A preclinical model for laryngeal transplantation: anatomy and mucosal immunology of the porcine larynx

Prospective, Multi-Center Study of the Anatomic Distribution of Recurrent Respiratory Papillomatosis

OBJECTIVES/HYPOTHESIS

To create a model of the anatomic distribution, recurrence, and growth patterns of recurrent respiratory papillomatosis (RRP).

STUDY DESIGN

Prospective, multi-institutional cohort study.

METHODS

Adult patients with a diagnosis of RRP evaluated between August 1, 2018 and February 1, 2021 at six participating centers were invited to enroll. At each office or operating room encounter, laryngologists recorded the location and size of RRP lesions using a 22-region schematic. A generalized linear mixed effects model was used to compare region variations in lesion prevalence and recurrence.

RESULTS

The cohort comprised 121 patients: 74% were male, 81% had been diagnosed with adult-onset RRP, and a plurality (34%) had undergone 0 to 3 RRP interventions prior to enrollment. Across the study period, the odds of a lesion occurring in the glottis was significantly higher (odds ratio [OR]: 26.51; 95% confidence interval [CI]: 11.76-59.75, P < .001) compared with all other areas of the larynx and trachea. Within the true vocal folds, the membranous vocal folds had significantly higher odds (OR: 6.16; 95% CI: 2.66-14.30, P < .001) of lesion occurrence compared to the cartilaginous vocal folds. Despite these strong trends in lesion distribution, there were no differences in the odds of lesion recurrence, growth, or in the time to recurrence, between anatomic subsites.

CONCLUSIONS

RRP lesions are most likely to occur in the glottis, particularly the membranous vocal folds, compared with other regions of the larynx or trachea. However, all lesions demonstrate similar behavior with respect to recurrence, growth, and time to recurrence regardless of anatomic location.

LEVEL OF EVIDENCE

3 Laryngoscope, 132:2403-2411, 2022.

Extracellular matrix deformations of the porcine recurrent laryngeal nerve in response to hydrostatic pressure

Damage to the recurrent laryngeal nerve (RLN) caused by supraphysiological compression or tension imposed by adjacent tissue structures, such as the aorta, may contribute to onset of idiopathic unilateral vocal fold paralysis (iUVP) resulting in difficulty speaking, breathing, and swallowing. We previously demonstrated in adolescent pigs that the right RLN epineurium exhibits uniform composition of adipose tissue, with larger quantities along its length within the neck region in contrast to the left RLN that shows greater collagen composition in the thoracic region and greater quantities of adipose tissue in the neck region. In contrast, the epineurium in piglets was primarily composed of collagen tissue that remained uniform along the length of the left and right RLNs. Tensile testing of the left and right RLN in piglets and pigs showed associated differences in strain by RLN side and segment by age. The goal of this study was to investigate how external hydrostatic compression of the RLN affects the nerve's connective tissue and microstructure. RLN segments were harvested from the distal (cervical/neck) regions and proximal (subclavian for the right RLN, thoracic for the left RLN) regions from eight adolescent pigs and nine piglets. RLN segments were isolated and assessed under fluid compression to test hypotheses regarding epineurium composition and response to applied forces. Second harmonic generation (SHG) imaging of epineurial collagen was conducted at 0, 40, and 80 mmHg of compression. The cartesian strain tensor, principal strain (Eps1), and principal direction of the RLN collagen fibers were determined at each pressure step. Significantly larger values of the 1st principal strain occurred in the proximal segments of the pig left RLN when compared to the same segment in piglets (p = 0.001, pig = 0.0287 [IQR = 0.0161 - 0.0428], piglet = 0.0061 [IQR = 0.0033 - 0.0156]). Additionally, the median transverse strain Eyy) for the second pressure increment was larger in the right proximal segment of pigs compared to piglets (p < 0.001, pig = 0.0122 [IQR = 0.0033 - 0.0171], piglet = 0.0013 [IQR = 0.00001 - 0.0028]). Eyy values were significantly larger in the right proximal RLN versus the left proximal RLNs in pigs but not in piglets (p < 0.001). In contrast to piglets, histological analysis of pig RLN demonstrated increased axial alignment of epineurial and endoneurial collagen in response to compressive pressure. These findings support the hypothesis that the biomechanical response of the RLN to compressive pressure changed from being similar to being different between the right and left RLNs during development in the porcine model. Further investigation of these findings associated with age-related onset of idiopathic UVP may illuminate underlying etiologic mechanisms. STATEMENT OF SIGNIFICANCE: Damage to the recurrent laryngeal nerve (RLN) caused by compression imposed by the aorta may contribute to the onset of left-sided idiopathic unilateral vocal fold paralysis resulting in difficulty speaking, breathing, and swallowing. The goal of this study was to investigate how compression affects the connective tissue and microstructure of the RLN. We quantified the pressure induced deformation of the RLN using multiphoton imaging as a function of both location (proximal versus distal) and age (piglets, adolescent pigs). Our results demonstrate that the biomechanical response of the RLN to compression changes in the right versus left RLN throughout development, providing further evidence that the the left RLN is exposed to increasing dynamic loads with age.

A New Animal Model of Laryngeal Transplantation

Only three laryngeal transplants have been described in the literature to date, and none of the techniques has enabled a completely satisfactory functional result to be obtained. This article presents a new model of laryngeal transplantation, with quality of revascularisation of the transplant being the principal objective and optimisation of the various steps of the procedure, with the integration of a new reinnervation technique as a secondary objective. We present a preclinical animal study. Three pig larynges removed in vivo underwent allotransplantation according to the same protocol. The quality of the revascularisation was examined immediately after the surgery as well as by endoscopy for one animal on the fourth day after the operation. The mean time of cold ischaemia was 3 h 15 min. The anaesthetic tolerance of the pigs was excellent. Revascularisation was achieved and judged to be excellent for the three transplants immediately after the operation and the endoscopy performed for one pig on the fourth day after the operation confirmed this result. The anatomical similarities also enabled the application and integration of an innovative technique of laryngeal reinnervation into the various phases of the operation. We describe a reliable and reproducible animal model for laryngeal transplantation. Its application in humans can be envisaged.

