Assessment of Changes in Laryngeal Configuration and Voice Parameters Among Different Frequencies of Neuromuscular Electrical Stimulation (NMES) and Cumulative Effects of NMES in a Normophonic Subject: A Pilot Study.

INTRODUCTION: Neuromuscular electrical stimulation (NMES) is a complementary resource to voice therapy that can be used for the treatment of hypofunctional voice disorders. Although positive clinical studies have been reported, neutral and even potentially harmful effects of NMES are also described in the literature. Furthermore, in the studies examined by the authors, the use of different methods of NMES have been identified, which further contributes to the inconsistent results found among studies. Moreover, limited rationale is provided for the chosen NMES parameters such as electrode placement, frequency of NMES and length of treatment. The aims of this pilot study were to investigate the a) impact of different frequencies of NMES on glottal configuration and vocal fold vibration patterns and b) changes in laryngeal configuration and vocal output across 12 minutes of NMES. METHOD: Three experiments were carried out looking at changes in laryngeal configuration and voice output using different imaging techniques (fibreoptic nasolaryngoscopy and high-speed video), acoustical analysis (F0, formant analysis, SPL, CPPS and LHSR values), electroglottography (EGG) and Relative Fundamental Frequency (RFF) analyses. Glottal parameters and acoustical measures were recorded before, during, and after stimulation. Data was collected at rest and during phonation. RESULTS: Overall the results showed global changes in laryngeal configuration from normal to hyperfunctional (ie, increased RFF, SPL, CQ, and stiffness). Changes were more pronounced for lower frequencies of NMES and were significant within less than three minutes of application. CONCLUSION: NMES is an effective resource for the activation of intrinsic laryngeal muscles producing significant levels of adduction within few minutes of application. Lower NMES frequencies produced greater muscle activation when compared to higher frequencies.

Optical flow based waveform for the assessment of the vocal fold vibrations.

Assessing vocal fold (VF) vibrations is important for the diagnosis of several diseases, and is made possible through the analysis of videoendoscopy recordings. However, the visual analysis of these recordings is hard due to the high acquisition rate. For this reason, it is commonly used to extract the laryngeal activity information from the recordings and represent it in a way suitable to be visually analyzed. Waveforms, images and playbacks are examples of representations reported in the literature. The main limitation of some of them is the lack of precisely locating the pathology within the VFs. Whereas others require the segmentation of the glottis in all the images of the video which is a complex and hard task given the high amount of images in the video and the necessity for the user intervention. To overcome these problems, the present study proposes a new waveform that maps the local vibrations of the VFs without the need for segmenting all the images of the video. Instead, the segmentation is restricted to only one image per vibratory cycle. Then, a new optical flow based technique is proposed to deduce the cycle-to-cycle dynamics of the VFs. The ability of the proposed approach to provide a reliable visual assessment is experimentally evaluated using different types of phonation and different vocal pathologies.

A Novel Lateral Approach to the Assessment of Vocal Cord Movement by Ultrasonography.

BACKGROUND: Ultrasonography is a non-invasive technique that is commonly used by endocrinologists and endocrine surgeons to examine the thyroid region and could be useful for the assessment of vocal cord movement by these specialists. However, previous studies reported a low rate of successful visualization of vocal cord movement by ultrasonography. To address this issue, we devised a novel ultrasonographic procedure for assessing vocal cord movement indirectly by observing the arytenoid movement from a lateral view. METHODS: Subjects were 188 individuals, including 23 patients with vocal cord paralysis and 13 with vocal cord paresis. We performed ultrasonographic assessment of vocal cord movement using two different procedures: the conventional middle transverse procedure and the novel lateral vertical procedure. RESULTS: The rate of visualization of vocal cords with the middle transverse procedure was 70.2% and that of the arytenoid cartilage with the lateral vertical procedure was 98.4%. The lateral vertical procedure enabled visualization of all patients with vocal cord paresis/paralysis and detected all 23 patients with vocal paralysis; only one of 13 patients with vocal cord paresis was positively identified. The conventional procedure enabled visualization of 21 of 36 patients with vocal cord paresis/paralysis with high accuracy. There was no false-positive case in either procedure. CONCLUSION: The proposed lateral vertical procedure improved the rate of visualization of vocal cord movement by ultrasonography, suggesting that it is a useful technique to screen for vocal cord paralysis by ultrasonography.

Functional assessment of the ex vivo vocal folds through biomechanical testing: A review.

