to trigger inflammatory cascades and can lead to fluid leakage. They also have the potential for pharmacologic control with beta-agonists.

CONCLUSIONS

Intravascular pressure likely rises significantly during vocal fold vibration and may lead to the type of injury seen in benign vocal fold lesions. The results support voice therapy aimed at reducing vibratory amplitude. More vibratory amplitude measurements need to be performed in a wider range of subjects before the full range of human vocal fold vascular pressures can be estimated.

Paxillin modulates squamous cancer cell adhesion and is important in pressure-augmented adhesion

Paxillin is an adapter protein regulating signaling and focal adhesion assembly that has been linked to malignant potential in many malignancies. Overexpression of paxillin has been noted in aggressive tumors. Integrin-mediated binding through the focal adhesion complex is important in metastatic adhesion and is upregulated by extracellular pressure in malignant colonocytes through FAK and Src activation. Neither head and neck cancers nor paxillin have been studied in this regard. We hypothesized that paxillin would play a role in modulating squamous cancer adhesion both at baseline and under conditions of increased extracellular pressure. Using SCC25 tongue squamous cancer cells stably transfected with either an empty selection vector or paxillin expression and selection vectors, we studied adhesion to collagen, paxillin, FAK, and Src expression and phosphorylation in cells maintained for 30 min under ambient or 15 mmHg increased pressure conditions. Paxillin-overexpressing cells exhibited adhesion 121 +/- 2.9% of that observed in vector-only cells (n = 6, P < 0.001) under ambient pressure. Paxillin-overexpression reduced FAK phosphorylation. Pressure stimulated adhesion to 118 +/- 2.3% (n = 6, P < 0.001) of baseline in vector-only cells, similar to its effect in the parental line, and induced paxillin, FAK, and Src phosphorylation. However, increased pressure did not stimulate adhesion or phosphorylate paxillin, FAK, or Src further in paxillin-overexpressing cells. Metastasizing squamous cancer cell adhesiveness may be increased by paxillin-overexpression or by paxillin activation by extracellular pressure during surgical manipulation or growth within a constraining compartment. Targeting paxillin in patients with malignancy and minimal tumor manipulation during surgical resection may be important therapeutic adjuncts.

Simulated effects of cricothyroid and thyroarytenoid muscle activation on adult-male vocal fold vibration

Adjustments to cricothyroid and thyroarytenoid muscle activation are critical to the control of fundamental frequency and aerodynamic aspects of vocal fold vibration in humans. The aerodynamic and physical effects of these muscles are not well understood and are difficult to study in vivo. Knowledge of the contributions of these two muscles is essential to understanding both normal and disordered voice physiology. In this study, a three-mass model for voice simulation in adult males was used to produce systematic changes to cricothyroid and thyroarytenoid muscle activation levels. Predicted effects on fundamental frequency, aerodynamic quantities, and physical quantities of vocal fold vibration were assessed. Certain combinations of these muscle activations resulted in aerodynamic and physical characteristics of vibration that might increase the mechanical stress placed on the vocal fold tissue.

Strain distribution in an elastic substrate vibrated in a bioreactor for vocal fold tissue engineering

A bioreactor previously described was used to quantify the shear strain along a bioengineered tissue scaffold driven at low audio frequencies (20-200 Hz). Standing wave patterns were calculated analytically by solving a classical boundary value problem for a vibrating string under tension and bending stiffness. Boundary conditions were non-traditional in that small pivot arms at the endpoints allowed neither the displacement nor the velocity to go to zero. The calculations were corroborated with stroboscopic measurement of the motion of the material in the bioreactor. Results indicate that shear strains up to 0.2 can be obtained at low frequencies (20 Hz), with a gradual decrease at higher frequencies due to the decaying amplitude response of the mechanical driver. The bioreactor may be useful for approximating the Young's modulus of the material in situ by probing for resonance frequencies in the standing wave pattern. A yet unsolved problem is a variable drag coefficient along the length of the material due to fluid turbulence in the culture medium.

Advances in our understanding of the Reinke space

PURPOSE OF REVIEW

Normal vocal fold vibration depends critically upon the composition of the Reinke space or the lamina propria extracellular matrix. Alterations in the normal composition of the extracellular matrix result in a loss of normal vibratory function. In this article, the present literature on the Reinke space in normal and disease states is reviewed including publications in the multidisciplinary fields of biomechanics, histology, molecular biology, and tissue engineering.

