Validation of Animal Models for Simulation Training in Pediatric Laryngotracheal Reconstruction

Impact of Rehydration Following Systemic Dehydration on Vocal Fold Gene Expression

OBJECTIVE

Biological data on the beneficial effects of vocal fold rehydration are lacking. This study aimed to examine the effects of acute systemic dehydration on vocal fold gene expression and determine whether rehydration would reverse these changes.

METHODS

Male New Zealand White rabbits (N = 24, n = 8/group) provided the animal model. Systemic dehydration was induced by 5 days of water volume restriction. Rehydration was provided by ad-lib water for 3 days following dehydration. Euhydrated rabbits were used as the control group. Vocal fold tissue was dissected. Seventeen genes were selected based on physiological function and role in supporting vocal fold structure, oxidative stress, hemodynamics, and extracellular matrix turnover. Relative gene expression was assessed by RT-qPCR.

RESULTS

Rehydration following systemic dehydration can modulate gene expression, with expression patterns suggesting that rehydration reverses dehydration-induced changes in over half of the tested genes. CLIC5 (chloride intracellular channel 5) and EFEMP1 (EGF containing fibulin extracellular matrix protein 1) genes were significantly upregulated in the dehydration group compared with the euhydrated control. A1BG (alpha-1B-glycoprotein) and IL1RAP (interleukin 1 receptor accessory protein) were downregulated by rehydration compared with the dehydration group.

CONCLUSION

This study provides molecular evidence for a transcriptional response to rehydration following acute systemic dehydration in the vocal folds. These data are the first to study gene expression following realistic dehydration and rehydration paradigms and provide biological data to support clinical recommendations to increase water intake after acute dehydration.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:3499-3505, 2023.

Proteomic analysis reveals that aging rabbit vocal folds are more vulnerable to changes caused by systemic dehydration

BACKGROUND

Older adults are more prone to develop systemic dehydration. Systemic dehydration has implications for vocal fold biology by affecting gene and protein expression. The objective of this study was to quantify vocal fold protein changes between two age groups and hydration status, and to investigate the interaction of age and hydration status on protein expression, which has not been investigated in the context of vocal folds before. Comparative proteomics was used to analyze the vocal fold proteome of 6.5-month-old and > 3-year-old rabbits subjected to water ad libitum or water volume restriction protocol.

RESULTS

Young and older adult rabbits (n = 22) were either euhydrated (water ad libitum) or dehydrated by water volume restriction. Dehydration was confirmed by body weight loss of - 5.4% and - 4.6% in young and older groups, respectively, and a 1.7-fold increase of kidney renin gene expression in the young rabbits. LC-MS/MS identified 2286 proteins in the rabbit vocal folds of young and older adult rabbits combined. Of these, 177, 169, and 81 proteins were significantly (p ≤ 0.05) affected by age, hydration status, or the interaction of both factors, respectively. Analysis of the interaction effect revealed 32 proteins with opposite change patterns after dehydration between older and young rabbit vocal folds, while 31 proteins were differentially regulated only in the older adult rabbits and ten only in the young rabbits in response to systemic dehydration. The magnitude of changes for either up or downregulated proteins was higher in the older rabbits. These proteins are predominantly related to structural components of the extracellular matrix and muscle layer, suggesting a disturbance in the viscoelastic properties of aging vocal fold tissue, especially when subjected to systemic dehydration.

CONCLUSIONS

Water restriction is a laboratory protocol to assess systemic dehydration-related changes in the vocal fold tissue that is translatable to human subjects. Our findings showed a higher number of proteins differentially regulated with a greater magnitude of change in the vocal folds of older adult rabbits in the presence of systemic dehydration compared to younger rabbits. The association of these proteins with vocal fold structure and biomechanical properties suggests that older human subjects may be more vulnerable to the effects of systemic dehydration on vocal function. The clinical implications of these protein changes warrant more investigation, but age should be taken into consideration when evaluating vocal treatment recommendations that interfere with body fluid balance.

