Tracheal Lesions Research Articles

Efficacy of commercial live vaccines against QX-like infectious bronchitis virus in Japan

Infectious bronchitis, an acute and highly contagious disease that affects chickens, is caused by the infectious bronchitis virus (IBV). The antigenic variant QX-like IBV was first reported in China in 1996 and is now endemic in many countries. Our previous study reported the first detection and isolation of QX-like IBVs in Japan and that they were genetically related to the recently detected strains in China and South Korea. The pathogenicity of 2 Japanese QX-like IBV strains (JP/ZK-B7/2020 and JP/ZK-B22/2020) was evaluated by inoculating specific pathogen-free (SPF) chickens with 102 to 106 median embryo infectious dose. Both strains caused clinical signs of respiratory symptoms, gross tracheal lesions, and moderate-to-severe suppression of tracheal ciliostasis. To evaluate the efficacy of commercial IBV live vaccines against the JP/ZK-B7/2020 strain, vaccinated SPF chickens were challenged with the JP/ZK-B7/2020 strain at 104 EID50 (median embryo infectious dose). Only the JP-Ⅲ vaccine provided high levels of protection (reduced suppression of tracheal ciliostasis and reduced viral loads in organs), whereas the Mass vaccine showed little protective effect. Virus neutralization test results and comparisons between IBV genotypes based on the S1 gene suggested that QX-like and JP-III genotypes were closely related. These results suggest that the JP-III IBV vaccine, which has relatively high S1 gene homology with QX-like IBVs, is effective against Japanese QX-like IBV strain.

Surgical Management of Post-Intubation Tracheal Injuries: A Single-Center Experience from Nepal

Introduction: Despite various improvements in technology and patient care, tracheal intubation and tracheostomy still result in significant tracheal injuries like stenosis and airway fistula. Pressure necrosis by the inflated balloon is the commonest culprit. Post-intubation tracheal stenosis is a major indication for tracheal resection and anastomosis. This study was done to find out the indications and results of surgery for post-intubation tracheal lesions. Methods: It was a descriptive observational study of patients with post- intubation tracheal lesions managed in Manmohan Cardiothoracic Vascular and Transplant Center over a period of 20 years (2001 to 2021). Results: Twenty-five patients were treated for post-intubation tracheal lesions. Four had isolated tracheo-esophageal fistula (TEF); eighteen had an isolated tracheal stenosis and three had both. Most had a tracheal resection and end-end anastomosis (REEA) via a cervical approach, resecting an average of 2.7 cm of tracheal length. The average size of stenotic lumen was 4.32 mm. There were no operative deaths. Two patients expired within a month of surgery: one due to fatal restenosis and the other due to sepsis. There were a few immediate and a few long-term complications. The average follow-up period was 5 years. Conclusion: Among the various post-intubation lesions, tracheal stenosis is the commonest indications for surgery. The management is challenging but safe and feasible, with a multidisciplinary team approach.

The efficiency of endoscopic versus open surgical interventions in adult benign laryngotracheal stenosis: a meta-analysis.

The optimal treatments for adult benign laryngotracheal stenosis presently remains controversial. The majority of the disadvantages of endoscopic interventions with high recurrence rate and open surgical therapy accompanied by sophisticated techniques, complication and mortality, highlights the dilemma of option for treatments. To compare endoscopic treatments with open surgical interventions in adult patients with benign laryngotracheal stenosis, analyze their clinical outcomes, recurrence, complication and mortality. In the meta-analysis, the databases including PubMed, Embase, Ovid and Web of Science were searched for studies reporting adult benign laryngotracheal stenosis, and clinical outcomes were compared. The duplicate publications, reviews, comments or letters, conference abstracts, case reports were excluded. The random effect model was used for calculating the pooled effect estimates. Eight studies (1627 cases) referring to six retrospective and two prospective researches were ultimately included in the meta-analysis. The decreased risk estimates of recurrence rate in patients receiving open surgical interventions were detected, comparing with endoscopic interventions (P < 0.05). Subgroup analysis revealed that decreased risk estimates of restenosis rate were also observed in patients receiving open surgical interventions compared with endoscopic interventions (P < 0.05), based on prospective studies, Europe and America, < 2-year follow-up, laryngeal stenosis, stenotic length without inter-group difference or stenotic grade II alone. However, there were no statistically significant difference of recurrence rate between the two interventions (P > 0.05) based on retrospective studies, South Asia and Africa, ≥ 2-year follow-up, involving tracheal lesion, stenotic length with inter-group difference, or stenotic grades of I-IV. No notable difference in the incidence of complication or mortality were identified. Open surgical interventions were more suitable for most laryngotracheal stenosis without contraindications. Endoscopic interventions are increasingly being used to treat simple laryngotracheal stenosis, as well as complex airway stenosis in carefully selected cases. Multi-center prospective randomized controlled trials should be conducted to search for the standard treatments for laryngotracheal stenosis.

