Nd-YAG Laser Treatment of Tracheal Stenosis

We administered Nd-YAG laser treatments in four patients aged 56 to 68 years for severe tracheal stenosis, the tracheal diameters varying between 2.5 and 5 mm. These patients were all dyspneic at rest with talking or dressing and their peak flows ranged from 8% to 36% of predicted. They were not felt to be candidates for surgical excision. Immediate palliative relief was achieved in all patients and lasted two to four months after a single treatment in three patients. One patient died three weeks after laser treatment due to respiratory failure from underlying emphysema. There were no complications of laser therapy. Postlaser therapy the tracheal diameter in each patient was at least 9 mm and peak flow improved to between 25% and 76% of predicted. The results suggest that laser treatment may be beneficial in cases of severe tracheal stenosis.     

Computed tomography and bronchoscopy in chest radiographically occult main-stem neoplasm diagnosis and Nd-YAG laser treatment in 8 patients.

We studied 8 adult patients with variable symptoms of cough, dyspnea, stridor, wheezing, or hemoptysis. Fiberoptic bronchoscopy in all showed complete or nearly complete endobronchial obstruction of a main-stem bronchus by neoplasm with a mean bronchial diameter of 1.9 mm +/- 1.6 mm (mean +/- standard deviation). In 4 patients, a lobar bronchus was also completely obstructed. No mass was visible on chest radiographs of any patient; however, computed tomography in each showed main-stem endobronchial obstruction, lobar obstruction (4 instances in 3 patients), and in 6 patients hypoperfusion of the involved lung. Computed tomographic scan showed additional abnormalities that were unsuspected on viewing chest radiographs or at bronchoscopy, including mediastinal adenopathy in 3 patients and an extraluminal tumor component in 4. After therapy with Nd-YAG laser, main-stem airway diameter increased to a mean of 9.6 mm +/- 1.0 mm (P less than .05) and pulmonary functions improved. Results suggest the complementary role of computed tomography and fiberoptic bronchoscopy in the detection and laser-treatment planning of chest radiographically occult severe neoplastic obstruction of the main-stem bronchus.     

Simultaneous LFA-1 and CD40 ligand antagonism prevents airway remodeling in orthotopic airway transplantation: implications for the role of respiratory epithelium as a modulator of fibrosis

Airway remodeling is a prominent feature of certain immune-mediated lung diseases such as asthma and chronic lung transplant rejection. Under conditions of airway inflammation, the respiratory epithelium may serve an important role in this remodeling process. Given the proposed role of respiratory epithelium in nonspecific injury models, we investigated the respiratory epithelium in an immune-specific orthotopic airway transplant model. MHC-mismatched tracheal transplants in mice were used to generate alloimmune-mediated airway lesions. Attenuation of this immune injury and alteration of antidonor reactivity were achieved by the administration of combined anti-LFA-1/anti-CD40L mAbs. By contrast, without immunotherapy, transplanted airways remodeled with a flattening of respiratory epithelium and significant subepithelial fibrosis. Unopposed alloimmune injury for 10 days was associated with subsequent epithelial transformation and subepithelial fibrosis that could not be reversed with immunotherapy. The relining of donor airways with recipient-derived epithelium was delayed with immunotherapy resulting in partially chimeric airways by 28 days. Partial chimerism was sufficient to prevent luminal fibrosis. However, epithelial chimerism was also associated with airway remodeling. Therefore, there appears to be an intimate relationship between the morphology and level of chimerism of the respiratory epithelium and the degree of airway remodeling following alloimmune injury.     

