Preliminary study on the quantitative analysis of vocal loading effects on vocal fold dynamics using phonovibrograms

OBJECTIVES: The purpose of the present study was to determine whether high-speed digital imaging with phonovibrogram (PVG) analysis would identify changes in vocal fold vibratory characteristics following prolonged reading (vocal fatigue) in subjects with normal voice to evaluate the voice effects of vocal loading. METHODS: Three healthy subjects' larynges were examined with an endoscopic high-speed imaging system at 4 different levels of vocal load. Vocal fold dynamics were segmented and processed by PVGs. The PVG images were quantitatively described by a parameter set enabling an individual characterization of vocal fold dynamics. To reveal differences between the subjects, we performed a linear discrimination analysis. Within each subject, the identification of vocal loading effects was performed by statistical analysis (1-way analysis of variance), and 2-tailed paired t-tests were used as a consistency check between left and right vocal fold sides. RESULTS: For each subject, the PVG analysis enabled a precise quantification of the entire range of vocal fold dynamics. Independently of the high-speed videos (vocal loads), each subject could be identified by his or her PVG parameters on linear discrimination analysis. In all subjects, the effect of vocal loading was reflected by alterations of PVG parameters representing the posterior opening and closing dynamics. Evaluation within subjects revealed slight asymmetric vibratory behavior between the left and right vocal folds, confirming earlier assumptions. CONCLUSIONS: Within the investigated subjects, vocal loading does affect the vibratory characteristics of the vocal folds. Left-right vocal fold vibratory asymmetries do occur in healthy voices and can be identified by PVGs. High-speed digital imaging in combination with PVG analysis seems to be a promising tool for investigation of vocal fold fatigue and disorders resulting even from small dynamic changes.     

Vocal fold vibration irregularities caused by different types of laryngeal asymmetry

The common symptom of hoarseness is regarded to be caused by (1) turbulences and air loss due to incomplete glottic closure and (2) irregular vibrations of the vocal folds. With real time resolution, the latter can only be observed using high-speed recording techniques (> or =2,000 images/s). In this paper an actual recording method is described, called high-speed glottography (HGG), which quantifies vibration irregularities. It combines imaging and image processing techniques with a functional endoscopy of the disordered voice and delivers motion curves separately for each vocal fold. They are fitted with a computer simulation in order to identify the underlying driving parameters of the vibration. A vocal fold is assumed to vibrate as a system of two coupled oscillators ("two-mass model"). From the model fit to bilateral motion curves, the subglottal pressure, muscular tension and oscillating masses of the vocal folds can be computed with reasonable accuracy. Besides normal voices, HGG has been applied to selected clinical cases of voice disorders. Two types of irregularities have been measured: there is a frequency difference either between left and right vocal folds (horizontal asymmetry) or on one side between the ventral and dorsal third (vertical asymmetry). By modeling, both categories of irregular motion curves can be explained in detail. It is presumed that laryngeal asymmetry (either in mass or tension) causes irregular vibrations.     

Qualification of a quantitative laryngeal imaging system using videostroboscopy and videokymography

OBJECTIVES: We sought to determine whether full-cycle glottal width measurements could be obtained with a quantitative laryngeal imaging system using videostroboscopy, and whether glottal width and vocal fold length measurements were repeatable and reliable. METHODS: Synthetic vocal folds were phonated on a laboratory bench, and dynamic images were obtained in repeated trials by use of videostroboscopy and videokymography (VKG) with an imaging system equipped with a 2-point laser projection device for measuring absolute dimensions. Video images were also obtained with an industrial videoscope system with a built-in laser measurement capability. Maximum glottal width and vocal fold length were compared among these 3 methods. RESULTS: The average variation in maximum glottal width measurements between stroboscopic data and VKG data was 3.10%. The average variations in width measurements between the clinical system and the industrial system were 1.93% (stroboscopy) and 3.49% (VKG). The variations in vocal fold length were similarly small. The standard deviations across trials were 0.29 mm for width and 0.48 mm for length (stroboscopy), 0.18 mm for width (VKG), and 0.25 mm for width and 0.84 mm for length (industrial). CONCLUSIONS: For stable, periodic vibration, the full extent of the glottal width can be reliably measured with the quantitative videostroboscopy system.     

