In vivo evaluation of the effectiveness of bronchial thermoplasty with computed tomography

Effect of bronchial thermoplasty on static and dynamic lung compliance and resistance in patients with severe persistent asthma

RATIONALE

Bronchial thermoplasty (BT) reduces severity and frequency of bronchoconstriction and symptoms in severe, persistent asthmatics although it is usually not associated with change in spirometric variables. Other than spirometry. there are almost no data on changes in lung mechanics following BT.

OBJECTIVE

To assess lung static and dynamic lung compliance (Cst,L and Cdyn,L, respectively) and static and dynamic lung resistance (Rst,L and Rdyn,L, respectively) before and after BT in severe asthmatics using the esophageal balloon technique.

METHODS

Rdyn,L and Cdyn,L were measured at respiratory frequencies up to 145 breaths/min, using the esophageal balloon technique in 7 patients immediately before and 12-50 weeks after completing a series of 3 BT sessions.

RESULTS

All patients experienced improved symptoms within a few weeks following completion of BT. Pre-BT, all patients exhibited frequency dependency of lung compliance, with mean Cdyn,L decreasing to 63% of Cst,L at maximum respiratory rates. Post-BT, Cst,L did not change significantly from pre-thermoplasty values, while Cdyn,L diminished to 62%% of Cst,L. In 4 of 7 patients, post-BT values of Cdyn,L were consistently higher than pre-BT over the range of respiratory rates. RL in 4 of 7 patients during quiet breathing and at higher respiratory frequencies decreased following BT.

CONCLUSIONS

Patients with severe persistent asthma exhibit increased resting lung resistance and frequency dependence of compliance, the magnitudes of which are ameliorated in some patients following bronchial thermoplasty and associated with variable change in frequency dependence of lung resistance. These findings are related to asthma severity and may be related to the heterogeneous and variable nature of airway smooth muscle modeling and its response to BT.

Response of individual airways in vivo to bronchial thermoplasty

Bronchial thermoplasty (BT) is a treatment for moderate-to-severe asthma, which generally improves quality-of-life scores but not conventional measures of lung function. Newer methodologies have begun to demonstrate the underlying physiological changes and elucidate the mechanism of action. We postulated that systematic, computed tomography (CT)-based assessment of the response of individual airways to BT is feasible, and our aim was to determine the distribution of these responses and the relationship with airway size. Twenty patients meeting the European Respiratory Society/American Thoracic Society (ERS/ATS) definition of severe asthma underwent BT and assessment including CT, Asthma Control Questionnaire (ACQ), and spirometry. Treatment was structured so that the left and right lungs are treated sequentially with a midtreatment assessment providing an internal control. Pairs of CT scans were analyzed using a new semiautomatic processing algorithm that matched individual segmented airways for quantitative comparison. Cross-sectional airway lumen area from matched airway pairs in treated lungs increased on average by 6.4% after BT (P < 0.02) but showed no change in the untreated lung. Matched airway length was also unchanged. Breakdown by airway size showed amplified response in more distal airways, with the smallest quintile of measured airways dilating by 13.2% (P < 0.001). ACQ improved from 3.5 ± 0.9 to 1.9 ± 1.2 (P < 0.001). These data show that the response to BT in individual airways can be assessed by CT and that dilation is heterogeneous and predominant in distal compared with proximal airways. A CT-based approach may further our understanding of the physiological changes in BT and aid in the development of refined and personalized versions of the therapy.NEW & NOTEWORTHY CT scanning was used to evaluate the response of individual airways in patients undergoing bronchial thermoplasty. Airways dilated after treatment by 6.4% on average with substantial heterogeneity and a greater response in the most distal airways measured.

Treatment options in type-2 low asthma

Monoclonal antibodies targeting IgE or the type-2 cytokines interleukin (IL)-4, IL-5 and IL-13 are proving highly effective in reducing exacerbations and symptoms in people with severe allergic and eosinophilic asthma, respectively. However, these therapies are not appropriate for 30-50% of patients in severe asthma clinics who present with non-allergic, non-eosinophilic, "type-2 low" asthma. These patients constitute an important and common clinical asthma phenotype, driven by distinct, yet poorly understood pathobiological mechanisms. In this review we describe the heterogeneity and clinical characteristics of type-2 low asthma and summarise current knowledge on the underlying pathobiological mechanisms, which includes neutrophilic airway inflammation often associated with smoking, obesity and occupational exposures and may be driven by persistent bacterial infections and by activation of a recently described IL-6 pathway. We review the evidence base underlying existing treatment options for specific treatable traits that can be identified and addressed. We focus particularly on severe asthma as opposed to difficult-to-treat asthma, on emerging data on the identification of airway bacterial infection, on the increasing evidence base for the use of long-term low-dose macrolides, a critical appraisal of bronchial thermoplasty, and evidence for the use of biologics in type-2 low disease. Finally, we review ongoing research into other pathways including tumour necrosis factor, IL-17, resolvins, apolipoproteins, type I interferons, IL-6 and mast cells. We suggest that type-2 low disease frequently presents opportunities for identification and treatment of tractable clinical problems; it is currently a rapidly evolving field with potential for the development of novel targeted therapeutics.