Upper airway and respiratory muscle responses to continuous negative airway pressure

To determine upper airway and respiratory muscle responses to nasal continuous negative airway pressure (CNAP), we quantitated the changes in diaphragmatic and genioglossal electromyographic activity, inspiratory duration, tidal volume, minute ventilation, and end-expiratory lung volume (EEL) during CNAP in six normal subjects during wakefulness and five during sleep. During wakefulness, CNAP resulted in immediate increases in electromyographic diaphragmatic and genioglossal muscle activity, and inspiratory duration, preserved or increased tidal volume and minute ventilation, and decreased EEL. During non-rapid-eye-movement and rapid-eye-movement sleep, CNAP was associated with no immediate muscle or timing responses, incomplete or complete upper airway occlusion, and decreased EEL. Progressive diaphragmatic and genioglossal responses were observed during non-rapid-eye-movement sleep in association with arterial O2 desaturation, but airway patency was not reestablished until further increases occurred with arousal. These results indicate that normal subjects, while awake, can fully compensate for CNAP by increasing respiratory and upper airway muscle activities but are unable to do so during sleep in the absence of arousal. This sleep-induced failure of load compensation predisposes the airways to collapse under conditions which threaten airway patency during sleep. The abrupt electromyogram responses seen during wakefulness and arousal are indicative of the importance of state effects, whereas the gradual increases seen during sleep probably reflect responses to changing blood gas composition.     

Reduction in airway hyperresponsiveness to methacholine by the application of RF energy in dogs.

We delivered controlled radio frequency energy to the airways of anesthetized, ventilated dogs to examine the effect of this treatment on reducing airway narrowing caused by a known airway constrictor. The airways of 11 dogs were treated with a specially designed bronchial catheter in three of four lung regions. Treatments in each of the three treated lung regions were controlled to a different temperature (55, 65, and 75 degrees C); the untreated lung region served as a control. We measured airway responsiveness to local methacholine chloride (MCh) challenge before and after treatment and examined posttreatment histology to 3 yr. Treatments controlled to 65 degrees C as well as 75 degrees C persistently and significantly reduced airway responsiveness to local MCh challenge (P < or = 0.022). Airway responsiveness (mean percent decrease in airway diameter after MCh challenge) averaged from 6 mo to 3 yr posttreatment was 79 +/- 2.2% in control airways vs. 39 +/- 2.6% (P < or = 0.001) for airways treated at 65 degrees C, and 26 +/- 2.7% (P < or = 0.001) for airways treated at 75 degrees C. Treatment effects were confined to the airway wall and the immediate peribronchial region on histological examination. Airway responsiveness to local MCh challenge was inversely correlated to the extent of altered airway smooth muscle observed in histology (r = -0.54, P < 0.001). We conclude that the temperature-controlled application of radio frequency energy to the airways can reduce airway responsiveness to MCh for at least 3 yr in dogs by reducing airway smooth muscle contractility.     

Laser treatment for carcinoma of the bronchus.

Laser treatment in carcinoma of the bronchus is essentially palliative and is suitable for only a few patients. Patients selected for laser treatment must have predominantly endobronchial growth with normal bronchial anatomy still identifiable and symptoms due to the obstruction or to haemoptysis. A total of 34 patients with carcinoma of the bronchus were treated with argon gas or neodynium yttrium aluminium garnet crystal lasers. Good palliation was obtained in just over half the cases of partial obstruction of the trachea or main bronchus, but best results were obtained in lesions of the trachea or main carina. Re-expansion of the collapsed lung was achieved in some cases but with considerable risk of pneumonia. Haemoptysis was controlled at least partly in several cases. Laser treatment has the advantage of having no toxicity or dose limit and may be used in cases of poor respiratory function. The procedure was better tolerated than radiotherapy or chemotherapy and its relatively lower cost may justify setting up laser units in major cities.     

Proteases and cystic fibrosis

Cystic fibrosis is the most common, inherited fatal disease in Caucasians. The major cause of morbidity and mortality is chronic lung disease due to infection and inflammation in the airways leading to bronchiectasis and respiratory failure. The signature pathologic features of CF lung disease including abnormal mucus obstructing airways, chronic infection with Staphylococcus aureus, Pseudomonas aeruginosa and other gram negative bacteria, and a robust neutrophil-dominant airway inflammation, are exacerbated by unopposed proteases present at high concentrations in the ASL. There is strong evidence that proteases, particularly neutrophil elastase, contribute to the pathology of CF by impairing mucociliary clearance, interfering with innate immune functions, and perpetuating neutrophilic inflammation. The mechanisms employed by proteases to impact airway function in CF will be reviewed.     

