Aerodynamic and acoustic effects of ventricular gap

Synchronized and Desynchronized Dynamics Observed from Physical Models of the Vocal and Ventricular Folds

The ventricular folds, located superiorly to the vocal folds, do not usually vibrate during normal phonations. It has been shown, however, that they do vibrate together with the vocal folds under special circumstances such as voice pathology and singing voice. Towards understanding the effect of the ventricular fold oscillations on the vocal fold oscillations, the present study developed a synthetic model that takes into account anatomical features of the human ventricular folds. The synthetic model is made of flexible silicone compounds with material properties comparable to those of human ventricular fold tissues. In our experiment, an air-flow was injected into the vocal and ventricular fold models. As the distance between the left and right ventricular folds was reduced, the ventricular folds started to co-vibrate with the vocal folds. Depending upon the distance, various oscillation patterns of the vocal-ventricular folds were observed, e.g., synchronized dynamics with 1:1 or 1:2 frequency ratio and desynchronized chaotic dynamics. The observed chaotic dynamics might be related to voice pathology induced by the ventricular phonation. A computational model was further presented to elucidate the experimental findings.

Methodological Approaches for Vocal Folds Experiments in Laryngology: A Scoping Review

OBJECTIVE

The aim of this study was to describe the methodological approaches adopted in experimental researches in laryngology intervention studies.

METHODS

The study was performed as a scoping review using the electronic databases Medline (PubMed), Web of Science, Embase, BioMed Central and SCOPUS. These databases were manually searched from 1995 (or its inception) until the most recently published articles in June 2022. The inclusion criteria were as follows: a) studies performed with animal models in voice and/or larynx therapy, intervention and/or surgery; b) studies with participant populations composed with animals; c) studies containing original research; d) studies performed with at least one objective measurement for treatment and or intervention; e) studies reporting at least one method of larynx intervention; and f) publications written in English, Spanish or Portuguese. The exclusion criteria were as follows: a) studies considering without any objective intervention and or treatment; b) studies without animal models; and c) studies that reviewed articles or books. These criteria were set to increase inter-study comparability.

RESULTS

There were found 26 studies that showed that in experimental laryngology. There were retrieved four main characteristics in the retrieved studies. It was observed five major groups of experimental models used for assessing vocal folds: dog (38.5%), rat/mouse (23,1%), pig (23.1%), rabbit (19.2%), human (11.5%), and sheep (3.8%). In addition, three characteristics were observed: sample (up to 20 subjects 88.5%), type of surgery/intervention (100%) and duration (up to 30 days 61.5%).

CONCLUSION

In experimental laryngology, the state of the art is grounded on mainly in dog, rat and pig in vocal folds assessment. Up to 20 subjects, surgery/intervention and experimental trial lasting no more than 30 days are frequent methodological approaches in this research field.

Experimental study of vocal-ventricular fold oscillations in voice production

Ventricular folds are located in the supraglottal region above the vocal folds. Although the ventricular folds do not vibrate under normal vocalizations, they vibrate under certain conditions, e.g., throat singing or ventricular fold dysphonia. In throat singing, the ventricular folds vibrate at the same frequency as (or at integer ratios of) the vocal fold vibration frequency. In ventricular fold dysphonia, on the other hand, the ventricular folds interfere with the vocal folds, giving rise to a hoarse voice. In the present study, the synthetic larynx model was utilized to examine the vocal-ventricular fold oscillations. Our experiments revealed that the vocal and ventricular folds can co-oscillate at the same frequency with an out-of-phase relation. Compared to the control condition, under which no ventricular folds exist, the phonation threshold pressure was increased in the presence of the ventricular folds. Acoustic analysis indicated that jitter was reduced and vocal efficiency was increased by the ventricular folds. Distance between the vocal and ventricular folds did not alter these oscillation properties. A computational model was further simulated to elucidate the mechanism underlying the observed vocal-ventricular fold oscillations. It has been suggested that out-of-phase oscillations of the vocal and ventricular folds are important for sustaining periodic laryngeal vibrations.