The effect of bronchial thermoplasty on airway volume measured 12 months post-procedure

Bronchial thermoplasty induces atrophy of the airway smooth muscle layer, but the mechanism whereby this improves patient health is unclear. In this study, we use computed tomography (CT) to evaluate the effects of bronchial thermoplasty on airway volume 12 months post-procedure. 10 consecutive patients with severe asthma were evaluated at baseline by the Asthma Control Questionnaire (ACQ), and high-resolution CT at total lung capacity (TLC) and functional residual capacity (FRC). The CT protocol was repeated 4 weeks after the left lung had been treated by bronchial thermoplasty, but prior to right lung treatment, and then again 12 months after both lungs were treated. The CT data were also used to model the implications of including the right middle lobe (RML) in the treatment field. The mean patient age was 62.7±7.7 years and forced expiratory volume in 1 s (FEV₁) 42.9±11.5% predicted. 12 months post-bronchial-thermoplasty, the ACQ improved, from 3.4±1.0 to 1.5±0.9 (p=0.001), as did the frequency of oral steroid-requiring exacerbations (p=0.008). The total airway volume increased 12 months after bronchial thermoplasty in both the TLC (p=0.03) and the FRC scans (p=0.02). No change in airway volume was observed in the untreated central airways. In the bronchial thermoplasty-treated distal airways, increases in airway volume of 38.4±31.8% at TLC (p=0.03) and 30.0±24.8% at FRC (p=0.01) were observed. The change in distal airway volume was correlated with the improvement in ACQ (r=-0.71, p=0.02). Modelling outputs demonstrated that treating the RML conferred no additional benefit. Bronchial thermoplasty induces long-term increases in airway volume, which correlate with symptomatic improvement.

Bronchial thermoplasty: Redefining its role

In this review, we trace (i) the origins of bronchial thermoplasty, (ii) the development of a solid evidence base for efficacy and safety, (iii) the emerging understanding of the pathophysiological mechanisms of action and (iv) the place in therapy today. Future challenges are then discussed.

Unraveling a Clinical Paradox: Why Does Bronchial Thermoplasty Work in Asthma?

Bronchial thermoplasty is a relatively new but seemingly effective treatment in subjects with asthma who do not respond to conventional therapy. Although the favored mechanism is ablation of the airway smooth muscle layer, because bronchial thermoplasty treats only a small number of central airways, there is ongoing debate regarding its precise method of action. Our aim in the present study was to elucidate the underlying method of action behind bronchial thermoplasty. We employed a combination of extensive human lung specimens and novel computational methods. Whole left lungs were acquired from the Prairie Provinces Fatal Asthma Study. Subjects were classified as control (n = 31), nonfatal asthma (n = 32), or fatal asthma (n = 25). Simulated lungs for each group were constructed stochastically, and flow distributions and functional indicators (e.g., resistance) were quantified both before and after a 75% reduction in airway smooth muscle in the "thermoplasty-treated" airways. Bronchial thermoplasty triggered global redistribution of clustered flow patterns wherein structural changes to the treated central airways led to a reopening cascade in the small airways and significant improvement in lung function via reduced spatial heterogeneity of flow patterns. This mechanism accounted for progressively greater efficacy of thermoplasty with both severity of asthma and degree of muscle activation, broadly consistent with existing clinical findings. We report a probable mechanism of action for bronchial thermoplasty: alteration of lung-wide flow patterns in response to structural alteration of the treated central airways. This insight could lead to improved therapy via patient-specific, tailored versions of the treatment-as well as to implications for more conventional asthma therapies.

Patient-specific targeted bronchial thermoplasty: predictions of improved outcomes with structure-guided treatment

Bronchial thermoplasty is a recent treatment for asthma in which ablative thermal energy is delivered to specific large airways according to clinical guidelines. Therefore, current practice is effectively "blind," as it is not informed by patient-specific data. The present study seeks to establish whether a patient-specific approach based on structural or functional patient data can improve outcomes and/or reduce the number of procedures required for clinical efficacy. We employed a combination of extensive human lung specimens and novel computational methods to predict bronchial thermoplasty outcomes guided by structural or functional data compared with current clinical practice. Response to bronchial thermoplasty was determined from changes in airway responses to strong bronchoconstrictor simulations and flow heterogeneity after one or three simulated thermoplasty procedures. Structure-guided treatment showed significant improvement over current unguided clinical practice, with a single session of structure-guided treatment producing improvements comparable with three sessions of unguided treatment. In comparison, function-guided treatment did not produce a significant improvement over current practice. Structure-guided targeting of bronchial thermoplasty is a promising avenue for improving therapy and reinforces the need for advanced imaging technologies. The functional imaging-guided approach is predicted to be less effective presently, and we make recommendations on how this approach could be improved. NEW & NOTEWORTHY Bronchial thermoplasty is a recent treatment for asthma in which thermal energy is delivered via bronchoscope to specific airways in an effort to directly target airway smooth muscle. Current practice involves the treatment of a standard set of airways, unguided by patient-specific data. We consider the potential for guided treatments, either by functional or structural data from the lung, and show that treatment guided by structural data has the potential to improve clinical practice.