Assessment of heterogeneous airway constriction in dogs: a structure-function analysis

Obstructive lung diseases are often characterized by heterogeneous patterns of bronchoconstriction, although specific relationships between structural heterogeneity and lung function have yet to be established. We measured respiratory input impedance (Zrs) in eight anesthetized dogs using broadband forced oscillations at baseline and during intravenous methacholine (MCh) infusion. We also obtained high-resolution computed tomographic (HRCT) scans in 4 dogs and identified 20-30 individual airway segments in each animal. The Zrs spectra and HRCT images were obtained before and 5 min following a deep inspiration (DI) to 35 cmH(2)O. Each Zrs spectrum was fitted with two different models of the respiratory system: 1) a lumped airways model consisting of a single airway compartment, and 2) a distributed airways model incorporating a continuous distribution of airway resistances. For the latter, we found that the mean level and spread of airway resistances increased with MCh dose. Whereas a DI had no effect on average airway resistance during MCh infusion, it did increase the level of airway heterogeneity. At baseline and low-to-moderate doses of MCh, the lumped airways model was statistically more appropriate to describe Zrs in the majority of dogs. At the highest doses of MCh, the distributed airways model provided a superior fit in half of the dogs. There was a significant correlation between heterogeneity assessed with inverse modeling and the standard deviation of airway diameters obtained from HRCT. These data demonstrate that increases in airway heterogeneity as assessed with forced oscillations and inverse modeling can be linked to specific structural alterations in airway diameters.     

Airway epithelial cell inflammatory signalling in cystic fibrosis

Cystic fibrosis (CF) is the most common lethal monogenic disorder in Caucasians, estimated to affect one out of 2500-4000 new-borns. In patients with CF, lack of CF transmembrane conductance regulator (CFTR) Cl(-) channel function leads to progressive pulmonary damage and ultimately to death. Severe and persistent polymorphonuclear neutrophil-dominated endobronchial inflammation and chronic bacterial infection are characteristic hallmarks of CF lung disease. Whether CFTR dysfunction results directly in an increased predisposition to infection and whether inflammation arises independent of infection remains to be established. The loss of functional CFTR in airway epithelial cells promotes depletion and increased oxidation of the airway surface liquid. Activated neutrophils present in airways produce large amounts of proteases and reactive oxygen species (ROS). Together these changes are associated with diminished mucociliary clearance of bacteria, activation of epithelial cell signalling through multiple pathways, and subsequent hyperinflammatory responses in CF airways. The NF-kappaB pathway and Ca(2+) mobilization in airway epithelial cells are believed to be of key importance for control of lung inflammation through regulated production of mediators such as interleukin-8 that participate in recruitment and activation of neutrophils, modulation of apoptosis, and control of epithelial barrier integrity. In this review, the current understanding of the molecular mechanisms by which airway epithelial cells contribute to abnormal lung inflammation in CF, as well as the anti-inflammatory strategies that can be proposed are discussed.     

Airway pressures in an asymmetrically branched airway model of the dog respiratory system

A computer model of the mechanical properties of the dog respiratory system based on the asymmetrically branching airway model of Horsfield et al. (11) is described. The peripheral ends of this airway model were terminated by a lumped-parameter impedance representing gas compression in the alveoli, and lung and chest wall tissue properties were derived from measurements made in this laboratory. Using this model we predicted the respiratory system impedance and the distribution of pressures along the airways in the dog lung. Predicted total respiratory system impedances for frequencies between 4 and 64 Hz at three lung volumes were found to compare quite closely to measured impedances in dogs. Serial pressure distributions were found to be frequency-dependent and to result in higher pressures in the lung periphery than at the airway opening at some frequencies. The implications of this finding for high-frequency ventilation are discussed.     

