Clinical potential for imaging in patients with asthma and other lung disorders

The role of radiological imaging in the management of severe and difficult-to-treat asthma

Radiological imaging has proven to be a useful tool in the assessment of asthma, its comorbidities and potential complications. Characteristic chest radiograph and computed tomography scan findings can be seen in asthma and in other conditions that can coexist with or be misdiagnosed as asthma, including chronic rhinosinusitis, inducible laryngeal obstruction, excessive dynamic airway collapse, tracheobronchomalacia, concomitant COPD, bronchiectasis, allergic bronchopulmonary aspergillosis, eosinophilic granulomatosis with polyangiitis, and eosinophilic pneumonia. The identification of the characteristic radiological findings of these conditions is often essential in making the correct diagnosis and provision of appropriate management and treatment. Furthermore, radiological imaging modalities can be used to monitor response to therapy.

The New Paradigm: The Role of Proteins and Triggers in the Evolution of Allergic Asthma

Epithelial barrier damage plays a central role in the development and maintenance of allergic inflammation. Rises in the epithelial barrier permeability of airways alter tissue homeostasis and allow the penetration of allergens and other external agents. Different factors contribute to barrier impairment, such as eosinophilic infiltration and allergen protease action-eosinophilic cationic proteins' effects and allergens' proteolytic activity both contribute significantly to epithelial damage. In the airways, allergen proteases degrade the epithelial junctional proteins, allowing allergen penetration and its uptake by dendritic cells. This increase in allergen-immune system interaction induces the release of alarmins and the activation of type 2 inflammatory pathways, causing or worsening the main symptoms at the skin, bowel, and respiratory levels. We aim to highlight the molecular mechanisms underlying allergenic protease-induced epithelial barrier damage and the role of immune response in allergic asthma onset, maintenance, and progression. Moreover, we will explore potential clinical and radiological biomarkers of airway remodeling in allergic asthma patients.

Do subtle findings on chest X-ray predict worse outcomes for paediatric asthma?

BACKGROUND

Asthma, a common childhood condition, often presents with chronic cough. While evaluating for chronic cough, many specialists obtain a baseline chest radiograph (CR) to assess for other causes. Usually read as 'normal', sometimes CRs will reveal evidence of airway inflammation in the form of subtle findings, such as 'increased interstitial markings' or 'peribronchial thickening'. There is sparse literature in the outpatient setting correlating findings on baseline CRs with adverse outcomes such as systemic steroid use, emergency department (ED) visit or hospitalisation.

METHODS

This was a retrospective study of patients seen at our institution's Pediatric Pulmonology outpatient clinic. We reviewed the charts of all new patients aged 0-18 years who presented between January 2015 and December 2017. Patients were included if they were diagnosed with asthma, had a CR after the initial visit and were followed up at least twice. Adverse outcomes include systemic steroid use, ED visit or hospitalisation.

RESULTS

130 subjects were included. 89 subjects had clear CRs and 41 subjects had CRs with airway inflammation. Overall events were higher in the airway inflammation group (22.5% vs 46.3%, respectively, p<0.0058). There were no significant differences between in terms of oral corticosteroid use or hospitalisations. There was a significant difference between the two groups in terms of ED visits (2.2% vs 14.6%, respectively, p=0.0121).

CONCLUSION

This study shows a positive correlation between airway inflammation findings on baseline CR and subsequent ED visits in patients with asthma.

Approaching Clinical Trials in Childhood Interstitial Lung Disease and Pediatric Pulmonary Fibrosis

Childhood interstitial lung disease (chILD) comprises a spectrum of rare diffuse lung disorders. chILD is heterogeneous in origin, with different disease manifestations occurring in the context of ongoing lung development. The large number of disorders in chILD, in combination with the rarity of each diagnosis, has hampered scientific and clinical progress within the field. Epidemiologic and natural history data are limited. The prognosis varies depending on the etiology, with some forms progressing to lung transplant or death. There are limited treatment options for patients with chILD. Although U.S. Food and Drug Administration-approved treatments are now available for adult patients with idiopathic pulmonary fibrosis, no clinical trials have been conducted in a pediatric population using agents designed to treat lung fibrosis. This review will focus on progressive chILD disorders and on the urgent need for meaningful objective outcome measures to define, detect, and monitor fibrosis in children.

