An animal model for laryngotracheal injuries: An experimental study: Animal Model for Laryngotracheal Injuries

Comparative evaluation of mechanical injury methods for establishing stable tracheal stenosis animal models

The study aimed to assess the stability of various mechanical injury techniques in creating tracheal stenosis animal models using endoscopic assistance and investigate the viability of tracheal stoma in this process. Twenty-six healthy adult New Zealand white rabbits were randomly assigned to an experimental and control group. The experimental group underwent tracheal incision followed by steel brush scraping with endoscopic assistance, while the control group received nylon brush scraping. Within the control group, two subgroups were formed: Group A underwent scraping without tracheal stoma, and Group B underwent scraping followed by tracheal stoma. Additionally, a sham operation was performed on a separate group without subsequent scratching, resulting in no stenosis formation. Endoscopic observations were conducted at 7, 14, and 21 days post-scraping, followed by histological examinations of euthanized rabbits on the 21st day. Notably, all rabbits in the non-stoma group survived without complications, whereas Group B rabbits faced mortality post-operation. Histological assessments revealed inflammatory cell infiltration, fibroblast proliferation, and collagen fiber deposition in narrowed tracheal specimens. Steel brush scraping with endoscopic assistance proved more effective in inducing stable tracheal stenosis compared to nylon brush scraping. However, the survival challenges of rabbits with tracheal fistula require further investigation.

The role of tracheal wall injury in the development of benign airway stenosis in rabbits

To investigate the role of tracheal wall injury in the development of benign airway stenosis in rabbits. Prospective study. We injured the tracheal walls of 28 New Zealand white rabbits using four different methods. Experimental group: Group A (n = 7, mild injury of tracheal mucosa by ordinary brush under bronchoscopy); Group B (n = 7, severe injury of tracheal mucosa by nylon brush under tracheotomy); Group C (n = 7, tracheal cartilage was injured by vascular clamp after tracheotomy); Group D (n = 7, the tracheal cartilage was injured with vascular forceps and the tracheal mucosa was injured with a nylon brush after tracheotomy). Bronchoscopy was performed on each experimental rabbit at 1, 2, 3 and 4 weeks after operation. High-resolution computed tomography (HRCT) and endobronchial optical coherence tomography (EB-OCT) were performed at 4 weeks, and the rabbits were sacrificed after the examination. Their gross and histological findings were comparatively determined whether the experimental rabbit stenosis was established. No airway stenosis was observed in group A. In group B, 28.57% of experimental rabbits developed tracheal stenosis (granulation tissue proliferation was observed in rabbits No. 2 and No. 6 at 1, 2 and 3 weeks after operation, and the tracheal scar contracture was observed in No.6 rabbit at 4 weeks after operation). Fourteen rabbits in group C and group D had tracheal stenosis caused by granulation tissue proliferation at 1, 2 and 3 weeks after operation. At the fourth week after operation, 71.43% of experimental rabbits had tracheal stenosis due to granulation tissue hyperplasia, 7.14% of experimental rabbits had tracheal stenosis due to scar contracture and granulation hyperplasia, and 21.43% of experimental rabbits had tracheal stenosis due to scar contracture. EB-OCT scan showed that the cartilage layer with low signal reflection band was discontinuous. The injury of cartilage is the key factor of benign airway stenosis. Acute injury of airway mucosa alone is unlikely to cause airway stenosis, but combined with cartilage injury may aggravate airway stenosis. EB-OCT can clearly identify the airway layers of rabbits, which is helpful to evaluate the damage of tracheal cartilage and mucosa. The diagnostic potential of this technique makes EB-OCT a promising approach for the study and monitoring of airway diseases.

Clinical, Histological, and Profibrotic Extracellular Matrix Protein Changes in a Model of Tracheal Stenosis Induced by Cervical Tracheal Autotransplantation

BACKGROUND

Tracheal stenosis (TS) is a complication of prolonged intubation, tracheotomy, and tracheal surgery that compromises the vascular supply. Animal models are essential for studying its pathophysiology and the effect of interventions.

