Characterizing liquid redistribution in a biphasic vibrating vocal fold using finite element analysis

The effect of sound field amplification systems on vocal demand response in teachers during lessons

PURPOSE

Sound pressure level (SPL), fundamental frequency (F0), time dose (Dt), cycle dose (Dc), and distance dose (Dd) are components affecting a vocal demand response. The study aimed to investigate the impact of sound field amplification systems (SFAS) on teachers' vocal parameters and determine the user comfort of SFAS use in teachers.

METHODS

Twenty female teachers underwent long-term voice dosimetry with Vocal Holter Med (PR.O.Voice Srl) during everyday teaching activities. The SFAS PentaClassRuna (Certes) was installed in classrooms. Voice dosimetry was provided in two different acoustical conditions-without the use of SFAS (one to two days) and with SFAS (one to three days). Teachers underwent voice acoustic and laryngoscopic evaluation before voice dosimetry. Two teachers' groups were formed: teachers with and without vocal nodules. The visual analogue scale measured the user comfort of SFAS.

RESULTS

There were no significant differences in vocal parameters and vocal doses between teachers with and without vocal nodules. Voice amplification significantly decreased average F0(-4.4 Hz), Dt%(-3.1%), Dc (-0.4 kcycles), and Dd (-1.3 m) in teachers without vocal nodules and F0 (-8.9 Hz) in teachers with vocal nodules. Vocal doses (Dt%, Dc, Dd) significantly decreased in classrooms with longer reverberation time. The user comfort of the SFAS during the lessons was high in both teachers groups.

CONCLUSIONS

SFAS was a mediator between the classroom's environment and the teacher's vocal demand response; it changed teachers' voice production parameters and reduced vocal demand response to satisfy the communication requirements. In addition, voice amplification was more beneficial for teachers without vocal fold lesions.

Von Mises stress peak (VMSP) and laryngomalacia severity score (LSS) are extremely useful in the selection of treatment for laryngomalacia

OBJECTIVE

To analyze the judgment efficiency of a computer stress model and severity score in severity evaluation and treatment plan selection of laryngomalacia patients.

METHODS

Twenty-two children (12 cases in the operation group and 10 cases in the follow-up group) with moderate to severe laryngomalacia were assessed by laryngomalacia severity score (LSS) which included visual analogue scale (VAS) and clinical score. A computer stress model of the laryngeal cavity was constructed for all children, with the von Mises stress peak (VMSP) of the model used as another quantitative evaluation method. The ROC curves of two quantitative evaluation methods, the LSS and the VMSP, were analyzed respectively, according to the clinical guideline which is regarded as the gold standard for judging whether surgery is needed. The diagnostic efficiency indexes such as sensitivity, specificity, and accuracy were calculated. The area under ROC curves (AUC) of the two methods were compared by a DeLong model. Spearman correlation analysis and Kappa test were used to test the correlation and consistency of the two quantitative evaluation methods. The independent sample t test was used to compare the difference of LSS and VMSP between operation group and follow-up group.

RESULTS

The sensitivity, specificity, and accuracy of LSS in judging whether laryngomalacia was operated or not were 83.33%, 80.00% and 81.82%, respectively, and the area under ROC curve (AUC) was 0.825 (p < 0.05). The sensitivity, specificity, and accuracy of the computer stress model for laryngomalacia were 58.33%, 90.00% and 72.73%, respectively, and the AUC was 0.796 (p < 0.05). The spearman correlation coefficient between LSS and VMSP was 0.833, p < 0.001, which is statistically significant. LSS (t = 3.251, p = 0.004) and VMSP (t = 2.435, p = 0.024) of the two groups were statistically different.

CONCLUSION

VMSP and LSS have high diagnostic efficacy in the quantitative evaluation of the severity of laryngomalacia and the selection of treatment plan. The consistency of the two quantitative evaluation methods is good, which has practical value for the evaluation of the severity of laryngomalacia and has guiding significance for surgery.

Direct measurement and modeling of intraglottal, subglottal, and vocal fold collision pressures during phonation in an individual with a hemilaryngectomy