MUCUS OR MELANOMA? A CASE REPORT

MUCUS OR MELANOMA? A CASE REPORT

RECURRENT TRACHEAL LESIONS IN DISTAL METASTATIC MELANOMA: A ZEBRA AMONG HORSES

RECURRENT TRACHEAL LESIONS IN DISTAL METASTATIC MELANOMA: A ZEBRA AMONG HORSES

A RARE CASE OF HUMAN PAPILLOMAVIRUS-ASSOCIATED TRACHEAL SMALL CELL CARCINOMA

A RARE CASE OF HUMAN PAPILLOMAVIRUS-ASSOCIATED TRACHEAL SMALL CELL CARCINOMA

PULMONARY INVOLVEMENT WITH PLEOMORPHIC ADENOMA: 30-YEAR EXPERIENCE WITH THIS RARE ENTITY AT A TERTIARY REFERRAL CENTER

PULMONARY INVOLVEMENT WITH PLEOMORPHIC ADENOMA: 30-YEAR EXPERIENCE WITH THIS RARE ENTITY AT A TERTIARY REFERRAL CENTER

Novel Therapy for Acquired Tracheomalacia with a Tissue-Engineered Extraluminal Tracheal Splint and Autologous Mesenchymal-Derived Chondrocytes.

Introduction Acquired tracheomalacia (ATM) is characterized by a loss of structural strength of the tracheal framework, resulting in airway collapse during breathing. Near half of the patients undergoing prolonged invasive mechanical ventilation will suffer tracheal lesions. Treatment for ATM includes external splinting with rib grafts, prosthetic materials, and tracheal resection. Failure in the use of prosthetic materials has made reconsidering natural origin scaffolds and tissue engineering as a suitable alternative. Objective To restore adequate airway patency in an ovine model with surgically-induced ATM employing a tissue-engineered extraluminal tracheal splint (TE-ETS). Methods In the present prospective pilot study, tracheal rings were partially resected to induce airway collapse in 16 Suffolk sheep ( Ovis aries ). The TE-ETS was developed with autologous mesenchymal-derived chondrocytes and allogenic decellularized tracheal segments and was implanted above debilitated tracheal rings. The animals were followed-up at 8, 12, and 16 weeks and at 1-year postinsertion. Flexible tracheoscopies were performed at each stage. After sacrifice, a histopathological study of the trachea and the splint were performed. Results The TE-ETS prevented airway collapse for 16 weeks and up to 1-year postinsertion. Tracheoscopies revealed a noncollapsing airway during inspiration. Histopathological analyses showed the organization of mesenchymal-derived chondrocytes in lacunae, the proliferation of blood vessels, and recovery of epithelial tissue subjacent to the splint. Splints without autologous cells did not prevent airway collapse. Conclusion It is possible to treat acquired tracheomalacia with TE-ETS without further surgical removal since it undergoes physiological degradation. The present study supports the development of tissue-engineered tracheal substitutes for airway disease.

Tracheal cellular immune response in chickens inoculated with Mycoplasma synoviae vaccine, MS-H or its parent strain 86079/7NS