OBJECTIVE

To establish a TS model in rats secondary to tracheal autotransplantation with a graft submerged in bleomycin (Atx-Bleo). Additionally, to evaluate the clinical and histological changes, as well as the expression of newly formed collagen (NFC), isoforms of transforming growth factor beta (TGFβ), fibronectin (FN), elastin (ELN), integrin β1 (ITGβ1), and matrix metalloproteinase 1 (MMP1) in TS.

METHODS

Twenty Wistar rats were divided into three groups: group I (n = 20) control; group II (n = 10) end-to-end anastomosis of the trachea (tracheoplasty); and group III (n = 10) Atx-Bleo. The animals were evaluated clinically, tomographically, macroscopically, morphometrically, and microscopically. NFC deposition, and the expression of profibrotic and antifibrotic proteins were evaluated in tracheal scars.

RESULTS

All animals survived the surgical procedure and the study period. Compared with the other study groups, the Atx-Bleo group developed TS and fibrosis, exhibited higher expression of NFC, TGFβ1, TGFβ2, FN, ELN, and ITGβ1, and mild expression of TGFβ3 and MMP1 (p < 0.005; analysis of variance, Dunnett and Tukey tests).

CONCLUSION

Atx-Bleo in TS model rats produces tomographic and histological changes, and induces the upregulation of profibrotic proteins (TGFβ1, TGFβ2, collagen, FN, ELN, ITGβ1) and downregulation of antifibrotic proteins (TGFβ3, MMP1). Therefore, this model may be used to test new pharmacological treatments for reversing or preventing TS, and conduct basic studies regarding its pathophysiology.

Establishing an Endoscopic Chronic Subglottic Stenosis Rabbit Model

OBJECTIVES/HYPOTHESIS

To develop a reproducible and consistent chronic subglottic stenosis (SGS) in an endoscopic animal model.

STUDY DESIGN

Prospective study.

METHODS

We conducted a prospective study using New Zealand white rabbits. Chronic SGS was induced endoscopically by Bugbee electrocautery to 50% to 75% of the subglottic area's circumference, followed by 4-hour endotracheal intubation. The rabbit airways were endoscopically assessed and sized with uncuffed endotracheal tubes (ETTs) before the injury, during follow-up, and at the endpoints. There were four endpoints: 2, 4, 6, and 8 weeks post SGS induction. Animals were humanely euthanized for histopathological examination of the subglottic injury site and microscopic measurement of the cricoid lumen.

RESULTS

Twenty-two rabbits reached the endpoints, and 18 rabbits developed chronic SGS. ETT size significantly decreased by 0.5 from preinjury to the endpoint in all groups, P < .001. Control median cricoid lumen measurements were 20.48 mm² , the median cricoid lumen measurement for the 2 weeks endpoint was 14.3 mm² , 4 weeks 11.69 mm² , 6 weeks 16.03 mm² , and 8 weeks endpoint median was 16.33 mm² . Histopathological examination showed chronic scar tissue and new cartilage formation at the cricoid level, mainly at the posterior subglottic injury site starting from 4 weeks postinjury. Collagen staining revealed substantial amounts of organized collagen and different collagen orientation starting 4 weeks postinjury lasting until 8 weeks postinjury.

CONCLUSION

We developed an animal model to study chronic SGS. This model will be utilized to compare different endoscopic treatment interventions in acute SGS versus chronic SGS and further define the molecular basis of SGS.

LEVEL OF EVIDENCE

NA Laryngoscope, 2021.

Rabbit model of consistently survivable subglottic stenosis using a modified brush technique

INTRODUCTION

Several animal models of subglottic stenosis (SGS) have been described in the literature, however many result in severe stenosis that requires early intervention and carry a high mortality rate. This limits the application of the model and may require the use of additional animals to achieve desired results due to procedural complications. A novel endoscopic method of inducing SGS in a rabbit model was developed as part of a larger investigation on the treatment of this condition. The objective of this study was to develop an animal model for survivable subglottic stenosis.