Simulation of laryngotracheal reconstruction with 3D ‐printed models and porcine cadaveric models

Objectives

Laryngotracheal reconstruction (LTR) is a complex operation used to treat subglottic stenosis. The use of simulator models is a valuable tool in surgical trainee education, particularly for operations such as LTR that are less common outside high‐volume centers. Three‐dimensional (3D) printing of the human airway may provide an effective and more accessible alternative to porcine cadaveric models. The objective of this study is to compare the educational value of a 3D‐printed model and a porcine cadaveric model as LTR simulation methods.

Methods

Simulated LTR procedures were completed by 12 otolaryngology residents and a faculty physician on the cadaveric model and the 3D‐printed simulator model. Both models were evaluated by fellowship‐trained pediatric otolaryngologists to establish construct validity. Pre‐procedure surveys of participants evaluated confidence and attitude toward models and post‐procedure surveys evaluated confidence, overall impressions, relevance, content validity, and face validity.

Results

Participants reported a similar mean increase in confidence after performing LTR on the 3D‐printed model (14%) and cadaveric model (11%). Participants rated both models similarly for utility as an overall training tool and in teaching surgical planning and improving operative techniques. However, participants found the 3D‐printed model more useful for teaching anatomy (p = .047).

Conclusion

3D‐printed models have practical benefits over cadaveric models; they do not decompose and can be custom made to model a disease state such as subglottic stenosis. Participants reported a similar mean increase in confidence after using either simulation. The 3D‐printed model is a promising simulation candidate as it compares well to an animal model and has the advantage of being more anatomically true to pediatric patients.

Level of Evidence: Level 2.

Ultrasound-Guided Selective Bronchial Intubation: A Feasibility Study in Pediatric Animal Model

Objective

Selective one-lung ventilation used to optimize neonatal and pediatric surgical conditions is always a demanding task for anesthesiologists, especially during minimally invasive thoracoscopic surgery. This study aims to introduce an ultrasound-guided bronchial intubation and exclusion technique in a pediatric animal model.

Methods

Seven rabbits were anesthetized and airway ultrasound acquisitions were done.

Results

Tracheal tube progression along the trachea to the right bronchus and positioning of the bronchial blocker in the left bronchus were successfully done with consistent ultrasound identification of relevant anatomical structures.

Conclusion

The study provided a new application of ultrasound in airway management. More advanced experimental studies are needed since this technique has the potential for translation to pediatric anesthesia.

Furosemide-induced systemic dehydration alters the proteome of rabbit vocal folds

Whole-body dehydration (i.e., systemic dehydration) leads to vocal fold tissue dehydration. Furosemide, a common diuretic prescribed to treat hypertension and edema-associated conditions, induces systemic dehydration. Furosemide also causes voice changes in human speakers, making this method of systemic dehydration particularly interesting for vocal fold dehydration studies. Our objective was to obtain a comprehensive proteome of vocal folds following furosemide-induced systemic dehydration. New Zealand White rabbits were used as the animal model and randomly assigned to euhydrated (control) or furosemide-dehydrated groups. Systemic dehydration, induced by injectable furosemide, was verified by an average body weight loss of -5.5% and significant percentage changes in blood analytes in the dehydrated rabbits compared to controls. Vocal fold specimens, including mucosa and muscle, were processed for proteomic analysis using label-free quantitation LC-MS/MS. Over 1600 proteins were successfully identified across all vocal fold samples; and associated with a variety of cellular components and ubiquitous cell functions. Protein levels were compared between groups showing 32 proteins differentially regulated (p ≤ 0.05) in the dehydrated vocal folds. These are mainly involved with mitochondrial translation and metabolism. The downregulation of proteins involved in mitochondrial metabolism in the vocal folds suggests a mechanism to prevent oxidative stress associated with systemic dehydration. SIGNIFICANCE: Voice disorders affect different population demographics worldwide with one in 13 adults in the United States reporting voice problems annually. Vocal fold systemic hydration is clinically recognized for preventing and treating voice problems and depends on optimal body hydration primarily achieved by water intake. Herein, we use the rabbit as a translatable animal model, and furosemide as a translatable method of systemic dehydration, to reveal a comprehensive proteomic profile of vocal fold mucosa and muscle in response to systemic dehydration. The significant subset of proteins differentially regulated due to furosemide-induced dehydration offer novel insights into the molecular mechanisms of systemic dehydration in the vocal folds. These findings also deepen our understanding of changes to tissue biology after diuretic administration.