Mycoplasma synoviae causes respiratory tract disease in chickens characterised by mild to moderate lymphoplasmacytic infiltration of the tracheal mucosa. MS-H (Vaxsafe1 MS, Bioproperties Pty Ltd.) is an effective live attenuated vaccine for M. synoviae, but the immunological basis for its mechanism of protection has not been investigated, and the phenotypes of lymphocytes and associated cytokines involved in the local adaptive immune response have not been described previously. In this study, specific-pathogen-free chickens were inoculated intra-ocularly at 3 weeks of age with either M. synoviae vaccine strain MS-H or vaccine parent strain 86079/7NS (7NS), or remained uninoculated. At 2-, 7- and 21 days post-inoculation (dpi), tracheal mucosal pathology, infiltrating lymphocytes subsets and transcription levels of mRNA encoding 8 cytokines were assessed using light microscopy, indirect immunofluorescent staining and RT-qPCR, respectively. After inoculation, tracheal mucosal thickness, tracheal mucosal lesions, and numbers of infiltrating CD4+CD25- cells, B-cells, and macrophages were greater in MS-H- and 7NS-inoculated chickens compared with non-inoculated. Inoculation with 7NS induced up-regulation of IFN-γ, while vaccination with MS-H induced up-regulation of IL-17A, when compared with non-inoculated birds. Both inoculated groups had a moderate infiltrate of CD4+CD25+ T cells in the tracheal mucosa. These findings reveal that the tracheal local cellular response after MS-H inoculation is dominated by a Th-17 response, while that of 7NS-inoculated chickens is dominated by a Th-1 type response.

Decellularized Wharton Jelly Implants Do Not Trigger Collagen and Cartilaginous Tissue Production in Tracheal Injury in Rabbits

Background: Tracheal lesions are pathologies derived from the most diverse insults that can result in a fatal outcome. Despite the number of techniques designed for the treatment, a limiting factor is the extent of the extraction. Therefore, strategies with biomaterials can restructure tissues and maintain the organ’s functionality, like decellularized Wharton’s jelly (WJ) as a scaffold. The aim is to analyze the capacity of tracheal tissue regeneration after the implantation of decellularized WJ in rabbits submitted to a tracheal defect. Methods: An in vivo experimental study was undertaken using twenty rabbits separated into two groups (n = 10). Group 1 submitted to a tracheal defect, group 2 tracheal defect, and implantation of decellularized WJ. The analyses were performed 30 days after surgery through immunohistochemistry. Results: Inner tracheal area diameter (p = 0.643) didn’t show significance. Collagen type I, III, and Aggrecan highlighted no significant difference between the groups (both collagens with p = 0.445 and the Aggrecan p = 0.4). Conclusion: The scaffold appears to fit as a heterologous implant and did not trigger reactions such as rejection or extrusion of the material into the recipient. However, these results suggested that although the WJ matrix presents several characteristics as a biomaterial for tissue regeneration, it did not display histopathological benefits in trachea tissue regeneration.

Abstract 4121: Durable stable disease with nivolumab, PD-1 inhibitor, and subsequent bevacizumab, Anti-VEGF monoclonal antibody, in long standing recurrent respiratory papillomatosis with lung squamous cell carcinoma

Abstract Background: Recurrent respiratory papillomatosis (RRP) is a human papilloma virus (HPV) associated benign disease, which, in rare cases, can develop into lung squamous cell carcinoma. Treatment options are limited with no approved systemic adjuvant therapy and the disease requires frequent surgical resection to prevent airway obstruction. Therefore, expanding available treatment options remains a highly important, but unmet need in RRP. Herein, we present a case of RRP with squamous cell carcinoma of lung that demonstrated durable stable disease with nivolumab and subsequent bevacizumab. Case presentation: A 48-year-old woman with long standing RRP since teenager, who underwent multiple microsuspension laryngoscopies, debridements including laryngeal lesions, and ultimately, 5 years ago, video assisted thoracic surgery (VATS) resection of right upper lobe mass, confirming squamous cell carcinoma, has been managed with debulking surgery on tracheal lesions by ENT on regular basis. Nivolumab, a programmed death-1 blockade, 3 mg/kg every 2 weeks was started given squamous cell carcinoma of lung. Stable disease (SD) in lung lesions was achieved on nivolumab for one year but she required more frequent debulking of tracheal lesions. After multidisciplinary discussion with Otorhinolaryngology, she was started on bevacizumab, vascular endothelial growth factor inhibitor, 10 mg/kg every 6 weeks. Follow-up CT scans in 10 weeks showed a decrease in size of a left lower lobe mass to 27 mm from 32 mm in the previous image. After one year, administration of bevacizumab was spaced out to every 12 weeks. She requires less debulking surgery and the last debulking surgery was approximately 3 years ago. She maintains SD for over 4 years since starting bevacizumab. Discussion: Our patient with RRP and squamous cell carcinoma of lung demonstrated SD on nivolumab before she was switched to bevacizumab. In addition, her SD on bevacizumab of more than 4 years with 12 weeks of maintenance interval is encouraging as there is no current standard of care treatment for RRP. Despite difficulty in running clinical trials in RRP due to its rareness, additional studies evaluating the efficacy of PD-1 inhibitor or anti-VEGF monoclonal antibody on RRP are warranted. Citation Format: Horyun Choi, Jinah Kim, Yeun Ho Lee, Leeseul Kim, Young Kwang Chae. Durable stable disease with nivolumab, PD-1 inhibitor, and subsequent bevacizumab, Anti-VEGF monoclonal antibody, in long standing recurrent respiratory papillomatosis with lung squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4121.