METHODS

12 New Zealand white rabbits underwent 2 trials of prolonged intubation that were not successful in inducing SGS. A partially sheathed nylon brush injury technique was then designed and implemented. Airway assessment consisted of rigid bronchoscopy 6 weeks and 8 months after injury.

RESULTS

12 rabbits undergoing subglottic brush injury had focal posteriorly based subglottic stenosis on bronchoscopy at 6 weeks and 8 months post-injury. One rabbit was euthanized after the brush induced subglottic injury but prior to 6 week bronchoscopy due to an unrelated orthopedic injury. This animal was therefore excluded from analysis and replaced. No rabbits required early airway intervention or sacrifice. All survived a period of 8 months.

CONCLUSION

Inducing subglottic injury with a partially-sheathed nylon brush safely and reliably creates a controlled SGS with zero procedure-related mortality over 8 months. This model could be the basis for a longer-term evaluation of subglottic scar evolution and intervention.

Subglottic Stenosis: Development of a Clinically Relevant Endoscopic Animal Model

OBJECTIVE

Develop a clinically relevant and reproducible endoscopic animal model for subglottic stenosis amenable to testing of minimally invasive therapeutic modalities.

STUDY DESIGN

Cohort study.

SETTING

Division of Laboratory Animals Research, University of Pittsburgh.

SUBJECTS AND METHODS

Subglottic stenosis was induced endoscopically via microsuspension laryngoscopy in 26 New Zealand white rabbits. A trimmed polypropylene brush connected to a novel electronic stenosis induction apparatus was used to create circumferential trauma to the subglottis. By using open source image analysis software, the cross-sectional areas of the stenotic and native airways were compared to calculate the percentage of stenosis and the Myer-Cotton classification grade.

RESULTS

Of the 26 rabbits, 24 (92%) exhibited stenosis after the first attempt. The mean percentage of airway stenosis was 57% (range, 34%-85%; SD, 15%). Five rabbits (19.2%) died on the day of stenosis induction from procedural complications. Of the 21 rabbits, 2 demonstrated no stenosis 7 days after initial injury and so underwent reinduction of airway injury, upon which they developed stenosis. Overall, 14 of the 21 rabbits (67%) exhibited moderate to severe stenosis (grade 2 or 3).

CONCLUSION

The stenosis induction apparatus reliably induced stenosis with a low mortality rate as compared with that of other methods in the literature. The device could be improved to generate a predetermined potentially reproducible grade of stenosis as desired by the operator. This method sets the stage for a clinically relevant and reproducible subglottic stenosis disease model that is amenable to testing of minimally invasive treatment modalities.

Development of a survival animal model for subglottic stenosis

OBJECTIVE

To develop a reproducible survival animal model for subglottic stenosis.

STUDY DESIGN

Prospective study.

METHODS

We evaluated five methods of inducing airway injury in 30 New Zealand white rabbits to produce a subglottic stenosis model. Experimental groups comprised: group 1 (n = 5), which underwent 4-hour intubation; group 2 (n = 5), which underwent induced subglottic injury with a nylon brush; group 3 (n = 10), which underwent subglottic injury with a nylon brush, followed by 4-hour intubation; group 4 (n = 5), which underwent subglottic injury with Bugbee cautery in 50% of the subglottic circumference, followed by 4-hour intubation; and group 5 (n = 5), which underwent subglottic injury with Bugbee cautery in 75% of the subglottic circumference, followed by 4-hour intubation. Five animals were used as controls. Endoscopy of the airway and sacrifice of animals were planned at an interval of 14 days postinjury. Histologic measurements were analyzed.