Changes in airway diameter and mucus plugs in patients with asthma exacerbation

Background

Airway obstruction due to decreased airway diameter and increased incidence of mucus plugs has not been directly observed in asthma exacerbation. We studied the changes in the inner diameter of the airway (Din) and the frequency of mucus plugs by airway generation in patients with asthma exacerbation. We compared these patients to those in a stable phase using high-resolution computed tomography (HRCT).

Methods and findings

Thirteen patients with asthma were studied by HRCT during asthma exacerbation and in a stable period. The HRCT study was performed on patients who could safely hold their breath for a short while in a supine position 1 hour after initial treatment for asthma exacerbation. Using a curved multiplanar reconstruction (MPR) software, we reconstructed the longitudinal airway images and the images exactly perpendicular to the airway axis to measure the Din and mucus plugs from the second- (segmental) to sixth-generation bronchi in all segments of the lungs.The ratios of Din (exacerbation/stable) were 0.91(P = 0.016), 0.88 (P = 0.002), 0.83 (P = 0.001), 0.80 (P = 0.001), and 0.87 (NS) in the second-, third-, fourth-, fifth-, and sixth-generation bronchi, respectively. The percentages of airway obstruction due to mucus plugs were notably higher in the fourth- and fifth-generation bronchi (17.9%/18.1% in stable phase and 43.2%/45.9% in the exacerbation phase, respectively) than in the other generations of bronchi.

Conclusions

Among the bronchi examined, the fourth- and fifth-generation bronchi were significantly obstructed during asthma exacerbation compared with the stable phase in terms of a decreased airway diameter and mucus plugs.

Advances in asthma in 2017: Mechanisms, biologics, and genetics

This review summarizes some of the most significant advances in asthma research over the past year. We first focus on novel discoveries in the mechanism of asthma development and exacerbation. This is followed by a discussion of potential new biomarkers, including the use of radiographic markers of disease. Several new biologics have become available to the clinician in the past year, and we summarize these advances and how they can influence the clinical delivery of asthma care. After this, important findings in the genetics of asthma and heterogeneity in phenotypes of the disease are explored, as is the role the environment plays in shaping the development and exacerbation of asthma. Finally, we conclude with a discussion of advances in health literacy and how they will affect asthma care.

Estimating regions of air trapping from electrical impedance tomography data

OBJECTIVE

Electrical impedance tomography (EIT) has been shown to be a viable non-invasive, bedside imaging modality to monitor lung function. This paper introduces a method for identifying regions of air trapping from EIT data collected during tidal breathing and breath-holding maneuvers.

APPROACH

Ventilation-perfusion index maps are computed from dynamic EIT images. These maps are then used to identify regions of air trapping in the area of the lung as regions that are poorly ventilated but well perfused throughout the breathing and cardiac cycles. These EIT-identified regions are then compared with independently identified regions of low attenuation, or air trapping, on chest CT. Results of this method are demonstrated in two children with cystic fibrosis and on a healthy control subject.

MAIN RESULTS

In both CF children, the EIT-identified regions of air trapping matched the regions indicated from the chest CT. The EIT-based method is only validated with CT scans within 4 cm of the chest cross-section defined by the electrode plane.

SIGNIFICANCE

The results indicate the potential use of EIT-derived ventilation-perfusion index maps as a non-invasive method for identifying regions of air trapping.

Oscillometry and pulmonary MRI measurements of ventilation heterogeneity in obstructive lung disease: relationship to quality of life and disease control