Utilization of an Acellular Cartilage Matrix‐Based Photocrosslinking Hydrogel for Tracheal Cartilage Regeneration and Circumferential Tracheal Repair

AbstractAcellular cartilage matrix (ACM)‐based hydrogels hold promise for use in the context of tracheal cartilage regeneration owing to the ease with which they can be molded into specific shapes and their intrinsic cartilage‐specific microenvironmental properties. In this report, an acrylic anhydride‐modified ACM (Ac‐matrix) hydrogel is fabricated for utilization in the context of tracheal cartilage regeneration and circumferential tracheal repair. Hydrogels are successfully prepared with a range of Ac‐matrix concentrations (4%, 6%, and 8%) and found that mechanical strength increases with rising Ac‐matrix concentrations whereas swelling and degradation ratio values decline. These Ac‐matrix hydrogels exhibit satisfactory cytocompatibility when loaded with chondrocytes. Chondrocyte‐loaded 6% hydrogels are able to support cartilage formation both in vitro and in vivo across a range of chondrocyte densities (5, 10, 20, and 40 million chondrocytes per mL), with increasing density being conducive to more homogenous cartilage formation. A homogeneously tubular tracheal cartilage construct is additionally generated and supports circumferential tracheal reconstruction in a rabbit tracheal lesion model system, with a biological structure and function consistent with those of the native trachea. These results suggest that this Ac‐matrix hydrogel platform is well‐suited to use in the context of tracheal cartilage regeneration, thus offering the potential to support circumferential tracheal reconstruction.

Respiratory health of broilers following chronic exposure to airborne endotoxin

In and around poultry farms, high concentrations of endotoxins are found that have a negative impact on the health of farmers and local residents. However, little is known about the effects of chronic exposure to endotoxins on the health of poultry. The aim of this study was to identify effects of chronic exposure to airborne endotoxins (E. coli LPS) on the immune system, respiratory tract, disease susceptibility and welfare of broilers. Effects of high (HE) and low endotoxin (LE) concentrations on natural antibody titers (NAb), performance and behavior of broilers were determined. After treatment with a respiratory virus infection, infectious bronchitis virus (IBV), mRNA expression of cytokines and Toll-like receptor (TLR) 4 in the lung, tracheal ciliary activity and lesions in the respiratory tract were determined. Endotoxin affected the immune system and respiratory tract, where HE broilers tended to have lower IgM NAb binding Phosphorylcholine-conjugated to Bovine Serum Albumin, and higher interferon (IFN)-α mRNA expression and more lesions in the nasal tissue compared to LE broilers. Furthermore, HE broilers had higher TLR4 mRNA expression compared to LE broilers. However, endotoxin did not affect NAb levels binding Keyhole Limpet Hemocyanin, IFN-β and interleukin-10 mRNA expression, IBV replication or lesions in the lung and trachea. HE and LE broilers further had similar body weight, but HE broilers showed numerically more passive behavior compared to LE broilers. In conclusion, chronic exposure to high airborne endotoxin concentrations affects components of the immune system and respiratory tract in broilers and could therefore influence disease susceptibility.

Resection and reconstruction via median sternotomy incision for tracheal tumors.