Three-Dimensional Endoscopic Mode for Observation of Laryngeal Structures by Helical Computed Tomography

We produced high-quality three-dimensional (3D) endoscopic images of the larynx using helical scanning computed tomography. Subjects included two normal volunteers and 10 patients: five with laryngeal cancer, four with unilateral recurrent laryngeal nerve (RLN) palsy, and one with atrophied vocal folds. Two vertically split hemilaryngeal images were displayed together with the oral and tracheal views. Although motion artifacts were seen in four patients, laryngeal structures including the vocal fold, ventricular fold, and ventricle were clearly identified in all subjects. In the patients with cancer, axial images showing the extent of the tumor in each patient provided more information than 3D endoscopic images. In the patients with RLN palsy and atrophied vocal fold, combination of 3D endoscopic and cross-sectional images offered more diagnostic information than axial images alone.     

Echo-Planar Magnetic Resonance Imaging of Deglutitive Vocal Fold Closure: Normal and Pathologic Patterns of Displacement

Abnormalities of vocal fold closure during deglutition predispose to aspiration due to impairment of airway protection. Conventional assessment of deglutitive vocal fold motion with laryngoscopy does not permit visualization through a complete adduction-abduction cycle. We determined spatiotemporal patterns of deglutitive vocal fold adduction through echo-planar magnetic resonance imaging in 15 normal volunteers and 6 patients with vocal fold paralysis. In normal volunteers, deglutitive vocal fold adduction was synchronized with laryngeal elevation, with complete vocal fold closure at the apex. Patients with unilateral vocal fold paralysis demonstrated reduced elevation and medial movement of the involved vocal fold. At maximal laryngeal elevation the uninvolved vocal fold attained a position superior to the paralyzed fold, resulting in level differences and an interglottic gap. Patients with bilateral vocal fold paralysis demonstrated reduced elevation and medial movement of both vocal folds. These findings indicate that normal and abnormal patterns of vocal fold displacement can be distinguished noninvasively through the use of echo-planar imaging. Laryngoscope, 106:568-572, 1996     

Imaging the human vocal folds in vivo with optical coherence tomography: a preliminary experience

OBJECTIVES: Optical coherence tomography (OCT) and polarization-sensitive OCT (PS-OCT) are promising noninvasive methods for in vivo, cross-sectional imaging of the microstructure of the vocal folds. Previous studies in other tissues have shown an axial resolution of less than 10 microm and a maximum imaging depth of about 2 mm. The objectives of this pilot study were to obtain images from the vocal folds of subjects who were being evaluated and/or treated for vocal fold disease and to evaluate how well normal and pathologic microstructure could be seen in these images. METHODS: Twenty-six vocal folds in 13 subjects were imaged with a flexible OCT probe. The images were successfully collected from subjects who were either topically anesthetized or under general anesthesia for microlaryngoscopic procedures. RESULTS: The thickness of the epithelium, the relative collagen content of the subepithelial connective tissue, and certain characteristic features of lesions (including cysts, scarring, and papilloma) were seen in the OCT and PS-OCT images. CONCLUSIONS: "Live microscopy" of the human vocal folds is very promising for improved diagnosis, mapping, and treatment planning. To our knowledge, this study is the first application of PS-OCT for in vivo imaging of the human vocal folds.     