RECENT FINDINGS

With recent technology advances, the etiology for benign lesions has been investigated with computer models and bioreactors. Particular extracellular matrix constituents in various benign vocal fold lesions--fibronectin, fibromodulin and hyaluronan--appear to be involved in altering the viscoelastic properties of the Reinke space. Significant basic science approaches to the investigation of the characterization of the Reinke space in vocal fold scarring has produced several potential future treatment avenues. Tissue-engineering approaches for regeneration of the Reinke space are the most recent addition to the literature showing promising research directions.

SUMMARY

Voice disorders represent a significant clinical problem. Research attempting to discover the underlying molecular and genetic regulation and homeostasis of the extracellular matrix of the Reinke space are essential. Effective future clinical interventions must be based upon the knowledge of how genetic and biologic features are disturbed in vocal diseases and how they relate to vocal symptoms.

Vocal and Laryngeal Effects of Voiced Tongue Vibration Technique According to Performance Time

Our objective is to study the vocal and laryngeal effect as well as the negative signs and sensations related to the voiced tongue vibration technique (VTVT), regarding the time of performance (from 0 to 7 minutes). Thirty adults (15 men and 15 women) with no vocal complaints nor laryngeal disorders were involved. All subjects underwent laryngostroboscopic and auditory perceptual analysis and answered about the existence of uncomfortable sensations that occurred during the exercise (1, 3, 5, and 7 minutes) and postexercise. For the auditory perceptual analysis, the female group presented better outcomes in the third minute of exercise, whereas in general the male group showed no modification because of performance time. Some men presented a significant change in the parameters involved from the fifth minute on. Men and women showed a gradual increase of undesirable sensations. It is extremely important that the performance time of the VTVT is properly prescribed to provide the expected results, without causing undue injuries to the vocal system. Therefore, we suggest this technique should be recommended for 3 and 5 minutes for women and men, respectively.

Perceived phonatory effort and phonation threshold pressure across a prolonged voice loading task: a study of vocal fatigue

Although the problem of vocal fatigue is not uncommon in people with voice disorders, research on objective quantifiable indicators of vocal fatigue is limited. It has been suggested that a speaker's perception of increased phonatory effort associated with periods of prolonged voice use is related to increased lung pressure required to initiate and sustain phonation. The purpose of this study was to examine the relationship among perceived phonatory effort (PPE), which was used as a subjective index of vocal fatigue, and phonation threshold pressure (PTP), a quantifiable measure defined as the minimal lung pressure required to initiate and sustain vocal fold oscillation. PTP and PPE were recorded before, during, and after five adult male and five adult female speakers engaged in a prolonged oral reading task designed to induce vocal fatigue. The results supported a direct, moderately strong relationship between PTP and PPE, particularly when PTP was measured during speech produced at comfortable and low-speaking pitch levels. No gender effects were found. PTP returned to baseline levels within 1 hour after the fatiguing task. PPE returned to baseline within 1 day. The data support the use of PTP as an objective index of vocal fatigue.

Modeling mechanical stresses as a factor in the etiology of benign vocal fold lesions

Vocal fold tissue lesions such as nodules and polyps are thought to develop in response to mechanical stress that occurs during vocal fold collision. Two computational models of vocal fold collision during voice production are used to investigate this hypothesis. A one-dimensional lumped mass model, whose parameters are derived from vocal fold tissue dimensions and material properties, predicts stress perpendicular to the direction of impact (normal stress). A previously published three-dimensional finite element model that incorporates the same dimensions and properties predicts the entire stress tensor. The hypothesis is supported by predictions from the finite element model that three components of normal stress and one component of shear stress are increased during collision in the typical location of lesions (i.e. the center of the superior medial edge of the vocal fold in the middle of the vibrating and contact region). The lumped mass model predicts that mechanical stress is negatively correlated with mucosal thickness (increased by voice warm-up and hydration), is positively correlated with driving force (proportional to voice intensity), and is affected by voice production method. These relationships are consistent with clinical observations of vocal fold lesion risk factors and have implications for improving prevention and treatment of benign vocal fold lesions.