Biochemical basis of vocal fold mobilization after microflap surgery in a rabbit model

Clinical Voice Outcomes for Two Voice Rest Protocols after Phonomicrosurgery

OBJECTIVES

Voice rest is commonly recommended for patients with benign vocal fold lesions (BVFLs) after phonomicrosurgery. The study compares the clinical voice outcomes of two protocols, 7-day complete voice rest (CVR) and 3-day CVR followed by 4-day relative voice rest (CVR + RVR), for patients with BVFLs after phonomicrosurgery.

STUDY DESIGN

Prospective, randomized controlled trial.

METHOD

Patients with BVFLs undergoing phonomicrosurgery were recruited prospectively and randomly assigned to either protocol. Outcomes were assessed on objective measures of acoustics (fundamental frequency, frequency range, mean intensity, cepstral peak analysis) and aerodynamics (vital capacity, airflow rate, subglottal pressure, phonation threshold pressure), as well as subjective measures, both provider-reported through the Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V), and patient-reported through the Voice Handicap Index (VHI). Clinical measures were collected at three-time points: preoperatively, 1-week postoperatively (on voice rest), and 1-month postoperatively. In addition, adherence was estimated using a vocal dosimeter.

RESULTS

Twenty-five patients were recruited and randomized to 7-day CVR (n = 13) and CVR + RVR regimen (n = 12). Statistically significant changes were found within both groups for subglottal pressure (p = 0.03) and VHI score (p < 0.001) comparing pre-operative baseline to 1-month postoperative follow-up. There were no statistically significant differences between the groups. Regardless of group assignment, a significant decrease in overall severity ratings for the CAPE-V was found by comparing the preoperative scores to postoperative scores at 1-week (p < 0.001) and 1-month (p < 0.001).

CONCLUSION

Both groups improved their overall voice quality comparably 1 month after undergoing phonomicrosurgery as measured by objective and subjective parameters.

LEVELS OF EVIDENCE

2. Laryngoscope, 134:2812-2818, 2024.

Vocal Fold Submucosal Mesna Injection and Microflap Elevation in a Rabbit Model

OBJECTIVE

Mesna triggers chemical dissection in tissues by breaking down disulfide bonds and is used during surgical dissections in several areas. In this study, we aimed to investigate the effect of submucosal mesna infiltration on microflap elevation and the histopathological findings of its effects on the vocal fold lamina propria in a rabbit model.

METHODS

Eight adult male New Zealand white rabbits were used in the study. Each vocal fold was randomized, and 0.1 mL of mesna was injected into one-fold and 0.1 mL of saline to the contralateral fold. An incision was made on the epithelium and elevation was performed. The animals were sacrificed after two weeks, and the vocal folds were excised. Inflammatory response, fibrosis, and epithelial thickness were evaluated with hematoxylin eosin and Masson's Trichrome staining. Elevation time and histopathological features were compared between the two groups.

RESULTS

The elevation time (20.9 ± 1.6 second) in the saline group was significantly higher (P < 0.05) than in the mesna group (15.0 ± 3.4 second). The inflammation (1.3 ± 0.5 vs. 1.1 ± 1.0, respectively) and fibrosis scores (1.0 ± 0.8 vs. 0.8 ± 0.7, respectively) did not differ significantly (P > 0.05 in both). Epithelial thickness (12.5 ± 4.7 vs. 10.3 ± 5.3, respectively) did not differ significantly (P ˃ 0.05) in the mesna and saline groups either.

CONCLUSION

We determined that mesna facilitates the microflap elevation of the vocal folds in rabbits and does not damage the histological structure of vocal folds. This study encourages future studies to evaluate the use of mesna, now actively used across disciplines, in phonosurgery as well.

A Simple and Reproducible In Vivo Rabbit Phonation Model for Glottic Insufficiency

OBJECTIVE

The objective of this study is to describe an in vivo rabbit phonation model for glottic insufficiency that is simple and reproducible by means of unilateral transcricothyroid laryngeal muscle stimulation and high-speed video recordings of evoked phonation.

STUDY DESIGN

Nonrandomized controlled animal trial.

SETTING

Academic medical center.