Bronchial thermoplasty as a treatment for severe asthma: controversies, progress and uncertainties

INTRODUCTION

Bronchial thermoplasty is a licensed non-pharmacological treatment for severe asthma. Area covered: This article considers evidence for the efficacy and safety of bronchial thermoplasty from clinical trials and observational studies in clinical practice. Its place in the management of severe asthma, predictors of response and mechanisms of action are reviewed. Expert commentary: Bronchial thermoplasty improves quality of life and reduces exacerbations in moderate to severe asthma. Morbidity from asthma is increased during treatment. Overall, patients treated in clinical practice have worse baseline characteristics and comparable clinical outcomes to trial data. Follow-up studies provide reassurance on long-term safety. Despite some progress, future research needs to investigate uncertainties about predictors of response, mechanism of action and place in management of asthma.

Early computed tomography modifications following bronchial thermoplasty in patients with severe asthma

Bronchial thermoplasty (BT) is a recent, promising and well-tolerated technique for the treatment of severe asthma. By delivering thermal energy to the airway wall, this procedure can induce early pulmonary opacities seen on computed tomography (CT). We aimed to examine early CT modifications induced by BT and to determine their association with respiratory symptoms.Unenhanced chest CT was performed the day after each BT session in 13 patients with severe asthma, leading to the examination of 38 treated lobes. A total of 15 BT-treated lobes were evaluated in 11 patients at 1 month. The first two patients also underwent CT at 1 week.No symptoms suggestive of pulmonary infection were noted following BT in any patient. Peribronchial consolidations and ground-glass opacities were observed in all treated lobes on day 1, with three lower lobes showing complete collapse. Mild involvement of an adjacent untreated lobe was observed in 12 out of 38 (32%) cases. Opacities had decreased in 5 out of 15 (33%) and disappeared in 10 out of 15 (67%) at 1 month.BT induced early pulmonary peribronchial hyperdensities in all treated lobes. These alterations were unrelated to clinical symptoms and spontaneously decreased or disappeared after 1 month.

Acute administration of ivacaftor to people with cystic fibrosis and a G551D-CFTR mutation reveals smooth muscle abnormalities

BACKGROUND

Airflow obstruction is common in cystic fibrosis (CF), yet the underlying pathogenesis remains incompletely understood. People with CF often exhibit airway hyperresponsiveness, CF transmembrane conductance regulator (CFTR) is present in airway smooth muscle (ASM), and ASM from newborn CF pigs has increased contractile tone, suggesting that loss of CFTR causes a primary defect in ASM function. We hypothesized that restoring CFTR activity would decrease smooth muscle tone in people with CF.

METHODS

To increase or potentiate CFTR function, we administered ivacaftor to 12 adults with CF with the G551D-CFTR mutation; ivacaftor stimulates G551D-CFTR function. We studied people before and immediately after initiation of ivacaftor (48 hours) to minimize secondary consequences of CFTR restoration. We tested smooth muscle function by investigating spirometry, airway distensibility, and vascular tone.

RESULTS

Ivacaftor rapidly restored CFTR function, indicated by reduced sweat chloride concentration. Airflow obstruction and air trapping also improved. Airway distensibility increased in airways less than 4.5 mm but not in larger-sized airways. To assess smooth muscle function in a tissue outside the lung, we measured vascular pulse wave velocity (PWV) and augmentation index, which both decreased following CFTR potentiation. Finally, change in distensibility of <4.5-mm airways correlated with changes in PWV.

CONCLUSIONS

Acute CFTR potentiation provided a unique opportunity to investigate CFTR-dependent mechanisms of CF pathogenesis. The rapid effects of ivacaftor on airway distensibility and vascular tone suggest that CFTR dysfunction may directly cause increased smooth muscle tone in people with CF and that ivacaftor may relax smooth muscle.

FUNDING

This work was funded in part from an unrestricted grant from the Vertex Investigator-Initiated Studies Program.

Bronchial thermoplasty: a new therapeutic option for the treatment of severe, uncontrolled asthma in adults

Bronchial thermoplasty is a young yet promising treatment for severe asthma whose benefit for long-term asthma control outweighs the short-term risk of deterioration and hospitalisation in the days following the treatment. It is an innovative treatment whose clinical efficacy and safety are beginning to be better understood. Since this is a device-based therapy, the overall evaluation of risk-benefit is unlike that of pharmaceutical products; safety aspects, regulatory requirements, study design and effect size assessment may be unfamiliar. The mechanisms of action and optimal patient selection need to be addressed in further rigorous clinical and scientific studies. Bronchial thermoplasty fits in perfectly with the movement to expand personalised medicine in the field of chronic airway disorders. This is a device-based complimentary asthma treatment that must be supported and developed in order to meet the unmet needs of modern severe asthma management. The mechanisms of action and the type of patients that benefit from bronchial thermoplasty are the most important challenges for bronchial thermoplasty in the future.

Bronchial thermoplasty: a non-pharmacological approach

INTRODUCTION

Asthma is a chronic inflammatory disorder of the airway characterized by the episodic symptoms of breathlessness, wheezes and cough. Even with the use of maximum anti-asthmatic pharmacological treatment sometimes it remains uncontrolled. For such patients, bronchial thermoplasty is the new mode of treatment.

OBJECTIVE

To review published article on bronchial thermoplasty.

METHODS

We identified 102 English articles on PubMed, and 56 were excluded by the abstract. The remaining articles were retrieved for full-text detailed evaluation by authors, and 28 relevant articles were selected for final review.

RESULTS

Bronchial thermoplasty is the radiofrequency ablation of the airway smooth muscle with the help of flexible fiberoptic bronchoscope. It reduces the smooth muscle mass of the bronchial wall and decreases its contractility.

