Quantitative study of vibrational symmetry of injured vocal folds via digital kymography in excised canine larynges

Visual and Automatic Evaluation of Vocal Fold Mucosal Waves Through Sharpness of Lateral Peaks in High-Speed Videokymographic Images

INTRODUCTION

The sharpness of lateral peaks is a visually helpful clinical feature in high-speed videokymographic (VKG) images indicating vertical phase differences and mucosal waves on the vibrating vocal folds and giving insights into the health and pliability of vocal fold mucosa. This study aims at investigating parameters that can be helpful in objectively quantifying the lateral peak sharpness from the VKG images.

METHOD

Forty-five clinical VKG images with different degrees of sharpness of lateral peaks were independently evaluated visually by three raters. The ratings were compared to parameters obtained by automatic image analysis of the vocal fold contours: Open Time Percentage Quotients (OTQ) and Plateau Quotients (PQ). The OTQ parameters were derived as fractions of the period during which the vocal fold displacement exceeds a predetermined percentage of the vibratory amplitude. The PQ parameters were derived similarly but as a fraction of the open phase instead of a period.

RESULTS

The best correspondence between the visual ratings and the automatically derived quotients were found for the OTQ and PQ parameters derived at 95% and 80% of the amplitude, named OTQ₉₅, PQ₉₅, OTQ₈₀ and PQ₈₀. Their Spearman's rank correlation coefficients were in the range of 0.73 to 0.77 (P < 0.001) indicating strong relationships with the visual ratings. The strengths of these correlations were similar to those found from inter-rater comparisons of visual evaluations of peak sharpness.

CONCLUSION

The Open time percentage and Plateau quotients at 95% and 80% of the amplitude stood out as the possible candidates for capturing the sharpness of the lateral peaks with their reliability comparable to that of visual ratings.

Synthetic multi-line kymographic analysis: A spatiotemporal data reduction technique for high-speed videoendoscopy

High-speed videoendoscopy (HSV) enables observation of the true vibratory behavior of the vocal folds. To quantify the vocal fold vibration captured by the HSV, lateral movement features (e.g., glottal width and vocal fold edge displacements) have been extracted as functions of time. The most common analysis method is to extract the features on a lateral strip used to form digital kymogram. The weakness of this method is that it can only capture the vibrational behavior local to the strip location. While the multi-line kymographic approach has been utilized to capture the spatial diversity, the observation points are either fixed or manually positioned. Behaviors of pathological vocal folds, especially those with lesions, are expected to be spatially diverse and also diverse among speakers, making fixed observation points ineffective. This paper proposes a technique to synthesize kymographic waveforms from full spatiotemporal HSV feature data to extract distinctive behaviors automatically. Each synthesized waveform represents a non-overlapping section of the glottis, where vocal folds are locally behaving homogeneously. The efficacy of the algorithm is demonstrated with four HSV recordings (three pathological) and discussed, including mitigation of the known drawbacks.

Objective quantification of pre- and postphonosurgery vocal fold vibratory characteristics using high-speed videoendoscopy and a harmonic waveform model

PURPOSE

The model-based quantitative analysis of high-speed videoendoscopy (HSV) data at a low frame rate of 2,000 frames per second was assessed for its clinical adequacy. Stepwise regression was employed to evaluate the HSV parameters using harmonic models and their relationships to the Voice Handicap Index (VHI). Also, the model-based HSV parameters were compared with those using conventional analysis techniques.

METHOD

Eight pairs of HSV recordings of vocal folds before and after surgery for benign lesions were investigated. Five glottal area waveform features-fundamental frequency (F0), open quotient (OQ), speed index (SI), relative glottal gap (RGG), and harmonics-to-noise ratio (HNR)-were measured using model-based and conventional approaches. The statistical analyses were conducted on the mean (M) and standard deviation (SD) of the feature measurements over 1 s during sustained phonation.