Blinded evaluation of the effects of high definition and magnification on perceived image quality in laryngeal imaging

OBJECTIVES: Advances in commercial video technology have improved office-based laryngeal imaging. This study investigates the perceived image quality of a true high-definition (HD) video camera and the effect of magnification on laryngeal videostroboscopy. METHODS: We performed a prospective, dual-armed, single-blinded analysis of a standard laryngeal videostroboscopic examination comparing 3 separate add-on camera systems: a 1-chip charge-coupled device (CCD) camera, a 3-chip CCD camera, and a true 720p (progressive scan) HD camera. Displayed images were controlled for magnification and image size (20-inch [50-cm] display, red-green-blue, and S-video cable for 1-chip and 3-chip cameras; digital visual interface cable and HD monitor for HD camera). Ten blinded observers were then asked to rate the following 5 items on a 0-to-100 visual analog scale: resolution, color, ability to see vocal fold vibration, sense of depth perception, and clarity of blood vessels. Eight unblinded observers were then asked to rate the difference in perceived resolution and clarity of laryngeal examination images when displayed on a 10-inch (25-cm) monitor versus a 42-inch (105-cm) monitor. A visual analog scale was used. These monitors were controlled for actual resolution capacity. RESULTS: For each item evaluated, randomized block design analysis demonstrated that the 3-chip camera scored significantly better than the 1-chip camera (p < .05). For the categories of color and blood vessel discrimination, the 3-chip camera scored significantly better than the HD camera (p < .05). For magnification alone, observers rated the 42-inch monitor statistically better than the 10-inch monitor. CONCLUSIONS: The expense of new medical technology must be judged against its added value. This study suggests that HD laryngeal imaging may not add significant value over currently available video systems, in perceived image quality, when a small monitor is used. Although differences in clarity between standard and HD cameras may not be readily apparent on small displays, a large display size coupled with HD technology may impart improved diagnosis of subtle vocal fold lesions and vibratory anomalies.     

High-precision measurement of the vocal fold length and vibratory amplitudes

OBJECTIVE/HYPOTHESIS: Standard laryngoscopy suffers from a lack of information about the actual size of the observed objects (i.e., vocal fold length and oscillating amplitudes). However, there is much interest in absolute measures for both clinical and research purposes. Therefore, a laser projection device has been developed that enables the precise determination of absolute units in endoscopic investigation during respiration and phonation. STUDY DESIGN: An experimental study in which 9 adults underwent high-speed endoscopy combined with a laser projection device. METHODS: The projection system consists of two parallel laser beams with a distance of 3.8 mm. It is mounted on the tip of a rigid endoscope, which is attached to a digital high-speed camera During development and design, examination situations were taken into account. Two laser spots are projected onto the vocal folds and enable the definition of a metric scale within the endoscopic image. Knowledge-based image processing algorithms were used for evaluation. RESULTS: First measurements of the vocal fold length during phonation were performed in a group of nine healthy male students. The determination of glottal length during phonation agrees with former results. Quantifying vocal fold velocities in absolute units makes it possible to estimate the initial collision forces. CONCLUSIONS: The presented laser projection system allows the determination of absolute measures in the larynx. Because of the simple functional principle, the system is open for use without digital high-speed recording as well. Absolute units may also be helpful in voice diagnosis and in monitoring during voice therapy.     

Study of movements of individual structures of the larynx during swallowing

OBJECTIVE: The purpose of this study was to reveal movements of individual structures of the larynx during swallowing. METHODS: Subjects were 7 healthy adults, aged 24 to 32 years (average 27 years), who had no organic or functional disease of the pharynx and larynx and 2 adults with unilateral recurrent nerve palsy, aged 49 and 60 years, respectively. We used the Toshiba IIDR system, which is composed of an X-ray TV system and a digital image managing circuit. One-fifth diluted Omnipark 300 was used as contrast medium (lohexol), with 15 cc for each swallow. The mask image for subtraction was designated as the frame before laryngeal elevation during swallowing for subtraction. We obtained the images for observation and analysis after subtracting the mask image from continuously obtained images. These images were captured into a personal computer at 30 frames per s and thereafter frame-by-frame observation and analysis were performed by means of NIH image 1.56. RESULTS: We observed that the vocal folds underwent a series of movements during swallowing. (1) They adduct slowly and do not ascend; (2) then begin to ascend and continue adducting; whereby (3) they abduct for a moment while ascending. (4) Again, they adduct and achieve closure. (5) While maintaining closure, vocal folds elevate further to reach their maximal elevation; and (6) begin to abduct rapidly while maintaining maximal elevation. Finally, (7) they begin to descend and undergo repeated irregular abduction and adduction while descending. In examining the relationship between closure and opening at levels of the vocal fold and false vocal fold, we found that closure at the false vocal fold level precedes that at the vocal fold level and that opening at the vocal fold level precedes that at the level of the false vocal fold. CONCLUSION: Closure of the false vocal fold level appears important in the protection of the lower respiratory tract during swallowing.     