CONCLUSION

Bronchial thermoplasty causes improvement in the quality of life, and causes reduction in the emergency room visit and exacerbation due to asthma. Long-term safety has been established by various prospective studies.

Bronchial thermoplasty in asthma: current perspectives

Bronchial thermoplasty (BT) is a novel therapy for patients with severe asthma. Using radio frequency thermal energy, it aims to reduce the airway smooth muscle mass. Several clinical trials have demonstrated improvements in asthma-related quality of life and a reduction in the number of exacerbations following treatment with BT. In addition, recent data has demonstrated the long-term safety of the procedure as well as sustained improvements in rates of asthma exacerbations, reduction in health care utilization, and improved quality of life. Further study is needed to elucidate the underlying mechanisms that result in these improvements. In addition, improved characterization of the asthma subphenotypes likely to exhibit the largest clinical benefit is a critical step in determining the precise role of BT in the management of severe asthma.

Critical review of bronchial thermoplasty: where should it fit into asthma therapy?

Bronchial thermoplasty is a device-based therapy for treatment of severe refractory asthma that uses radiofrequency energy to reduce airway smooth muscle and decrease bronchoconstriction. BT improves quality of life and decreases the rate of severe exacerbations with no known major long-term complications. The effectiveness of bronchial thermoplasty persists at least 5 years after the treatment is completed. Further investigation is needed to better define the specific subpopulation of patients with severe asthma who would best benefit from this treatment.

Bronchial thermoplasty for moderate or severe persistent asthma in adults

BACKGROUND

Bronchial thermoplasty is a procedure that consists of the delivery of controlled radiofrequency-generated heat via a catheter inserted into the bronchial tree of the lungs through a flexible bronchoscope. It has been suggested that bronchial thermoplasty works by reducing airway smooth muscle, thereby reducing the ability of the smooth muscle to bronchoconstrict. This treatment could then reduce asthma symptoms and exacerbations, resulting in improved asthma control and quality of life.

OBJECTIVES

To determine the efficacy and safety of bronchial thermoplasty in adults with bronchial asthma.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register of Trials (CAGR) up to January 2014.

SELECTION CRITERIA

We included randomised controlled clinical trials that compared bronchial thermoplasty versus any active control in adults with moderate or severe persistent asthma. Our primary outcomes were quality of life, asthma exacerbations and adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed risk of bias.

MAIN RESULTS

We included three trials (429 participants) with differences regarding their design (two trials compared bronchial thermoplasty vs medical management and the other compared bronchial thermoplasty vs a sham intervention) and participant characteristics; one of the studies included participants with more symptomatic asthma compared with the others.The pooled analysis showed improvement in quality of life at 12 months in participants who received bronchial thermoplasty that did not reach the threshold for clinical significance (3 trials, 429 participants; mean difference (MD) in Asthma Quality of Life Questionnaire (AQLQ) scores 0.28, 95% confidence interval (CI) 0.07 to 0.50; moderate-quality evidence). Measures of symptom control showed no significant differences (3 trials, 429 participants; MD in Asthma Control Questionnaire (ACQ) scores -0.15, 95% CI -0.40 to 0.10; moderate-quality evidence). The risk of bias for these outcomes was high because two of the studies did not have a sham intervention for the control group.The results from two trials showed a lower rate of exacerbation after 12 months of treatment for participants who underwent bronchial thermoplasty. The trial with sham intervention showed a significant reduction in the proportion of participants visiting the emergency department for respiratory symptoms, from 15.3% on sham treatment to 8.4% over 12 months following thermoplasty. The trials showed no significant improvement in pulmonary function parameters (with the exception of a greater increase in morning peak expiratory flow (PEF) in one trial). Treated participants who underwent bronchial thermoplasty had a greater risk of hospitalisation for respiratory adverse events during the treatment period (3 trials, 429 participants; risk ratio 3.50, 95% CI 1.26 to 9.68; high-quality evidence), which represents an absolute increase from 2% to 8% (95% CI 3% to 23%) over the treatment period. This means that six of 100 participants treated with thermoplasty (95% CI 1 to 21) would require an additional hospitalisation over the treatment period. No significant difference in the risk of hospitalisation was noted at the end of the treatment period.Bronchial thermoplasty was associated with an increase in respiratory adverse events, mainly during the treatment period. Most of these events were mild or moderate, appeared in the 24-hour post-treatment period, and were resolved within a week.

AUTHORS' CONCLUSIONS

Bronchial thermoplasty for patients with moderate to severe asthma provides a modest clinical benefit in quality of life and lower rates of asthma exacerbation, but no significant difference in asthma control scores. The quality of life findings are at risk of bias, as the main benefits were seen in the two studies that did not include a sham treatment arm. This procedure increases the risk of adverse events during treatment but has a reasonable safety profile after completion of the bronchoscopies. The overall quality of evidence regarding this procedure is moderate. For clinical practice, it would be advisable to collect data from patients systematically in independent clinical registries. Further research should provide better understanding of the mechanisms of action of bronchial thermoplasty, as well as its effect in different asthma phenotypes or in patients with worse lung function.

