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Description of the Features and Vibratory Behaviors of the Nyquist Plot Analyzed From Laryngeal High-Speed Videoendoscopy Images

Mohd Khairuddin KA, Ahmad K, Mohd Ibrahim H, Yan Y

J Voice, 2020 Aug 26.
PMID: 32861565 DOI: 10.1016/j.jvoice.2020.07.036

Facilitative playback-based subjective measures offer a more reliable evaluation of the vocal fold vibration than those derived from direct inspection of video playback. One of the measures is a Nyquist plot, which presents the analyzed cycle-to-cycle vibratory information in a graphical form. While the potential is evident, the information of the features of the Nyquist plot, which the evaluation is based on, is still incomplete. The current identified features and their vibratory behaviors may be inadequate to guarantee accurate interpretation of the findings. The present study aims to address this issue by examining the features of the Nyquist plot and their vibratory behaviors. A total of 56 young normophonic speakers, that is, 20 males and 36 females were recruited as the participants. Each of them underwent laryngeal high-speed videoendoscopy to record the images of the vocal fold vibration, which were then analyzed to generate the Nyquist plots. The features were identified by inspecting the properties of the plot points forming the Nyquist plots. For each identified feature, its vibratory behaviors were examined. The results revealed four features: rim contour depicting the longitudinal phase difference; left edge shape signifying the glottal configuration, phase closure, and closed phase duration; rim width and rim pattern visualizing the regularity of glottal areas and the regularity of the intracycle variations, respectively. The findings present a more complete reference of the features and their vibratory behaviors that is pertinent for the Nyquist plot interpretation.
Analysis Method for Laryngeal High-Speed Videoendoscopy: Development of the Criteria for the Measurement Input

Mohd Khairuddin KA, Ahmad K, Mohd Ibrahim H, Yan Y

J Voice, 2021 Jul;35(4):636-645.
PMID: 31864891 DOI: 10.1016/j.jvoice.2019.12.005

Despite its clear advantages, laryngeal high-speed videoendoscopy (LHSV) has not yet been accepted as a routine imaging tool for the evaluation of vocal fold vibration due to the unavailability of methods to effectively analyze the huge number of images from the LHSV recording. Recently, a promising LHSV-based analysis method has been introduced. The ability of this analysis method in studying the vocal fold vibratory behaviors had been substantially demonstrated. However, some practical aspects of its clinical applications still require further attention. Most fundamental is that the criteria for the measurement input ie, a segment of interest (SOI), which has not been fully defined. Particularly, the length of the SOI and the location along the sample, where it needs to be selected require further confirmation. Meanwhile, the analysis using any options of a well-delineated glottal area demands verification. Without clear criteria for the SOI, it is difficult to demonstrate the relevance of this analysis method in clinical voice assessment. Therefore, the aim of the present study is to establish the criteria for the SOI, which involved the investigations on the length of the SOI and the location along the sample, where it needs to be selected, as well as the use of any options of a well-delineated glottal area for analysis. The participants in the present study consisted of 36 young normophonic females. The methods involved LHSV recording of the images of the vibrating vocal folds. The captured images were then analyzed using the method. The LHSV-based measures from the analyses were compared according to the specified procedures of each investigation. Results indicated that 2000 frames should be used as the SOI length. The SOI could be selected at any location along the sample as long as well-delineated glottal areas were observed. With the current findings, a more conclusive measurement protocol is available to ensure reliable LHSV-based measures. The findings further support this analysis method for clinical application, which in turn promote LHSV as a reliable laryngeal imaging tool in clinical setting.
Effects of Using Laryngeal High-Speed Videoendoscopy Images Visualizing Partial Views of The Glottis on Measurement Outcomes

Mohd Khairuddin KA, Ahmad K, Ibrahim HM, Yan Y

J Voice, 2022 Jan;36(1):106-112.
PMID: 32456835 DOI: 10.1016/j.jvoice.2020.04.027