RESULTS

No animals in groups 1 or 2 developed stenosis. In group 3, 50% of animals developed symptomatic grade 3 subglottic and tracheal stenosis, necessitating early endoscopy and sacrifice in three animals. Four animals in group 4 developed grade 1 subglottic stenosis, and four in group 5 developed grade 2 subglottic stenosis. Histologic measurements of lumen areas within each of these two groups were similar; all animals survived the follow-up period.

CONCLUSION

We successfully developed a reproducible survival model for induced subglottic stenosis using a combination of cautery-induced subglottic injury followed by 4-hour intubation. This model lays the foundation for future studies that evaluate endoscopic interventions for the management of subglottic stenosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:989-994, 2019.

Ex vivo ovine model for teaching open laryngotracheal surgery

Objective

To develop an animal model for teaching open laryngotracheal surgical procedures.

Methods

The heads and necks from 5 pre-pubescent sheep were harvested after humane anesthesia. After 2–5 days to allow for rigor mortis to resolve, a specimen was supported with sandbags on an operating table. Operative procedures including tracheotomy, medialization laryngoplasty, anterior cartilage grafting, tracheal resection with primary anastomosis, and laryngectomy with closure of the pharynx were attempted.

Results

The ovine head and neck provided an accurate model for simulation of all attempted procedures. Ovine tissue resembled that of humans in mechanical properties and handling. Postsurgical endoscopy confirmed graft alignment.

Conclusions

The sheep head and neck provides an inexpensive, realistic, and safe model for surgical training for a variety of open laryngotracheal procedures. This is particularly relevant given the recent emphasis on surgical simulation and the relative rarity of some of these procedures in residency training.

Local delivery of mometasone furoate from an eluting endotracheal tube

Laryngeal and tracheal morbidity is a common complication of endotracheal tube (ETT)-based airway management, and manifests as local irritation, inflammation, and edema. Systemic corticosteroids are commonly administered to manage these conditions; however, their efficacy is inadequate and limited by potential severe side effects. In the present study, a steroid delivery system for local therapy was developed to generate relatively high local drug concentrations and to improve drug efficacy. ETTs were coated with electrospun poly (lactic-co-glycolic acid) (PLGA) nanofibers loaded with mometasone furoate (MF), creating a microscale thick layer. MF exhibited sustained release from coated ETTs over 14days in vitro. An in vivo efficacy study in rats demonstrated the therapeutic benefit of MF-coated ETTs over bare ETTs, as measured by reduced laryngeal mucosal thickness and submucosal laryngeal edema. The fiber coating remained intact during tube intubation and extubation, demonstrating good adhesion to the tubes even after 24h in aqueous solution at 37°C. These findings demonstrate the potential of drug-loaded ETTs to revolutionize the standard of care for endotracheal intubation.

Reproducing severe acute subglottic stenosis in a rabbit model

OBJECTIVES

The objectives of this study were to develop an animal model with consistent, severe subglottic stenosis (SGS), and to develop the timeline needed for intervention to limit rabbit mortality.

METHODS

Subglottic stenosis was created endoscopically using either a nylon or polypropylene brush in sixteen New Zealand White rabbits. The subglottic cross-sectional area was measured endoscopically using a right-angled probe and an open source image analysis software The cross-sectional areas of the stenotic and native airways were compared to calculate the subglottic stenosis percentage and Myer-Cotton grade classification.

RESULTS

The average diameter of the native subglottis was 4.7 mm (SD 0.4). The mean subglottic stenosis percentage was 73% (SD 32) for all rabbits. The three rabbits injured with the nylon brush had 30, 52, and 76% stenosis. Nine of the 12 surviving rabbits (75%) injured with the polypropylene brush had a >86% subglottic stenosis. Four rabbits in the polypropylene brush cohort died from procedural complications.

CONCLUSION

This study demonstrates a reliable model using a polypropylene brush to create severe acute subglottic stenosis. Cartilage exposure after creating the injury was associated with more severe stenosis. Mortality rate may have been reduced if endoscopic balloon dilation was performed electively seven days after injury, rather than emergently nine days after injury.