BackgroundThe tracheal tumor is a rare disease with low incidence in the upper airway. Surgical resection and reconstruction are effective and radical treatments for such conditions, but the approaches vary depending on the tumor location. The current report tends to illustrate the clinical practice and advantage of the median sternotomy approach for treating tracheal tumors.MethodsWe summarized and demonstrated four cases of tracheal tumors patients who received tracheal resection and reconstruction via median sternotomy approach in our institute. Their clinical data and surgical procedures were also described. The follow-up would be carried on to monitor their prognosis after the operations.ResultsTwo patients with lower tracheal tumors involving carina received sternotomies, one with the tumor in cervical, thoracic junction, and the other one with thyroid carcinoma involving and extending to the thoracic trachea received half-sternotomies. The surgical procedures were completed smoothly with ideal surgical vision and sufficient operative space. Case 1 and 2 patients underwent tracheal-bronchial end-to-side anastomosis, while the other two patients received end-to-end anastomosis. The thymus and mediastinal tissue were used as the anastomotic buttress. They were discharged no more than 2 weeks after operations. Case 4 was suffered from aspiratory pneumonia and experienced prolonged intensive care unit (ICU) stay and antibiotic use. No other severe complications were recorded in other cases. No anastomotic dehiscence was observed in the postoperative bronchoscopy.ConclusionsTracheal resection and reconstruction via sternotomy or half-sternotomy is a practical approach for intrathoracic tracheal lesions. It facilitates a satisfying field and anastomosis procedure. The reported cases had ideal surgical outcomes. Although it is convenient in some specific cases, further studies are warranted for its safety and efficacy.

Cohen’s Comprehensive Thoracic Anesthesia

Cohen’s Comprehensive Thoracic Anesthesia

Progressive tension pneumomediastinum in an adult miniature schnauzer

AbstractA 1.5‐year‐old, female, spayed miniature schnauzer presented for a 1‐month history of progressive tachypnoea, exercise intolerance, weight loss and lethargy. Radiographs identified progressive pneumomediastinum and subcutaneous emphysema. Thoracic computed tomography confirmed the radiographic findings and did not show any underlying inciting aetiology. No oesophageal or tracheal lesions were identified during oesophagoscopy and tracheoscopy. No gross pathological lesions were visualised during the exploratory thoracotomy. The patient died 7 days following surgery. The final diagnosis was tension pneumomediastinum of uncertain aetiology. This case report highlights the imaging features of canine tension pneumomediastinum and the first documentation of the computed tomography imaging features.

Covid-19 associated mucormycosis

: Corona virus disease-2019 (COVID-19) is associated with various opportunistic, bacterial, and fungal infections. High risk groups include people with diabetes especially diabetic ketoacidosis, solid organ transplantation, long-term systemic corticosteroid use, and iron overload. Many cases of mucormycosis were reported worldwide. Mucormycosis is an invasive fungal infection with high morbidity and mortality. Early diagnosis and treatment with appropriate anti-fungals lead to improved outcomes. The aim of this study is to establish the factors associated with mucormycosis in a COVID-19 setting, like comorbidities and treatment protocols for treatment of COVID-19. The histological patterns and tissue reactions to mucormycosis also were studied. In patients with ongoing COVID-19 infection and in a post COVID-19 scenario, we studied the biopsy findings of mucormycosis in various sites like rhino-orbital, lung, gastric and trachea. Material for this study is from a tertiary care hospital in South India. Patient age ranged from 30 years to 74 years. Mean age of the patients was 51 years. Male to female ratio was 1:1.1. Tissue from sino- nasal mucosa, peri orbital tissue, exenterated eyeball, lung tissue and tissue from rare sites like gastric and tracheal mucosal lesions were also included in this study. Tissue was fixed in 10% buffered formalin. Routine Haematoxylin and Eosin(H&amp;E) stains were done. Gomori’s Methenamine silver (GMS) stains were done on all cases. Tissue was submitted for fungal cultures in all the cases.Total of twenty-three cases were diagnosed as mucormycosis based on the morphology and special stains in this analysis. Histology revealed areas of infarction in all cases with neutrophilic infiltration. Granulomatous reaction was seen in seven cases and melanin pigment was seen in two cases. 100% of patients were diabetics. There was neutrophilia in 100% of cases. Lymphopenia was seen in 85.7%, C-Reactive Protein (CRP) was elevated in 100% of cases.Ferritin was done in 14 patients and D-dimer was done in 17 patients and in all patients, these were elevated. All patients were treated with steroids according to the treatment protocol for COVID-19, Remdesivir was given in 72.7% of cases and second immunomodulator drugs like Tocilizumab in four cases and Baricitinib in one case.Mucormycosis is an emerging problem with COVID-19. It is important to carefully monitor blood glucose levels and take into account underlying medical conditions of patients before initiation of steroid therapy. Early recognition of symptoms and early diagnosis has a better outcome in patients with mucormycosis associated with COVID-19 infection.

