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

Pharmacological ablation of the airway smooth muscle layer-Mathematical predictions of functional improvement in asthma

Airway smooth muscle (ASM) plays a major role in acute airway narrowing and reducing ASM thickness is expected to attenuate airway hyper‐responsiveness and disease burden. There are two therapeutic approaches to reduce ASM thickness: (a) a direct approach, targeting specific airways, best exemplified by bronchial thermoplasty (BT), which delivers radiofrequency energy to the airway via bronchoscope; and (b) a pharmacological approach, targeting airways more broadly. An example of the less well‐established pharmacological approach is the calcium‐channel blocker gallopamil which in a clinical trial effectively reduced ASM thickness; other agents may act similarly. In view of established anti‐proliferative properties of the macrolide antibiotic azithromycin, we examined its effects in naive mice and report a reduction in ASM thickness of 29% (p < .01). We further considered the potential functional implications of this finding, if it were to extend to humans, by way of a mathematical model of lung function in asthmatic patients which has previously been used to understand the mechanistic action of BT. Predictions show that pharmacological reduction of ASM in all airways of this magnitude would reduce ventilation heterogeneity in asthma, and produce a therapeutic benefit similar to BT. Moreover there are differences in the expected response depending on disease severity, with the pharmacological approach exceeding the benefits provided by BT in more severe disease. Findings provide further proof of concept that pharmacological targeting of ASM thickness will be beneficial and may be facilitated by azithromycin, revealing a new mode of action of an existing agent in respiratory medicine.

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.

Phenotype- and patient-specific modelling in asthma: Bronchial thermoplasty and uncertainty quantification

Theoretical models can help to overcome experimental limitations to better our understanding of lung physiology and disease. While such efforts often begin in broad terms by determining the effect of a disease process on a relevant biological output, more narrowly defined simulations may inform clinical practice. Two such examples are phenotype-specific and patient-specific models, the former being specific to a group of patients with common characteristics, and the latter to an individual patient, in view of likely differences (heterogeneity) between patients. However, in order for such models to be useful, they must be sufficiently accurate, given the available data about the specific characteristics of the patient. We show that, for asthma in particular, this approach is promising: phenotype-specific targeting may be an effective way of selecting patients for treatment based on their airway remodelling phenotype, and patient-specific targeting may be viable with the use of a clinically-plausible dataset. Specifically we consider asthma and its treatment by bronchial thermoplasty, in which the airway smooth muscle layer is directly targeted by thermal energy. Patient-specific and phenotype-specific models in this context are considered using a combination of biobank data from ex vivo tissue samples, CT imaging, and optical coherence tomography which allows more detailed resolution of the airway wall structures.