LEVEL OF EVIDENCE

4.

Role of Topical Medication in Prevention of Post-extubation Subglottic Stenosis

Iatrogenic laryngotracheal injury is the most serious complication of endotracheal intubation since this method of establishing airway was first described by Eugene Bouchut in 1858. Even today, subglottic stenosis is the most dreaded complication of intubation. This animal study is focused on the host tissue response to intubation induced injury resulting in subglottic stenosis and methods to prevent this complication. To assess the role of topically applied Mitomycin-C and Triamcinolone Acetonide in wound healing process following post-extubation subglottic injury. Prospective Randomized block, single-blinded, experimental study. Forty New-Zealand white rabbits where block randomized and allocated into 4 groups based on the type of topical medication that was applied post-extubation. Further these groups where subdivided into 3 subgroups based on the time of sacrifice (4, 6 and 12 weeks) to study the histopathological changes that occurred in a temporal sequence at the subglottis. It was observed that the rabbits in the control group and those that received Mitomycin-C only had more respiratory distress compared to those treated with Triamcinolone Acetonide. Statistically significant histopathological changes were observed in all the 4 groups. Mitomycin-C applied topically did not alter the wound healing process following post-extubation injury in the subglottis. Triamcinolone Acetonide significantly altered wound healing in the subglottis and prevented occurrence of respiratory distress.

A growing animal model for neonatal repair of large diaphragmatic defects to evaluate patch function and outcome

Objectives

We aimed to develop a more representative model for neonatal congenital diaphragmatic hernia repair in a large animal model, by creating a large defect in a fast-growing pup, using functional pulmonary and diaphragmatic read outs.

Background

Grafts are increasingly used to repair congenital diaphragmatic hernia with the risk of local complications. Growing animal models have been used to test novel materials.

Methods

6-week-old rabbits underwent fiberoptic intubation, left subcostal laparotomy and hemi-diaphragmatic excision (either nearly complete (n = 13) or 3*3cm (n = 9)) and primary closure (Gore-Tex patch). Survival was further increased by moving to laryngeal mask airway ventilation (n = 15). Sham operated animals were used as controls (n = 6). Survivors (90 days) underwent chest X-Ray (scoliosis), measurements of maximum transdiaphragmatic pressure and breathing pattern (tidal volume, Pdi). Rates of herniation, lung histology and right hemi-diaphragmatic fiber cross-sectional area was measured.

Results

Rabbits surviving 90 days doubled their weight. Only one (8%) with a complete defect survived to 90 days. In the 3*3cm defect group all survived to 48 hours, however seven (78%) died later (16–49 days) from respiratory failure secondary to tracheal stricture formation. Use of a laryngeal mask airway doubled 90-day survival, one pup displaying herniation (17%). Cobb angel measurements, breathing pattern, and lung histology were comparable to sham. Under exertion, sham animals increased their maximum transdiaphragmatic pressure 134% compared to a 71% increase in patched animals (p<0.05). Patched animals had a compensatory increase in their right hemi-diaphragmatic fiber cross-sectional area (p<0.0001).

Conclusions

A primarily patched 3*3cm defect in growing rabbits, under laryngeal mask airway ventilation, enables adequate survival with normal lung function and reduced maximum transdiaphragmatic pressure compared to controls.

