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

Quantification of smooth muscle in human airways by polarization-sensitive optical coherence tomography requires correction for perichondrium

Quantifying airway smooth muscle (ASM) in patients with asthma raises the possibility of improved and personalized disease management. Endobronchial polarization-sensitive optical coherence tomography (PS-OCT) is a promising quantitative imaging approach that is in the early stages of clinical translation. To date, only animal tissues have been used to assess the accuracy of PS-OCT to quantify absolute (rather than relative) ASM in cross sections with directly matched histological cross sections as validation. We report the use of whole fresh human and pig airways to perform a detailed side-by-side qualitative and quantitative validation of PS-OCT against gold-standard histology. We matched and quantified 120 sections from five human and seven pig (small and large) airways and linked PS-OCT signatures of ASM to the tissue structural appearance in histology. Notably, we found that human cartilage perichondrium can share with ASM the properties of birefringence and circumferential alignment of fibers, making it a significant confounder for ASM detection. Measurements not corrected for perichondrium overestimated ASM content several-fold (P < 0.001, paired t test). After careful exclusion of perichondrium, we found a strong positive correlation (r = 0.96, P < 0.00001) of ASM area measured by PS-OCT and histology, supporting the method's application in human subjects. Matching human histology further indicated that PS-OCT allows conclusions on the intralayer composition and in turn potential contractile capacity of ASM bands. Together these results form a reliable basis for future clinical studies.NEW & NOTEWORTHY Polarization-sensitive optical coherence tomography (PS-OCT) may facilitate in vivo measurement of airway smooth muscle (ASM). We present a quantitative validation correlating absolute ASM area from PS-OCT to directly matched histological cross sections using human tissue. A major confounder for ASM quantification was observed and resolved: fibrous perichondrium surrounding hyaline cartilage in human airways presents a PS-OCT signature similar to ASM for birefringence and optic axis orientation. Findings impact the development of automated methods for ASM segmentation.

Which airways should we treat? Structure-function relationships and estimation of the singular input modes from the forward model alone

Structure-function relationships occur throughout the sciences. Motivated by optimization of such systems, we develop a framework for estimating the input modes from the singular value decomposition from the action of the forward operator alone. These can then be used to determine the input (structure) changes, which induce the largest output (function) changes. The accuracy of the estimate is determined by reference to the method of snapshots. The proposed method is demonstrated on several example problems, and finally used to approximate the optimal airway treatment set for a problem in respiratory physiology.

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.

Heterogeneity of Airway Smooth Muscle Remodeling in Asthma

Rationale: Ventilatory defects in asthma are heterogeneous and may represent the distribution of airway smooth muscle (ASM) remodeling. Objectives: To determine the distribution of ASM remodeling in mild-severe asthma. Methods: The ASM area was measured in nine airway levels in three bronchial pathways in cases of nonfatal (n = 30) and fatal asthma (n = 20) and compared with control cases without asthma (n = 30). Correlations of ASM area within and between bronchial pathways were calculated. Asthma cases with 12 large and 12 small airways available (n = 42) were classified on the basis of the presence or absence of ASM remodeling (more than two SD of mean ASM area of control cases, n = 86) in the large or small airway or both. Measurements and Main Results: ASM remodeling varied widely within and between cases of nonfatal asthma and was more widespread and confluent and more marked in fatal cases. There were weak correlations of ASM between levels within the same or separate bronchial pathways; however, predictable patterns of remodeling were not observed. Using mean data, 44% of all asthma cases were classified as having no ASM remodeling in either the large or small airway despite a three- to 10-fold increase in the number of airways with ASM remodeling and 81% of asthma cases having ASM remodeling in at least one large and small airway. Conclusions: ASM remodeling is related to asthma severity but is heterogeneous within and between individuals and may contribute to the heterogeneous functional defects observed in asthma. These findings support the need for patient-specific targeting of ASM remodeling.

Quantitative Imaging Metrics for the Assessment of Pulmonary Pathophysiology: An Official American Thoracic Society and Fleischner Society Joint Workshop Report

Multiple thoracic imaging modalities have been developed to link structure to function in the diagnosis and monitoring of lung disease. Volumetric computed tomography (CT) renders three-dimensional maps of lung structures and may be combined with positron emission tomography (PET) to obtain dynamic physiological data. Magnetic resonance imaging (MRI) using ultrashort-echo time (UTE) sequences has improved signal detection from lung parenchyma; contrast agents are used to deduce airway function, ventilation-perfusion-diffusion, and mechanics. Proton MRI can measure regional ventilation-perfusion ratio. Quantitative imaging (QI)-derived endpoints have been developed to identify structure-function phenotypes, including air-blood-tissue volume partition, bronchovascular remodeling, emphysema, fibrosis, and textural patterns indicating architectural alteration. Coregistered landmarks on paired images obtained at different lung volumes are used to infer airway caliber, air trapping, gas and blood transport, compliance, and deformation. This document summarizes fundamental "good practice" stereological principles in QI study design and analysis; evaluates technical capabilities and limitations of common imaging modalities; and assesses major QI endpoints regarding underlying assumptions and limitations, ability to detect and stratify heterogeneous, overlapping pathophysiology, and monitor disease progression and therapeutic response, correlated with and complementary to, functional indices. The goal is to promote unbiased quantification and interpretation of in vivo imaging data, compare metrics obtained using different QI modalities to ensure accurate and reproducible metric derivation, and avoid misrepresentation of inferred physiological processes. The role of imaging-based computational modeling in advancing these goals is emphasized. Fundamental principles outlined herein are critical for all forms of QI irrespective of acquisition modality or disease entity.