Is HFJV a better alternative ventilation technique for percutaneous dilatational tracheostomy? A randomized trial.

High-frequency jet ventilation (HFJV) has been used for the treatment of tracheal lesions, airway surgery, and treatment of secondary lesions after tracheostomy for many years however, reports on the use of HFJV during percutaneous dilatational tracheostomy (PDT) are limited. This study compares the use of traditional method, ventilation with laryngeal mask airway (LMA), and HFJV through endotracheal tube (ETT) with respect to the duration of PDT procedure and complications. Seventy-five patients were randomized into one of the three groups with computer-generated random numbers: Group ETT (N.=25), group LMA (N.=25), and group HFJV (n=25). Demographic data, duration of PDT, complications such as ETT cuff puncture and tube transaction, accidental extubation, difficult cannula insertion, bleeding, desaturation during the procedure, arterial blood gases immediately before and after the procedure have been recorded. Mean time for successful PDT in group ETT was 5.9±1.35 minutes, in group LMA 4.96±0.78 minutes, and 3.88±0.78 minutes in group HFJV. PDT duration was shorter in the LMA group than in the ETT group (P<0.05). In the HFJV group, the PDT duration was shorter than the LMA group (P<0.05) and the ETT group (P<0.001). In terms of the total number of complications, significantly fewer complications were observed in the HFJV group compared with group ETT and group LMA. HFJV may be a more effective alternative method for airway management during PDT, facilitating and reducing the duration of the intervention.

Genetic and pathogenic characteristics of a novel infectious bronchitis virus strain in genogroup VI (CK/CH/FJ/202005)

Infectious bronchitis virus (IBV) has a significant impact on the poultry industry, and genogroup VI (GVI) IBVs, such as the TC07−2 strain, were reported in China since 2007. We isolated a novel strain, CK/CH/FJ/202005 (henceforth 202005), from broilers that were vaccinated with different attenuated IBV strains (H120, 4/91, or QX) in Fujian, China during 2020. Based on comparison with the SNU8065 strain (GI-22), the 1ab genes were the locations of recombination in this new isolate. Pathogenicity testing of 1-day-old and 15-day-old specific pathogen-free (SPF) chickens indicated varying severities of air sacculitis beginning 5 days-post-inoculation (DPI). Histopathological analysis indicated that tracheal lesions started at 5 DPI and persisted throughout the 30-day experiments in 1-day-old infected chickens. Virus re-isolation and viral load tests indicated this strain was mainly in the trachea, and not the kidneys. Our findings showed that the 202005 strain was pathogenic in 1-day-old and 15-day-old chickens. These results should be considered when developing strategies to control IBV infections.

Experimental Assessment of Cuff Pressures on the Walls of a Trachea-Like Model Using Force Sensing Resistors: Insights for Patient Management in Intensive Care Unit Settings.

The COVID-19 outbreak has increased the incidence of tracheal lesions in patients who underwent invasive mechanical ventilation. We measured the pressure exerted by the cuff on the walls of a test bench mimicking the laryngotracheal tract. The test bench was designed to acquire the pressure exerted by endotracheal tube cuffs inflated inside an artificial model of a human trachea. The experimental protocol consisted of measuring pressure values before and after applying a maneuver on two types of endotracheal tubes placed in two mock-ups resembling two different sized tracheal tracts. Increasing pressure values were used to inflate the cuff and the pressures were recorded in two different body positions. The recorded pressure increased proportionally to the input pressure. Moreover, the pressure values measured when using the non-armored (NA) tube were usually higher than those recorded when using the armored (A) tube. A periodic check of the cuff pressure upon changing the body position and/or when performing maneuvers on the tube appears to be necessary to prevent a pressure increase on the tracheal wall. In addition, in our model, the cuff of the A tube gave a more stable output pressure on the tracheal wall than that of the NA tube.