Bronchial thermoplasty

Bronchial thermoplasty is a relatively new therapy for the management of severe asthma. It involves the direct bronchoscopic application of thermal energy to airways by a catheter-directed expandable basket. The airways of the lower and upper lobes are treated in 3 separate sessions spaced 3 weeks apart. The therapy targets airway smooth muscle, with studies showing a decrease in airway smooth muscle after bronchial thermoplasty therapy. After therapy, an improvement in quality of life and decrease in asthma exacerbations can be expected. Adverse events can occur with bronchial thermoplasty and careful patient selection is critical to ensure benefits outweigh the potential risks.

Bronchial thermoplasty: a new treatment paradigm for severe persistent asthma

Patients with severe asthma represent only a minority of the total asthma population; however, they account for the majority of the mortality, morbidity, and health care-related cost of this chronic illness. Bronchial thermoplasty is a novel treatment modality that employs radiofrequency energy to alter the smooth muscles of the airways. This therapy represents a radical change in our treatment paradigm from daily repetitive dosing of medications to a truly long-term and potentially permanent attenuation of perhaps the most feared component of asthma--smooth muscle-induced bronchospasm. A large, multicentered, double-blinded, randomized controlled trial employed the unprecedented (but now industry standard for bronchoscopic studies) approach of using sham bronchoscopy as a control. It demonstrated that bronchial thermoplasty is safe, improved quality of life, and decreased frequency of severe exacerbations in the treatment group compared to the control group. Although the mechanism of action of bronchial thermoplasty is not currently completely understood, it should be considered as a valid and potentially valuable option for patients who have severe persistent asthma and who remain symptomatic despite inhaled corticosteroids and long-acting beta-2 agonists. Such patients should however be carefully evaluated at centers with expertise in managing severe asthma patients and with physicians who have experience with this promising new treatment modality.

Bronchial thermoplasty for severe asthma

PURPOSE OF REVIEW

Bronchial thermoplasty, which involves the delivery of radio frequency energy to the airways to reduce airway smooth muscle mass, has been recently introduced for the treatment of severe asthma. This review summarizes the preclinical development, efficacy and adverse effects of bronchial thermoplasty. In addition, the potential mechanisms of action and place in management of severe asthma are discussed.

RECENT FINDINGS

The efficacy and adverse profile of bronchial thermoplasty has been assessed in three randomized controlled trials, the first two of which showed clinical benefits of bronchial thermoplasty compared with usual care in patients with moderate or severe asthma. The third trial reports the results of a comparison with sham bronchial thermoplasty in 288 adults with severe asthma. Bronchial thermoplasty improved asthma quality of life questionnaire scores compared with sham bronchial thermoplasty; in the posttreatment period, there were fewer severe exacerbations and emergency department visits. Bronchial thermoplasty causes short-term increases in asthma-related morbidity. Follow-up data to date support the long-term safety of the procedure.

SUMMARY

Bronchial thermoplasty has a role in the management of patients with severe asthma who have uncontrolled symptoms despite current therapies. Future studies need to identify factors that predict a beneficial clinical response.

Bronchial thermoplasty for severe asthma

Bronchial thermoplasty (BT) is a novel treatment of patients with severe asthma who continue to be symptomatic despite maximal medical treatment. It aims to reduce the smooth muscle mass in the airways by delivering controlled thermal energy to the airway walls during a series of three bronchoscopies. Randomized controlled clinical trials of BT in severe asthma have not been able to show a reduction in airway hyperresponsiveness or change in FEV(1) but have suggested an improvement in quality of life, as well as a reduction in the rate of severe exacerbations, emergency department visits, and days lost from school or work. Strict inclusion and exclusion criteria of these trials resulted in the elimination of patients with severe asthma who experienced more than three exacerbations per year. Therefore, the generalizability of this treatment to the broader severe asthma population still needs to be determined. The short-term adverse events consist primarily of airway inflammation and occasionally more severe events requiring hospitalization. Long-term safety data are evolving and have shown thus far clinical and functional stability up to 5 years after BT treatment. Additional studies on BT are needed to establish accurate phenotyping of positive responders, durability of effect, and long-term safety.

Emerging therapies for severe asthma

Many patients with asthma have poorly controlled symptoms, and particularly for those with severe disease, there is a clear need for improved treatments. Two recent therapies licensed for use in asthma are omalizumab, a humanized monoclonal antibody that binds circulating IgE antibody, and bronchial thermoplasty, which involves the delivery of radio frequency energy to the airways to reduce airway smooth muscle mass. In addition, there are new therapies under development for asthma that have good potential to reach the clinic in the next five years. These include biological agents targeting pro-inflammatory cytokines such as interleukin-5 and interleukin-13, inhaled ultra long-acting β2-agonists and once daily inhaled corticosteroids. In addition, drugs that block components of the arachidonic acid pathway that targets neutrophilic asthma and CRTH2 receptor antagonists that inhibit the proinflammatory actions of prostaglandin D2 may become available. We review the recent progress made in developing viable therapies for severe asthma and briefly discuss the idea that development of novel therapies for asthma is likely to increasingly involve the assessment of genotypic and/or phenotypic factors.