Eliciting and Characterizing Porcine Vocalizations: When Pigs Fly

BACKGROUND/OBJECTIVES

While voice-related therapeutic interventions are often researched preclinically in the porcine model, there are no well-established methods to induce porcine glottic phonation. Described approaches, such as training animals to phonate for positive reinforcement are time-consuming and plagued by inherent variability in the type of phonation produced and contamination of background noise. Thus, a reliable method of assessing glottic phonation in the porcine model is needed.

METHODS

In this study, we have created a novel pulley-based apparatus with harness for "pig-lifting" with surrounding acoustic insulation and high-directional microphone with digital recorder for recording phonation. Praat and Matlab were used to analyze all porcine vocalizations for fundamental frequency (F0), intensity, duration of phonation and cepstral peak prominence (CPP). Glottic phonation was detected using F0 (≥2000 hz), duration (≥3 seconds) and researcher perceptual judgment. Partial-glottic phonations were also analyzed. Reliability between researcher judgment and acoustic measures for glottic phonation detection was high.

RESULTS

Acoustic analysis demonstrated that glottic and partial-glottic phonation was consistently elicited, with no formal training of the minipigs required. Glottic vocalizations increased with multiple lifts. Glottic phonation continued to be elicited after multiple days but became less frequent. Glottic and partial-glottic phonations had similar CPP values over the 6 experimental days.

CONCLUSION

Our cost-effective, reliable method of inducing and recording glottic phonation in the porcine model may provide a cost effective, preclinical tool in voice research.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Minipig

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the minipig used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Laryngeal Reconstruction Using Tissue-Engineered Implants in Pigs: A Pilot Study

OBJECTIVE/HYPOTHESIS

There are currently no treatments available that restore dynamic laryngeal function after hemilaryngectomy. We have shown that dynamic function can be restored post hemilaryngectomy in a rat model. Here, we report in a first of its kind, proof of concept study that this previously published technique is scalable to a porcine model.

STUDY DESIGN

Animal study.

METHODS

Muscle and fat biopsies were taken from three Yucatan minipigs. Muscle progenitor cells (MPCs) and adipose stem cells (ASCs) were isolated and cultured for 3 weeks. The minipigs underwent a left laterovertical partial laryngectomy sparing the left arytenoid cartilage and transecting the recurrent laryngeal nerve. Each layer was replaced with a tissue-engineered implant: 1) an acellular mucosal layer composed of densified Type I oligomeric collagen, 2) a skeletal muscle layer composed of autologous MPCs and aligned oligomeric collagen differentiated and induced to express motor endplates (MEE), and 3) a cartilage layer composed of autologous ASCs and densified oligomeric collagen differentiated to cartilage. Healing was monitored at 2 and 4 weeks post-op, and at the 8 week study endpoint.

RESULTS

Animals demonstrated appropriate weight gain, no aspiration events, and audible phonation. Video laryngoscopy showed progressive healing with vascularization and re-epithelialization present at 4 weeks. On histology, there was no immune reaction to the implants and there was complete integration into host tissue with nerve and vascular ingrowth.

CONCLUSIONS

This pilot study represents a first in which a transmural vertical partial laryngectomy was performed and successfully repaired with a customized, autologous stem cell-derived multi-layered tissue-engineered implant.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:2277-2284, 2021.

Flexible fibreoptic intubation in swine - improvement for resident training and animal safety alike

Background

Efficient airway management to facilitate tracheal intubation encompasses essential skills in anaesthesiologic and intensive care. The application of flexible fibreoptic intubation in patients with difficult airways has been identified as the recommended method in various international guidelines. However, providing the opportunity to adequately train residents can be challenging. Using large animals for practice during ongoing studies could help to improve this situation, but there is no recent data on fibreoptic intubation in swine available.

Methods

Thirty male German landrace pigs were anesthetized, instrumented and randomized into two groups. The animals were either intubated conventionally using direct laryngoscopy or a single-use flexible video-endoscope. The intervention was carried out by providers with 3 months experience in conventional intubation of pigs and a brief introduction into endoscopy. Intubation attempts were supervised and aborted, when SpO2 dropped below 93%. After three failed attempts, an experienced supervisor intervened and performed the intubation. Intubation times and attempts were recorded and analysed.

Results

Flexible fibreoptic intubation showed a significantly higher success rate in first attempt endotracheal tube placement (75% vs. 47%) with less attempts overall (1.3 ± 0.6 vs. 2.1 ± 1.3, P = 0.043). Conventional intubation was faster (42 s ± 6 s vs. 67 s ± 10s, P < 0.001), but showed a higher complication rate and more desaturation episodes during the trial.

Conclusions

Flexible fibreoptic intubation in swine is feasible and appears to be a safer and more accessible method for inexperienced users to learn. This could not only improve resident training options in hospitals with animal research facilities but might also prevent airway complications and needless animal suffering.

Adding Flexible Instrumentation to a Curved Videolaryngoscope: A Novel Tool for Laryngeal Surgery

OBJECTIVES

Transoral surgery of the larynx with rigid instruments is not always possible. This may result in insufficient therapy or in an increased need for open surgery. For these patients, alternative surgical systems are needed. Here, we demonstrate a curved prototype for laryngeal surgery equipped with flexible instruments.

STUDY DESIGN

Pre-clinical user study in an ex vivo porcine laryngeal model.

METHODS

The prototype was built from established medical devices, namely a hyperangulated videolaryngoscope and modified flexible instruments as well as three-dimensional printed parts. Feasibility of laryngeal manipulation was evaluated in a user study (n = 19) with a porcine ex vivo laryngeal model. Using three different visualization technologies, the participants performed various fine motor skills tasks and rated the usability of the system on a 5-point Likert scale.

RESULTS

Exposure, accessibility, and manipulation of important laryngeal structures were always possible using the new prototype. The participants needed considerably less time (mean, 96.4 seconds ± 6.4 seconds vs. 111.5 seconds ± 4.5 seconds, P = .18), reported significantly better general impression (mean score 3.0 vs. 3.8, P = .041) and significantly lower user head and neck strain (2.6 vs. 1.7, P = .022) using a 40-inch television screen as compared to a standard videolaryngoscope monitor.