RESULTS

Two model-based HSV parameters, OQ M (ρ = .67) and HNR M (ρ = -.56), were selected and explained 55% of the VHI variation. The conventional techniques yielded a regression model with OQ SD (ρ = -.60) and F0 SD (ρ = .44), explaining 61% of the VHI variation.

CONCLUSIONS

Although the selected model-based HSV parameters explained less variation in the VHI than the conventionally computed HSV parameters, the behaviors of the model-based parameters were more consistent with expectations and theory than the conventional analysis techniques.

Combined type IIIB with bilateral type I thyroplasty for pitch lowering with maintenance of vocal fold tension

To evaluate type IIIB thyroplasty using the excised larynx bench apparatus and determine how altering vocal fold contour by performing bilateral medialization of the inferior vocal fold affects phonation. This procedure could be performed in patients for whom pitch lowering is desirable, such as female-to-male transsexuals or male patients with mutational falsetto in whom intensive voice therapy was insufficient. Aerodynamic, acoustic, and high-speed videokymographic data were collected for nine larynges at three subglottal pressure inputs for each of three conditions: normal; type IIIB thyroplasty; and combined type IIIB with modified bilateral type I thyroplasty intended to create a more rectangular glottal configuration. Each larynx served as its own control. Phonation threshold flow (p = 0.005), phonation threshold power (p = 0.031), and airflow varied across conditions with highest values for type IIIB thyroplasty and lowest for the combined procedure. Fundamental frequency was significantly different (p < 0.001), decreasing by approximately 100 Hz from control to type IIIB trials, and then by approximately 15 Hz from IIIB to combined procedure trials. Vibratory amplitudes and intrafold phase difference were highest for type IIIB trials. Addition of bilateral inferior medialization to type IIIB thyroplasty provided some further decrease in frequency, but mostly served to increase tension, reduce airflow, and produce a vibratory pattern which more closely mirrored control trials. Exploration of this combined procedure in patients may be warranted if not completely satisfied with the results from type IIIB thyroplasty alone.

Excised larynx evaluation of wedge-shaped adjustable balloon implant for minimally invasive type I thyroplasty

OBJECTIVES/HYPOTHESIS

To describe the method of inserting a wedge-shaped adjustable balloon implant (wABI) via a minithyrotomy for medialization thyroplasty and evaluate its effect on a range of phonatory parameters using the excised larynx bench apparatus.

STUDY DESIGN

Repeated measures with each larynx serving as its own control.

METHODS

A prototype wABI was deployed in six excised canine larynges of various sizes through a minithyrotomy and then filled with saline. Mucosal wave, aerodynamic, and acoustic parameters were measured for three conditions: normal, vocal fold paralysis, and paralysis with the wABI.

RESULTS

Phonation threshold pressure (P < .001), flow (P < .001), and power (P = .002) were significantly lower for wABI compared to paralysis trials; values did not differ significantly from normal trials. Percent jitter (P = .002) and percent shimmer (P = .007) were also significantly decreased compared to the paralysis condition, and values were not significantly different compared to normal. The mucosal wave was preserved after insertion of the wABI.

CONCLUSIONS

Effective vocal fold medialization with preservation of the mucosal wave was observed with the wABI in this preliminary excised larynx experiment. The wABI offers the potential for a minimally invasive insertion in addition to postoperative adjustability. Further studies in living animals and humans are warranted to evaluate clinical utility.

LEVEL OF EVIDENCE

NA.

Recovery of vibratory function after vocal fold microflap in a rabbit model

OBJECTIVES/HYPOTHESIS

The purpose of this study was to evaluate the return of vibratory function and restoration of vibration amplitude and symmetry after vocal fold microflap surgery.

STUDY DESIGN

Prospective in vivo animal model.

METHODS

Microflap surgery was performed on 30 New Zealand white breeder rabbits. The left vocal fold received a 3-mm epithelial incision and mucosal elevation, while the contralateral vocal fold was left intact to serve as an internal control. Quantitative analysis of amplitude ratio and lateral phase difference were measured using high-speed laryngeal imaging at a frame rate of 10,000 frames per second from animals undergoing evoked phonation on postoperative days 0, 1, 3, 5, and 7.