Effect of Ventricular Folds on Vocalization Fundamental Frequency in Domestic Pigs (Sus scrofa domesticus)

This study investigates the effect of the ventricular folds on fundamental frequency (f_o) in the voice production of domestic pigs (Sus scrofa domesticus). The excised larynges of six subadult pigs were phonated in two preparation stages, with the ventricular folds present (PS1) and removed (PS2). Vocal fold resonances were tested with a laser vibrometer, and a four-mass computational model was created. Highly significant f_o differences were found between PS1 and PS2 (means at 93.7 and 409.3 Hz, respectively). Two tissue resonances were found at 115 Hz and 250-290 Hz. The computational model had unique solutions for abducted and adducted ventricular folds at about 150 and 400 Hz, roughly matching the f_o measured ex vivo for PS1 and PS2. The differing f_o encountered across preparation stages PS1 and PS2 is explained by distinct activation of either a high or a low eigenfrequency mode, depending on the engagement of the ventricular folds. The inability of the investigated larynges to vibrate at frequencies below 250 Hz in PS2 suggests that in vivo low-frequency calls of domestic pigs (pre-eminently grunts) are likely produced with engaged ventricular folds. Allometric comparison suggests that the special, mechanically coupled "double oscillator" has evolved to prevent signaling disadvantages. Given these traits, the porcine larynx might - apart from special applications relating to the involvement of ventricular folds - not be an ideal candidate for emulating human voice production in excised larynx experimentation.

A 4-year Retrospective Review of the Presence and Pattern of Ventricular Hyperadduction Following Unilateral Vocal Fold Paralysis, Paresis, and Unilateral Cordectomy

BACKGROUND

The aim of our study was to determine the presence and pattern of ventricular hyperadduction (VH) following unilateral vocal fold (VF) paralysis/paresis and that following unilateral cordectomy (UC).

METHODS

The authors independently reviewed charts and flexible videostroboscopic recordings of 214 patients diagnosed with unilateral VF paralysis/paresis and those who had undergone UC from 2015 to 2018. The presence and pattern of VH was noted. VH was considered to be present when the false vocal fold (FVF) obliterated 50% or more of the true vocal fold width during phonation, with or without FVF vibration. The true vocal fold width was considered to be that which was visible on abduction of the VFs. Categorical variables were presented in numbers and percentages and qualitative variables were correlated using Chi-Square test. Odds ratio with 95% Confidence Interval was calculated.

RESULTS

In 154 patients diagnosed as unilateral VF paralysis/paresis 85 patients had a VH pattern (55.19%) with contralateral VH observed in 74 (87.05%), ipsilateral VH observed in 6 (7.05%) and bilateral VH observed in five patients (5.88 %). The total number of patients of UC was 60 with 36 of these patients developing a VH (60%). Ipsilateral VH was observed in 28 of these 36 patients (77.77%), three patients developed contralateral VH (8.33%) and five patients developed bilateral VH (13.88%).

CONCLUSION

Ipsilateral ventricular hyper-adduction following unilateral cordectomy in the group of patients that develop hyperadduction is a significant finding in our study suggesting possibility of unilateral central phonatory control of the FVF. Contralateral ventricular hyper-adduction following unilateral paralysis and paresis, in the group of patients that develop hyperadduction is a significant finding in our study and this finding resonates with previously published papers. A finding of unilateral VH may serve as a possible indicator of the occasionally challenging diagnosis of vocal fold paresis.

STUDY TYPE

Retrospective, Observational.

Does More Compression Mean More Pressure? A New Classification for Muscle Tension Dysphonia

Objective The aims of this study were to test the hypothesis that greater supraglottic compression (anteroposterior or lateral) correlates with higher subglottic pressure (SGP) and to develop a classification of muscle tension dysphonia (MTD), based on the degree of supraglottic compression during speech. Method A prospective, cross-sectional study was conducted in a series of 37 consecutive patients diagnosed with MTD with an altered aerodynamic profile characterized by high SGP (more than 90 mmH₂O). Supraglottic anteroposterior and lateral compression were categorized in three grades and assessed during the laryngoscopic examination. All patients completed the Spanish Voice Handicap Index (VHI) questionnaire and completed an acoustic and aerodynamic voice assessment. The relationship between compression grade and VHI with SGP was analyzed. Results More than 90% of patients demonstrated some degree of anteroposterior compression, and 67% had some degree of lateral compression. The mean (SD) SGP was 111.03 (16.7) mmH₂O, and the mean VHI was 27.86 (12.5). The degree of SGP was statistically different in the different grades of anteroposterior compression, and also anteroposterior compression correlated with an SGP (p < .05). The degree of lateral compression was not correlated with SGP. Neither the degree of anteroposterior or lateral compression nor the value of SGP was found to correlate with VHI. Conclusions Because grade of anteroposterior compression correlates with SGP, these grades can be used for diagnosis and follow-up of MTD patients. To this end and on this basis, we propose a new classification for MTD. Unlike the established classification, our proposed one makes it possible to combine different laryngoscopic features, improving the description of the larynx during phonation.