CONCLUSION

The results indicate that our curved prototype and large monitor visualization may provide a cost-effective minimally invasive alternative for difficult laryngeal exposure. Its special advantages include avoiding the need for a straight line of sight and a simple and cost-effective construction. The system could be further improved through advances in camera chip technology and smaller instruments. Laryngoscope, 131:E561-E568, 2021.

Comparison of Recording Electrode Arrays in Endotracheal Thyroid Monitoring Tubes in a Porcine Model

OBJECTIVES

Alteration in positioning or head manipulation during thyroid surgery can lead to endotracheal tube movement and potentially a change in intraoperative neural monitoring readings. We sought to study the impact of positional changes on two different commercially available recording electrode arrays.

MATERIALS

Eight pigs divided equally into two study groups based on recording electrode arrays were used: Neurosign Lantern Laryngeal Electrode (LLE) (Neurosign_Technomed, The Netherlands) and Medtronic NIM EMG [neural integrity monitor electromyogram] endotracheal tube (ETT) (Medtronic, Jacksonville, FL). Neck movement and reposition were performed for all pigs. Signal data, including amplitude and latency, were collected for vagus nerve, recurrent laryngeal nerve (RLN), and external branch of superior laryngeal nerve (EBSLN) before and after repositioning. The differences of amplitude and latency by pre- and post-repositioning were compared for all animals.

RESULTS

Eight pigs were included in the current study. ETT group (Medtronic) had a significant decrease in amplitude of all tested nerves: for the vagus nerve on the left side by 36.30% (P = .021) and on the right by 49.29% (P = .024), for RLN on the left by 30.22% (P = .014) and on the right by 42.34% (P = .004), and for EBSLN on the left by 63.62% (P = .003) and on the right by 13.58% (P = .010). The amplitude changes in LLE group (Neurosign) repositioning were not statistically significant in all nerves.

CONCLUSION

Recording electrode array configuration can impact the stability of nerve monitoring signal during thyroid surgeries. Repositioning was associated with changes in nerve signal amplitude in ETT group (Medtronic), whereas LLE (Neurosign) did not show any significant differences. Human studies are warranted.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:2499-2505, 2020.

A Randomized Comparison of Bougie-Assisted and TracheoQuick Plus Cricothyrotomies on a Live Porcine Model

Objectives

Cricothyrotomy is a rescue procedure in “cannot intubate, cannot oxygenate” scenarios where other methods of nonsurgical airway management have failed. We compared 2 cuffed cricothyrotomy sets, bougie-assisted cricothyrotomy (BACT) and novel percutaneous TracheoQuick Plus, on a live porcine model in a simulated periarrest situation.

Methods

Thirty-four anesthetized minipigs were randomly allocated into two groups: BACT technique (n = 17) and TracheoQuick Plus (n = 17). The primary outcome was duration of cricothyrotomy while secondary outcomes were total success rate, number of attempts, location of incision, changes in heart rate, oxygen saturation, and the incidence of complications.

Results

BACT was significantly faster than TracheoQuick Plus cricothyrotomy, with a median time of 69 sec (IQR 56–85) versus 178 sec (IQR 152–272). The total success rate was without difference. 94% of BACT was performed successfully on the first attempt, while in the TracheoQuick Plus group, it was only 18% (P < 0.001). Trauma to the posterior tracheal wall was observed once in the BACT group and 5 times in the TracheoQuick Plus group. Oxygen saturation was significantly higher in the BACT group both during and after the procedure.

Conclusions

BACT is superior to TracheoQuick Plus cricothyrotomy on a live animal model.

A Method to Administer Agents to the Larynx in an Awake Large Animal

PURPOSE

This research note describes an adapted experimental methodology to administer an exogenous agent to the larynx and upper airway of awake animals. The exogenous agent could be a perturbation. In the current study, the agent was isotonic saline. Isotonic saline was selected because it is safe, of similar composition to extracellular fluid, and used in voice studies. The described approach allowed large animals such as pigs to be comfortably restrained without chemical sedation or anesthesia for extended periods while receiving the agent.

METHOD

Six Sinclair pigs were successfully trained with positive reinforcement to voluntarily enter and then be restrained in a Panepinto Sling. Once restrained, the pigs accepted a nose cone that delivered nebulized isotonic saline. This procedure was repeated 3 times per day for 20 days. At the end of the study, the larynx and airway tissues were excised and examined using histology and transmission electron microscopy.

RESULTS

Pathology related to the procedure (i.e., nebulized inhaled isotonic saline or stress) was not identified in any examined tissues.

CONCLUSIONS

This methodology allowed for repeated application of exogenous agents to awake, unstressed animals. This method can be used repeatedly in the laboratory to test various therapeutics for safety, toxicity, and dosage. Future studies will specifically manipulate the type of agent to further our understanding of laryngeal pathobiology.

Laryngeal T regulatory cells in the setting of smoking and reflux

OBJECTIVES/HYPOTHESIS

The larynx is a mucosal organ rich in lymphatic tissue that is regularly exposed to a multitude of inhaled, ingested, and refluxed microorganisms and irritants. The first line of mucosal immune defense is the barrier, including resident immune cells. T regulatory (Treg) cells are a specialized subset of CD4+ T cells that suppress or dampen immune responses to prevent damaging immunopathology. As Treg cells have been shown to preferentially accumulate at sites of infection, and Treg responses may contribute to persistence of infection by impairing antibacterial immunity, we sought to quantify these cells in laryngeal tissue exposed to smoking and reflux.

STUDY DESIGN

Cross-sectional study.

METHODS

Using an epigenetic assay, we quantified Treg and T cells and calculated the ratio of Treg to T cells (i.e., cellular ratio of immune tolerance [ImmunoCRIT]) in disease-free laryngeal biopsies representing four inflammatory states: 1) tobacco-exposed tissue, 2) refluxate and tobacco-exposed tissue, 3) refluxate-exposed tissue, and 4) unexposed tissue.

