Systematic review of evidence for relationships between physiological and CT indices of small airways and clinical outcomes in COPD

Early Diagnosis of High-Risk Chronic Obstructive Pulmonary Disease Based on Quantitative High-Resolution Computed Tomography Measurements

Purpose

Quantitative computed tomography (QCT) techniques, focusing on airway anatomy and emphysema, may help to detect early structural changes of COPD disease. This retrospective study aims to identify high-risk COPD participants by using QCT measurements.

Patients and Methods

We enrolled 140 participants from the Second Affiliated Hospital of Shenyang Medical College who completed inspiratory high-resolution CT scans, pulmonary function tests (PFTs), and clinical characteristics recorded. They were diagnosed Non-COPD by PFT value of FEV1/FVC >70% and divided into two groups according percentage predicted FEV1 (FEV1%), low-risk COPD group: FEV1% ≥ 95%, high-risk group: 80% < FEV1% < 95%. The QCT measurements were analyzed by the Student's t-test (or Mann-Whitney U-test) method. Then, feature candidates were identified using the LASSO method. Meanwhile, the correlation between QCT measurements and PFTs was assessed by the Spearman rank correlation test. Furthermore, support vector machine (SVM) was performed to identify high-risk COPD participants. The performance of the models was evaluated in terms of accuracy (ACC), sensitivity (SEN), specificity (SPE), F1-score, and area under the ROC curve (AUC), with p <0.05 considered statistically significant.

Results

The SVM based on QCT measurements achieved good performance in identifying high-risk COPD patients with 85.71% of ACC, 88.34% of SEN, 84.00% of SPE, 83.33% of F1-score, and 0.93 of AUC. Further, QCT measurements integration of clinical data improved the performance with an ACC of 90.48%. The emphysema index (%LAA-950) of left lower lung was negatively correlated with PFTs (P < 0.001). The airway anatomy indexes of lumen diameter (LD) were correlated with PFTs.

Conclusion

QCT measurements combined with clinical information could provide an effective tool for an early diagnosis of high-risk COPD. The QCT indexes can be used to assess the pulmonary function status of high-risk COPD.

HRCT quantitative analysis of airway remodeling and airway trapping in the small airway asthma phenotype and its correlation with pulmonary function

OBJECTIVES

We aimed to explore whether large airway remodeling and small airway structural changes exist in subjects with small airway asthma phenotype and to evaluate the relationships between quantitative high-resolution computed tomography (qHRCT) parameters and lung function.

METHODS

We enrolled 15 subjects with small airway asthma phenotype and 18 healthy controls. The two groups were matched by age, sex and body square area (BSA) with propensity score matching (PSM). Pulmonary function and qHRCT parameters [wall thickness (WT), wall area (WA), lumen area (LA), wall area percentage (WA%) of the 4th-6th generations in the right upper lobe apical segmental bronchus (RB1), adjusted by BSA, WT/BSA, WA/BSA, and LA/BSA, relative volume change -860 HU to -950 HU (RVC_{-860 to -950}) and the expiration to inspiration ratio of mean lung density (MLD_E/I)) were compared between the groups. Correlation analysis was employed to assess the relationship between qHRCT parameters and pulmonary function.

RESULTS

The small airway asthma phenotype had significantly higher WA%, RVC_{-860 to -950} and MLD_E/I and lower LA/BSA than the healthy control. Additionally, we found moderate to strong correlations between impulse oscillation (IOS) indices and WA6% and WT6/BSA. No significant correlation was found between bronchial parameters and air trapping parameters (p > 0.05).

CONCLUSIONS

Combining physiological tests with imaging approaches can lead to better evaluation of small airway disfunction (SAD) in asthmatic patients. Additionally, despite nonexistent airflow obstruction in patients with small airway asthma phenotype, large airway remodeling and small airway structural changes may appear simultaneously in the early stage of disease.

Discordant Spirometry and Impulse Oscillometry Assessments in the Diagnosis of Small Airway Dysfunction

