An Excised Canine Model of Anterior Glottic Web and Its Acoustic, Aerodynamic, and High-speed Measurements

A Modified Approach for Preventing Anterior Glottic Web Formation Using Mitomycin C in Bilateral Vocal Fold Lesions

Objectives: Laryngeal keel insertion, mucosal suture, application of mitomycin-C (MMC), and staged operations are approaches to prevent the anterior glottic web, but there are limitations. Our study suggests a modified approach to prevent the formation of an anterior glottic web. Methods: This retrospective single-institution tertiary center study (N = 23) involved the simultaneous removal of bilateral vocal fold lesions with topical MMC application. If exudate was identified after 4 to 6 weeks, second laryngomicroscopic surgery (LMS) was performed to remove it with topical MMC application. Extent of anterior glottic web was measured as a percentage of the total length of the membranous vocal fold. Results: After the initial surgery, 18 patients recovered without anterior web or fibrin exudate. Thick exudate was observed in 5 patients. After the second LMS, all patients showed improvement and did not develop anterior web. Conclusion: This modified method has been developed to prevent the anterior glottic web without complications.

Excised human larynx in N-vinyl-2-pyrrolidone-embalmed cadavers can produce voiced sound by pliable vocal fold vibration

Tissue-hardening effect and health-hazard issue of formaldehyde (FA) have long been a great disadvantage of this conventional fixative in anatomical research. We recently developed a FA-free embalming method for cadavers which utilizes N-vinyl-2-pyrrolidone (NVP) and enables assessment of motion kinetics by maintaining the softness of embalmed tissue. By assessing the feasibility of NVP-embalmed tissue to mimic vocalization, this study aimed to prove the potential of embalmed cadavers, which have previously been used only for the understanding of anatomical morphology, for the assessment of precise motion physiology in the human body. Ten cadavers embalmed in NVP (n = 6) and FA (n = 4) were incorporated in this study. Excised larynges underwent experimental phonation to mimic vocalization with fast and pliable vibration of vocal folds. High-speed digital imaging was utilized for the assessment of vocal fold vibration. Furthermore, acoustic analysis of the voiced sound, and reproducibility examination were also performed. Regular vocal fold vibrations successfully produced voiced sounds during experimental phonation using NVP-embalmed larynges. The vibratory frequency, vibration amplitude, and stretch rate of the vocal folds were comparable to those of living humans. Six months after the first experiment, the vocal parameters were reproduced, to suggest the long-term preservation potential of our NVP-embalming technique. On the other hand, neither voiced sound nor vocal fold vibration were observed in FA-embalmed larynges. This novel embalming technique could pioneer the next era to utilize embalmed cadavers for the examination of motion physiology in the human body.

Anterior glottoplasty: the effect of inclusion of the vocal fold lamina propria to frequency elevation

BACKGROUND

Anterior glottoplasty is a commonly used treatment for voice feminization. But it remains in dispute over whether to suture of the ligament as part of the procedure.

OBJECTIVES

This study aimed to explore the effect of inclusion of the vocal lamina propia.

MATERIAL AND METHODS

Anterior webs were created in 8 excised canine larynges by sutures placed at 10%, 20%, and 30% of the vocal fold length, respectively. The suture depth was divided into two groups: epithelium layer (Shallow Suture, SS group) and deep layers of vocal fold lamina propia (Deep Suture, DS group).

RESULTS

For anterior webs between 0% and 30%, the frequency elevation ranged from 3% to 151% of the pre-web fundamental frequency (fo) in SS group and from 13% to 222% in DS group. No significance was found between two groups at three different sutures (p = .486 for suture at 10% of vocal fold length, 0.686 for 20%, 0.886 for 30%, respectively).

CONCLUSIONS AND SIGNIFICANCE

The frequency in excised canine larynx increased continuously as the anterior glottic webs ranged from 0% to 30%. The inclusion of the vocal fold lamina propia does not affect the frequency elevation.

Subglottic Mucosal Flap: Endoscopic Single-Stage Reconstruction for Anterior Glottic Stenosis

OBJECTIVES/HYPOTHESIS

Anterior glottic stenosis (AGS) results from surgical intervention, carcinoma, papillomatosis, congenital, or idiopathic causes. It may be present as elastic web or fibrotic scar. It impairs vocal function and glottic airway. Reconstructive options include resection and placement of a keel or glottic web-based mucosal flaps to prevent restenosis. These methods may not be sufficient for reconstructing a thick anterior scar and may require multiple interventions. The aim of the study was to describe the anterior subglottic mucosal flap (ASGMF), a one-stage, keel-free technique for AGS repair.

STUDY DESIGN

A retrospective cohort.

METHODS

Patients with AGS were operated using the ASGMF between 2017 and 2020. The stenotic segment was excised, and then an ASGMF was developed. A unilateral oblique incision was performed to allow rotation and advancement of the flap toward the contralateral vocal fold. The flap was sutured to the mucosal edge of the vocal fold to create mucosal continuity and prevent restenosis. Vocal fold length ratio (VFLR), which is between the free part and the total vocal fold length, as well as stroboscopic measures, were calculated before and after surgery.