RESULTS

There was epigenetic evidence of Treg cells in all tissues, and we found no differences in Treg cell frequency relative to smoking and reflux in laryngeal tissue collected from 42 non-treatment-seeking participants. There was a decrease in total T cell frequency and an increase in ImmunoCRIT values in smokers regardless of reflux status.

CONCLUSIONS

In this study, laryngeal tissue from smokers show decreased overall T cells and increased ImmunoCRIT values. Our findings indicate that laryngeal inflammation is not directly mediated by loss of Treg cells in response to smoking and reflux in local tissue and increased ImmunoCRIT values in smokers implicate a role for this environmental exposure in modulating laryngeal immune homeostasis. More studies are indicated to explore Treg cell dysfunction in the pathophysiology of laryngeal disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:882-887, 2017.

Toward an Understanding of the Pathophysiology of Chronic Laryngitis

Chronic laryngitis, characterized by inflammation of the laryngeal tissues, is the most commonly diagnosed organic voice disorder, yet treatments targeting suspected etiologic factors have demonstrated limited efficacy. A major barrier to the development of improved medical therapies for chronic laryngitis is a fundamental gap in knowledge related to the pathophysiology of laryngeal inflammation. This article provides a review of the literature specific to laryngeal immunity in health and disease.

Evaluation of a novel Surgicric® cricothyroidotomy device for emergency tracheal access in a porcine model

A can't intubate, can't ventilate scenario can result in morbidity and death. Although a rare occurrence (1:50 000 general anaesthetics), it is crucial that anaesthetists maintain the skills necessary to perform cricothyroidotomy, and are well-equipped with appropriate tools. We undertook a bench study comparing a new device, Surgicric(®) , with two established techniques; the Melker Emergency Cricothyroidotomy, and a surgical technique. Twenty-five anaesthetists performed simulated emergency cricothyroidotomy on a porcine model, with the primary outcome measure being insertion time. Secondary outcomes included success rate, tracheal trauma and ease of use. The surgical technique was fastest. The median (IQR [range]) was 81 (62-126 [37-300]) s, followed by the Melker 124 (100-217 [71-300]) s, and the Surgicric 127 (68-171 [43-300]), p = 0.003. The Surgicric device was the most traumatic, as evaluated by a blinded Ear, Nose and Throat surgeon. Subsequently, the authors contacted the device manufacturer, who has now modified the kit in the hope that its clinical application might be improved. Further studies are required to evaluate the revised model.

Innate Immune Response of the Pig Laryngeal Mucosa to Endotracheal Intubation

Objective

The aim of this study was to measure the effects of endotracheal intubation on innate immune response within the pig laryngeal mucosa.

Study Design

Prospective controlled basic science study.

Setting

The animal experiments and analyses were conducted at the University of Bristol.

Samples and Methods

Eighteen pigs, matched at the major histocompatibility complex (MHC), were used in the study. The pigs were divided into 9 pairs. One of each pair (9 pigs in total) was intubated with an endotracheal tube under general anesthesia for 90 minutes. Two days later, pinch biopsies were taken from the supraglottis (specifically the false cords) and subglottis of both pigs. The experiment was repeated 8 more times. Based on quantitative immunohistochemistry, percentage areas of positive staining for CD172a, CD163, MHC class II, CD14, and CD16 were calculated separately for the epithelium and lamina propria of each biopsy.

Results

Total areas of laryngeal mucosa (epithelium and lamina propria) expressing CD172a and coexpressing CD163 and CD172a were significantly reduced at 2 days following endotracheal intubation ( P = .039 and P = .037, respectively). MHC class II expression and MHC class II coexpression with CD172a were similarly reduced following intubation ( P = .003 and P = .005, respectively). In the supraglottis, MHC class II coexpression with CD16 and CD14 was also reduced following endotracheal intubation ( P = .037).

Conclusions

Our results indicate that endotracheal intubation reduces the number of innate immune cells within the upper airway mucosa. This may be an important first step in a cascade leading to chronic wound and scar formation causing airway stenosis.

In vivo investigation of acidified pepsin exposure to porcine vocal fold epithelia

OBJECTIVES/HYPOTHESIS

The study objective was to investigate epithelial changes in response to direct, repeated, acidified pepsin exposures in an in vivo porcine model. We hypothesized that 12 acidified pepsin applications to simulate reflux would elicit a vocal fold response characterized by inflammation, epithelial proliferation, and increased intercellular space, as well as changes in the gene expression of epithelial junctional proteins, ion transporter proteins, and proinflammatory cytokines.

STUDY DESIGN

Prospective, in vivo study.

METHODS

Pigs received acidified pepsin (pH = 4) or saline (sham) applied directly to vocal folds. Larynges were collected following three exposures per week for 4 weeks. Vocal fold tissue morphology, collagen, and elastin were evaluated histologically. Gene expression of E-cadherin, zona occludens-1, cystic fibrosis transmembrane conductance regulator, epithelial sodium channel, interleukin-1β, tumor necrosis factor-α, and interferon-γ were measured. Ultrastructural alterations, epithelial intercellular space diameter, and microridge height were measured using transmission electron microscopy.

RESULTS

There were no significant differences in histology, gene transcripts, epithelial ultrastructure, intercellular space, and microridge height after acidified pepsin exposure.

CONCLUSIONS

Twelve simulated reflux challenges were insufficient to elicit epithelial changes, demonstrating the resistance of healthy vocal folds to direct, repeated acidified pepsin exposures. These data increase our understanding of healthy vocal fold defenses and lay the groundwork for a prospective, uninjured, nonsurgical, laryngopharyngeal reflux model where pigs can be exposed directly to acidified pepsin.