Therapeutic response to bronchial thermoplasty: toward feasibility of patient selection based on modeling predictions

Bronchial thermoplasty (BT) is a treatment for moderate-to-severe asthma in which the airway smooth muscle layer is targeted directly using thermal ablation. Although it has been shown to be safe and effective in long-term follow-up, questions remain about its mechanism of action, patient selection, and optimization of protocol based on structural phenotype. Using a cohort of 20 subjects who underwent thermoplasty and assessment by computed tomography (CT), we demonstrate that response to BT can be feasibly predicted based on pretreatment airway dimensions that inform a subject-specific computational model. Analysis revealed the need for CT assessment at total lung capacity, rather than functional residual capacity, which was less sensitive to the effects of BT. Final model predictions compared favorably with observed outcomes in terms of airway caliber and asthma control, suggesting that this approach could form the basis of improved clinical practice.NEW & NOTEWORTHY Bronchial thermoplasty is a treatment for asthma that targets the airway smooth muscle directly. We demonstrate the feasibility and constraints of predicting patient-specific response to thermoplasty using a computational model informed by pretreatment CT scans at different lung volumes. Predictions are compared with functional outcomes and posttreatment CT scans. This has the potential to form the basis for improved clinical practice.

Endobronchial treatment of severe asthma and severe emphysema with hyperinflation

PURPOSE OF REVIEW

The field of interventional pulmonology has ushered in a wave of innovations for individuals with obstructive airways disease in whom established medical therapies have failed. Leading the charge are bronchial thermoplasty for severe refractory asthma and uni-directional valves for severe emphysema with hyperinflation: both have received regulatory approvals in the United Kingdom and United States. With the commissioning of these novel treatments comes new challenges relating to implementation, positioning within therapeutic algorithms, honing of patient selection, and establishing long-term safety and benefits beyond 5 years.

RECENT FINDINGS

This review summarises the evidence for their safety and efficacy, predictors of therapeutic response, mechanism(s) of action and emerging data supporting the durability of outcomes out to at least ten years.

SUMMARY

It is anticipated the experience of treating increasing numbers of patients, the adoption of international registries, and ongoing research evaluations will serve to optimise these therapies for future generations of patients.

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.

Integrative Computational Models of Lung Structure-Function Interactions

Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in both structure and function within the normal lung, yet it remains capable of relatively efficient gas exchange by providing close matching of air delivery (ventilation) and blood delivery (perfusion) to regions of gas exchange tissue from the scale of the whole organ to the smallest continuous gas exchange units. This is despite remarkably different mechanisms of air and blood delivery, different fluid properties, and unique scale-dependent anatomical structures through which the blood and air are transported. This inherent heterogeneity can be exacerbated in the presence of disease or when the body is under stress. Current computational power and data availability allow for the construction of sophisticated data-driven integrative models that can mimic respiratory system structure, function, and response to intervention. Computational models do not have the same technical and ethical issues that can limit experimental studies and biomedical imaging, and if they are solidly grounded in physiology and physics they facilitate investigation of the underlying interaction between mechanisms that determine respiratory function and dysfunction, and to estimate otherwise difficult-to-access measures. © 2021 American Physiological Society. Compr Physiol 11:1501-1530, 2021.

Single-Session Bronchial Thermoplasty Guided by 129Xe Magnetic Resonance Imaging. A Pilot Randomized Controlled Clinical Trial

Rationale: Adverse events have limited the use of bronchial thermoplasty (BT) in severe asthma.Objectives: We sought to evaluate the effectiveness and safety of using ¹²⁹Xe magnetic resonance imaging (¹²⁹Xe MRI) to prioritize the most involved airways for guided BT.Methods: Thirty subjects with severe asthma were imaged with volumetric computed tomography and ¹²⁹Xe MRI to quantitate segmental ventilation defects. Subjects were randomized to treatment of the six most involved airways in the first session (guided group) or a standard three-session BT (unguided). The primary outcome was the change in Asthma Quality of Life Questionnaire score from baseline to 12 weeks after the first BT for the guided group compared with after three treatments for the unguided group.Measurements and Main Results: There was no significant difference in quality of life after one guided compared with three unguided BTs (change in Asthma Quality of Life Questionnaire guided = 0.91 [95% confidence interval, 0.28-1.53]; unguided = 1.49 [95% confidence interval, 0.84-2.14]; P = 0.201). After one BT, the guided group had a greater reduction in the percentage of poorly and nonventilated lung from baseline when compared with unguided (-17.2%; P = 0.009). Thirty-three percent experienced asthma exacerbations after one guided BT compared with 73% after three unguided BTs (P = 0.028).Conclusions: Results of this pilot study suggest that similar short-term improvements can be achieved with one BT treatment guided by ¹²⁹Xe MRI when compared with standard three-treatment-session BT with fewer periprocedure adverse events.