The human vocal folds are complex structures made up of distinct layers that vary in cellular and extracellular composition. The mechanical properties of vocal fold tissue are fundamental to the study of both the acoustics and biomechanics of voice production. To date, quantitative methods have been applied to characterize the vocal fold tissue in both normal and pathologic conditions. This review describes, summarizes, and discusses the most commonly employed methods for vocal fold biomechanical testing. Force-elongation, torsional parallel plate rheometry, simple-shear parallel plate rheometry, linear skin rheometry, and indentation are the most frequently employed biomechanical tests for vocal fold tissues and each provide material properties data that can be used to compare native tissue to diseased or treated tissue. Force-elongation testing is clinically useful, as it allows for functional unit testing, while rheometry provides physiologically relevant shear data, and nanoindentation permits micrometer scale testing across different areas of the vocal fold as well as whole organ testing. Thoughtful selection of the testing technique during experimental design to evaluate a hypothesis is critical to optimize biomechanical testing of vocal fold tissues.

Comprehensive, Population-Based Sensitivity Analysis of a Two-Mass Vocal Fold Model.

Previous vocal fold modeling studies have generally focused on generating detailed data regarding a narrow subset of possible model configurations. These studies can be interpreted to be the investigation of a single subject under one or more vocal conditions. In this study, a broad population-based sensitivity analysis is employed to examine the behavior of a virtual population of subjects and to identify trends between virtual individuals as opposed to investigating a single subject or model instance. Four different sensitivity analysis techniques were used in accomplishing this task. Influential relationships between model input parameters and model outputs were identified, and an exploration of the model's parameter space was conducted. Results indicate that the behavior of the selected two-mass model is largely dominated by complex interactions, and that few input-output pairs have a consistent effect on the model. Results from the analysis can be used to increase the efficiency of optimization routines of reduced-order models used to investigate voice abnormalities. Results also demonstrate the types of challenges and difficulties to be expected when applying sensitivity analyses to more complex vocal fold models. Such challenges are discussed and recommendations are made for future studies.

A Preliminary Quantitative Comparison of Vibratory Amplitude Using Rigid and Flexible Stroboscopic Assessment.

STUDY OBJECTIVE: The purpose of this study was to establish preliminary, quantitative data on amplitude of vibration during stroboscopic assessment in healthy speakers with normal voice characteristics. Amplitude of vocal fold vibration is a core physiological parameter used in diagnosing voice disorders, yet quantitative data are lacking to guide the determination of what constitutes normal vibratory amplitude. METHODS/STUDY DESIGN: Eleven participants were assessed during sustained vowel production using rigid and flexible endoscopy with stroboscopy. Still images were extracted from digital recordings of a sustained /i/ produced at a comfortable pitch and loudness, with F0 controlled so that levels were within ±15% of each participant's comfortable mean level as determined from connected speech. Glottal width (GW), true vocal fold (TVF) length, and TVF width were measured from still frames representing the maximum open phase of the vibratory cycle. To control for anatomic and magnification differences across participants, GW was normalized to TVF length. GW as a ratio of TVF width was also computed for comparison with prior studies. RESULTS: Mean values and standard deviations were computed for the normalized measures. Paired t tests showed no significant differences between rigid and flexible endoscopy methods. Interrater and intrarater reliability values for raw measurements were found to be high (0.89-0.99). CONCLUSIONS: These preliminary quantitative data may be helpful in determining normality or abnormality of vocal fold vibration. Results indicate that quantified amplitude of vibration is similar between endoscopic methods, a clinically relevant finding for individuals performing and interpreting stroboscopic assessments.

Tripling the maximum imaging depth with third-harmonic generation microscopy.

The growing interest in performing high-resolution, deep-tissue imaging has galvanized the use of longer excitation wavelengths and three-photon-based techniques in nonlinear imaging modalities. This study presents a threefold improvement in maximum imaging depth of ex vivo porcine vocal folds using third-harmonic generation (THG) microscopy at 1552-nm excitation wavelength compared to two-photon microscopy (TPM) at 776-nm excitation wavelength. The experimental, analytical, and Monte Carlo simulation results reveal that THG improves the maximum imaging depth observed in TPM significantly from 140 to 420 µm in a highly scattered medium, reaching the expected theoretical imaging depth of seven extinction lengths. This value almost doubles the previously reported normalized imaging depths of 3.5 to 4.5 extinction lengths using three-photon-based imaging modalities. Since tissue absorption is substantial at the excitation wavelength of 1552 nm, this study assesses the tissue thermal damage during imaging by obtaining the depth-resolved temperature distribution through a numerical simulation incorporating an experimentally obtained thermal relaxation time (τ). By shuttering the laser for a period of 2τ, the numerical algorithm estimates a maximum temperature increase of ∼2°C at the maximum imaging depth of 420 µm. The paper demonstrates that THG imaging using 1552 nm as an illumination wavelength with effective thermal management proves to be a powerful deep imaging modality for highly scattering and absorbing tissues, such as scarred vocal folds.