METHODS

A single operation including evoked phonation with bilateral and unilateral transcricothyroid laryngeal muscle stimulation conditions was modeled using 6 New Zealand white rabbits. The effect of stimulation method on glottic cycle, pitch, and loudness was compared. Endoscopic recordings using 5000 frames-per-second image capture technology and audiologic recordings were obtained for all phonation conditions. Primary outcome measures included means of maximum glottal area (MGA)/length pixel ratio, right and left amplitude/length pixel ratios, calculated cycle frequency, auditory recorded frequency, and maximum auditory intensity. Measurements were obtained via pixel counts using ImageJ.

RESULTS

Mean MGA/length was significantly greater with unilateral, 20.30, vs bilateral, 9.62, stimulation (P = .043). Mean frequency of 479.92 Hz vs 683.46 Hz (P = .027) and mean maximum intensity of 76.3 dB vs 83.5 dB (P = .013) were significantly increased from unilateral to bilateral stimulation. There was no significant difference in mean right amplitude/length between unilateral and bilateral.

CONCLUSION

The described model demonstrates a simple and reproducible means of producing glottic insufficiency due to unilateral vocal fold bowing and represents a pathway for better understanding the biomechanics and pathophysiology of glottic insufficiency due to superior laryngeal nerve injury and vocal fold immobility and offers the potential to compare treatment modalities through in vivo study.

Epithelial response to vocal fold microflap injury in a preclinical model

OBJECTIVES

Functional outcomes following microflap surgery for vocal fold pathology are favorable. Although the stratified squamous epithelium appears to heal rapidly, persistent physiologic tissue alterations are likely. We sought to elucidate key biochemical processes including recruitment of immune cells, regulation of cellular junction proteins, and long-term alterations to epithelial tissue permeability following microflap with an eye toward enhanced clinical outcomes.

METHODS

Forty New Zealand rabbits were assigned to eight groups (n = 5/group): no-injury control or bilateral microflap with survival for 0 h, 12 h, 1 day, 3 days, 7 days, 30 days, and 60 days post-microflap. The epithelium was dissected from one vocal fold and transepithelial resistance was quantified. The contralateral fold was subjected to transmission electron microscopy. Images were evaluated by a blinded rater and paracellular space dilation was quantified using ImageJ. Immune cell infiltration was evaluated and recorded qualitatively.

RESULTS

Increased innate immune response was observed 12 h as well as 7 and 30 days after microflap. At 60 days following injury, decreased epithelial resistance was observed. Paracellular spaces were dilated at all time-points following injury.

CONCLUSIONS

The vocal fold epithelium was significantly altered at 60 days following microflap. The implications for this tissue phenotype are unclear. However, compromised epithelial barrier function is implicated in various diseases and may increase the risk of subsequent injury.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:350-356, 2023.

Voice Handicap Index Changes After Microflap Surgery for Benign Vocal Fold Lesions Are Not Associated With Recommended Absolute Voice Rest Duration

PURPOSE

Voice rest is frequently prescribed after phonosurgery, but optimal type and duration for voice outcomes have not been demonstrated. Studies to date have been characterized by heterogeneity in surgical procedures and laryngeal diagnoses. We sought to analyze the effect of recommended absolute voice rest duration on outcomes of microflap surgery for benign vocal fold lesions. A secondary purpose was to identify patient factors associated with postoperative voice outcomes.

METHOD

Forty-three patients were included in this retrospective review of patients aged 18 years and above who underwent direct microlaryngoscopy with microflap for vocal fold polyp or cyst over a 5-year period at a multidisciplinary voice center. Duration of recommended postoperative absolute voice rest was classified as less than 7 days, 7 days, and more than 7 days. Demographic and vocal hygiene data and voice treatment history were collected. Outcome measures consisted of one pre- and two postoperative Voice Handicap Index (VHI) scores. Effects of recommended voice rest on outcomes were analyzed using mixed models for repeated measures. Effects of patient factors on outcomes were analyzed as exploratory measures. Stroboscopy ratings were analyzed descriptively.

