Electron microscopy of hyperphonated canine vocal cords

Toward Development of a Vocal Fold Contact Pressure Probe: Sensor Characterization and Validation Using Synthetic Vocal Fold Models

Excessive vocal fold collision pressures during phonation are considered to play a primary role in the formation of benign vocal fold lesions, such as nodules. The ability to accurately and reliably acquire intraglottal pressure has the potential to provide unique insights into the pathophysiology of phonotrauma. Difficulties arise, however, in directly measuring vocal fold contact pressures due to physical intrusion from the sensor that may disrupt the contact mechanics, as well as difficulty in determining probe/sensor position relative to the contact location. These issues are quantified and addressed through the implementation of a novel approach for identifying the timing and location of vocal fold contact, and measuring intraglottal and vocal fold contact pressures via a pressure probe embedded in the wall of a hemi-laryngeal flow facility. The accuracy and sensitivity of the pressure measurements are validated against ground truth values. Application to in vivo approaches are assessed by acquiring intraglottal and VF contact pressures using a synthetic, self-oscillating vocal fold model in a hemi-laryngeal configuration, where the sensitivity of the measured intraglottal and vocal fold contact pressure relative to the sensor position is explored.

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.

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.

Characterization of raised phonation in an evoked rabbit phonation model

OBJECTIVES/HYPOTHESIS

Our laboratory has developed an in vivo rabbit model to investigate the effects of phonation on expression and turnover of the vocal fold extracellular matrix. As a logical outgrowth of this research to include phonotrauma in the present study, we investigated the hypothesis that an increase in airflow rate delivered to the glottis produces a change in glottal configuration and an increase in mean phonation intensity.

STUDY DESIGN

Prospective animal study.

METHODS

Six New Zealand white breeder rabbits weighing 3 to 5 kg were used in this study. A rigid endoscope and camera were used to document glottal configuration. Acoustic signals of modal and raised phonation were recorded and digitized. Two separate one-way repeated measures analysis of variance (ANOVA) tests were used to investigate within subject differences in phonation intensity and fundamental frequency between modal and raised phonation.

RESULTS

Phonation intensity was 54.19 dB SPL (6.21 standard deviations [SD]) during modal phonation, and 60.31 dB SPL (5.68 SD) during raised phonation. Endoscopic images revealed a convergent glottis, with greater separation of the vocal folds during raised phonation. Results of ANOVA revealed a significant within subjects effect for phonation intensity (P = .011). Pairwise comparisons revealed that phonation intensity increased significantly during raised phonation, compared to modal phonation (P = .008). No differences in mean fundamental frequency were observed between phonation conditions.

CONCLUSIONS

Improved understanding of factors that control phonation output in the in vivo rabbit model will result in improved capabilities to match phonation dose across animals and provide immediate direction to future biochemical studies.

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.

Epidemiological study of voice disorders among teaching professionals of La Rioja, Spain

The purpose of the present study was to calculate the prevalence and incidence of voice disorders among teaching staff and find out the associated occupational risk factors. A case-control study was performed with 905 teachers, 579 cases and 326 controls; 492 were randomly selected and 413 volunteered. All teachers were asked to fill out a standard questionnaire. Next, a complete laryngeal exam was performed including a general ear, nose, and throat evaluation and videolaryngostroboscopy. The prevalence of voice disorders among teaching staff was 57%. The most prevalent lesions were vocal overstrain (18%), nodular lesions (14%), and hyperfunctional dysphonia (8%). The incidence rate was 3.87 new cases per year per 1000 teachers. Women had organic lesions three times more than men (odds ratio [OR]: 3.52, confidence interval [CI]: 2.04-6.09). However, men had chronic laryngitis three times more than women (OR: 2.93, CI: 1.50-5.71) and functional dysphonia nearly twice more than women (OR: 1.81, CI: 1.21-2.69). We find a significant risk of suffering voice disorders in teachers who smoke daily (OR: 2.31, CI: 1.58-3.37) and who drink several cups of coffee or tea (OR: 1.87, CI: 1.36-2.56). It is advisable to carry out an annual evaluation of all teaching staff on account of the high prevalence of voice disorders among them.

April 16th: The World Voice Day

Although the voice is used as an everyday basis of speech, most people realize its importance only when a voice problem arises. Increasing public awareness of the importance of the voice and alertness to voice problems are the main goals of the World Voice Day, which is celebrated yearly on April 16th. The event started as a national initiative in Brazil in 1999 and quickly spread internationally. The article provides a brief history of the World Voice Day, together with basic background information.