Assessment of three placement techniques for individualized positioning of the tip of the tracheal tube in children under the age of 4 years.

BACKGROUND: Accurate positioning of the tip of the tracheal tube (tube tip) is challenging in young children. Prevalent clinical methods include placement of intubation depth marks, palpation of the tube cuff in the suprasternal notch, or deliberate mainstem intubation with subsequent withdrawal. To compare the predictability of tube tip positions, variability of the resulting positions in relation to the carina was determined applying the three techniques in each patient. METHODS: In 68 healthy children aged ≤4 years, intubation was performed with an age-adapted, high-volume low-pressure cuffed tube adjusting the imprinted depth mark to the level of the vocal cords. The tube tip-to-carina distance was measured endoscopically. Thereafter, placements using (I) cuff palpation in the suprasternal notch and (II) auscultation to determine change in breath sounds during withdrawal after bronchial mainstem intubation were completed in random order. RESULTS: Tube tip position above the carina was higher when using depth marks (mean = 36.8 mm) compared with cuff palpation in the suprasternal notch (mean = 19.0 mm). Variability, expressed as sd, was lowest with the mainstem intubation technique (5.2 mm) followed by the cuff palpation (7.4 mm) and the depth mark technique (11.2 mm) (P < 0.005). CONCLUSION: Auscultation after deliberate mainstem intubation and cuff palpation resulted in a tube tip position above the carina that was shorter and more predictable than placement of the tube using depth markings.

The importance of sonographic landmarks by transcutaneous laryngeal ultrasonography in post-thyroidectomy vocal cord assessment.

INTRODUCTION: During examination of the vocal cords (VC) using transcutaneous laryngeal ultrasonography (TLUSG), 3 sonographic landmarks (namely, false VC [FC], true VC [TC], and arytenoids [AR]) are often seen. However, it remains unclear which landmark provides a more reliable assessment and whether seeing more landmarks improves the diagnostic accuracy and reliability. METHODS: We evaluated prospectively 245 patients from 2 centers. One assessor from each center performed all TLUSG examinations and their findings were validated by direct laryngoscopy. All 3 sonographic landmarks were routinely visualized whenever possible. The rate of visualization and diagnostic accuracy between the 3 landmarks were compared. RESULTS: Eighteen patients suffered postoperative VC palsy (VCP). Both centers had comparable visualization or assessability rate of ≥ 1 sonographic landmark (94.9 and 95.3%; P = 1.000) and 100% sensitivity on postoperative TLUSG. The rates of FC, TC, and AR visualization were 92.7%, 36.7%, and 89.8%, respectively. The sensitivity, specificity, and diagnostic accuracy and the proportion of true positives, false positives, and true negatives between using 1, 2, landmarks and 3 landmarks were comparable (P > .05). CONCLUSION: Each sonographic landmark had similar reliability and diagnostic accuracy. Identifying all 3 sonographic landmarks was not mandatory and visualizing normal movement in one of the sonographic landmarks would be sufficient to exclude VCP.

Visual assessment of voice disorders in patients with occupational dysphonia.

INTRODUCTION: In a group of persons using the voice occupationally, the frequent symptoms are hoarseness, voice fatigability and aphonia. Pathological changes in the larynx may have organic or functional character which require different methods of treatment and rehabilitation. Visualization of vibrations of the vocal folds is an essential condition for an appropriate assessment of the causes of dysphonia. OBJECTIVE: The purpose of the study is assessment of the usefulness of a high-speed imaging (HSI) system in the diagnosis of functional and organic dysphonia of occupational character, compared with digital kymography (DKG) and digital stroboscopy (DS) with a high resolution module. MATERIAL AND METHODS: The study group consisted of 64 patients with voice quality disorders with features of occupational dysphonia. The control group consisted of 15 patients with euphonic voice. Analysis of the voice quality parameters during phonation of the 'e' vowel was performed using HSI, DKG and stroboscopy of high resolution, by means of a digital HS camera (HRES Endocam, Richard Wolf GmbH, Knittlingen, Germany). Vocal folds vibrations were registered at the rate of 4,000 frames per second. RESULTS: HSI is the most reliable diagnostic tool giving the possibility of an analysis of the true vibrations of the vocal folds. It also enables an observation of the aperiodicity of vibrations of the vocal folds, while DS with high resolution allows diagnosis of the periodicity of the vibrations. CONCLUSIONS: HSI is particularly useful in the diagnosis of neurologically-based pathology of the voice (paralytic dysphonia) and organic dysphonia. The quickest method of diagnosing the phonatory paresis of the glottis is DKG. The advantage of both HSI and DKG is the non-invasiveness of examinations; however, their limitations are time-consuming and the high cost of equipment.