RESULTS

Thirteen patients were recommended 7 days of absolute voice rest, 15 were recommended less than 7 days, and 15 were recommended more than 7 days. Postoperatively, VHI scores significantly improved for all patients. Voice rest as a continuous variable was associated with the Functional subscale score in the short term, but there was no effect on VHI total score and no longer term effect of voice rest on any outcome. Age, sex, and preoperative voice therapy were associated with at least one VHI subscale score on at least one time point.

CONCLUSION

VHI outcomes of microflap surgery for polyps and cysts do not differ by duration of recommended absolute postoperative voice rest.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.19178459.

The role of voice rest after micro-laryngeal surgery for benign vocal fold lesions

PURPOSE

To compare post-operative vocal outcomes of a voice rest regimen versus no voice restrictions following micro-laryngeal surgery for benign glottic lesions.

METHODS

This was a combined prospective and retrospective cohort study on 167 patients who underwent micro-laryngeal surgery for benign focal fold lesion removal. Participants were divided into two regimens: standard voice rest (n = 92) or no voice restriction (n = 75). The primary outcome was post-operative vocal improvement, evaluated using voice handicap index questionnaire (VHI-10), GRBAS scale, and computerised acoustic analysis (shimmer, jitter, and the harmonic-to-noise ratio). The secondary outcome was emergence of vocal fold mucosal abnormalities in the immediate post-operative period. Parameters were collected at baseline and at the last clinical visit.

RESULTS

There was no statistically significant difference between the voice rest and no-voice rest groups regarding baseline parameters of age, gender, laryngeal pathology, and voice use. Improvement in GRBAS scale values and VHI-10 scores between pre- and post-operative periods between groups did not demonstrate any statistically significant differences (P = 0.5303 and P = 0.1457, respectively). Similarly, the results of computerized voice analysis also showed no differences between groups in terms of shimmer (P = 0.9590), jitter (P = 0.5692), and harmonic-to-noise ratio (P = 0.1871). No correlation was found between the post-operative vocal fold's mucosal abnormalities and the type of voice rest regimen.

CONCLUSION

Voice quality and wound healing were similar regardless of the type of voice rest regimen applied. No voice rest at all was as good as voice rest after micro-laryngeal surgery.

Blue Light Laser Results in Less Vocal Fold Scarring Compared to KTP Laser in Normal Rat Vocal Folds

OBJECTIVES

Preliminary investigations suggest that a novel blue light (BL) laser with a wavelength of 445 nm is comparable to the commonly utilized potassium titanyl phosphate (KTP) laser (532 nm) for treatment of various laryngeal pathologies. The objective of the current study is to make a direct histological comparison of the degree of vocal fold scarring after either BL or KTP laser treatment in an animal model.

STUDY DESIGN

This was a randomized controlled study using rats.

METHODS

Twenty-four Sprague-Dawley rats were randomized to BL or KTP laser treatment. Laser was delivered in non-overlapping pulses to normal rat vocal folds. Larynges in each group were harvested at three time points: post-operative day 1, 30, and 90. Three animals served as negative controls. The excised whole larynges were sectioned transversely and stained with hematoxylin/eosin and trichrome. Presence of subepithelial inflammation and protein deposition/fibrosis indicative of scarring were scored semi-quantitatively (from grade 1-3) by two pathologists blinded to treatment groups.

RESULTS

Between-group comparison showed that both laser treatments resulted in significantly elevated subepithelial protein deposition/fibrosis 90 days after treatment compared to negative controls (BL: 2 ± 0; KTP: 2.67 ± 0.29; control: 1.17 ± 0.29; P < .05). However, the degree of protein deposition/fibrosis was significantly higher in the KTP group compared to the BL group (P = .016). Within-group comparison showed that the KTP group showed evidence of fibrosis as early as 30 days after treatment, which was not observed in the BL group.

CONCLUSIONS

The current study suggests that the degree of scarring is significantly less after BL laser treatment compared to KTP in normal rat vocal fold tissue.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:853-858, 2021.