Asthma: Pharmacological degradation of the airway smooth muscle layer

Asthma: A disease characterised by excessive and variable airway narrowing, and pathologies of inflammation and remodelling, particularly thickening of the airway smooth muscle (ASM). Treatment approaches dilate narrowed airways and reduce inflammation; however, remodelling seems largely neglected. This review considers the evolution of remodelling in asthma and whether conventional hypotheses that inflammation causes ASM thickening has mislead the medical community into thinking that anti-inflammatories will remedy this ASM defect. There is instead reasonable evidence that ASM thickening occurs independently of inflammation, such that therapies should employ strategies to directly modify ASM growth. Lessons have been learned from the use of untargeted bronchial thermoplasty and there should also be consideration of pharmacological therapies to ablate ASM. We discuss several new approaches to target ASM remodelling in asthma. A major current obstacle is our inability to image the ASM layer and assess treatment response. In this regard, polarisation-sensitive optical coherence tomography offers future promise.

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.

Maturation of nasal microbiota and antibiotic exposures during early childhood: a population-based cohort study

OBJECTIVES

Little is known about maturation of the airway microbiota during early childhood and the consequences of early-life antibiotic exposure.

METHODS

In a population-based birth cohort of 902 healthy Finnish children, we applied deep neural network models to investigate the relationship between the nasal microbiota (measured by 16S rRNA gene sequencing at up to three time points) and child age during the first 24 months. We also performed stratified analyses according to antibiotic exposure during the age period 0-2 months.

RESULTS

The dense deep neural network analysis successfully modelled the relationship between 232 bacterial genera and child age with a mean absolute error of 4.3 (95%CI 4.0-4.7) months. Similarly, the recurrent neural network analysis also successfully modelled the relationship between 215 genera and child age with a mean absolute error of 0.45 (95%CI 0.42-0.47) months. Among the genera, Staphylococcus spp. and members of the Corynebacteriaceae decreased with age, while Dolosigranulum and Moraxella increased with age in the first 2 years of life (all false discovery rate (FDR) = 0.001). In children without early-life antibiotic exposure, Dolosigranulum increased with age (FDR = 0.001). By contrast, in those with early-life antibiotic exposure, Haemophilus increased with age (FDR = 0.002).

CONCLUSIONS

In this prospective birth cohort of healthy children, we demonstrated the development of the nasal microbiota, with shifts in specific genera constituting maturation, in the first 2 years of life. Antibiotic exposures during early infancy were related to different age-discriminatory bacteria.

Recent Developments In Bronchial Thermoplasty For Severe Asthma

PURPOSE

Bronchial thermoplasty is approved in many countries worldwide as a non-pharmacological treatment for severe asthma. This review summarizes recent publications on the selection of patients with severe asthma for bronchial thermoplasty, predictors of a beneficial response and developments in the procedure and discusses specific issues about bronchial thermoplasty including effectiveness in clinical practice, mechanism of action, cost-effectiveness, and place in management.

RESULTS

Bronchial thermoplasty is a treatment option for patients with severe asthma after assessment and management of causes of difficult-to-control asthma, such as nonadherence, poor inhaler technique, comorbidities, under treatment, and other behavioral factors. Patients treated with bronchial thermoplasty in clinical practice have worse baseline characteristics and comparable clinical outcomes to clinical trial data. Bronchial thermoplasty causes a reduction in airway smooth muscle mass although it is uncertain whether this effect explains its efficacy since other mechanisms of action may be relevant, such as alterations in airway epithelial, gland, and/or nerve function; improvements in small airway function; or a placebo effect. The cost-effectiveness of bronchial thermoplasty is greater in countries where the costs of hospitalization and emergency department are high. The place of bronchial thermoplasty in the management of severe asthma is not certain, although some experts propose that bronchial thermoplasty should be considered for patients with severe asthma associated with non-type 2 inflammation or who fail to respond favorably to biologic therapies targeting type 2 inflammation.

CONCLUSION

Bronchial thermoplasty is a modestly effective treatment for severe asthma after assessment and management of causes of difficult-to-control asthma. Asthma morbidity increases during and shortly after treatment. Follow-up studies provide reassurance on the long-term safety of the procedure. Uncertainties remain about predictors of response, mechanism(s) of action, and place in management of severe asthma.

Understanding the mechanism of bronchial thermoplasty using airway volume assessed by computed tomography

High-resolution CT assessment of airway volumes after bronchial thermoplasty (BT), together with model predictions regarding the efficacy and underlying mechanism of action of the treatment, combine to help to elucidate the underlying mechanism of BT http://bit.ly/2WPHY6y.