Cross-sample validation provides enhanced proteome coverage in rat vocal fold mucosa

The vocal fold mucosa is a biomechanically unique tissue comprised of a densely cellular epithelium, superficial to an extracellular matrix (ECM)-rich lamina propria. Such ECM-rich tissues are challenging to analyze using proteomic assays, primarily due to extensive crosslinking and glycosylation of the majority of high M_r ECM proteins. In this study, we implemented an LC-MS/MS-based strategy to characterize the rat vocal fold mucosa proteome. Our sample preparation protocol successfully solubilized both proteins and certain high M_r glycoconjugates and resulted in the identification of hundreds of mucosal proteins. A straightforward approach to the treatment of protein identifications attributed to single peptide hits allowed the retention of potentially important low abundance identifications (validated by a cross-sample match and de novo interpretation of relevant spectra) while still eliminating potentially spurious identifications (global single peptide hits with no cross-sample match). The resulting vocal fold mucosa proteome was characterized by a wide range of cellular and extracellular proteins spanning 12 functional categories.

A novel endoscopically placed stent to relieve glottic obstruction from bilateral vocal fold paralysis

OBJECTIVE

Congenital bilateral vocal fold paralysis (BVP) is a rare but serious condition often requiring a tracheostomy to temporize the airway. In cases of idiopathic BVP, studies suggest waiting twelve months prior to laryngeal surgery because of a high rate of spontaneous recovery. Therefore a less invasive and reversible intervention would be optimal. A prospective study in a piglet model was undertaken to evaluate the efficacy of a novel spring-loaded stenting device designed to maintain laryngeal patency in an in vivo animal model of BVP.

METHODS

Eight Yorkshire piglets had BVP induced by surgical division of the recurrent laryngeal nerves. Stents were endoscopically deployed between the arytenoid vocal processes. Animals were recovered and monitored for stridor, dietary intake, and weight gain. Animals were sacrificed after five days. Airway resistance using a calibrated manometer was measured at four time-points: baseline, BVP induction, stent insertion, and pre-sacrifice.

RESULTS

Six of eight animals survived greater than five days with an average weight gain of 1.9kg (p=0.003). Relative inspiratory resistance increased from baseline after inducing BVP (1.00 vs. 1.468, p=0.0315) and decreased to baseline levels with stent insertion (1.468 vs. 1.092, p=0.0238). Expiratory resistance was not significantly influenced by stage of measurement (p=0.236). Of the two animals not surviving the protocol, one had an unrelated anesthesia complication and the other a malpositioned stent.

CONCLUSION

The novel stent was successful in relieving the inspiratory resistance associated with BVP, without compromising swallowing and daily function. This may hold promise in temporarily securing the pediatric airway in the setting of BVP.

Comparison of three cuffed emergency percutaneous cricothyroidotomy devices to conventional surgical cricothyroidotomy in a porcine model

BACKGROUND

Emergency cricothyroidotomy is a potentially life-saving procedure in the 'cannot intubate cannot ventilate (CICV)' scenario. Although surgical cricothyroidotomy remains the technique recommended in many 'CICV' algorithms, the insertion of a tracheostomy as a cannula over a trocar, or using the Seldinger method, may have advantages as they are more familiar to the anaesthetist. We compared the utility of three cuffed cricothyroidotomy devices: cuffed Melker®, Quicktrach 2®, and PCK® devices, with surgical cricothyroidotomy.

METHODS

After ethical committee approval and written informed consent, 20 anaesthetists performed cricothyroidotomy with all four devices in random order, in a pig larynx and trachea model covered in cured pelt. The primary endpoints were the rate of successful placement of the cricothyroidotomy device into the trachea and the duration of the insertion attempt.

RESULTS

The Melker® and Quicktrach 2® devices possessed advantages over the surgical approach, in contrast to the PCK® device, which performed less well. All 20 participants inserted the Melker®, with 19 being successful using the surgical approach and the Quicktrach 2®, whereas only 12 successfully inserted the PCK® device (PCK® vs surgical, P=0.02). The Quicktrach 2® had the fastest insertion times and caused least trauma to the posterior tracheal wall. The Melker® was rated highest by the participants and was the only device rated higher than the surgical technique.

CONCLUSIONS

The Melker® and Quicktrach 2® devices appear to hold particular promise as alternatives to surgical cricothyroidotomy. Further studies, in more clinically relevant models, are required to confirm these initial positive findings.

Interspecies comparison of mucosal wave properties using high-speed digital imaging

OBJECTIVES/HYPOTHESIS

The purpose of this study was to compare the vocal fold vibratory characteristics of ex vivo bovine, canine, ovine, and porcine larynges to human male and female vocal fold vibrations to determine the best model organism for laryngeal studies concerning vibratory and kinetic characteristics.

STUDY DESIGN

Prospective experimental.

METHODS

High-speed videos of phonation were gathered at 4,000 frames per second (fps) in the animal models and human high-speed endoscopy data were gathered at 2,000 fps. Videos were converted into kymograms, and the amplitude, oscillation frequency, and phase difference of vocal fold vibration were measured.

RESULTS

No statistically significant differences were found with respect to frequency, amplitude, or phase difference between canines and humans. Porcines were not significantly different from human females but did have an oscillation frequency significantly different from human males. Ovine vibrational amplitudes were significantly different from humans, and bovine frequency and amplitude differed significantly from humans.

CONCLUSIONS

Canine and porcine larynges are the most appropriate model specimens for laryngeal studies contingent on vibratory or kinetic properties of phonation.

Cricothyroidotomy: Comparison of three Different Techniques on a Porcine Airway

We compared three different cricothyroidotomy techniques on a cadaveric porcine airway model to determine the most rapid, successful and safe method in emergency situations. In this observational comparative bench-test, surgical or scalpel cricothyroidotomy (ST), Cook Melker Cricothyrotomy Kit (CM) and Portex Cricothyroidotomy Kit (PCK) were evaluated. After a familiarisation program, four operators performed five procedures using each of the techniques. A dissected pig airway was housed in an airway training manikin. Time to successful completion of the procedure, complications and anatomical variations in the pig larynx were recorded.

A patent airway was established in 20 of 20 (100%) attempts with CM technique, 11 of 20 (55%) with ST and six of 20 (30%) with PCK technique. The CM technique was associated with a higher success rate (P <0.001). There was no significant difference (P=0.4) in the median time (interquartile range) taken to achieve a patent airway; CM 50 seconds (40 to 57), ST 47 seconds (41 to 55) and PCK 63 seconds (41 to 150). There was a higher rate of posterior tracheal wall injury with the PCK technique (n=11) and ST technique (n=5). No complications were observed with CM technique. There were no significant anatomical variations in the pig larynxes.