RNA sequencing identifies transcriptional changes in the rabbit larynx in response to low humidity challenge

BACKGROUND

Voice disorders are a worldwide problem impacting human health, particularly for occupational voice users. Avoidance of surface dehydration is commonly prescribed as a protective factor against the development of dysphonia. The available literature inconclusively supports this practice and a biological mechanism for how surface dehydration of the laryngeal tissue affects voice has not been described. In this study, we used an in vivo male New Zealand white rabbit model to elucidate biological changes based on gene expression within the vocal folds from surface dehydration. Surface dehydration was induced by exposure to low humidity air (18.6% + 4.3%) for 8 h. Exposure to moderate humidity (43.0% + 4.3%) served as the control condition. Ilumina-based RNA sequencing was performed and used for transcriptome analysis with validation by RT-qPCR.

RESULTS

There were 103 statistically significant differentially expressed genes identified through Cuffdiff with 61 genes meeting significance by both false discovery rate and fold change. Functional annotation enrichment and predicted protein interaction mapping showed enrichment of various loci, including cellular stress and inflammatory response, ciliary function, and keratinocyte development. Eight genes were selected for RT-qPCR validation. Matrix metalloproteinase 12 (MMP12) and macrophage cationic peptide 1 (MCP1) were significantly upregulated and an epithelial chloride channel protein (ECCP) was significantly downregulated after surface dehydration by RNA-Seq and RT-qPCR. Suprabasin (SPBN) and zinc activated cationic channel (ZACN) were marginally, but non-significantly down- and upregulated as evidenced by RT-qPCR, respectively.

CONCLUSIONS

The data together support the notion that surface dehydration induces physiological changes in the vocal folds and justifies targeted analysis to further explore the underlying biology of compensatory fluid/ion flux and inflammatory mediators in response to airway surface dehydration.

Combining Voice Rest and Steroids to Improve Diagnostic Clarity in Phonotraumatic Vocal Fold Injury

OBJECTIVES

(1) To describe a combination voice rest and steroid regimen to clarify ambiguous diagnoses in singers who present with phonotraumatic lesions and (2) to determine which videostroboscopic parameters show the most consistent response to this regimen.

STUDY DESIGN

Chart review.

METHODS

Singers with phonotraumatic vocal fold lesions seen at a tertiary care voice center over a 10-year period were identified. Those who had uncertain diagnoses on initial presentation, completed a combination regimen including voice rest and steroids, and had follow-up examinations were included in the analysis. The effect of this combination regimen was assessed by ratings of pre- and postregimen videostroboscopy examinations and by auditory perceptual ratings. Whether the combination regimen clarified the diagnosis was noted.

RESULTS

Twenty-nine singers were prescribed the combination regimen with the intent to clarify the diagnosis. In 79% (23/29) of these singers, the regimen helped clarify diagnosis, for example, ruling in or ruling out specific lesions, confirming areas of scar, or distinguishing acute from chronic phonotraumatic injury. Stroboscopic exams were improved in 86% (25/29). The most common stroboscopic finding was a reduction in the lesion size (66%). Auditory perceptual ratings improved in 48% (14/29) of patients.

CONCLUSIONS

A "cool down" combination of voice rest and steroids can improve diagnostic clarity in a subset of singers with phonotraumatic lesions. This combination regimen can be considered, with both the side effect profile of steroids and possible financial ramifications of strict voice rest in mind, when the initial diagnosis is unclear.

Recovery of Vocal Fold Epithelium after Acute Phonotrauma

We investigated the timeline of tissue repair of vocal fold epithelium after acute vibration exposure using an in vivo rabbit model. Sixty-five New Zealand white breeder rabbits were randomized to 120 min of modal- or raised-intensity phonation. After the larynges were harvested at 0, 4, 8, and 24 h, and at 3 and 7 days, the vocal fold tissue was evaluated using electron microscopy and quantitative real-time polymerase chain reaction. There was an immediate decrease in the microprojection depth and height following raised-intensity phonation, paired with upregulation of cyclooxygenase-2. This initial 24-h period was also characterized by the significant downregulation of junction proteins. Interleukin 1β and transforming growth factor β1 were upregulated for 3 and 7 days, respectively, followed by an increase in epithelial cell surface depth at 3 and 7 days. These data appear to demonstrate a shift from inflammatory response to the initiation of a restorative process in the vocal fold epithelium between 24 h and 3 days. Despite the initial damage from raised-intensity phonation, the vocal fold epithelium demonstrates a remarkable capacity for the expeditious recovery of structural changes from transient episodes of acute phonotrauma. While structurally intact, the return of functional barrier integrity may be delayed by repeated episodes of phonotrauma and may also play an important role in the pathophysiology of vocal fold lesions.