Mechanical stress during phonation in a self-oscillating finite-element vocal fold model

The stress information during phonation in the vocal folds is helpful in understanding the etiologies of vocal trauma and its related vocal diseases, such as nodules. In this paper, a self-oscillating finite-element model, which combines aerodynamic properties, tissue mechanics, airflow-tissue interactions, and vocal fold collisions, was used to simulate the vocal fold vibration during phonation. The spatial and temporal characteristics of mechanical stress in the vocal folds were predicted by this model. Temporally, it was found that mechanical stress periodically undulates with vibration of the vocal folds and that vocal fold impact causes a jump in the normal stress value. Spatially, the normal stress is significantly higher on the vocal fold surface than inside of the vocal folds. At the midpoint of the medial surface, the peak-to-peak amplitude of the normal stress reaches its maximum value. Using different lung pressures (0-1.5kPa) to drive the self-oscillating model, we found that lower lung pressure can effectively decrease the mechanical stress in the vocal folds. This study supports the fatigue damage hypothesis of vocal trauma. With this hypothesis and the numerical simulation in this study, the clinical observations of vocal fold trauma risk can be explained. This implies the mechanical stress predicted by this self-oscillating model could be valuable for predicting, preventing, and treating vocal fold injury.

Voicing and silence periods in daily and weekly vocalizations of teachers

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

Simulation of vocal fold impact pressures with a self-oscillating finite-element model

Vocal fold impact pressures were studied using a self-oscillating finite-element model capable of simulating vocal fold vibration and airflow. The calculated airflow pressure is applied on the vocal fold as the driving force. The airflow region is then adjusted according to the calculated vocal fold displacement. The interaction between airflow and the vocal folds produces a self-oscillating solution. Lung pressures between 0.2 and 2.5 kPa were used to drive this self-oscillating model. The spatial distribution of the impact pressure was studied. Studies revealed that the tissue collision during phonation produces a very large impact pressure which correlates with the lung pressure and glottal width. Larger lung pressure and a narrower glottal width increase the impact pressure. The impact pressure was found to be roughly the square root of lung pressure. In the inferior-superior direction, the maximum impact pressure is related to the narrowest glottis. In the anterior-posteriorfirection, the greatest impact pressure appears at the midpoint of the vocal fold. The match between our numerical simulations and clinical observations suggests that this self-oscillating finite-element model might be valuable for predicting mechanical trauma of the vocal folds.

Neto J, Pontes P. Diferenciação histopatológica e imunoistoquímica das alterações epiteliais no nódulo vocal em relação aos pólipos e ao edema de laringe

OBJETIVO: Avaliar, por meio de técnicas histológicas e imunoistoquímicas, o epitélio nos nódulos vocais em relação aos pólipos, ao edema de laringe e às pregas vocais sem lesões macroscópicas. FORMA DE ESTUDO: Clínico retrospectivo. MATERIAL E MÉTODO: Por meio de levantamento de prontuário, foram identificados vinte e seis pacientes com lesões laríngeas inflamatórias (nódulos, pólipos e edema de laringe), que haviam sido submetidos à cirurgia. Pregas vocais sem alterações macroscópicas foram obtidas a partir de autópsia de cadáveres. Para análise do epitélio, foram realizadas colorações pela técnica da hematoxilina-eosina e do ácido periódico de Schiff e técnicas de imunoistoquímica com anticorpos dirigidos contra laminina e colágeno IV. A leitura das lâminas foi realizada por meio de microscopia óptica. RESULTADOS: Houve maior imunoexpressão de laminina e colágeno IV nos nódulos quando comparados aos pólipos (p=0,034 e p=0, 036, respectivamente), assim como quando comparados às pregas vocais sem lesões macroscópicas (p=0,019 e p=0, 021, respectivamente). Nódulos tendem a apresentar maior espessura da membrana basal, quando utilizamos coloração pela técnica do PAS, em relação aos pólipos (p=0,102). O edema de laringe não se diferenciou das demais nas técnicas utilizadas (p> 0,10). CONCLUSÕES: O Nódulo Vocal diferencia-se dos pólipos, nas três técnicas utilizadas para detecção da membrana basal (PAS, laminina, colágeno IV), e das pregas vocais sem lesões macroscópicas em duas das técnicas utilizadas (laminina e colágeno IV). Edema de laringe não se diferencia das demais lesões, nem de pregas vocais sem lesões macroscópicas, quando utilizadas as técnicas anteriormente descritas, para estudo da membrana basal.