Individual canine airway response variability to a deep inspiration

In healthy individuals, a DI can reverse (bronchodilation) or prevent (bronchoprotection) induced airway constriction. For individuals with asthma or COPD, these effects may be attenuated or absent. Previous work showed that the size and duration of a DI affected the subsequent response of the airways. Also, increased airway tone lead to increased airway size variability. The present study examined how a DI affected the temporal variability in individual airway baseline size and after methacholine challenge in dogs using High-Resolution Computed Tomography. Dogs were anesthetized and ventilated, and on 4 separate days, HRCT scans were acquired before and after a DI at baseline and during a continuous intravenous infusion of methacholine (Mch) at 3 dose rates (17, 67, and 200 μg/min). The Coefficient of Variation was used as an index of temporal variability in airway size.We found that at baseline and the lowest dose of Mch, variability decreased immediately and 5 minutes after the DI (P < 0.0001). In contrast, with higher doses of Mch, the DI caused a variable response. At a rate of 67 μg/min of Mch, the temporal variability increased after 5 minutes, while at a rate of 200 μg/min of Mch, the temporal variability increased immediately after the DI. Increased airway temporal variability has been shown to be associated with asthma. Although the mechanisms underlying this temporal variability are poorly understood, the beneficial effects of a DI to decrease airway temporal variability was eliminated when airway tone was increased. If this effect is absent in asthmatics, this may suggest a possible mechanism for the loss of bronchoprotective and bronchodilatory effects after a DI in asthma.

Bronchial thermoplasty: a novel therapeutic approach to severe asthma

Bronchial thermoplasty is a non-drug procedure for severe persistent asthma that delivers thermal energy to the airway wall in a precisely controlled manner to reduce excessive airway smooth muscle. Reducing airway smooth muscle decreases the ability of the airways to constrict, thereby reducing the frequency of asthma attacks. Bronchial thermoplasty is delivered by the Alair System and is performed in three outpatient procedure visits, each scheduled approximately three weeks apart. The first procedure treats the airways of the right lower lobe, the second treats the airways of the left lower lobe and the third and final procedure treats the airways in both upper lobes. After all three procedures are performed the bronchial thermoplasty treatment is complete. Bronchial thermoplasty is performed during bronchoscopy with the patient under moderate sedation. All accessible airways distal to the mainstem bronchi between 3 and 10 mm in diameter, with the exception of the right middle lobe, are treated under bronchoscopic visualization. Contiguous and non-overlapping activations of the device are used, moving from distal to proximal along the length of the airway, and systematically from airway to airway as described previously. Although conceptually straightforward, the actual execution of bronchial thermoplasty is quite intricate and procedural duration for the treatment of a single lobe is often substantially longer than encountered during routine bronchoscopy. As such, bronchial thermoplasty should be considered a complex interventional bronchoscopy and is intended for the experienced bronchoscopist. Optimal patient management is critical in any such complex and longer duration bronchoscopic procedure. This article discusses the importance of careful patient selection, patient preparation, patient management, procedure duration, postoperative care and follow-up to ensure that bronchial thermoplasty is performed safely. Bronchial thermoplasty is expected to complement asthma maintenance medications by providing long-lasting asthma control and improving asthma-related quality of life of patients with severe asthma. In addition, bronchial thermoplasty has been demonstrated to reduce severe exacerbations (asthma attacks) emergency rooms visits for respiratory symptoms, and time lost from work, school and other daily activities due to asthma.

Effects of pharmacological and non-pharmacological interventions

BACKGROUND

Asthma is recognised as a condition with variable airway obstruction with pathophysiological features that include activation of a wide range of inflammatory and structural cells. Additionally, structural changes in the airways have been demonstrated. This includes increased thickening of components in the basement membrane region, increased smooth muscle mass, increased vascularisation and many other events that is often referred to as remodelling of the airways. These processes and the underlying mechanisms have attracted considerable attention.

METHODS AND RESULTS

This review describes the different interventive approaches that have been tried in order to improve asthma control and affect the underlying pathophysiological pathways. These include elimination of harmful environmental and occupational exposures, a wide range of pharmacological agents as well as bronchial thermoplasty. The existing evidence for effects on airway inflammation and airway remodelling is discussed in relationship to mechanistic aspects and short- and long-term outcome.

CONCLUSION

It is expected that modulation of the asthmatic airway remodelling will become an even more important endpoint in the near future.

Airway smooth muscle modulation and airway hyper-responsiveness in asthma: new cellular and molecular paradigms

There is growing evidence indicating the existence of a causal relationship between abnormal airway smooth muscle (ASM) function and airway hyper-responsiveness, a poorly understood feature of asthma that can be defined as an excessive bronchospastic response. In recent years, there has been a veritable explosion of articles suggesting that ASM exposed to proasthmatic cytokines can elicit a hyper-responsive state to contractile G-protein-coupled receptor (GPCR) agonists. Aberrant airway responsiveness could result from abnormal calcium signaling, with changes occurring at various levels of GPCR-associated signal transduction. This review presents the latest observations describing novel mechanistic models that could explain the involvement of ASM in airway hyper-responsiveness. This review will discuss the role of ASM in beta(2)-agonist-mediated bronchial hyper-responsiveness and the clinical significance of cell-cell contact between ASM and mast cells recently described to be intimately infiltrated within the ASM tissues in asthmatic patients. The possibility that allergens could trigger airway hyper-responsiveness by directly acting on ASM via activation of immunoglobulin E receptors, FcepsilonRI and FCepsilonRII will also be discussed. These important findings further support the notion that targeting ASM could offer new treatment for many features of asthma, including airway hyper-responsiveness. Future therapeutic intervention includes: the prevention of ASM-inflammatory cell physical and/or functional interaction, the inhibition of Immunoglobulin E receptor-dependent signal transduction, and the abrogation of cytokine-dependent pathways that modulate receptor-associated calcium metabolism.