Structurally and functionally characterized in vitro model of rabbit vocal fold epithelium

In this paper, we describe a method for primary culture of a well differentiated electrically tight rabbit vocal fold epithelial cell multilayer and the measurement of transepithelial electrical resistance (TEER) for the evaluation of epithelial barrier function in vitro. Rabbit larynges were harvested and enzymatically treated to isolate vocal fold epithelial cells and to establish primary culture. Vocal fold epithelial cells were co-cultured with mitomycin C-treated feeder cells on collagen-coated plates. After 10-14 days in primary culture, cells were passaged and cultured until they achieved 70-90% confluence on collagen-coated plates. Epithelial cells were then passaged onto collagen-coated cell culture inserts using 4.5cm2 membrane filters (1.0μm pore size) with 10% fetal bovine serum or 30μg/mL bovine pituitary extract to investigate the effects of growth-promoting additives on TEER. Additional experiments were performed to investigate optimal seeding density (1.1, 2.2, 4.4, or 8.9×105 cells/cm2), the effect of co-culture with feeder cells, and the effect of passage number on epithelial barrier function. Characterization of in vitro cultures was performed using hematoxylin and eosin staining and immunostaining for vocal fold epithelial cell markers and tight junctions. Results revealed higher TEER in cells supplemented with fetal bovine serum compared to bovine pituitary extract. TEER was highest in cells passaged at a seeding density of 2.2×104 cells/cm2, and TEER was higher in cells at passage two than passage three. Ultrastructural experiments revealed a well-differentiated epithelial cell multilayer, expressing the epithelial cell markers CK13, CK14 and the tight junction proteins occludin and ZO-1.

Basic Science: The Foundation of Evidence-Based Voice Therapy

Basic science research is part of the circle of translational research that provides the scientific underpinning for evidence-based practice. The translation from bench to bedside, however, is sometimes not obvious. This short review seeks to demonstrate ways in which basic science can inform our clinical practice as voice therapists. From in vitro molecular and cellular studies to in vivo animal models, basic science can investigate biological mechanisms of vocal health, such as vocal fold hydration, and voice use, such as voice rest and vocal exercise, in ways that are impossible in human clinical studies. Knowledge of these mechanisms inform and guide our clinical investigations and help provide evidence for behavioral voice therapy.

Recovery of vibratory function after vocal fold microflap in a rabbit model

OBJECTIVES/HYPOTHESIS

The purpose of this study was to evaluate the return of vibratory function and restoration of vibration amplitude and symmetry after vocal fold microflap surgery.

STUDY DESIGN

Prospective in vivo animal model.

METHODS

Microflap surgery was performed on 30 New Zealand white breeder rabbits. The left vocal fold received a 3-mm epithelial incision and mucosal elevation, while the contralateral vocal fold was left intact to serve as an internal control. Quantitative analysis of amplitude ratio and lateral phase difference were measured using high-speed laryngeal imaging at a frame rate of 10,000 frames per second from animals undergoing evoked phonation on postoperative days 0, 1, 3, 5, and 7.

RESULTS

Quantitative measures revealed a significantly reduced amplitude ratio and lateral phase difference on day 0 after microflap. These impairments of vibratory function on day 0 were associated with separation of the vocal fold's body-cover layer. Amplitude ratio increased significantly by day 3 after microflap, with further increases in vibration amplitude on days 5 and 7. While the amplitude ratio improved significantly on day 3, lateral phase difference decreased significantly on day 3, and returned to normal on days 5 and 7.

CONCLUSIONS

High-speed laryngeal imaging was used to investigate the natural time course of postmicroflap recovery of vibratory function. Results revealed the restoration of vibration amplitude and lateral phase difference by days 3 to 7 after microflap. The time period of improved vibratory function observed in this study coincides with the end of the well-documented inflammatory phase of vocal fold wound repair.

LEVEL OF EVIDENCE

N/A.