Electroglottography and vocal fold physiology

The electroglottogram (EGG) is known to be related to vocal fold motion. A major hypothesis undergoing examination in several research centers is that the EGG is related to the area of contact of the vocal folds. This hypothesis is difficult to substantiate with direct measurements using human subjects. However, other supporting evidence can be offered. For this study we made measurements from synchronized ultra high-speed laryngeal films and from EGG waveforms collected from subjects with normal larynges and patients with vocal disorders. We compare certain features of the EGG waveform to (a) the instant of the opening of the glottis, (b) the instant of the closing of the glottis, and (c) the instant of the maximum opening of the glottis. In addition, we compare both the open quotient and the relative average perturbation measured from the glottal area to that estimated from the EGG. All of these comparisons indicate that vocal fold vibratory characteristics are reflected by features of the EGG waveform. This makes the EGG useful for speech analysis and synthesis as well as for modeling laryngeal behavior. The limitations of the EGG are discussed.     

Clinical feasibility of the new technique of functional 3D laryngeal CT

CONCLUSIONS: Functional 3D laryngeal CT (F3DLxCT) is an informative tool for visualizing the active changes in length, tension and mass of the vocal folds for pitch control. Furthermore, volume defects and level differences of paralyzed vocal folds are easily detectable with this new technique. OBJECTIVE: To evaluate the clinical feasibility of F3DLxCT images, which can provide clear coronal images of the vocal fold in each anteroposterior direction during phonation and in the resting state. MATERIAL AND METHODS: FLxCT images were reconstructed to three dimensions to visualize laryngeal motion. FLxCT was performed in four normal controls and in four patients with unilateral vocal fold paralysis in the resting state and during phonation with three vowel sounds of different pitch. 3D images were reconstructed with segmentation and a surface-rendering algorithm on a PC, using the DICOM file of axial images. RESULTS: The dynamic vocal fold 3D image during phonation could visualize that the thickness and volume were decreased in relatively to the pitch increase. Typical subglottic shoulder-like image formation and ventricular widening were noted with the high-pitch tone.     

Videostrobokymography: a new method for the quantitative analysis of vocal fold vibration

OBJECTIVES: To develop a new analysis method for the quantitative assessment of vibration of the vocal folds, using conventional videostroboscopic image data. METHODS: We used prerecorded videostroboscopic images to evaluate quantitatively the vibration of the vocal folds. Successive images were converted as digital images by means of an image-grabbing board, processed for analysis, and reconstructed as kymograms by rearranging the same lines of all processed images along the time axis. RESULTS: We developed a new technique for evaluating the vibration of the vocal folds. The vibrations of multiple vocal fold regions were easily and objectively evaluated by this technique. The objective parameters, such as open quotient and asymmetry index, could be obtained easily using this technique. CONCLUSIONS: Videostrobokymography demonstrated objectively the vibrations of several vocal fold regions at the same time. This technique has the potential to be a new tool to analyze and monitor the pathological changes and treatment results of vocal fold movement in a more refined quantitative fashion, using videostroboscopic images.     