Ventilation heterogeneity is a hallmark finding in obstructive lung disease and may be evaluated using a variety of methods, including multiple-breath gas washout and pulmonary imaging. Such methods provide an opportunity to better understand the relationships between structural and functional abnormalities in the lungs, and their relationships with important clinical outcomes. We measured ventilation heterogeneity and respiratory impedance in 100 subjects [50 patients with asthma, 22 ex-smokers, and 28 patients with chronic obstructive pulmonary disease (COPD)] using oscillometry and hyperpolarized ³He magnetic resonance imaging (MRI) and determined their relationships with quality of life scores and disease control/exacerbations. We also coregistered MRI ventilation maps to a computational airway tree model to generate patient-specific respiratory impedance predictions for comparison with experimental measurements. In COPD and asthma patients, respectively, forced oscillation technique (FOT)-derived peripheral resistance (5-19 Hz) and MRI ventilation defect percentage (VDP) were significantly related to quality of life (FOT: COPD ρ = 0.4, P = 0.004; asthma ρ = -0.3, P = 0.04; VDP: COPD ρ = 0.6, P = 0.003; asthma ρ = -0.3, P = 0.04). Patients with poorly controlled asthma (Asthmatic Control Questionnaire >2) had significantly increased resistance (5 Hz: P = 0.01; 5-19 Hz: P = 0.006) and reactance (5 Hz: P = 0.03). FOT-derived peripheral resistance (5-19 Hz) was significantly related to VDP in patients with asthma and COPD patients (asthma: ρ = 0.5, P < 0.001; COPD: ρ = 0.5, P = 0.01), whereas total respiratory impedance was related to VDP only in patients with asthma (resistance 5 Hz: ρ = 0.3, P = 0.02; reactance 5 Hz: ρ = -0.5, P < 0.001). Model-predicted and FOT-measured reactance (5 Hz) were correlated in patients with asthma (ρ = 0.5, P = 0.001), whereas in COPD patients, model-predicted and FOT-measured resistance (5-19 Hz) were correlated (ρ = 0.5, P = 0.004). In summary, in patients with asthma and COPD patients, we observed significant, independent relationships for FOT-measured impedance and MRI ventilation heterogeneity measurements with one another and with quality of life scores. NEW & NOTEWORTHY In 100 patients, including patients with asthma and ex-smokers, ³He MRI ventilation heterogeneity and respiratory system impedance were correlated and both were independently related to quality of life scores and asthma control. These findings demonstrated the critical relationships between respiratory system impedance and ventilation heterogeneity and their role in determining quality of life and disease control. These observations underscore the dominant role that abnormalities in the lung periphery play in ventilation heterogeneity that results in patients' symptoms.

Lumen area change (Delta Lumen) between inspiratory and expiratory multidetector computed tomography as a measure of severe outcomes in asthmatic patients

BACKGROUND

Quantitative computed tomographic (QCT) biomarkers of airway morphology hold potential for understanding and monitoring regional airway remodeling in asthmatic patients.

OBJECTIVE

We sought to determine whether the change in airway lumen area between total lung capacity (TLC) and functional residual capacity (FRC) lung volumes measured from CT imaging data was correlated with severe outcomes in asthmatic patients.

METHODS

We studied 152 asthmatic patients (90 female and 62 male patients) and 33 healthy subjects (12 female and 21 male subjects) using QCT. Postprocessing of airways at generations 1 to 5 (1 = trachea) was performed for wall area percentage, wall thickness percentage (WT%), lumen area at baseline total lung capacity (LA_TLC), lumen area at baseline functional residual capacity (LA_FRC), and low attenuation area at FRC. A new metric (reflecting remodeling, distal air trapping, or both), Delta Lumen, was determined as follows: Percentage difference in lumen area (LA_TLC - LA_FRC)/LA_TLC × 100.

RESULTS

Postprocessing of 4501 airway segments was performed (3681 segments in the 152 patients with asthma and 820 segments in the 33 healthy subjects; range, 17-28 segments per subject). Delta Lumen values were negatively correlated with WT% and low attenuation area (P < .01) in asthmatic patients. Delta Lumen values were significantly lower for airway generations 3 to 5 (segmental airways) in subjects undergoing hospitalization because of exacerbation and in patients with refractory asthma requiring treatment with systemic corticosteroids. WT% and low attenuation area were positively and Delta Lumen values were negatively associated with systemic corticosteroid treatment (P < .05), suggesting that a reduced Delta Lumen value is a potential outcome biomarker in patients with severe asthma.

CONCLUSION

Reduced Delta Lumen value in the central airways measured by using QCT is a promising exploratory biomarker of unstable refractory asthma that warrants further study.