Persistent airway hyperresponsiveness after neonatal viral bronchiolitis in rats.

Viral bronchiolitis in human infants has been associated with permanent changes in small airways and gas exchange and an increased incidence of hyperresponsive airways later in life. Respiratory infection by Sendai virus in neonatal rats also has been reported to cause permanent changes in lung morphology and increased numbers of bronchiolar mast cells and eosinophils. We evaluated pulmonary mechanics, gas exchange, and airway responsiveness in rats at 7 and 13-16 wk after neonatal Sendai virus infection. Rats from the virus group had lower arterial PO2 and increased total lung resistance compared with controls. There were no significant differences between groups for arterial PCO2, dynamic lung compliance, quasi-static respiratory system compliance, or vital capacity. Rats from the infected group were significantly more sensitive to aerosolized methacholine than were controls, although both virus and control groups became less sensitive with age. We conclude that neonatal Sendai virus infection in rats results in persistent alterations in lung function and airway responsiveness. This phenomenon may be valuable for the study of the relationships among airway inflammation, lung morphology, and airway hyperresponsiveness, and it may be relevant to human airway disease.     

Local small airway epithelial injury induces global smooth muscle contraction and airway constriction

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-μm diameter) in rat lung slices (～250-μm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ～70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.     

beta-Catenin is required for specification of proximal/distal cell fate during lung morphogenesis

The lungs are divided, both structurally and functionally, into two distinct components, the proximal airways, which conduct air, and the peripheral airways, which mediate gas exchange. The mechanisms that control the specification of these two structures during lung development are currently unknown. Here we show that beta-catenin signaling is required for the formation of the distal, but not the proximal, airways. When the gene for beta-catenin was conditionally excised in epithelial cells of the developing mouse lung prior to embryonic day 14.5, the proximal lung tubules grew and differentiated appropriately. The mice, however, died at birth because of respiratory failure. Analysis of the lungs by in situ hybridization and immunohistochemistry, using molecular markers of the epithelial and mesenchymal components of both proximal and peripheral airways, showed that the lungs were composed primarily of proximal airways. These observations establish, for the first time, both the sites and timing of specification of the proximal and peripheral airways in the developing lung, and that beta-catenin is one of the essential components of this specification.     

Regenerative growth of respiratory bronchioles in dogs

Loss of lung units due to pneumonectomy stimulates growth of the remaining lung. It is generally believed that regenerative lung growth involves only alveoli but not airways, a dissociated response termed "dysanaptic growth." We examined the structural response of respiratory bronchioles in immature dogs raised to maturity after right pneumonectomy. In another group of adult dogs, we also examined the effect of preventing mediastinal shift after right pneumonectomy on the response of respiratory bronchioles. In immature dogs after pneumonectomy, the volume of the remaining lung increased twofold, with no change in volume density, numerical density, or mean diameter of respiratory bronchiole, compared with that in the control lung. The number of respiratory bronchiole segments and branch points increased proportionally with lung volume. In adult dogs after pneumonectomy, prevention of mediastinal shift reduced lung strain at a given airway pressure, but lung expansion and regenerative growth of respiratory bronchiole were not eliminated. We conclude that postpneumonectomy lung growth is associated with proliferation of intra-acinar airways. The proportional growth of acinar airways and alveoli should optimize gas exchange of the regenerated lung by enhancing gas conductance and mixing efficiency within the acinus.     

Patient-Specific Modeling of Regional Antibiotic Concentration Levels in Airways of Patients with Cystic Fibrosis: Are We Dosing High Enough?