Laryngoscopic, acoustic, perceptual, and functional assessment of voice in rock singers.

OBJECTIVE: The present study aimed to vocally assess a group of rock singers who use growl voice and reinforced falsetto. METHOD: A group of 21 rock singers and a control group of 18 pop singers were included. Singing and speaking voice was assessed through acoustic, perceptual, functional and laryngoscopic analysis. RESULTS: No significant differences were observed between groups in most of the analyses. Acoustic and perceptual analysis of the experimental group demonstrated normality of speaking voice. Endoscopic evaluation showed that most rock singers presented during singing voice a high vertical laryngeal position, pharyngeal compression and laryngeal supraglottic compression. Supraglottic activity during speaking voice tasks was also observed. However, overall vocal fold integrity was demonstrated in most of the participants. Slightly abnormal observations were demonstrated in few of them. Singing voice handicap index revealed that the most affected variable was the physical sphere, followed by the social and emotional spheres. CONCLUSIONS: Although growl voice and reinforced falsetto represent laryngeal and pharyngeal hyperfunctional activity, they did not seem to contribute to the presence of any major vocal fold disorder in our subjects. Nevertheless, we cannot rule out the possibility that more evident vocal fold disorders could be found in singers who use these techniques more often and during a longer period of time.

Real-time ultrasonographic assessment of true vocal fold length in professional singers.

PURPOSE: To assess changing true vocal fold (TVF) length with ultrasonography. MATERIALS: Thirty-five professional singers (12 tenors and 23 sopranos) were included in this study. Each subject had a documented TVF length with laryngeal ultrasonography (SonoAce X6 scanner; Samsung Medison, Seoul, Korea) during respiration, phonation, and singing. RESULTS: The average TVF lengths could be measured in each situation with real-time laryngeal ultrasonography. The mean (standard deviation [SD]) of TVF length was 1.71 cm (0.29) at inspiration, 1.56 cm (0.26) at expiration, 1.70 cm (0.21) at comfort phonation, 2.00 cm (0.22) at the highest tone, and 1.47 cm (0.19) at the lowest tone in tenors. In sopranos, the mean (SD) was 1.35 cm (0.12) at inspiration, 1.17 cm (0.12) at expiration, 1.42 cm (0.12) at comfort phonation, 1.65 cm (0.12) at the highest tone, and 1.14 cm (0.15) at the lowest tone. All variables had significant differences between both sexes (P<0.01). The lengths showed statistically significant differences in each phase (P<0.01). The differences in length between each phase were evaluated as well. When analyzed in each sex, all variables were statistically different except few of them. In both sexes, the highest tone and comfort phonation showed no difference (P=0.081 in tenors and P=0.289 in sopranos). The inspiratory phase and comfort phonation had significant difference only in sopranos (P<0.01) in contrast to tenors (P=0.905). CONCLUSION: Ultrasonographic measurement of TVF could be used to assess physiological variation of TVF. To reach a high-pitched voice, the professional singers used similar range of TVF length at comfort phonation. TVF length was affected more by inspiration in tenors. In sopranos, TVF at comfort phonation was significantly lengthened than in tenors.

Quantitative assessment of the anisotropy of vocal fold tissue using shear rheometry and traction testing.

The human vocal folds are layered structures with intrinsically anisotropic elastic properties. Most testing methods assume isotropic behavior. Biaxial testing of vocal folds is strictly difficult because the very soft tissue tends to delaminate under transverse traction loads. In the present study, a linear transversely isotropic model was used to characterize the tissue in-vitro. Shear rheometry was used in conjunction with traction testing to quantify the elasticity of porcine vocal fold tissue. Uniaxial traction testing along with optical measurements were used to obtain the longitudinal modulus. The alternate vocal fold of each animal was subjected to a test-specific sample preparation and concurrently tested using dynamic shear rheometry. The stiffness ratio (i.e., the ratio of the longitudinal modulus and the transverse modulus) varied between ∼5 and ∼7 at low frequencies. The proposed methodology can be applied to other soft tissues.