Development of Excised Larynx

The larynx is a complex organ which has a role in a variety of functions such as phonation, breathing, and swallowing. To research these functions, it is widely accepted that in vivo studies provide more anatomically and physiologically relevant findings. However, invasive procedures are generally needed to measure variables such a subglottal pressure, vocal fold tension and stiffness, and cricothyroid muscle stretch. Performing studies using excised larynges is a useful technique which makes it possible to not only measure phonation parameters but control them as well. Early studies using excised larynges mainly focused on controlling specific parameters and mathematical modeling simulations. The use of these studies has helped further research in laryngeal anatomy, imaging techniques, as well as aerodynamic, acoustic, and biomechanical properties. Here, we describe the progress of this research over the past 5 years. The number of accepted animal models has increased and ideas from excised larynx studies are starting to be applied to treatment methods for laryngeal disorders. These experiments are only valid for an excised situation and must continue to be combined with animal experimentation and clinical observations.

Evaluation of Surgical Strategies for Bilateral Vocal Fold Paralysis Using Excised Canine Larynges

OBJECTIVE

The objective of this study was to provide a theoretical basis for the selection of optimal surgical procedures in ex vivo simulated bilateral vocal fold paralysis (BVFP).

STUDY DESIGN

Four surgical stages were sequentially performed on 10 excised canine larynges with simulated BVFP: (1) transverse cordotomy, (2) medial arytenoidectomy, (3) subtotal arytenoidectomy, and (4) total arytenoidectomy.

MATERIALS AND METHODS

The sound pressure level, the signal-to-noise ratio, the glottal resistance, the glottal airflow (GF), the maximal glottal area (MGA), and spectrograms were measured after each stage. For comparative analysis of variance, a randomized block design and the Student-Newman-Keuls test were performed.

RESULTS

Under stable phonation, the sound pressure level showed no significant differences among the four stages. The signal-to-noise ratio was significantly different between the preoperative period and stage 1, as well as between stages 2 and 3. Glottal resistance was significantly different between the preoperative period and stage 1 and between stages 1 and 2. GF and MGA were significantly different among all stages, compared with those between stages 3 and 4 for GF and the preoperative period and stage 1 for MGA. The spectrograms indicated that the degree of disorder in the acoustic signals gradually increased.

CONCLUSIONS

Based on a comprehensive analysis of GF and voice quality in excised canine larynges, which simulated BVFP, our results suggest that the optimal surgical choice for BVFP is either medial or subtotal arytenoidectomy.

Establishment and Analysis of False Vocal Folds Hypertrophy Model in Excised Canine Larynges

OBJECTIVE

This study aimed to investigate the role of false vocal folds (FVFs) medialization in phonation and the acoustic impact of ventricular hypertrophy by establishing an FVF hypertrophy model.

STUDY DESIGN

A prospective in vitro experiment was carried out.

SETTING

The study was carried out using a pseudolung platform with high-speed camera in a soundproof room.

MATERIALS AND METHODS

Control, degree I, and degree II FVFs hypertrophy were simulated in 10 excised larynges via fructose injection of 0.1 mL for degree I and 0.25 mL for degree II. Mean flow rate (MFR), fundamental frequencies (F0), formants, and sound pressure level were measured with a subglottal pressure of 1.5 kPa and 2.5 kPa, respectively.

RESULTS

When the subglottal pressure was controlled at both at 1.5 kPa and at 2.5 kPa, the degree of FVF hypertrophy significantly influenced the distribution of the formants, F0, and MFR in excised canine larynges. Increasing the degree of hypertrophy was associated with a decrease in F0 and an increase in MFR. In degree II FVF hypertrophy models, the sound pressure level and the first formant were significantly higher (P < 0.05) than in normal models.

CONCLUSION

Hypertrophy of the FVFs has a significant influence on the distribution of sound energy and is associated with changes in sound quality.

Are Instructions to Manipulate Specific Parameters of Laryngeal Function Associated with Auditory-Perceptual Ratings of Voice Quality in Nondisordered Speakers?

OBJECTIVES/HYPOTHESIS

This preliminary study investigated whether auditory-perceptual judgments of voice quality by experienced speech language pathologists were associated with instructions given to speakers to manipulate specific laryngeal postures.

STUDY DESIGN

Experimental, within-subject design.

METHODS

Nine speakers were instructed and trained to manipulate three vocal parameters implicated in functional voice disorders-false vocal fold constriction, vocal fold mass, and larynx height-while reading a standard passage. Experienced judges rated these standard passages in terms of the widely used perceptual voice qualities breathiness, roughness, vocal strain, glottal fry, tone onset, tone color, loudness, and pitch.