Background

Pseudomonas aeruginosa (Pa) infection is an important contributor to the progression of cystic fibrosis (CF) lung disease. The cornerstone treatment for Pa infection is the use of inhaled antibiotics. However, there is substantial lung disease heterogeneity within and between patients that likely impacts deposition patterns of inhaled antibiotics. Therefore, this may result in airways below the minimal inhibitory concentration of the inhaled agent. Very little is known about antibiotic concentrations in small airways, in particular the effect of structural lung abnormalities. We therefore aimed to develop a patient-specific airway model to predict concentrations of inhaled antibiotics and to study the impact of structural lung changes and breathing profile on local concentrations in airways of patients with CF.

Methods

In- and expiratory CT-scans of children with CF (5–17 years) were scored (CF-CT score), segmented and reconstructed into 3D airway models. Computational fluid dynamic (CFD) simulations were performed on 40 airway models to predict local Aztreonam lysine for inhalation (AZLI) concentrations. Patient-specific lobar flow distribution and nebulization of 75 mg AZLI through a digital Pari eFlow model with mass median aerodynamic diameter range were used at the inlet of the airway model. AZLI concentrations for central and small airways were computed for different breathing patterns and airway surface liquid thicknesses.

Results

In most simulated conditions, concentrations in both central and small airways were well above the minimal inhibitory concentration. However, small airways in more diseased lobes were likely to receive suboptimal AZLI. Structural lung disease and increased tidal volumes, respiratory rates and larger particle sizes greatly reduced small airway concentrations.

Conclusions

CFD modeling showed that concentrations of inhaled antibiotic delivered to the small airways are highly patient specific and vary throughout the bronchial tree. These results suggest that anti-Pa treatment of especially the small airways can be improved.     

Altered allergen-induced eosinophil trafficking and physiological dysfunction in airways with preexisting virus-induced injury

Although both asthmatics and allergic rhinitics develop an acute inflammatory response to lower airway allergen challenge, only asthmatics experience airway obstruction resulting from chronic environmental allergen exposure. Hypothesizing that asthmatic airways have an altered response to chronic allergic inflammation, we compared the effects of repeated low-level exposures to inhaled Alternaria extract in sensitized rats with preexisting chronic postbronchiolitis airway dysfunction versus sensitized controls with normal airways. Measurements of air space (bronchoalveolar lavage) inflammatory cells, airway goblet cells, airway wall collagen, airway wall eosinophils, airway alveolar attachments, and pulmonary physiology were conducted after six weekly exposures to aerosolized saline or Alternaria extract. Postbronchiolitis rats, but not those starting with normal airways, had persistent increases in airway wall eosinophils, goblet cell hyperplasia in small airways, and loss of lung elastic recoil after repeated exposure to aerosolized Alternaria extract. Despite having elevated airway wall eosinophils, the postbronchiolitis rats had no eosinophils in bronchoalveolar lavage at 5 days after the last allergen exposure, suggesting altered egression of tissue eosinophils into the air space. In conclusion, rats with preexisting airway pathology had altered eosinophil trafficking and allergen-induced changes in airway epithelium and lung mechanics that were absent in sensitized control rats that had normal airways before the allergen exposures.     

Effect of Parenchymal Stiffness on Canine Airway Size with Lung Inflation

Although airway patency is partially maintained by parenchymal tethering, this structural support is often ignored in many discussions of asthma. However, agonists that induce smooth muscle contraction also stiffen the parenchyma, so such parenchymal stiffening may serve as a defense mechanism to prevent airway narrowing or closure. To quantify this effect, specifically how changes in parenchymal stiffness alter airway size at different levels of lung inflation, in the present study, we devised a method to separate the effect of parenchymal stiffening from that of direct airway narrowing. Six anesthetized dogs were studied under four conditions: baseline, after whole lung aerosol histamine challenge, after local airway histamine challenge, and after complete relaxation of the airways. In each of these conditions, we used High resolution Computed Tomography to measure airway size and lung volume at five different airway pressures (0, 12, 25, 32, and 45 cm H₂O). Parenchymal stiffening had a protective effect on airway narrowing, a fact that may be important in the airway response to deep inspiration in asthma. When the parenchyma was stiffened by whole lung aerosol histamine challenge, at every lung volume above FRC, the airways were larger than when they were directly challenged with histamine to the same initial constriction. These results show for the first time that a stiff parenchyma per se minimizes the airway narrowing that occurs with histamine challenge at any lung volume. Thus in clinical asthma, it is not simply increased airway smooth muscle contraction, but perhaps a lack of homogeneous parenchymal stiffening that contributes to the symptomatic airway hyperresponsiveness.     