A canine model of tracheal stenosis induced by cuffed endotracheal intubation

Postintubation tracheal stenosis is a complication of endotracheal intubation. The pathological mechanism and risk factors for endotracheal intubation-induced tracheal stenosis remain not fully understood. We aimed to establish an animal model and to investigate risk factors for postintubation tracheal stenosis. Beagles were intubated with 4 sized tubes (internal diameter 6.5 to 8.0 mm) and cuff pressures of 100 to 200 mmHg for 24 hr. The status of tracheal wall was evaluated by bronchoscopic and histological examinations. The model was successfully established by cuffed endotracheal intubation using an 8.0 mm tube and an intra-cuff pressure of 200 mmHg for 24 hr. When the intra-cuff pressures were kept constant, a larger sized tube would induce a larger tracheal wall pressure and more severe injury to the tracheal wall. The degree of tracheal stenosis ranged from 78% to 91% at 2 weeks postextubation. Histological examination demonstrated submucosal infiltration of inflammatory cells, hyperplasia of granulation tissue and collapse of tracheal cartilage. In summary, a novel animal model of tracheal stenosis was established by cuffed endotracheal intubation, whose histopathological feathers are similar to those of clinical cases of postintubation tracheal stenosis. Excessive cuff pressure and over-sized tube are the risk factors for postintubation tracheal stenosis.

Diagnosis of subglottic stenosis in a rabbit model using long-range optical coherence tomography

OBJECTIVES/HYPOTHESIS

Current imaging modalities lack the necessary resolution to diagnose subglottic stenosis. The aim of this study was to use optical coherence tomography (OCT) to evaluate nascent subglottic mucosal injury and characterize mucosal thickness and structural changes using texture analysis in a simulated intubation rabbit model.

STUDY DESIGN

Prospective animal study in rabbits.

METHODS

Three-centimeter-long sections of endotracheal tubes (ETT) were endoscopically placed in the subglottis and proximal trachea of New Zealand White rabbits (n = 10) and secured via suture. OCT imaging and conventional endoscopic video was performed just prior to ETT segment placement (day 0), immediately after tube removal (day 7), and 1 week later (day 14). OCT images were analyzed for airway wall thickness and textural properties.

RESULTS

Endoscopy and histology of intubated rabbits showed a range of normal to edematous tissue, which correlated with OCT images. The mean airway mucosal wall thickness measured using OCT was 336.4 μm (day 0), 391.3 μm (day 7), and 420.4 μm (day 14), with significant differences between day 0 and day 14 (P = .002). Significance was found for correlation and homogeneity texture features across all time points (P < .05).

CONCLUSIONS

OCT is a minimally invasive endoscopic imaging modality capable of monitoring progression of subglottic mucosal injury. This study is the first to evaluate mucosal injury during simulated intubation using serial OCT imaging and texture analysis. OCT and texture analysis have the potential for early detection of subglottic mucosal injury, which could lead to better management of the neonatal airway and limit the progression to stenosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:64-69, 2017.

Rabbit model of tracheal stenosis induced by prolonged endotracheal intubation using a segmented tube

OBJECTIVE

Animal model of tracheal stenosis based on pathophysiology of prolonged endotracheal intubation has been rarely reported. We sought to verify the feasibility of inducing an animal model of tracheal stenosis by segmented endotracheal tube insertion in the New Zealand white rabbit model.

METHODS

Tracheal stenosis was induced by inserting a segmented endotracheal tube of 1.5cm length which was wrapped with a commercialized absorbable hemostat in 15 New Zealand white rabbits, while sham surgery controls (n=3) underwent tracheotomy and direct closure of tracheal exposure. The tube was removed transorally, 1 week after tube insertion. All rabbits were evaluated endoscopically at 1 week, 2 weeks and 3 weeks after the tube insertion. The rabbits were sacrificed 3 weeks after the surgery, and the excised tissue of trachea was processed along with the procedure of standard hematoxylin eosin staining and observed under a microscope.

RESULTS

Tracheal stenosis was induced in all rabbits (range 32-84% stenosis) with no death of rabbits during the study. The histological features of tracheal stenosis demonstrated thickening and fibrosis of lamina propria and submucosa with relatively intact cartilage framework.

CONCLUSIONS

We developed a rabbit model of tracheal stenosis induced by endotracheal intubation using a segmented tracheal tube. Since the model is based on the physiologic condition of prolonged endotracheal intubation, it may be used in variable studies related to tracheal stenosis.