The harmonic-to-noise ratio applied to dog barks

Dog barks are typically a mixture of regular components and irregular (noisy) components. The regular part of the signal is given by a series of harmonics and is most probably due to regular vibrations of the vocal folds, whereas noise refers to any nonharmonic (irregular) energy in the spectrum of the bark signal. The noise components might be due to chaotic vibrations of the vocal-fold tissue or due to turbulence of the air. The ratio of harmonic to nonharmonic energy in dog barks is quantified by applying the harmonics-to-noise ratio (HNR). Barks of a single dog breed were recorded in the same behavioral context. Two groups of dogs were considered: a group of ten healthy dogs (the normal sample), and a group of ten unhealthy dogs, i.e., dogs treated in a veterinary clinic (the clinic sample). Although the unhealthy dogs had no voice disease, differences in emotion or pain or impacts of surgery might have influenced their barks. The barks of the dogs were recorded for a period of 6 months. The HNR computation is based on the Fourier spectrum of a 50-ms section from the middle of the bark. A 10-point moving average curve of the spectrum on a logarithmic scale is considered as estimator of the noise level in the bark, and the maximum difference of the original spectrum and the moving average is defined as the HNR measure. It is shown that a reasonable ranking of the voices is achievable based on the measurement of the HNR. The HNR-based classification is found to be consistent with perceptual evaluation of the barks. In addition, a multiparametric approach confirms the classification based on the HNR. Hence, it may be concluded that the HNR might be useful as a novel parameter in bioacoustics for quantifying the noise within a signal.

The prevalence of voice disorders among day care center teachers compared with nurses: a questionnaire and clinical study

The acceptance of voice disorders by day care center teachers as an occupational disease is not an invariably established practice. This is due to the lack of reliable evidence of a higher risk for voice disorders in this profession. To find out the risk of voice disorders, an epidemiological study was conducted among day care center teachers (n = 262), using hospital nurses (n = 108) as a control group. Symptoms were charted by a questionnaire. In a clinical examination made by a laryngologist, the voice quality was assessed and the laryngeal status noted. Teachers at day care centers had significantly more voice disorders than did nurses. Vocal nodules and laryngitis findings appeared significantly more frequently among day care center teachers than among those in the control group. The results prove voice disorders to be more frequent among day care center teachers than among control group subjects, and also that the main cause for this may be a higher vocal loading among day care center teachers than among control group subjects.

A quantitative output-cost ratio in voice production

A quantitative output-cost ratio (OCR) is proposed for objective use in voice production and is defined as the ratio of the acoustic output intensity to the collision intensity of the vocal folds. Measurement of the OCR is demonstrated in a laboratory experiment using 5 excised larynges and a transducer designed for use on human subjects. Data were gathered at constant fundamental frequency (150 Hz). Subglottal pressure was varied from 1.0 to 1.6 kPa, and glottal width at the vocal processes was varied from a pressed condition to a 2-mm gap. The OCR was plotted as a function of glottal width. With no vocal tract, the excised larynx experiments yielded a broad maxima in the OCR curves, across all subglottal pressure conditions, at about 0.6 mm. Computer simulations indicate that sharper maxima may occur when the influence of the vocal tract is taken into account. The potential clinical utility of the OCR is discussed for treatment of a wide range of voice disorders, including those involving both hyper- and hypoadduction.

Correspondence of electroglottographic closed quotient to vocal fold impact stress in excised canine larynges

The purpose of this study was to explore the possible use of the electroglottographic closed quotient (EGG CQ) as a noninvasive estimate of vocal fold impact stress (SI). Two excised canine larynges were used. Each larynx was mounted and vocal fold oscillation was induced using a humidified air source. Twenty-seven experimental trials were conducted for each larynx. Trials involved variations in vocal process gap, vocal fold elongation, and subglottic pressure. Simultaneous measures were made of vocal fold SI at the midpoint of the membranous vocal folds, and EGG CQ (dimensionless ratio). The results indicated that when threshold and saturation effects were excluded, the SI and the CQ were strongly related (linear correlation r = .83 and .96 for the two individual larynges, and .81 for the combined data). Within the region of linear relation, an increase of.15 in the CQ corresponded to about 1 kPa increase in SI for the combined data. Discussion focuses on possible clinical implications and the likely reasons for threshold and saturation phenomena.