Bronchial thermoplasty

Asthma, by definition is a variable disease. When there is more than normal natural variation in airflow, asthma can be provoked by a wide range of stimuli that include infectious, allergic, and environmental agents. Bronchoconstriction determines much of the short-term variability in airflow that characterizes asthma. Current treatments do not redress the excess smooth muscle mass that is present in the remodeled airway in chronic asthma. Thus, it is intriguing to consider the potential contribution of bronchial thermoplasty (a procedure that involves controlled heat treatment to reduce the mass of the airway smooth muscle) as an effective therapy for poorly controlled asthma.

Bronchial thermoplasty for the treatment of asthma

Asthma is an increasingly prevalent disease, particularly in industrialized countries. With modern treatment, many patients can expect good asthma control; however, a significant minority continue to have excessive symptoms. Bronchial thermoplasty is a novel approach to treating asthma in which the hypertrophied airway smooth muscle present in the asthmatic airway is specifically targeted and depleted using thermal energy. In this article, we review the early animal and human development of the technique, summarize the randomized trials carried out in patients to date, discuss proposed mechanisms of action, and suggest directions for future work.

Bronchial thermoplasty in the treatment of asthma

Despite the numerous guidelines and treatments available for asthma, the disease remains poorly controlled in some patients, who remain symptomatic, are a considerable burden on the health system, and account for most of the hospitalizations due to asthma. Bronchial thermoplasty is a novel experimental therapeutic option that consists of delivering radiofrequency-generated heat to the airways via a catheter inserted in the bronchial tree through a flexible bronchoscope to reduce smooth muscle quantity and contractility. The first investigations were conducted using an animal model. Subsequently, 2 randomized clinical trials designed to evaluate the safety and efficacy of thermoplasty in patients with moderate to severe asthma with a 1-year follow-up period showed the procedure to be safe, with mostly transient adverse affects and several clinical benefits. Although results from ongoing clinical trials are still awaited, thermoplasty may become an innovative therapeutic approach to asthma.

An imbalance in C/EBPs and increased mitochondrial activity in asthmatic airway smooth muscle cells: novel targets in asthma therapy?

The asthma prevalence was increasing over the past two decades worldwide. Allergic asthma, caused by inhaled allergens of different origin or by food, is mediated by inflammatory mechanisms. The action of non-allergic asthma, induced by cold air, humidity, temperature or exercise, is not well understood. Asthma affects up to 15% of the population and is treated with anti-inflammatory and muscle relaxing drugs which allow symptom control. Asthma was first defined as a malfunction of the airway smooth muscle, later as an imbalanced immune response of the lung. Recent studies placed the airway smooth muscle again into the focus. Here we summarize the molecular biological basis of the deregulated function of the human airway smooth muscle cell as a cause or important contributor to the pathology of asthma. In the asthmatic human airway smooth muscle cells, there is: (i) a deregulation of cell differentiation due to low levels of maturation-regulating transcription factors such as CCAAT/enhancer binding proteins and peroxisome proliferator-activated receptors, thereby reducing the cells threshold to proliferate and to secrete pro-inflammatory cytokines under certain conditions; (ii) a higher basal energy turnover that is due to increased number and activity of mitochondria; and (iii) a modified feedback mechanism between cells and the extracellular matrix they are embedded in. All these cellular pathologies are linked to each other and to the innate immune response of the lung, but the sequence of events is unclear and needs further investigation. However, these findings may present the basis for the development of novel curative asthma drugs.

Novel targets of therapy in asthma

PURPOSE OF REVIEW

The use of inhaled corticosteroids, short and long acting beta2-adrenoceptor agonists and inhibitors of leukotrienes provide most asthmatic patients with good disease control. However, none of these therapies are specifically directed to the underlying causal pathways of asthma. In this review the role of selective inhibitors of the inflammatory cascade are presented with a particular emphasis on biologics.

RECENT FINDINGS

Apart from antihuman immunoglobulin E, biologics have had little impact on this disease. However, with the definition of critical pathways in driving ongoing inflammation and airway remodelling, the situation is about to change with several exciting new approaches being on the horizon. Specific cytokines that are considered central to the Th2 inflammatory response as therapeutic targets are discussed along with some entirely new approaches such as restoration of mucosal innate immunity and epithelial barrier function and the application of radiofrequency ablation of airway smooth muscle or thermal bronchoplasty.

SUMMARY

What is becoming clear in filling the pipeline with new asthma therapies that treat the underlying disease causes is the need for closer working between clinical academics and industry to ensure that there is a rapid and sustained transfer of knowledge on novel targets through to their validation, proof of concept studies and clinical trials.