Recurring exposure to low humidity induces transcriptional and protein level changes in the vocal folds of rabbits

Voice disorders are an important human health condition. Hydration is a commonly recommended preventive measure for voice disorders though it is unclear how vocal fold dehydration is harmful at the cellular level. Airway surface dehydration can result from exposure to low humidity air. Here we have induced airway surface dehydration in New Zealand White rabbits exposed to a recurring 8-h low humidity environment over 15 days. This model mimics an occupational exposure to a low humidity environment. Exposure to moderate humidity was the control condition. Full thickness soft-tissue samples, including the vocal folds and surrounding laryngeal tissue, were collected for molecular analysis. RT-qPCR demonstrated a significant upregulation of MUC4 (mucin 4) and SCL26A9 (chloride channel) and a large fold-change though statistically non-significant upregulation of SCNNA1 (epithelial sodium channel). Proteomic analysis demonstrated differential regulation of proteins clustering into prospective functional groups of muscle structure and function, oxidative stress response, and protein chaperonin stress response. Together, the data demonstrate that recurring exposure to low humidity is sufficient to induce both transcriptional and translational level changes in laryngeal tissue and suggest that low humidity exposure induces cellular stress at the level of the vocal folds.

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.

Simulation of Pediatric Endoscopic Cricoid Reduction and Expansion

Endoscopic cricoid expansion and reduction are newer approaches to the management of pediatric bilateral vocal fold immobility and postlaryngotracheal reconstruction glottic insufficiency, respectively. These procedures offer a less invasive, endoscopic alternative to procedures that typically required open management with a more prolonged recovery. These technically demanding procedures are currently performed only in select centers, and there is no currently described training model for practicing them. We present a modification to a laryngeal dissection station that allows for simulation of endoscopic cricoid reduction and expansion with excised larynges. The model allows trainees to practice endoscopic posterior cricoid exposure, incision of the cricoid cartilage, placement of a simulated costal cartilage graft for expansion, and endoscopic suturing for reduction. Development of simulators for procedures that are infrequently performed have the potential to help trainees reach surgical competency faster and more safely.

Feasibility of ovine and porcine models for simulation training in parotid surgery and facial nerve dissection

PURPOSE

To assess and compare the feasibility of using ovine and porcine models as surgical simulation training tools for otolaryngology trainees performing parotid surgery and facial nerve dissection.

METHODS

Trainees performed parotid surgery (total parotidectomy, retrograde facial nerve dissection and facial nerve grafting) on an ovine and porcine model. Participants completed a 22-item, five-point Likert scale questionnaire on each model, assessing three validation domains; face validity (FV), global content validity (GCV) and task-specific content validity (TSCV). Data were prospectively collected and analysed using descriptive and non-parametric statistics.

RESULTS

Twelve trainees completed two consecutive parotidectomies and facial nerve dissections on an ovine and porcine model. Twenty-four dissections were completed. Validation questionnaires were completed for each model by all trainees. The ovine model achieved median validation threshold scores (≥ 4/5) for all aspects of FV, GCV and TSCV. The porcine model did not achieve validation threshold scores for any aspect of the validation questionnaire. Comparison of the ovine and porcine model demonstrated that the ovine model was statistically superior to the porcine model across most validation criteria excluding realistic appearance of skin, identification and ligation of the trans-oral parotid duct and facial nerve grafting.

CONCLUSION

Adequate experience with facial nerve dissection during parotid surgery is vital to ensuring good outcomes and avoiding complications. This study is the first to compare validity of two animal models for simulation training in parotid surgery and facial nerve dissection. We have validated the ovine model as a useful tool for simulation training and advocate its incorporation into otolaryngology training programmes.