An Acoustic-Perceptual Study of Vocal Tremor

Voice Improvement After Essential Tremor Treatment via Focused Ultrasound and Deep Brain Stimulation

OBJECTIVES

The primary objective of this study was to determine whether two neurosurgical procedures, deep brain stimulation (DBS) and focused ultrasound (FUS), to treat essential tremor (ET) of the upper limb also reduce vocal tremor (VT) in patients with comorbid dysphonia.

METHODS

Twelve patients with ET and concomitant VT scheduled for neurosurgical intervention (FUS or DBS) or returning for follow-up after DBS implantation were assessed. FUS patients were assessed pre- and post-intervention and DBS patients were assessed with the electrodes turned on and off post-implantation. Three voice recordings of a sustained /a/ were obtained for each participant condition. Percent fundamental frequency variability (FFV) was calculated for each recorded sustained vowel. Additionally, blinded expert perceptual VT rating (VTR) was performed to assess subjective changes in tremors.

RESULTS

Of the 12 patients, seven underwent unilateral FUS, and five underwent bilateral DBS. Mean FFV without neurosurgical intervention was 18.3%, SD = 7.8 and with neurosurgical intervention was 6.3%, SD = 3.0 (t (70) =8.7, p < 0.001). Mean FFV decreased in the FUS cohort from 22.0%, SD = 7.1 pre-ablation to 6.7%, SD = 2.4 post-ablation (t (40) = 7.7, p < 0.001). Mean FFV also decreased in the DBS cohort from 15.7%, SD = 7.0 to 6.0%, SD = 3.3 when stimulation was turned on (t (28)=5.7 p < 0.001). In the FUS group, mean VTR decreased from 4.0 to 1.4 post-ablation (Z = 7.8, p < 0.001). In the DBS group, mean VTR decreased from 3.3 to 2.1 with stimulation (Z = 4.1, p < 0.001).

CONCLUSION

Neurosurgical interventions for ET (bilateral DBS and unilateral FUS) demonstrate acoustic and perceptual benefits for VT.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:367-373, 2024.

Automatic Classification of Healthy Subjects and Patients With Essential Vocal Tremor Using Probabilistic Source-Filter Model Based Noise Robust Pitch Estimation

Essential voice tremor (EVT) is a voice disorder resulting from dyscoordination within the laryngeal musculature. A low-frequency fluctuations of fundamental voice frequency or the strength of excitation amplitude is the main consequence of the disorder. The automatic classification of healthy control and EVT is useful tool for the clinicians. A typical automatic EVT classification involves three steps. The first step is to compute the pitch contour from the speech. The second step is to compute the features from the pitch contour, and the final step is to use a classifier to classify the features into healthy or EVT. It is shown that a high-resolution pitch contour estimated from the glottal closure instants (GCIs) is useful for EVT classification. The HPRC estimation can be very poor in the presence of noise. Hence, a probabilistic source filter model based noise robust GCI detection is used for HPRC estimation. The Empirical mode decomposition based feature extraction is used followed by a support vector machine classifier. The EVT classification performance is evaluated using recordings from 45 subjects. The proposed method is found to perform better than the baseline techniques in eight different additive noise conditions with six SNR levels.

Multiparametric laryngeal assessment of the effect of thalamic deep brain stimulation on essential vocal tremor

OBJECTIVE

EVT is a refractory voice disorder that significantly affects quality of life. This work aims to conduct a multiparametric assessment of the effect of deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) on essential vocal tremor (EVT) and investigate the relation between DBS lead location and EVT outcomes.

METHODS

Nine participants underwent DBS for essential tremor and were diagnosed with co-occurring EVT in this prospective cohort study. Objective measurements including acoustic evaluation of vocal fundamental frequency (F0) and intensity modulation and subjective measurements including physiologic evaluation of the oscillatory movement of the laryngeal muscles and vocal tract and perceptual ratings of tremor severity were collected PRE and POST DBS. Finally, we investigated the relation between DBS lead location and EVT outcomes.

RESULTS

Acoustic modulations of F0 and intensity were significantly improved POST DBS. Physiologic assessment showed a POST DBS reduction of oscillatory movement in the laryngeal muscles and vocal tract, but not significantly. Listener and participant perception, of EVT severity was also significantly reduced. Finally, our results indicate better EVT control with increased distance to midline of left VIM thalamic stimulation.

CONCLUSIONS

By employing a battery of objective and subjective measures, our study supports the benefit of DBS for the treatment of EVT and specifies the acoustic and physiologic mechanisms that mediate its positive effect. We further provide preliminary results on the relation between lead location and EVT outcomes, laying the foundation for future studies to clarify the optimal DBS target for the treatment of EVT.