A quantitative study of the medial surface dynamics of an in vivo canine vocal fold during phonation

OBJECTIVES/HYPOTHESIS: The purpose of this study was to measure the medial surface dynamics of a canine vocal fold during phonation. In particular, displacements, velocities, accelerations, and relative phase velocities of vocal fold fleshpoints were reported across the entire medial surface. Although the medial surface dynamics have a profound influence on voice production, such data are rare because of the inaccessibility of the vocal folds. STUDY DESIGN: Medial surface dynamics were investigated during both normal and fry-like phonation as a function of innervation to the recurrent laryngeal nerve for conditions of constant glottal airflow. METHODS: An in vivo canine model was used. The larynx was dissected similar to methods described in previous excised hemilarynx experiments. Phonation was induced with artificial airflow and innervation to the recurrent laryngeal nerve. The recordings were obtained using a high-speed digital imaging system. Three dimensional coordinates were computed for fleshpoints along the entire medial surface. The trajectories of the fleshpoints were preprocessed using the method of Empirical Eigenfunctions. RESULTS: Although considerable variability existed within the data, in general, the medial-lateral displacements and vertical displacements of the vocal fold fleshpoints were large compared with anterior-posterior displacements. For both normal and fry-like phonation, the largest displacements and velocities were concentrated in the upper medial portion. During normal phonation, the mucosal wave propagated primarily in a vertical direction. Above a certain threshold of subglottal pressure (or stimulation to the recurrent laryngeal nerve), an abrupt transition from chest-like to fry-like phonation was observed. CONCLUSIONS: The study reports unique, quantitative data regarding the medial surface dynamics of an in vivo canine vocal fold during phonation, capturing both chest-like and fry-like vibration patterns. These data quantify a complex set of dynamics. The mathematical modeling of such complexity is still in its infancy and requires quantitative data of this nature for development, validation, and testing.     

A new generation videokymography for routine clinical vocal fold examination

OBJECTIVE: This study aims to introduce a new-generation videokymographic system, which provides simultaneous laryngoscopic and kymographic image, for routine clinical vocal fold examination. STUDY DESIGN: The authors explored a new imaging method for diagnosis and evaluation of voice disorders. METHODS: The new-generation videokymographic system includes two charge-coupled device image sensors, a color area image sensor, and a monochromic high-speed line-scan image sensor. The high-speed line-scan image sensor is used to capture the kymogram, and the color area image sensor is used to obtain the laryngoscopic image. The two images can be displayed simultaneously on a video monitor or stored in a standard video recorder. Three subjects with nonpathologic voice were investigated in detail with the new videokymographic system. RESULTS: The high-quality laryngoscopic image and kymogram can be used directly for clinical purposes with no further postprocessing. The scan position of the kymogram is always indicated in the laryngoscopic image, which provides feedback for the operator to easily locate the expected scanning position. All varieties of vocal fold vibration, including irregular vibrations, phonation onset and offset, can be observed with the presented method. The continuous kymogram of the vocal fold vibration can be retrieved from a kymographic image sequence for quantitative analysis. CONCLUSIONS: The new-generation videokymography provides a simple, quick means to investigate vocal fold vibration, especially for voice disorders. It can emerge as an important tool for routine clinical vocal fold examination.     

First results of clinical application of videokymography

Objectives: Stroboscopy is based on the assumption that the vibration of the vocal folds is stable and regular. Irregular vibrations, which are common in voice pathology, cannot easily be studied and described in a reliable way. Videokymography overcomes most of these drawbacks. Design: The use of the recently invented videokymography for studying vocal fold vibrations in patients is introduced. Method: Videokymography, using a modified CCD-video camera, works in two modes: standard and high speed. In standard mode the vocal folds are displayed on a video monitor in the usual way, providing 50 images per second (or 60 in the National Television Standards Committee (NTSC) system). This is used for routine laryngoscopic and stroboscopic examination of the larynx. In high-speed mode (nearly 8000 images per second) only one line from the whole image is selected and displayed on the x-axis of the monitor; the y-axis represents the time dimension. Results: All kinds of vocal fold vibrations, including those leading to pathological rough, breathy, hoarse, or diplophonic voice productions can be observed. Videokymography visualizes small left-right asymmetries, open quotient differences along the glottis, lateral propagation of mucosal waves, and movements of the upper margin and, sometimes in the closing phase, the lower margin of the vocal folds. Conclusion: Videokymography is advantageous for a more accurate diagnosis of voice disorders. Videokymography provides a simple way to study irregular vibrations of the vocal folds. Information is directly available for further processing and allows a first-time quantification of vibrations registered.     