Preoperative ultrasonography assessment of vocal cord movement during thyroid and parathyroid surgery.

BACKGROUND: Preoperative detection of vocal cord palsy is important in thyroid and parathyroid surgery. However, routine fiberoptic laryngoscopy may bring patients unnecessary discomfort. The aim of this study was to determine the feasibility of using surgeon-performed ultrasonography (US) as a screening tool for preoperative assessment of vocal cord movement. METHODS: In the first phase, patients had both laryngoscopic and US examination before surgery. In the second phase, patients had US evaluation first. Those with abnormal vocal cord movement on US, with invisible cord movement, or presenting with significant vocal symptoms underwent laryngeal examination. RESULTS: In all, 93 (82 %) of 114 patients had successful US evaluation of vocal cord movement during the first phase. Two of them had vocal cord paralysis. In the second phase, vocal cord movement could be evaluated by US in 349 (84 %) of 415 patients. Four patients with abnormal movement were confirmed to have vocal cord palsy by laryngoscopy. None of 46 symptomatic patients with normal movement on US had vocal cord palsy. One other patient whose cord movement could not be seen by US had vocal cord palsy on laryngoscopic examination. CONCLUSIONS: Surgeon-performed US appears to be a relatively accurate method for assessing vocal cord movement in the preoperative setting. It can be used to select patients to undergo laryngoscopic examination before thyroidectomy and parathyroidectomy.

Inter-speaker speech variability assessment using statistical deformable models from 3.0 tesla magnetic resonance images.

The morphological and dynamic characterisation of the vocal tract during speech production has been gaining greater attention due to the motivation of the latest improvements in magnetic resonance (MR) imaging; namely, with the use of higher magnetic fields, such as 3.0 Tesla. In this work, the automatic study of the vocal tract from 3.0 Tesla MR images was assessed through the application of statistical deformable models. Therefore, the primary goal focused on the analysis of the shape of the vocal tract during the articulation of European Portuguese sounds, followed by the evaluation of the results concerning the automatic segmentation, i.e. identification of the vocal tract in new MR images. In what concerns speech production, this is the first attempt to automatically characterise and reconstruct the vocal tract shape of 3.0 Tesla MR images by using deformable models; particularly, by using active and appearance shape models. The achieved results clearly evidence the adequacy and advantage of the automatic analysis of the 3.0 Tesla MR images of these deformable models in order to extract the vocal tract shape and assess the involved articulatory movements. These achievements are mostly required, for example, for a better knowledge of speech production, mainly of patients suffering from articulatory disorders, and to build enhanced speech synthesizer models.

Evaluation of vocal fold vibration with an assessment form for high-speed digital imaging: comparative study between healthy young and elderly subjects.

OBJECTIVES/STUDY DESIGN: We conducted a prospective study with a subjective assessment form for high-speed digital imaging (HSDI) to elucidate the features of vocal fold vibrations in vocally healthy subjects and to clarify gender- and age-related differences. METHODS: Healthy adult volunteers participated in this study. They were divided into young (aged 35 and younger) and elderly (aged 65 and older) groups, and the scores of an assessment form for HSDI characteristics elaborated at our institution were statistically analyzed. RESULTS: Twenty-six young subjects (males: 9, females: 17; mean age: 27 years) and 20 elderly subjects (males: 8, females: 12; mean age: 72 years) were assigned to our study. Posterior gap and posterior-to-anterior longitudinal phase difference were characteristic to young females, whereas in young males, mucosal wave, anterior-to-posterior longitudinal phase difference, and supraglottic hyperactivity were frequent. In elderly males, axis shift, asymmetry, supraglottic hyperactivity, increased mucosal wave, lateral phase difference, and anterior-to-posterior longitudinal phase difference were frequent; and in elderly females, high incidence of lateral phase difference, atrophic change, anterior gap, and asymmetry were observed. CONCLUSIONS: The results show that the behaviors of vocal fold vibrations were diverse even in healthy subjects with no vocal complaints or history of laryngeal diseases, and hence, the diversity of vocal fold vibrations in normal subjects must be taken into account in evaluating vocal fold vibrations.