Immunohistochemical characterization of benign laryngeal lesions

It has been proposed that laryngeal nodules and polyps represent injury to the basement membrane zone of the vocal fold. Repeated trauma from shearing forces produced by excessive or abusive phonation leads to basement membrane zone disruption and thickening. This thickening, along with poorly understood vascular changes, creates the characteristic clinical appearance of the vocal nodule or polyp. As such, to better understand vocal fold nodules it is imperative to characterize the extracellular matrix in this area of injury. Secondary to the small size and relatively acellular nature of these lesions, hematoxylin and eosin (H & E) preparations of histologic material are unsatisfying. A previous study examined this area with immunohistochemical techniques to better characterize its contents. The report, however, contained little information with regard to the clinical appearance of the lesions prior to excision. Therefore, we were prompted to review histologic material from 31 patients who underwent microsurgical excision of 41 benign lesions, vocal nodules (4), polyps (19), polypoid corditis (4), and cysts (14) with immunohistochemical techniques to characterize the patterns of fibronectin and collagen type IV within these lesions. Normal human vocal folds were stained for control. All material was correlated with the H & E preparations and the clinical diagnosis. Collagen type IV and fibronectin appeared present in relatively abnormal patterns in the areas adjacent to the lesion. This study validates earlier results. In addition, correlation with clinical data allows association of immunohistochemical staining patterns with clinical diagnosis.

Immunocytochemical study of proteoglycans in vocal folds

We evaluated the proteoglycan composition of normal vocal folds using immunocytochemical techniques. Frozen sections of 14 normal cadaveric vocal folds were obtained within 12 hours of death and sectioned immediately. Vocal fold sections were stained with antibodies against keratan sulfate, chondroitin sulfate, heparan sulfate proteoglycan (HSPG), decorin, and hyaluronate receptor. We found that the lamina propria has diffuse staining of fibrillar components with keratan sulfate and decorin. Intense staining was observed in the vocal ligament area with keratan sulfate. The HSPG was localized to be basement membrane zone. Chondroitin sulfate, HSPG, and hyaluronate receptor were detected in the cytoplasm of interstitial cells with immunocytochemical characteristics of macrophages. The keratan sulfate distribution suggests that fibromodulin may be significant in normal vocal folds. Production of HSPG and probably versican occurs in macrophages and fibroblasts in the lamina propria.

Benign pathologic responses of the larynx

Benign laryngeal lesions were examined for patterns of injury indicated by deposition of fibronectin and collagen type IV. An immunoperoxidase technique was used to compare 33 fresh or paraffin-embedded tissues with regard to their staining of monoclonal antibodies directed against fibronectin and collagen type IV. Two types of patterns were recognized. One pattern showed intense fibronectin deposition in the superficial layer of the lamina propria, often coupled with basement membrane zone injury, indicated by thick collagen type IV bands. The other pattern showed rare basement membrane zone injury and very little fibronectin deposition. The first pattern correlated more with nodules, the second pattern more with Reinke's edema and some polyps. A better understanding of the effects of excessive deposition of structural glycoproteins such as fibronectin and of abnormal proteoglycan deposition may lead to a better characterization of vocal fold disease and its causation and, ultimately, better treatment.

Mechanical stress in phonation

Mechanical stress is always encountered in phonation. This includes tensile stress, shear stress, impact stress during collision, maximum active contractile stress in laryngeal muscles, inertial stress, and aerodynamic stress (pressure). Order of magnitude calculations reveal that tensile stress can reach the greatest value (near 1.0 MPa), contractile stress is next in size (near 100 kPa), and aerodynamic stress is relatively small (1-10 kPa). Inertial stress and impact stress are greater than aerodynamic stress, but less than contractile stress. Excessive collision and acceleration may be responsible for the greatest tissue damage, even though they do not account for the greatest stresses. This is because they act perpendicularly to the direction of tissue load-bearing fibers and are applied directly to mucosal tissue.

Pathological changes of hyperphonated cat vocal folds

To investigate the pathological changes of hyperphonated vocal folds 15 cats were used and over-cry was induced by mechanical stimuli. The longest experiment time was 15 weeks. All of the larynges were taken and the vocal folds were examined grossly and microscopically. The results were as follows: 1) liquid exudate accumulation beneath the epithelium developed in all of the experimental animals; 2) thickening of the epithelium was noticed in cats which had hyperphonated for more than 4 weeks; 3) acute laryngitis occurred in three cats.

Histologic investigation of hyperphonated canine vocal cords

Vocal cord injury and its effect on the larynx are topics of considerable importance, yet a clear understanding of acute vocal cord injury from excessive phonation remains elusive. The inability to develop an animal model for vocal abuse has hampered research in this area. This project describes the development of a canine model for acute vocal cord injury from excessive phonation. The method of phonation consisted of a humidified, temperature-controlled, constant flow of air delivered subglottally by an external compressor. A small group of dogs underwent phonation for 2 and 4 hours. Vocal cord injury is described using histologic techniques. Damage to the vocal cords, other than hemorrhage (rare in dogs) and edema, proved to be too elusive for routine microscopy. Scanning and transmission electron microscopy showed extensive surface damage with destruction and loss of the surface microridges and premature desquamation of the vocal cord squamous epithelium. Injury extended to the lamina propria, where the collagen fibers were detached from the basement membrane.