Temporal variability in the responses of individual canine airways to methacholine

Previous work showed that individual airway size, before any spasmogen, varied widely in the same animals on different days. The effect of this variable baseline size on the airway response to a subsequent challenge is unknown. The present study examined how the variability in individual airway baseline size in dogs was related to that after methacholine challenge on 4 different days using high-resolution computed tomography scans. Dogs were anesthetized and ventilated, and on 4 separate days randomly varying between 1 and 8 wk apart, baseline scans were acquired, followed by a continuous intravenous infusion of methacholine at three rates in increasing order (17, 67, and 200 microg/min). As the measure of variability, we used the coefficient of variation (CV) of the four airway luminal measurements of each airway at baseline and at each dose of methacholine. For most airways, there was wide variability both between and within dogs in the response to a given dose of methacholine (CV = 33-38%). Airways with any level of methacholine stimulation had greater variability than those at baseline. The airway variability was greatest at the lowest dose of methacholine administered but was elevated at all the doses. In conclusion, there was substantial day-to-day variability in baseline airway size. Most importantly, the same dose of methacholine to the same individual airway showed even greater variability than that at baseline. If we consider that increased heterogeneity may potentiate clinical symptoms, then airway response variability may play an important role in the manifestation of airway disease.

Effect of Bronchial Thermoplasty on Airway Closure

BACKGROUND: Bronchial Thermoplasty, a procedure that applies thermal energy to the airway wall has been shown to impair the ability of airway to contract in response to methacholine chloride (Mch). The technique has been advocated as an alternative treatment for asthma that may permanently limit airway narrowing. In previous experimental studies in dogs and humans, it was shown that those airways treated with bronchial thermoplasty had significant impairment of Mch responsiveness. METHODS: In the present study, we investigated the ability of canine airways to close completely with very high concentrations of Mch after bronchial thermoplasty. Bronchial thermoplasty was performed on dogs using the Alair System, comprising a low power RF controller and a basket catheter with four electrodes. A local atomization of Mch agonist was delivered directly to the epithelium of the same airway locations with repeated challenges. Airway size was measured with computed tomography, and closure was considered to occur in any airway where the lumen fell below the resolution of the scanner (< 1 mm). RESULTS: Our results show that, while treated airways still have the capacity to close at very high doses of Mch, this ability is seriously impaired after treatment, requiring much higher doses. CONCLUSIONS: Bronchial thermoplasty as currently applied seems to simply shift the entire dose response curve toward increasing airway size. Thus, this procedure simply serves to minimize the ability of airways to narrow under any level of stimulation.

Complex airway behavior and paradoxical responses to bronchoprovocation

Heterogeneity of airway constriction and regional ventilation in asthma are commonly studied under the paradigm that each airway's response is independent from other airways. However, some paradoxical effects and contradictions in recent experimental and theoretical findings suggest that considering interactions among serial and parallel airways may be necessary. To examine airway behavior in a bronchial tree with 12 generations, we used an integrative model of bronchoconstriction, including for each airway the effects of pressure, tethering forces, and smooth muscle forces modulated by tidal stretching during breathing. We introduced a relative smooth muscle activation factor (Tr) to simulate increasing and decreasing levels of activation. At low levels of Tr, the model exhibited uniform ventilation and homogeneous airway narrowing. But as Tr reached a critical level, the airway behavior suddenly changed to a dual response with a combination of constriction and dilation. Ventilation decreased dramatically in a group of terminal units but increased in the rest. A local increase of Tr in a single central airway resulted in full closure, while no central airway closed under global elevation of Tr. Lung volume affected the response to both local and global stimulation. Compared with imaging data for local and global stimuli, as well as for the time course of airway lumen caliber during bronchoconstriction recovery, the model predictions were similar. The results illustrate the relevance of dynamic interactions among serial and parallel pathways in airway interdependence, which may be critical for the understanding of pathological conditions in asthma.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Bronchial thermoplasty in asthma

In this review we discuss the potential of a new procedure, termed Bronchial Thermoplasty to prevent serious consequences resulting from excessive airway narrowing. The most important factor in minimizing an asthmatic attack is limiting the degree of smooth muscle shortening. The premise that airway smooth muscle can be either inactivated or obliterated without any long-term alteration of other lung tissues, and that airway function will remain normal, albeit with reduced bronchoconstriction, has now been demonstrated in dogs, a subset of normal subjects, and mild asthmatics. Bronchial Thermoplasty may thus develop into a useful clinical procedure to effectively impair the ability for airway smooth muscle to reach the levels of pathologic narrowing that characterizes an asthma attack. It may also enable more successful treatment of asthma patients who are unresponsive to more conventional therapies. Whether this will remain stable for the lifetime of the patient still remains to be determined, but at the present time, there are no indications that the smooth muscle contractility will return. This successful preliminary experience showing that Bronchial Thermoplasty could be safely performed in patients with asthma has led to an ongoing clinical trial at a number of sites in Europe and North America designed to examine the effectiveness of this procedure in subjects with moderately severe asthma.

Mechanisms of limited airway dimension with lung inflation

Airways distend with each inspiration, while a sigh or deep inspiration (DI) leads to a significant or a maximum distension of the airways. Distension of the airways is thought to play an important role in maintaining airway patency. Limited distension of the airways with lung inflation may be a major factor in certain lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). High resolution computed tomography (HRCT) has gained wide acceptance as a diagnostic and investigational radiological tool for the evaluation of airway function. HRCT has been used to measure dynamic changes in airway caliber in vivo that are not detectable by conventional global lung measurements such as airway and lung resistance. HRCT is uniquely capable of imaging and quantifying airway size at different lung volumes. The current paper reviews the use of HRCT to examine the role of lung inflation on airway distension in animal models, and discusses potential mechanisms for limited distension of the airways with lung inflation in individuals with asthma and COPD.