[Relationship between etiology and morphological classification of benign central airway stenosis and its prognosis].

Objectives: To analyze the relationship between etiology and morphological classification of benign central airway stenosis and its prognosis. Methods: We performed a retrospective study of the medical records of 453 patients initially diagnosed with benign airway stenosis at Department of Respiratory Diseases in Beijing Tiantan Hospital affiliated to Capital Medical University from January 2003 to October 2019. Of 453 patients, 260 were male. The age of the study population was 12-86(44.0±24.5) years. Results: Among the 453 patients diagnosed with benign central airway stenosis, 161 case (35.5%, including 113 post-tracheostomy tracheal stenosis and 48 post-intubation tracheal stenosis) were iatrogenic; 88 cases were from benign tumors (19.4%), 77 cases from tracheal or bronchial tuberculosis (17.0%), 71 case from tracheal foreign bodies (15.7%). Disease causes varied among different gender or age groups. The main type of stenosis was structural stenosis, of which 241 cases (53.2%) were intra-luminal and 183 cases (40.4%) were scar contracture type. The site of stenosis showed a certain relationship with the causes of stenosis. The stenosis degree was mainly from grade 2 to grade 4 (76.4%), and the length was mainly within 3 cm (84.8%). Single factor analysis on the relationship between disease cause, morphological classification and prognosis of benign central airway stenosis showed statistically better prognosis in groups that were caused by benign tumor, intraductal stenosis or stenosis that were 3-4 in degree and 1-2 degree in length. Conclusion: The common causes of central airway stenosis included iatrogenic stenosis, benign tumor, tracheal or bronchial tuberculosis and tracheal foreign bodies. Benign airway stenosis with different disease causes and morphological classification had different prognosis after bronchoscopic interventional treatment. Clinicians should know the disease causes, morphological characterization and risk factors for benign airway stenosis for earlier diagnosis, treatment or prevention.

[Efficacy and safety of Montgomery T-tube placement for benign complex subglottic tracheal stenosis: a retrospective analysis of 29 cases].

Objective: To analyze the efficacy and safety of Montgomery T-tube (T-tube) placement for benign complex subglottic tracheal stenosis. Methods: A retrospective analysis of the clinical data of 29 patients with benign complex subglottic tracheal stenosis receiving T-tube placement in Beijing Tiantan Hospital from May 2015 to December 2019. The causes were postintubation tracheal stenosis [27 cases (93.1%), including 21 cases (72.4%) of tracheal stenosis after tracheotomy, 6 cases (20.7%) of tracheal stenosis after tracheal intubation], cervical post-traumatic tracheal stenosis (1 case, 3.4%) and tuberculous tracheal stenosis (1 case, 3.4%), respectively. Three-dimensional reconstruction of tracheal computerized tomography (CT) and bronchoscopy were used to grade the stenosis according to Cotton-Myer classification system before bronchoscopic intervention. The degree of stenosis was Cotton-Myer grade Ⅱ (7 cases, 24.1%), grade Ⅲ (11 cases, 37.9%) and grade Ⅳ (11 cases, 37.9%), respectively. All cases received placement of T-tubes and follow-up. Fisher's exact test was used for comparison between groups. Results: T-tube placement was performed 39 times in 29 patients. T-tubes were successfully placed for 24 cases (82.8%). The main complication during the operation was tracheal mucosal tear (6 cases, 20.7%), which resolved in all cases within 2 weeks. The main postoperative complication was secretion retention (27 cases, 93.1%), which was relieved after home nebulization treatment in 26 cases; and followed by granulation hyperplasia, especially located in T-tube upper margin (12 cases, 41.4%), of which 8 cases were cured after bronchoscopic intervention. None of the patients had T-tube migration. There were no statistically significant differences in the success rate of T-tube placement and the incidence of major complications in patients with benign complex subglottic tracheal stenosis with different degrees of stenosis. After 18 months to 24 months of follow-up, attempt was made to remove the T-tube in 9 patients but failed in 4 patients. The failure was due to collapse of the airway after the T-tube was removed. Conclusion: T-tube placement is a safe and reliable treatment for benign complex subglottic tracheal stenosis with high efficiency and manageable complications.

The dynamic process and microscopic mechanism of extraordinary terahertz transmission through perforated superconducting films.

Superconductor is a compelling plasmonic medium at terahertz frequencies owing to its intrinsic low Ohmic loss and good tuning property. However, the microscopic physics of the interaction between terahertz wave and superconducting plasmonic structures is still unknown. In this paper, we conducted experiments of the enhanced terahertz transmission through a series of superconducting NbN subwavelength hole arrays, and employed microscopic hybrid wave model in theoretical analysis of the role of hybrid waves in the enhanced transmission. The theoretical calculation provided a good match of experimental data. In particular, we obtained the following results. When the width of the holes is far below wavelength, the enhanced transmission is mainly caused by localized resonance around individual holes. On the contrary, when the holes are large, hybrid waves scattered by the array of holes dominate the extraordinary transmission. The surface plasmon polaritions are proved to be launched on the surface of superconducting film and the excitation efficiency increases when the temperature approaches critical temperature and the working frequency goes near energy gap frequency. This work will enrich our knowledge on the microscopic physics of extraordinary optical transmission at terahertz frequencies and contribute to developing terahertz plasmonic devices.

Low-loss terahertz metamaterial from superconducting niobium nitride films.

This paper reports a type of low Ohmic loss terahertz (THz) metamaterials made from low-temperature superconducting niobium nitride (NbN) films. Its resonance properties are studied by THz time domain spectroscopy. Our experiments show that its unloaded quality factor reaches as high as 178 at 8 K with the resonance frequency at around 0.58 THz, which is about 24 times that of gold metamaterial at the same temperature. The unloaded quality factor keeps at a high level, above 90, even when the resonance frequency increases to 1.02 THz, which is close to the gap frequency of NbN film. All these experimental observations fit well into the framework of Bardeen-Copper-Schrieffer theory and equivalent circuit model. These new metamaterials offer an efficient way to the design and implementation of high performance THz electronic devices.

Anomalous coherence peak in the microwave conductivity of c-axis oriented MgB2 thin films.

The temperature dependence of the real part of the microwave complex conductivity at 17.9 GHz obtained from surface impedance measurements of two c-axis oriented MgB2 thin films reveals a pronounced maximum at a temperature around 0.6 times the critical temperature. Calculations in the frame of a two-band model based on Bardeen-Cooper-Schrieffer (BCS) theory suggest that this maximum corresponds to an anomalous coherence peak resembling the two-gap nature of MgB2. Our model assumes there is no interband impurity scattering and a weak interband pairing interaction, as suggested by band structure calculations. In addition, the observation of a coherence peak indicates that the pi band is in the dirty limit and dominates the total conductivity of our films.