Intraoperative Evaluation of Essential Vocal Tremor in Deep Brain Stimulation Surgery

Purpose Essential vocal tremor (EVT) is a prevalent and difficult-to-manage voice disorder. There is evidence that deep brain stimulation (DBS) of the ventral intermediate nucleus (Vim) of the thalamus may be beneficial for treating EVT. The objective of this preliminary investigation was to conduct intraoperative voice assessments during Vim-DBS implantation in order to evaluate immediate voice outcomes in medication-refractory essential tremor patients with co-occurring EVT. Method Seven adult subjects diagnosed with EVT undergoing Vim-DBS surgery participated in this investigation. Voice samples of sustained vowels were collected by a speech-language pathologist preoperatively and intraoperatively, immediately following Vim-DBS electrode placement. Voice evaluation included objective acoustic assessment of the rate and extent of EVT fundamental frequency and intensity modulation and subjective perceptual ratings of EVT severity. Results The rate of intensity modulation, extent of fundamental frequency modulation, and perceptual rating of EVT severity were significantly reduced intraoperatively as compared to preoperatively. Moderate, positive correlations were appreciated between a subset of acoustic measures and perceptual severity ratings. Conclusions The results of this study demonstrate a speech-language pathologist can conduct intra-operative evaluation of EVT during DBS surgery. Using a noninvasive, simple acoustic recording method, we were able to supplement perceptual subjective observation with objective assessment and demonstrate immediate, intraoperative improvements in EVT. The findings of this analysis inform the added value of intraoperative voice evaluation in Vim-DBS patients and contribute to the growing body of literature seeking to evaluate the efficacy of DBS as a treatment for EVT.

Objective Acoustic Quantification of Perceived Voice Tremor Severity

Purpose This study compared auditory-perceptual measures of presence/absence and severity of vocal tremor to acoustic markers of vocal tremor. The validity (both concurrent and diagnostic) of various acoustic markers of vocal tremor was also assessed. Method Fifty-six midvowel sustained [a:] recordings were selected to yield a representative convenience sample of vocal tremor. After training with 10 synthesized samples, 4 female audiologists rated these samples on "voice tremor severity" on a continuous 10-cm scale. Afterward, 15 randomly selected recordings were presented a 2nd time for intrarater reliability assessment. Customized audio signal processing in Praat yielded 12 acoustic measures of rate, extent and perturbation of fundamental frequency (f ₀), and intensity level (IL) modulation. Enter-type multiple linear regression analysis was applied to weight and combine these acoustic variables into an acoustic model of vocal tremor severity. Results After removing the vocal tremor severity ratings of 1 of the audiologists because of insufficient intra- and interrater reliability, mean single-measures consistency-type intraclass correlation coefficients equaled .83 within raters and .72 between raters. Correlation between mean ratings and the 12 acoustic markers ranged from .76 for median extent of f ₀ modulation to .11 for rate of IL modulation. Correlation between mean ratings and the acoustic model was .89. Analysis of this model's receiver operating characteristics yielded an area under receiver operating characteristic curve of .93, denoting sensitivity of .87 and specificity of .91. Conclusions This study demonstrated that auditory-perceptual ratings of vocal tremor severity are guided primarily by f ₀ and IL modulation extent, less by modulation perturbation, and least by modulation rate. The acoustic model covering all these modulation properties yielded acceptable results in terms of both concurrent and diagnostic validity. However, external cross-validation of this model is warranted before applying it in clinical voice/speech assessment.

Reliability of High-speed Videoendoscopic Ratings of Essential Voice Tremor and Adductor Spasmodic Dysphonia

OBJECTIVES

The main objectives of this study were to (1) examine intrarater and inter-rater reliabilities in perceptual ratings of vocal fold vibratory patterns and supraglottic characteristics for essential vocal tremor and adductor spasmodic dysphonia (AdSD) using high-speed videoendoscopy (HSV), and (2) to investigate the specificity of the parameters in differentiating these two voice disorders.

METHODS

HSV recordings of 34 cases diagnosed with essential vocal tremor, AdSD, or AdSD with vocal tremor were evaluated blindly by two voice speech pathologists. The two raters examined all HSV video segments twice across nine supraglottic and vocal fold vibratory characteristics for inter-rater and intrarater reliabilities. A separate consensus rating was then developed, with the results analyzed to explore differentiation.

RESULTS

Raters demonstrated moderate intrarater reliability with mean Spearman's rho correlation coefficients of 0.68 (rater 1) and 0.73 (rater 2). Moderate inter-rater reliability for the two raters was seen across all parameters with a mean Cohen's kappa coefficient of 0.51. Raters showed higher intrarater and inter-rater reliabilities for supraglottic parameters. Only the presence of tremor differentiated between the two voice disorders in cases with a consistent diagnosis.

CONCLUSIONS

The high level of concomitance between vocal tremor and AdSD may affect subjective perceptual analysis of supraglottic and vocal fold vibratory patterns. Results indicate similar global involvement of supraglottic laryngeal structures for both vocal tremor and AdSD.

Transducer-based evaluation of tremor

The International Parkinson and Movement Disorder Society established a task force on tremor that reviewed the use of transducer-based measures in the quantification and characterization of tremor. Studies of accelerometry, electromyography, activity monitoring, gyroscopy, digitizing tablet-based measures, vocal acoustic analysis, and several other transducer-based methods were identified by searching PubMed.gov. The availability, use, acceptability, reliability, validity, and responsiveness were reviewed for each measure using the following criteria: (1) used in the assessment of tremor; (2) used in published studies by people other than the developers; and (3) adequate clinimetric testing. Accelerometry, gyroscopy, electromyography, and digitizing tablet-based measures fulfilled all three criteria. Compared to rating scales, transducers are far more sensitive to changes in tremor amplitude and frequency, but they do not appear to be more capable of detecting a change that exceeds random variability in tremor amplitude (minimum detectable change). The use of transducer-based measures requires careful attention to their limitations and validity in a particular clinical or research setting. © 2016 International Parkinson and Movement Disorder Society.