Ideally, an analysis method for laryngeal high-speed videoendoscopy (LHSV) based on the glottal area waveforms (GAW) requires images of a complete view of the glottis to ensure findings that are representatives of the vibratory behaviors of the whole vocal folds. However, in practice, the preferred images may not be obtained at all times. Often, the only available images that a clinician has to work with consist of a partial view of the glottis. This study aims to examine the effects of using images of a partial view of the glottis (ie, posterior-middle, anterior-middle, or middle) on the LHSV-based measures (ie, fundamental frequency (F0GAW), frequency perturbation (jitterGAW), amplitude perturbation (shimmerGAW), open quotient (OQGAW), and Nyquist plot). The participants consisted of 9 young normophonic females. The procedures involved LHSV recording of the vibration of the vocal folds. The images of the complete view of the glottis were analyzed to obtain the LHSV-based measures. The same images were used to simulate the images of partial views of the glottis by changing the outline of the region of interest to include only either the posterior-middle, anterior-middle, or middle parts of the glottis. The LHSV-based measures from the images of the partial views were then compared to those with the complete view . The results showed that all LHSV-based measures from the images of the posterior-middle view were similar to those of the complete view. However, only the F0GAW, jitterGAW, and shimmerGAW from the images of the anterior-middle and middle views were similar to those of the complete view. Lower OQGAW and different Nyquist plots than those of the complete view were generated by the images of the anterior-middle and middle views. In conclusion, all LHSV-based measures from the images of the posterior-middle view of the glottis, and only the F0GAW, jitterGAW, and shimmerGAW from the images of the anterior-middle and middle views of the glottis reflect the vibratory behaviors of the whole vocal folds. The same conclusion could not be applied to the OQGAW and Nyquist plots of the images of the anterior-middle and middle views of the glottis. A possible effect of the presence or absence of a posterior glottal gap on the findings warrants further confirmation.
Cross-cultural Adaptation of the Consensus Auditory-perceptual Evaluation of Voice (CAPE-V) Into Malay: A Validity Study

Mohd Mossadeq N, Mohd Khairuddin KA, Zakaria MN

J Voice, 2022 Jun 24.
PMID: 35760635 DOI: 10.1016/j.jvoice.2022.05.018

Auditory-perceptual rating of voice is one component of voice evaluation, and the CAPE-V is one of the tools for this purpose. Because of its advantages, the CAPE-V has been adapted into several languages. Accordingly, the adaptation of the CAPE-V into Malay is essential for its utility among the Malaysian population, which this study aimed to accomplish. This study involved translating the CAPE-V into Malay, termed the Malay CAPE-V, followed by establishing its validity. The translation processes (ie, forward translation and backward translation) involved four different translators ie, three speech-language therapists (SLTs), and one linguist with at least 14 years of experience. Most items were similarly translated, except for a few, which were subsequently accepted as similar, following consensus among the translators. In the examination of content validity, two raters (ie, SLTs) with at least 12 years of clinical experience reviewed and scored the tested items. Given that the scale-level content validity index average value (S-CVI/Ave) was above the acceptable level, all items were retained. The examination of construct validity and concurrent validity involved ratings of voice samples recorded from 38 participants, comprising 19 individuals with normal and disordered voices, respectively. The ratings were performed by three raters (ie, SLTs) with at least 12 years of clinical experience. For the construct validity, the Mann-Whitney U test indicated significantly higher scores of the vocal parameters of the Malay CAPE-V for the disordered voice group than for the normal voice group. Meanwhile, for the concurrent validity, the Spearman correlation indicated that all relationships between the scores of the vocal parameters of the Malay CAPE-V and GRBAS Scale were significant, with most of them achieving a very strong positive correlation. The results demonstrated that the Malay CAPE-V is a valid tool for an auditory-perceptual rating of voice among the Malaysian population.
Nyquist Plot Parametrization for Quantitative Analysis of Vibration of the Vocal Folds

Arias-Vergara T, Döllinger M, Schraut T, Mohd Khairuddin KA, Schützenberger A

J Voice, 2023 Feb 09.
PMID: 36774264 DOI: 10.1016/j.jvoice.2023.01.014

OBJECTIVES: The Nyquist plot provides a graphical representation of the glottal cycles as elliptical trajectories in a 2D plane. This study proposes a methodology to parameterize the Nyquist plot with application to support the quantitative analysis of voice disorders.
METHODS: We considered high-speed videoendoscopy recordings of 33 functional dysphonia (FD) patients and 33 normophonic controls (NC). Quantitative analysis was performed by computing four shape-based parameters from the Nyquist plot: Variability, Size (Perimeter and Area), and Consistency. Additionally, we performed automatic classification using a linear support vector machine and feature importance analysis by combining the proposed features with state-of-the-art glottal area waveform (GAW) parameters.
RESULTS: We found that the inter-cycle variability was significantly higher in FD patients compared to NC. We achieved a classification accuracy of 83% when the top 30 most important features were used. Furthermore, the proposed Nyquist plot features were ranked in the top 12 most important features.
CONCLUSIONS: The Nyquist plot provides complementary information for subjective and objective assessment of voice disorders. On the one hand, with visual inspection it is possible to observe intra- and inter-glottal cycle irregularities during sustained phonation. On the other hand, shaped-based parameters allow quantifying such irregularities and provide complementary information to state-of-the-art GAW parameters.