RESULTS

Between-subject factorial analysis of variance, controlling for judge unreliability, revealed some evidence that perceptual judgments are strongly associated with underlying laryngeal muscle activity that can then serve clinical planning of goals for intervention. Eta² effect sizes were large for all dependent measures, ranging from 0.39 for pitch to 0.77 for strained.

CONCLUSIONS

Although these results are encouraging, they were obtained under ideal conditions. Further research is warranted.

False Vocal Fold Characteristics in Presbylarynges and Recurrent Laryngeal Neuropathy

OBJECTIVE

Conflicting data exist regarding false vocal fold (FVF) anatomy; it is unclear if this structure is an extension of the thyroarytenoid muscle or an independent muscle system. This confusion is amplified by diverse clinical findings in the setting of unilateral recurrent laryngeal neuropathy and presbylarynges. We sought to characterize FVF behavior in these contexts.

METHODS

Laryngoscopic/stroboscopic examinations from 11 patients with unilateral recurrent laryngeal nerve paresis and 12 patients with presbylarynges were reviewed by 4 laryngologists, blinded to the goal of the study but informed of diagnosis. Variables related to FVF structure and function at rest and during phonation were rated.

RESULTS

In recurrent laryngeal neuropathy, no significant association between atrophic/paretic vocal fold (VF) and FVF size was observed at rest (P = .69). During phonation, FVF compression was noted bilaterally; contralateral FVF hypertrophy was more common (P = .002). In presbylarynges, neither FVF size at rest (P = .86) nor compression during phonation (P = .37) was associated with the more atrophic VF; FVF compression/hypertrophy was common.

CONCLUSIONS

Consistent with clinical dogma, FVF compression was more common contralateral to VF neuropathy. This finding, however, was inconsistent and may suggest individual variability in FVF innervation and/or morphology. Intra- and interrater reliability of these clinical findings was poor.

Analysis of Direct Simultaneous Measurement of Glottal Airflow Velocity, Subglottal Pressure, and High-Speed Imaging Using Flexible Transnasal Endoscope in a Human Subject

It is difficult to directly observe glottal airflow velocity just above the glottis due to sensor size requirements and limited accessibility. We developed a miniature hot-wire probe and flexible fiberscopic high-speed imaging system for human examinations. Simultaneous direct measurement of glottal airflow velocity, subglottal pressure, and vocal fold vibration was achieved in a patient who was treated with a T-tube for tracheal stenosis. Airflow velocity changes at the anterior midline of the vocal folds were synchronized with subglottal pressure changes during each phonation cycle. The velocity at the anterior midline of the vocal folds showed a rhythmic pattern of sharp, high peaks. The result of fast Fourier transform analysis indicated that glottal velocity at the anterior midline of the vocal folds had abundant high-frequency components that were not affected by resonance of the vocal tract. Airflow velocity was variable and diminished except at the anterior midline of the vocal folds.

Nonstimulated rabbit phonation model: Cricothyroid approximation

OBJECTIVES/HYPOTHESIS

To describe a nonstimulated in vivo rabbit phonation model using an Isshiki type IV thyroplasty and uninterrupted humidified glottal airflow to produce sustained audible phonation.

STUDY DESIGN

Prospective animal study.

METHODS

Six New Zealand white breeder rabbits underwent a surgical procedure involving an Isshiki type IV thyroplasty and continuous airflow delivered to the glottis. Phonatory parameters were examined using high-speed laryngeal imaging and acoustic and aerodynamic analysis. Following the procedure, airflow was discontinued, and sutures remained in place to maintain the phonatory glottal configuration for microimaging using a 9.4 Tesla imaging system.

RESULTS

High-speed laryngeal imaging revealed sustained vocal fold oscillation throughout the experimental procedure. Analysis of acoustic signals revealed a mean vocal intensity of 61 dB and fundamental frequency of 590 Hz. Aerodynamic analysis revealed a mean airflow rate of 85.91 mL/s and subglottal pressure of 9 cm H2 O. Following the procedure, microimaging revealed that the in vivo phonatory glottal configuration was maintained, providing consistency between the experimental and postexperimental laryngeal geometry. The latter provides a significant milestone that is necessary for geometric reconstruction and to allow for validation of computational simulations against the in vivo rabbit preparation.

CONCLUSION

We demonstrate a nonstimulated in vivo phonation preparation using an Isshiki type IV thyroplasty and continuous humidified glottal airflow in a rabbit animal model. This preparation elicits sustained vocal fold vibration and phonatory measures that are consistent with our laboratory's prior work using direct neuromuscular stimulation for evoked phonation.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:1589-1594, 2016.