The purpose of this paper is to report on the first in vivo application of a recently developed transoral, dual-sensor pressure probe that directly measures intraglottal, subglottal, and vocal fold collision pressures during phonation. Synchronous measurement of intraglottal and subglottal pressures was accomplished using two miniature pressure sensors mounted on the end of the probe and inserted transorally in a 78-year-old male who had previously undergone surgical removal of his right vocal fold for treatment of laryngeal cancer. The endoscopist used one hand to position the custom probe against the surgically medialized scar band that replaced the right vocal fold and used the other hand to position a transoral endoscope to record laryngeal high-speed videoendoscopy of the vibrating left vocal fold contacting the pressure probe. Visualization of the larynx during sustained phonation allowed the endoscopist to place the dual-sensor pressure probe such that the proximal sensor was positioned intraglottally and the distal sensor subglottally. The proximal pressure sensor was verified to be in the strike zone of vocal fold collision during phonation when the intraglottal pressure signal exhibited three characteristics: an impulsive peak at the start of the closed phase, rounded peak during the open phase, and minimum value around zero immediately preceding the impulsive peak of the subsequent phonatory cycle. Numerical voice production modeling was applied to validate model-based predictions of vocal fold collision pressure using kinematic vocal fold measures. The results successfully demonstrated feasibility of in vivo measurement of vocal fold collision pressure in an individual with a hemilaryngectomy, motivating ongoing data collection that is designed to aid in the development of vocal dose measures that incorporate vocal fold impact collision and stresses.

Three-dimensional finite element modeling for evaluation of laryngomalacia severity in infants and children

This study was performed to investigate the feasibility of using a three-dimensional (3D) finite element model for laryngomalacia severity assessment. We analyzed laryngeal computed tomography images of seven children with laryngomalacia using Mimics software. The gray threshold of different tissues was distinguishable, and a 3D visualization model and finite element model were constructed. The laryngeal structure parameters were defined. The peak von Mises stress (PVMS) value was obtained through laryngeal mechanical analysis. The PVMS values of the laryngeal soft tissue and cartilage scaffolds were independently correlated with disease severity. After stress loading the model, the relationship between laryngomalacia severity and the PVMS value was apparent. However, the PVMS value of laryngeal soft tissue was not correlated with laryngomalacia severity. This study established the efficacy of a finite element model to illustrate the morphological features of the laryngeal cavity in infants with laryngomalacia. However, further study is required before widespread application of 3D finite element modeling of laryngomalacia. PVMS values of the laryngeal cartilage scaffold might be useful for assessment of laryngomalacia severity. These findings support the notion that structural abnormalities of the laryngeal cartilage may manifest as quantifiable changes in stress variants of the supraglottic larynx.

Toward Development of a Vocal Fold Contact Pressure Probe: Bench-Top Validation of a Dual-Sensor Probe Using Excised Human Larynx Models

A critical element in understanding voice production mechanisms is the characterization of vocal fold collision, which is widely considered a primary etiological factor in the development of common phonotraumatic lesions such as nodules and polyps. This paper describes the development of a transoral, dual-sensor intraglottal/subglottal pressure probe for the simultaneous measurement of vocal fold collision and subglottal pressures during phonation using two miniature sensors positioned 7.6 mm apart at the distal end of a rigid cannula. Proof-of-concept testing was performed using excised whole-mount and hemilarynx human tissue aerodynamically driven into self-sustained oscillation, with systematic variation of the superior-inferior positioning of the vocal fold collision sensor. In the hemilarynx experiment, signals from the pressure sensors were synchronized with an acoustic microphone, a tracheal-surface accelerometer, and two high-speed video cameras recording at 4000 frames per second for top-down and en face imaging of the superior and medial vocal fold surfaces, respectively. As expected, the intraglottal pressure signal exhibited an impulse-like peak when vocal fold contact occurred, followed by a broader peak associated with intraglottal pressure build-up during the de-contacting phase. As subglottal pressure was increased, the peak amplitude of the collision pressure increased and typically reached a value below that of the average subglottal pressure. Results provide important baseline vocal fold collision pressure data with which computational models of voice production can be developed and in vivo measurements can be referenced.

A Computational Study of Vocal Fold Dehydration During Phonation

While vocal fold dehydration is often considered an important factor contributing to vocal fatigue, it still remains unclear whether vocal fold vibration alone is able to induce severe dehydration that has a noticeable effect on phonation and perceived vocal effort. A three-dimensional model was developed to investigate vocal fold systemic dehydration and surface dehydration during phonation. Based on the linear poroelastic theory, the model considered water resupply from blood vessels through the lateral boundary, water movement within the vocal folds, water exchange between the vocal folds and the surface liquid layer through the epithelium, and surface fluid accumulation and discharge to the glottal airway. Parametric studies were conducted to investigate water loss within the vocal folds and from the surface after a 5-min sustained phonation under different permeability and vibration conditions. The results showed that the dehydration generally increased with increasing vibration amplitude, increasing epithelial permeability, and reduced water resupply. With adequate water resupply, a large-amplitude vibration can induce an overall systemic dehydration as high as 3%. The distribution of water loss within the vocal folds was non-uniform, and a local dehydration higher than 5% was observed even under conditions of a low overall systemic dehydration (<1%). Such high level of water loss may severely affect tissue properties, muscular functions, and phonations characteristics. In contrast, water loss of the surface liquid layer was generally an order of magnitude higher than water loss inside the vocal folds, indicating that the surface dehydration level is likely not a good indicator of the systemic dehydration.