RESULTS

Twelve patients were enrolled. Etiologies were iatrogenic, dysplasia, papillomatosis, carcinoma, and congenital. Average VFLR improved from 0.33 to 0.87 (P-value < .0001). Median amplitude and mucosal wave propagation improved from 12.3% and 9.5% to 28.6% and 22.7%, respectively (P-values = .0278, .0385). Phase symmetry improved from 24.5% to 60.9% (P-value = .0413). No complications were encountered.

CONCLUSIONS

ASGMF for AGS is an effective surgical procedure, allowing for one stage, keel-free reconstruction of the anterior commissure. ASGMF can significantly elongate the free portion of the vocal folds and improve vibratory function.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Impact of Subharmonic and Aperiodic Laryngeal Dynamics on the Phonatory Process Analyzed in Ex Vivo Rabbit Models

Normal voice is characterized by periodic oscillations of the vocal folds. On the other hand, disordered voice dynamics (e.g., subharmonic and aperiodic oscillations) are often associated with voice pathologies and dysphonia. Unfortunately, not all investigations may be conducted on human subjects; hence animal laryngeal studies have been performed for many years to better understand human phonation. The rabbit larynx has been shown to be a potential model of the human larynx. Despite this fact, only a few studies regarding the phonatory parameters of rabbit larynges have been performed. Further, to the best of our knowledge, no ex vivo study has systematically investigated phonatory parameters from high-speed, audio and subglottal pressure data with irregular oscillations. To remedy this, the present study analyzes experiments with sustained phonation in 11 ex vivo rabbit larynges for 51 conditions of disordered vocal fold dynamics. (1) The results of this study support previous findings on non-disordered data, that the stronger the glottal closure insufficiency is during phonation, the worse the phonatory characteristics are; (2) aperiodic oscillations showed worse phonatory results than subharmonic oscillations; (3) in the presence of both types of irregular vibrations, the voice quality (i.e., cepstral peak prominence) of the audio and subglottal signal greatly deteriorated compared to normal/periodic vibrations. In summary, our results suggest that the presence of both types of irregular vibration have a major impact on voice quality and should be considered along with glottal closure measures in medical diagnosis and treatment.

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.

Survival in Vivo Canine Phonation Model Without Stimulation

OBJECTIVES

We describe a survival nonstimulated in vivo canine phonation model using distending laryngoscope, cramp frame, and constant humidified glottal airflow to elicit phonation.

METHODS

Five beagle dogs were involved in this study. One cuffed endotracheal tube was placed below the glottis through the tracheotomy and delivered humidified airflow to the glottis. Arytenoids approximation was maintained using a clamp under the distending laryngoscope. Acoustic and aerodynamic parameters were measured using synchronous signal collection system and analysis software. Vocal oscillation also was examined using stroboscope laryngeal imaging.

RESULTS

For the nonstimulated in vivo phonation animal, the sound intensity and fundamental frequency were 78.3 ± 6.8 dB and 127.6 ± 29.2 Hz in the first experiment and 82.9 ± 6.6 dB and 175.2 ± 4.4 Hz 4 weeks later. The aerodynamic analysis revealed the mean subglottal phonation threshold pressure (PTP) and phonation threshold flow (PTF) were 8.5 ± 4.0 cmH₂0 and 683.0 ± 356.4 mL/s in the first experiment and 16.1 ± 8.6 cmH₂0 and 384.8.0 ± 230.6 mL/s in the second experiment 4 weeks later. Stroboscope image revealed sustained vocal vibration during great airflow delivery to glottis in the phonation animal model.

CONCLUSIONS

We developed a survival nonstimulated in vivo phonation canine model that allows the study of long-term animal phonation study as its own control.

Evaluation of an asymmetric anterior glottic web in an excised canine larynx model

The main objective of the study is to model asymmetry within anterior glottic webs in excised larynges using sutures and apply aerodynamic and acoustic analyses. Anterior glottic webs (AGW) were modeled in eight excised larynges using sutures secured at the level of the glottis to mimic the scar tissue of the web. Each of the eight larynges were tested under three different pressure increments for each of the three models of AGW: symmetric, vertically asymmetric, and laterally asymmetric. Phonation threshold pressure (PTP) and flow (PTF) differed significantly across AGW conditions (p = 0.006 and p = 0.005, respectively). Additionally, vocal efficiency was significantly different among conditions (p = 0.005) as well as significantly lower in the asymmetric groups (p = 0.015 and p = 0.007). Perturbation measures were not significantly different across conditions. Correlation dimension (D2) was significantly different at PTP, 1.25 × PTP, and 1.5 × PTP (p = 0.003, p = 0.010, and p < 0.001, respectively) as well as significantly higher in the asymmetric groups at each pressure increment. The increased PTP, PTF, and D2 values as well as decreased vocal efficiency among the asymmetric conditions indicates a significant decrease in vocal function, and thus represents that asymmetries could be a contributing factor to the pathological symptoms associated with glottic webs.