We conclude that the CM technique is safe, rapid and has a significantly higher success rate in achieving an artificial airway in this airway model. Overall, all the participants in our study preferred to use this kit in an emergency situation.

Pilot study on acute voice and throat symptoms related to exposure to organic dust: preliminary findings from a provocation test

The aim of this pilot research was to investigate acute voice and throat symptoms related to organic dust exposure among nine subjects with suspected occupational rhinitis or asthma. Subjective voice and throat symptoms were recorded before and after an occupational exposure test. In addition, the study included perceptual assessment of subjects' voice samples recorded before and after the exposure tests. The results showed a number of (statistically) significant voice and throat changes in symptoms based on subjects' own assessments. These symptoms included a hoarse, husky, or tense voice, requiring an extra effort when speaking and difficulty in starting phonation (P < 0.05). Other significant symptoms included feeling of shortness of breath or the need to gasp for air and feeling that the voice is weak or that it does not resonate (P < 0.01). Such changes were not, however, detected by voice clinicians in the listening test of subjects' voice samples recorded before and after the exposure. These results suggest that the larynx reacts to organic dust with symptoms that are felt by the patient rather than heard by the voice clinician. The voice disorder in such cases is a diagnosis based on symptoms expressed by subjects.

In vitro study investigating post neck surgery haematoma airway obstruction

OBJECTIVES

To investigate whether the possible pressure produced by a haematoma in the neck would be sufficient to directly compress the trachea to the point of airway obstruction.

STUDY DESIGN

In vitro study.

METHODS

Varying pressures were applied over the second and third cartilaginous rings of 10 pig tracheas in vitro and the anterior-posterior compression was measured.

RESULTS

At pressures of 257 mmHg, equivalent to the maximum possible pressure in the neck (i.e. systolic blood pressure), there was an average compression of 20.8 per cent of the original anterior-posterior tracheal diameter.

CONCLUSIONS

This study suggests that the pressures in haematomas observed after neck surgery would not be sufficient to cause airway obstruction due to direct pressure on the trachea. Therefore, the most likely cause of airway obstruction would be supraglottic oedema secondary to venous obstruction.

The mucosal immune response to laryngopharyngeal reflux

RATIONALE

Laryngopharyngeal reflux (LPR) affects up to 20% of Western populations. Although individual morbidity is usually moderate, treatment costs are high and there are associations with other diseases, including laryngeal cancer. To date, there have been no studies of the mucosal immune response to this common inflammatory disease.

OBJECTIVES

To determine the mucosal immune response to LPR.

METHODS

We performed a prospective immunologic study of laryngeal biopsies from patients with LPR and control subjects (n = 12 and 11, respectively), and of primary laryngeal epithelial cells in vitro.

MEASUREMENTS AND MAIN RESULTS

Quantitative multiple-color immunofluorescence, using antibodies for lymphocytes (CD4, CD8, CD3, CD79, CD161), granulocytes (CD68, EMBP), monocytic cells (CD68, major histocompatibility complex [MHC] class II), and classical and nonclassical MHC (I, II, beta(2)-microglobulin, CD1d). Univariate and multivariate analysis and colocalization measurements were applied. There was an increase in percentage area of mucosal CD8(+) cells in the epithelium (P < 0.005), whereas other leukocyte and granulocyte antigens were unchanged. Although epithelial MHC class I and II expression was unchanged by reflux, expression of the nonclassical MHC molecule CD1d increased (P < 0.05, luminal layers). In vitro, laryngeal epithelial cells constitutively expressed CD1d. CD1d and MHC I expression were inversely related in all subjects, in a pattern which appears to be unique to the upper airway. Colocalization of natural killer T (NKT) cells with CD1d increased in patients (P < 0.01).

CONCLUSIONS

These data indicate a role for the CD1d-NKT cell axis in response to LPR in humans. This represents a useful target for novel diagnostics and treatments in this common condition.

From grunts to words: experiments in laryngeal transplantation

INTRODUCTION

Laryngeal transplantation remains an increasingly viable option for patients with irreversible disease or damage to the larynx. Successful organ transplantation relies on minimising surgical, ischaemic and immunological insults. The inherent immunogenicity of an organ is dependent on the amount of immunologically active cells within it. The presence of immunologically active cells within non-transplanted NIH-minipigs was investigated and an in vivo laryngeal transplant model was developed.

MATERIALS AND METHODS

Quantitative, multiple-colour immunofluorescence using pig-specific monoclonal antibodies was used to assess the normal immunological architecture and the short-term immunological changes associated with 3 h of cold ischaemia and 8 h of reperfusion in an MHC-matched animal model.

RESULTS AND CONCLUSIONS

There is a complex immunological architecture within the non-transplanted, healthy pig larynx. In addition, an in vivo laryngeal transplant model was developed that allowed successful perfusion for 8 h post transplantation. There were significant changes in cell numbers within different anatomical subsites of the larynx. However, the biological significance remains debatable in view of the large range of cell numbers both within and between individual animals.

Early immunological changes associated with laryngeal transplantation in a major histocompatibility complex-matched pig model

Laryngeal transplantation is an increasingly viable proposition for patients with irreversible diseases of the larynx. One human transplant has been performed successfully, but many questions remain before routine transplantation can begin. In order to measure the immunological changes in mismatched transplants, it is first necessary to know the immediate combined effects of ischaemia-reperfusion injury (IRI) plus the added insult of major surgery in a fully matched setting. We measured the changes in immunologically active mucosal cells following 3 h of cold ischaemia and 8 h of in situ reperfusion in a major histocompatibility complex (MHC)-matched minipig model (n = 4). Biopsies were prepared for quantitative, multiple-colour immunofluorescence histology. The number of immunologically active cells was significantly altered above (supraglottis) and below (subglottis) the vocal cords following transplantation and reperfusion (P < 0.05, P < 0.001, respectively). However, the direction of the change differed between the two subsites: cell numbers decreased post-transplant in the supraglottis and increased in the subglottis. Despite the statistical evidence for IRI, these changes were less than the large normal inter- and intrapig variation in cell counts. Therefore, the significance of IRI in exacerbating loss of function or rejection of a laryngeal allograft is open to question. Longer-term studies are required.