Regenerative potential of basic fibroblast growth factor contained in biodegradable gelatin hydrogel microspheres applied following vocal fold injury: Early effect on tissue repair in a rabbit model

IntroductionPostoperative dysphonia is mostly caused by vocal fold scarring, and careful management of vocal fold surgery has been reported to reduce the risk of scar formation. However, depending on the vocal fold injury, treatment of postoperative dysphonia can be challenging.ObjectiveThe goal of the current study was to develop a novel prophylactic regenerative approach for the treatment of injured vocal folds after surgery, using biodegradable gelatin hydrogel microspheres as a drug delivery system for basic fibroblast growth factor.MethodsVideoendoscopic laryngeal surgery was performed to create vocal fold injury in 14 rabbits. Immediately following this procedure, biodegradable gelatin hydrogel microspheres with basic fibroblast growth factor were injected in the vocal fold. Two weeks after injection, larynges were excised for evaluation of vocal fold histology and mucosal movement.ResultsThe presence of poor vibratory function was confirmed in the injured vocal folds. Histology and digital image analysis demonstrated that the injured vocal folds injected with gelatin hydrogel microspheres with basic fibroblast growth factor showed less scar formation, compared to the injured vocal folds injected with gelatin hydrogel microspheres only, or those without any injection.ConclusionA prophylactic injection of basic fibroblast growth factor -containing biodegradable gelatin hydrogel microspheres demonstrates a regenerative potential for injured vocal folds in a rabbit model.     

Sarcoidosis with vocal fold involvement and hypercalcaemia

Sarcoidosis affects many different organ systems. However, laryngeal involvement is rare and most cases with laryngeal involvement affect the supraglottis, occasionally secondarily extending to the vocal fold. The features of sarcoidosis in the supraglottic region have been described in several reports, but vocal fold involvement has not been presented in detail. We report an unusual case of laryngeal sarcoidosis initially involving the vocal folds in a 66-year-old man, associated with hypercalcaemia. Our report describes characteristics of the involved vocal folds. Hypercalcaemia is one of the characteristics of sarcoidosis. We concluded that laryngeal sarcoidosis should be added to the differential diagnosis of vocal fold lesions, particularly in patients with hypercalcaemia.     

Intraoperative laryngeal electromyography in children with vocal fold immobility: a simplified technique

OBJECTIVES: The primary objective of this study was to determine whether a simplified technique for intraoperative laryngeal electromyography was feasible using standard nerve integrity monitoring electrodes and audiovisual digital recording equipment. Our secondary objective was to determine if laryngeal electromyography data provided any additional information that significantly influenced patient management. METHODS: Between February 2006 and February 2007, 10 children referred to our institution with vocal fold immobility underwent intraoperative laryngeal electromyography of the thyroarytenoid muscles. A retrospective chart review of these 10 patients was performed after institutional review board approval. RESULTS: Standard nerve integrity monitoring electrodes can be used to perform intraoperative laryngeal electromyography of the thyroarytenoid muscles in children. In 5 of 10 cases reviewed, data from laryngeal electromyography recordings meaningfully influenced the care of children with vocal fold immobility and affected clinical decision-making, sometimes altering management strategies. In the remaining 5 children, data supported clinical impressions but did not alter treatment plans. Two children with idiopathic bilateral vocal fold paralysis initially presented with a lack of electrical activity on one or both sides but went on to develop motor unit action potentials that preceded recovery of motion in both vocal folds. CONCLUSIONS: Our findings suggest that standard nerve monitoring equipment can be used to perform intraoperative laryngeal electromyography and that electromyographic data can assist clinicians in the management of complex patients. Additionally, there may be a role for the use of serial intraoperative measurements in predicting recovery from vocal fold paralysis in the pediatric age group.