RESULTS

Quantitative measures revealed a significantly reduced amplitude ratio and lateral phase difference on day 0 after microflap. These impairments of vibratory function on day 0 were associated with separation of the vocal fold's body-cover layer. Amplitude ratio increased significantly by day 3 after microflap, with further increases in vibration amplitude on days 5 and 7. While the amplitude ratio improved significantly on day 3, lateral phase difference decreased significantly on day 3, and returned to normal on days 5 and 7.

CONCLUSIONS

High-speed laryngeal imaging was used to investigate the natural time course of postmicroflap recovery of vibratory function. Results revealed the restoration of vibration amplitude and lateral phase difference by days 3 to 7 after microflap. The time period of improved vibratory function observed in this study coincides with the end of the well-documented inflammatory phase of vocal fold wound repair.

LEVEL OF EVIDENCE

N/A.

Kymographic imaging of laryngeal vibrations

PURPOSE OF REVIEW

Kymographic imaging is a modern method for displaying and evaluating vibratory behaviour of the vocal folds which is crucial for voice production. This review summarizes the state of the art of this method, and focuses on the progress in this area within the last 5 years.

RECENT FINDINGS

Videokymography, using a special videocamera, offers high-speed (video)kymographic images in real time, which is advantageous in daily clinical practice. Two other methods use software to create kymograms retrospectively: digital kymography processes high-speed videolaryngoscopic recordings and offers numerous research possibilities, whereas strobovideokymography processes videostroboscopic recordings, and its use is limited to regular vibration patterns. Current studies reveal that high-speed kymographic images allow more reliable visual evaluation of vibrations than by watching video recordings. Image analysis procedures have been advanced to quantify the vibration properties of the vocal folds. New information has been obtained on asymmetry, mucosal waves, irregularities, phonation onset, and nonlinear dynamic phenomena in voice disorders, as well as in singing.

SUMMARY

High-speed kymography visualizes vibratory features which are not simply observable via traditional methods. It shows large potential in better understanding the functional origin of hoarseness and unsteady phonatory states. Further research in this area is envisioned.

Advanced waveform decomposition for high-speed videoendoscopy analysis

This article presents a novel approach to analyze nonperiodic vocal fold behavior of high-speed videoendoscopy (HSV) data. Although HSV can capture true vibrational motions of the vocal folds, its clinical advantage over the videostroboscopy has not widely been accepted. One of the key advantages of the HSV over the videostroboscopy is its ability to capture vocal folds' nonperiodic behavior, which is more prominent in pathological vocal folds. However, such nonperiodicity in the HSV data has not been fully explored quantitatively beyond simple perturbation analysis. This article presents an advanced waveform modeling and decomposition technique for HSV-based waveforms. Waveforms are modeled to have three components: harmonic signal, deterministic nonharmonic signal, and random nonharmonic signal. This decomposition is motivated by the fact that voice disorders introduce signal content that is nonharmonic but carries deterministic quality such as subharmonic or modulating content. The proposed model is aimed to isolate such disordered behaviors as deterministic nonharmonic signal and quantify them. In addition to the model, the article outlines model parameter estimation procedures and a family of harmonics-to-noise ratio (HNR) parameters. The proposed HNR parameters include harmonics-to-deterministic-noise ratio (HDNR) and harmonics-to-random-noise ratio. A preliminary study demonstrates the effectiveness of the extended model and its HNR parameters. Vocal folds with and without benign lesions (Nwith = 13; Nwithout = 20) were studied with HSV glottal area waveforms. All three HNR parameters significantly distinguished the disordered condition, and the HDNR reported the largest effect size (Cohen's d = 2.04).

Effect of vocal fold injury location on vibratory parameters in excised canine larynges

OBJECTIVE

To investigate the effect of vocal fold injury location on vibratory amplitude and lateral phase difference.