The postnatal development of the mucosal immune system and mucosal tolerance in domestic animals

The mucosal immune system is exposed to a range of antigens associated with pathogens, to which it must mount active immune responses. However, it is also exposed to a large number of harmless antigens associated with food and with commensal microbial flora, to which expression of active, inflammatory immune responses to these antigens is undesirable. The mucosal immune system must contain machinery capable of evaluating the antigens to which it is exposed and mounting appropriate effector or regulatory responses. Since the immune system is likely to have evolved initially in mucosal tissues, the requirement to prevent damaging allergic responses must be at least as old as the adaptive immune system, and studies of the mechanisms should include a range of non-mammalian species. Despite the importance for rational design of vaccines and for control of allergic reactions, the mechanisms involved are still largely unclear. It is not clear that the classical experimental protocol of "oral tolerance" is, in fact, measuring a biologically important phenomenon, nor is it clear whether tolerance is regulated in the evolutionarily recent organised lymphoid tissue (the lymph nodes) or the more ancient, diffuse architecture in the intestine. The capacity of the immune system to discriminate between "dangerous" and "harmless" antigens appears to develop with age and exposure to microbial flora. Thus, the ability of an individual or a group of animals to correctly regulate mucosal immune responses will depend on age, genetics and on their microbial environment and history. Attempts to manipulate the mucosal immune system towards active immune responses by oral vaccines, or towards oral tolerance, are likely to be confounded by environmentally-induced variability between individuals and between groups of animals.

Antigen presenting cells in mucosal sites of veterinary species

The ability of antigen presenting cells, in particular dendritic cells, to integrate a variety of environmental signals, together with their ability to respond appropriately by initiating either tolerance or defensive immune responses make them cells of particular relevance and importance in the mucosal environment. They have been demonstrated in a variety of mucosal tissues in veterinary species and have been characterized to varying degrees, showing that fundamental immunological principles apply throughout all species, but also highlighting some species differences. A major advantage of carrying out immunological research in veterinary species is their size: it is possible to cannulate lymphatic ducts and obtain information about cell migration between different tissues. It is also possible to obtain pure populations of relatively rare cell types such as the plasmacytoid dendritic cells or mucosal dendritic cells ex vivo for the study of immune responses to diseases in their natural host and for other thorough functional studies. Two major myeloid antigen presenting cell (APC) (dendritic cells, DC) cell populations have been described in gut draining lymph and other mucosal sites in ruminants and pigs, characterised by the presence or absence of surface molecules, their enzyme profiles, their ability to phagocytose and their different potential as APC. There is evidence that one of these subsets has migrated from the diffuse mucosal tissue, where it is found as a phagocytic as well as stimulatory APC population, which in turn may be derived from blood macrophages. In addition, the presence and role in viral infection of the IFN-alpha producing plasmacytoid DC in mucosal tissue is discussed, based on studies in pigs.

The isolation and characterisation of primary human laryngeal epithelial cells

We have shown that the larynx has a prominent immunological component that varies between individuals, and which is influenced by lifestyle factors implicated in the pathogenesis of the inflammatory and neoplastic diseases of the larynx. In order to explore the mechanisms of such links between laryngeal mucosal immunity and the development of lifestyle-related disease, reliable in vitro models are essential. In this study, we isolated and characterised primary laryngeal epithelial cells from normal individuals and show they can be cultured and manipulated to express MHC class II molecules in vitro.

The larynx as an immunological organ: immunological architecture in the pig as a large animal model

The larynx is a mucosal organ positioned at the divergence of the respiratory and digestive tracts. It is exposed to a wide variety of environmental components, including foreign antigens, tobacco smoke, laryngopharyngeal reflux and pollutants. The mucosal immune system generates either active immune responses or tolerance, depending on the nature of the antigen and we hypothesize that the larynx is important organ for immunological decision-making in the airway. Because the pig is an ideal large animal model in which to explore laryngological research questions, such as those relating to laryngeal transplantation, we investigated the normal mucosal immunology of the porcine larynx. Pig larynges and tracheae were processed and prepared for bright-field microscopy and quantitative, multiple-colour immunofluorescence histology using pig-specific monoclonal antibodies. There was an abundance of immunologically active cells within the mucosa of the larynx and trachea of both the newborn and adult animal. Specifically, major histocompatibility complex class II (MHC class II+) cells, CD4+ and CD8+ cells were identified, although regional differences in numbers were apparent: specifically, the supraglottis contained fewer immunologically relevant cells than other sites sampled. There was a significant correlation between the numbers of MHC class II+ and CD4+ cells indicating co-ordinate regulation and therefore functional local interactions. The presence of such an immunological structure suggests that the larynx may have important functions in respiratory immunology and that it may trigger strong alloresponses after laryngeal transplantation.

Laryngeal transplantation in 2005: a review

There is no good surgical, medical or prosthetic solution to the problems faced by those with a larynx whose function is irreversibly damaged by tumor or trauma. Over the past 10 years, the pace of research designed to establish laryngeal transplantation as a therapeutic option for these persons has increased steadily. The biggest milestone in this field was the world's first true laryngeal transplant performed in Cleveland, Ohio in 1998. The recipient's graft continues to function well, in many respects, even after 7 years. However, it has also highlighted the remaining barriers to full-scale clinical trials. Stimulated by these observations, several groups have accumulated data which point to answers to some of the outstanding questions surrounding functional reinnervation and immunomodulation. This review seeks to outline the progress achieved in this field by 2005 and to point the way forward for laryngeal transplantation research in the 21st century.