Influence of airway diameter and cell confluence on epithelial cell injury in an in vitro model of airway reopening.

Recent advances in the ventilation of patients with acute respiratory distress syndrome (ARDS), including ventilation at low lung volumes, have resulted in a decreased mortality rate. However, even low-lung volume ventilation may exacerbate lung injury due to the cyclic opening and closing of fluid-occluded airways. Specifically, the hydrodynamic stresses generated during airway reopening may result in epithelial cell (EpC) injury. We utilized an in vitro cell culture model of airway reopening to investigate the effect of reopening velocity, airway diameter, cell confluence, and cyclic closure/reopening on cellular injury. Reopening dynamics were simulated by propagating a constant-velocity air bubble in an adjustable-height parallel-plate flow chamber. This chamber was occluded with different types of fluids and contained either a confluent or a subconfluent monolayer of EpC. Fluorescence microscopy was used to quantify morphological properties and percentage of dead cells under different experimental conditions. Decreasing channel height and reopening velocity resulted in a larger percentage of dead cells due to an increase in the spatial pressure gradient applied to the EpC. These results indicate that distal regions of the lung are more prone to injury and that rapid inflation may be cytoprotective. Repeated reopening events and subconfluent conditions resulted in significant cellular detachment. In addition, we observed a larger percentage of dead cells under subconfluent conditions. Analysis of this data suggests that in addition to the magnitude of the hydrodynamic stresses generated during reopening, EpC morphological, biomechanical, and microstructural properties may also be important determinants of cell injury.     

Airway remodeling in asthma: clinical and functional correlates

Asthma is a chronic inflammatory disorder of the airways associated with bronchial hyperresponsiveness and permanent structural changes. Asthma can cause progressive lung impairment with a progressive decline of lung function leading to partially reversible or irreversible airway obstruction. These structural changes are called airway remodelling including loss of epithelial integrity, thickening of basement membrane, subepithelial fibrosis, goblet cell and submucosal gland enlargement, increase smooth muscle mass, decreased cartilage integrity and increased airway vascularity. These remodelling changes contribute to thickening of airway walls and consequently lead to airway narrowing, bronchial hyperresponsiveness, airway oedema and mucous hypersecretion. Airway remodelling is associated with a poorer clinical outcome among patients with asthma. Early diagnosis and prevention has the potential to decrease disease severity, to improve control and to prevent disease expression.     

Methacholine responsiveness of proximal and distal airways of monkeys and rats using videomicrometry.

Rat and monkey are species that are used in models of human airway hyperresponsiveness. However, the wall structures of rat and monkey airways are different from each other, with that of the monkey more closely resembling that of humans. We hypothesized that differences in wall structure would explain differences in airway responsiveness. Using videomicrometry, we measured airway luminal area in lung slices to compare proximal and distal airway responsiveness to methacholine in the rat and monkey. The airway type was then histologically identified. Proximal airways of the young rat and monkey were equally responsive to methacholine. In contrast, respiratory bronchioles of monkeys were less responsive than were their proximal bronchi, whereas the distal bronchioles of rats were more responsive than their proximal bronchioles. Both proximal and distal airways of younger monkeys were more responsive than those of older monkeys. Airway heterogeneity in young monkeys was greatest with regard to degree of airway closure of respiratory bronchioles. We conclude that responsiveness to methacholine varies with airway wall structure and location.