STUDY DESIGN

Repeated measures with each excised canine larynx serving as own control.

SETTING

Basic science study conducted in university laboratory.

METHODS

Vocal fold vibration of excised canine larynges was recorded with a high-speed camera before and after inducing vocal fold injury at 1 of 5 locations: anterior, middle, posterior, medial, or superior. Medial and superior injuries were created within the middle third of the vocal fold. Five larynges were used for each of the 5 injury locations. Kymography was performed at the midpoint of the vocal folds for each video. Pre- and postinjury vibratory amplitude and lateral phase difference were compared for each location.

RESULTS

The anterior and medial injuries produced consistent decreases in vibratory amplitude. Middle and posterior injuries might slightly decrease amplitude. Superior injuries seemed to have no effect on amplitude. Anterior and medial injuries induced phase asymmetry between the right and left vocal folds. Middle injuries appeared to affect phase difference slightly, whereas posterior and superior injuries had no effect.

CONCLUSION

Injury to the anterior or medial portions of the vocal fold may be most likely to cause abnormal vocal fold vibration. Using caution in these locations during phonosurgery may favor superior postoperative vocal outcomes.

Mitigation of temporal aliasing via harmonic modeling of laryngeal waveforms in high-speed videoendoscopy

High-speed videoendoscopy (HSV) enables the observation and measurement of vibratory behaviors of vocal folds by capturing the laryngeal imagery at high frame rates. The frame rates of commercially available HSVs, however, are still limited to carry out sample-based time-domain objective analyses. To mitigate the resulting lack of temporal resolution, existing studies have employed sum-of-harmonics parametric models to evaluate temporal vocal-fold behaviors. This paper focuses on the other weakness of HSV: its inherent susceptibility to temporal aliasing. Aliasing occurs when there are substantial harmonics above the Nyquist frequency of the HSV camera, and video cameras offer very little means to filter out these harmonics. Although the aliasing effect in HSV data minimally affects many of the laryngeal objective parameter measurements, some parameters, such as harmonics-to-noise ratio and derivative-based parameters, are sensitive to the aliased content. The use of a parametric model with a careful selection of the number of harmonics enables classification of the aliased harmonics as a part of the harmonic signal. Glottal area waveform examples are included to illustrate the modeling capability for cases of normal and disordered vocal folds.

Kymographic characterization of vibration in human vocal folds with nodules and polyps

OBJECTIVES/HYPOTHESIS

Digital kymography (DKG) can provide objective quantitative data about vocal fold vibration, which may help distinguish normal from pathological vocal folds as well as nodules from polyps.

STUDY DESIGN

Case-control study.

METHODS

There were 87 subjects who were separated into three groups: control, nodules, and unilateral polyps, and examined using a high-speed camera attached to an endoscope. Videos were analyzed using a custom MATLAB program, and three DKG line-scan positions (25%, 50%, and 75% of vocal fold length) were used in statistical analyses to compare vocal fold vibrational frequency, amplitude symmetry index (ASI), amplitude order, and vertical and lateral phase difference (VPD and LPD, respectively).

RESULTS

Significant differences among groups were found in all vibrational parameters except frequency. Polyps and nodules groups exhibited greater ASI values (less amplitude symmetry) than the control group. Although the control group consistently showed its largest amplitudes at the midline, the polyps group showed larger amplitudes toward the posterior end of the vocal folds. A significant anterior-posterior pattern in amplitude was not found in the nodules group. LPD values were usually largest (most symmetrical) in the control group, followed by nodules and polyps. LPD at the 25% position allowed for differentiation between polyp and nodule groups. The largest VPD (more pronounced mucosal wave) values were usually found in the control group.

CONCLUSIONS

Vibratory characteristics of normal and pathological vocal folds were quantitatively examined and compared using multiline DKG. These findings may allow for better characterization of pathologies and eventually assist in improving the clinical utility of DKG.