Smoking influences the immunological architecture of the human larynx

Little is known about the effects of demographic and lifestyle factors on laryngeal mucosal immunology. Pinch biopsies of laryngeal mucosa were studied from 63 patients without laryngeal disease. Areas of positive staining for HLA-DR, HLA-DQ, HLA-DP, CD45, CD45RA, CD45RO, CD4, CD8, and CD79 were calculated. Patients were stratified according to gender and smoking status. Analysis of covariance showed current cigarette smokers had increased numbers of CD4+ T cells and there was an association between older age and greater CD4+ T cell numbers in both epithelium and lamina propria. Older age and female gender were associated with decreased lamina propria CD4+ CD45RO+ T cells and an increase in CD4+ CD45RO- T cells. T cell populations in the larynx may therefore be influenced by smoking, age and gender. We hypothesize that smoking induces changes in normal immunological function of the larynx, which may contribute to the etiology of inflammatory disease and cancer.

A systematic review of case-control studies of human papillomavirus infection in laryngeal squamous cell carcinoma

A role for human papillomavirus (HPV) has been suggested in laryngeal squamous cell carcinoma (LSCC). In order to quantitate the available evidence, we reviewed studies examining the risk of laryngeal cancer-associated HPV. PubMed was searched for case-control studies conducted worldwide and published in any language since 1966. Relevant papers were hand-searched and cross-referenced. Six studies met the inclusion criteria. The studies are heterogeneous in the methods used to harvest tissue samples and techniques for detecting the virus within the tissue. HPV-16 positivity among cases ranged from 2.7% to 46.9% and 0-5.7% among controls. Two studies showed a significantly increased risk of LSCC if HPV-16 was present (OR 18.5, 95% CI 2.2-154.8, OR 2.6, 95% CI 1.1-6.0). An increased risk was also observed for glottic versus supraglottic cancer in one study (OR 9.69, 95% CI 1.47-64.04). The direction of effect is towards an increase in risk of LSCC in people with evidence of HPV-16 infection. There is marked heterogeneity in the methods used to detect the virus and frequency with which it is detected. An adequately powered study using a reliable detection technique is required to confirm and quantify this risk and to examine effect modification.

Intrinsic muscles and distribution of the recurrent laryngeal nerve in the pig larynx

To use the pig larynx in studies of laryngeal reinnervation, it is essential to have a clear understanding of its anatomy. We aimed to define the macroscopic anatomy of the intrinsic muscles and the course of the recurrent laryngeal nerve (RLN) in the pig larynx. Twelve large white pig larynges were used. Five larynges were preserved in formalin, then dissected to study the anatomy of the intrinsic muscles. Seven larynges were stained using the modified Sihler's staining technique, which results in nerves being stained dark purple while the remainder of the larynx is rendered translucent. The intrinsic muscles of the pig larynx were similar to those in the human. The RLN gives off a branch that enters the posterior cricoarytenoid muscle (PCA) on its deep surface and supplies the entire muscle, although the branching pattern of the nerve within the muscle varies considerably. These results facilitate detailed reinnervation studies in the pig laryngeal transplant model.

Differential major histocompatibility complex class II locus expression on human laryngeal epithelium

The survival of a laryngeal allograft will be dependent on the immunological composition of the donor larynx and, in particular, on the expression of major histocompatibility complex (MHC) class II antigens on professional and non-professional antigen-presenting cells. Laryngeal and tonsillar biopsies from normal individuals aged 18-78 years were processed and prepared for quantitative, multiple-colour immunofluorescence using mouse antihuman monoclonal antibodies to human leucocyte antigen (HLA)-DR, HLA-DQ and CD45. The laryngeal epithelium expressed HLA-DR locus products at variable levels, but expression of HLA-DQ was virtually absent. Tonsillar epithelial cells expressed HLA-DR at the basal layer only, while HLA-DQ was similarly not expressed. In contrast, both HLA-DR and -DQ locus products were present on lamina propria and intraepithelial leucocytes in both laryngeal and tonsillar mucosae, although at varying levels. The finding that laryngeal epithelial cells express MHC class II antigens has implications for the survival of laryngeal allografts and suggests that they may require significant immunomodulation. In addition, antigen presentation by epithelial cells has been hypothesized to contribute to the immunoregulatory function of mucosal tissues, and the finding that HLA-DQ locus products are only expressed at low levels by laryngeal epithelium raises questions about the repertoire of peptides to which the mucosal immune system can respond.

Rat model of laryngeal transplantation with normal circulation maintained by combination with the tongue

Recent research on laryngeal transplantation used a rat model with physiologically abnormal circulation, because the common carotid artery was used for venous drainage. Since a model with normal circulation is better for accurate assessment, we developed a vascularized laryngeal graft, using the common carotid artery as the arterial supply and the external jugular vein as the venous drainage. The transplant included other tributaries from the tongue and the pharynx by combination with the tongue, because the tributaries from the larynx were very small. Ten transplants were performed. The transplanted organs were examined daily. Seven days after transplantation, the composite grafts were evaluated histologically. The mortality rate was 10%. All composite grafts were fully viable, and their structure was maintained in the remaining nine rats. Our model is appropriate for experiments on laryngeal transplantation.

Model for experimental revascularized laryngeal allotransplantation

BACKGROUND

Although a human laryngeal transplant has been undertaken successfully, important questions remain that require a suitable animal model.

METHODS

A pig model for allotransplantation has been developed. Organ perfusion was studied in nine animals before four transplants were performed in congenic (unrecovered) animals and eight in unmatched (recovered) animals. Larynges were regularly examined endoscopically until death at 14 days. Immunosuppression included the use of tacrolimus. Revascularization was achieved by anastomosing the donor right cervical vascular tree to the recipient common carotid. In recovered animals, four allografts were placed orthotopically and four heterotopically.

RESULTS

The pig larynx was perfused adequately via the right cervical vascular tree and congenic grafts were well tolerated. Of eight allografts, seven were well tolerated and remained healthy for the duration of the study (14 days). One allograft became infected between days 4 and 7 after operation. Median operating time was 6 h, with a median cold ischaemia time of 3 h.

CONCLUSION

Revascularized allotransplants of the larynx can be undertaken reliably in pigs and this provides a preclinical model for studies of laryngeal transplantation.