Background and objective: Spirometry is commonly used to assess small airway dysfunction (SAD). Impulse oscillometry (IOS) can complement spirometry. However, discordant spirometry and IOS in the diagnosis of SAD were not uncommon. We examined the association between spirometry and IOS within a large cohort of subjects to identify variables that may explain discordant spirometry and IOS findings. Methods: 1,836 subjects from the ECOPD cohort underwent questionnaires, symptom scores, spirometry, and IOS, and 1,318 subjects were examined by CT. We assessed SAD with R₅-R₂₀ > the upper limit of normal (ULN) by IOS and two of the three spirometry indexes (maximal mid-expiratory flow (MMEF), forced expiratory flow (FEF)_50%, and FEF_75%) < 65% predicted. Multivariate regression analysis was used to analyze factors associated with SAD diagnosed by only spirometry but not IOS (spirometry-only SAD) and only IOS but not spirometry (IOS-only SAD), and line regression was used to assess CT imaging differences. Results: There was a slight agreement between spirometry and IOS in the diagnosis of SAD (kappa 0.322, p < 0.001). Smoking status, phlegm, drug treatment, and family history of respiratory disease were factors leading to spirometry-only SAD. Spirometry-only SAD had more severe emphysema and gas-trapping than IOS-only SAD in abnormal lung function. However, in normal lung function subjects, there was no statistical difference in emphysema and gas-trapping between discordant groups. The number of IOS-only SAD was nearly twice than that of spirometry. Conclusion: IOS may be more sensitive than spirometry in the diagnosis of SAD in normal lung function subjects. But in patients with abnormal lung function, spirometry may be more sensitive than IOS to detect SAD patients with clinical symptoms and CT lesions.

Spirometry parameters used to define small airways obstruction in population-based studies: systematic review

Background

The assessment of small airways obstruction (SAO) using spirometry is practiced in population-based studies. However, it is not clear what are the most used parameters and cut-offs to define abnormal results.

Methods

We searched three databases (Medline, Web of Science, Google Scholar) for population-based studies, published by 1 May 2021, that used spirometry parameters to identify SAO and/or provided criteria for defining SAO. We systematically reviewed these studies and summarised evidence to determine the most widely used spirometry parameter and criteria for defining SAO. In addition, we extracted prevalence estimates and identified associated risk factors. To estimate a pooled prevalence of SAO, we conducted a meta-analysis and explored heterogeneity across studies using meta regression.

Results

Twenty-five studies used spirometry to identify SAO. The most widely utilised parameter (15 studies) was FEF_25–75, either alone or in combination with other measurements. Ten studies provided criteria for the definition of SAO, of which percent predicted cut-offs were the most common (5 studies). However, there was no agreement on which cut-off value to use. Prevalence of SAO ranged from 7.5% to 45.9%. As a result of high heterogeneity across studies (I² = 99.3%), explained by choice of spirometry parameter and WHO region, we do not present a pooled prevalence estimate.

Conclusion

There is a lack of consensus regarding the best spirometry parameter or defining criteria for identification of SAO. The value of continuing to measure SAO using spirometry is unclear without further research using large longitudinal data.

PROSPERO registration number CRD42021250206

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01990-2.

Creating a training set for artificial intelligence from initial segmentations of airways

Airways segmentation is important for research about pulmonary disease but require a large amount of time by trained specialists. We used an openly available software to improve airways segmentations obtained from an artificial intelligence (AI) tool and retrained the tool to get a better performance. Fifteen initial airway segmentations from low-dose chest computed tomography scans were obtained with a 3D-Unet AI tool previously trained on Danish Lung Cancer Screening Trial and Erasmus-MC Sophia datasets. Segmentations were manually corrected in 3D Slicer. The corrected airway segmentations were used to retrain the 3D-Unet. Airway measurements were automatically obtained and included count, airway length and luminal diameter per generation from the segmentations. Correcting segmentations required 2–4 h per scan. Manually corrected segmentations had more branches (p < 0.001), longer airways (p < 0.001) and smaller luminal diameters (p = 0.004) than initial segmentations. Segmentations from retrained 3D-Unets trended towards more branches and longer airways compared to the initial segmentations. The largest changes were seen in airways from 6th generation onwards. Manual correction results in significantly improved segmentations and is potentially a useful and time-efficient method to improve the AI tool performance on a specific hospital or research dataset.

Spirometry parameters used to define small airways obstruction in population-based studies: systematic review protocol

INTRODUCTION

In recent years, there has been increasing interest in the use of spirometry for the assessment of small airways obstruction (SAO) driven by the idea that these changes occur prior to development of established obstructive lung disease. Maximal mid-expiratory and distal flow rates have been widely used despite a lack of agreement regarding parameter selection or definition of an abnormal result. We aim to provide evidence from population-based studies, describing the different parameters, definitions of normal range and the resulting impact on prevalence estimates for SAO. Summarising this evidence is important to inform development of future studies in this area.

METHODS AND ANALYSIS

A systematic review of population-based studies will be conducted. MEDLINE, Web of Science and Google Scholar will be searched from database inception to May 2021. Primary outcomes will include the spirometry parameter used to define SAO, and the definition of an abnormal result. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines will be followed for study selection. Study methods will be assessed using the Newcastle-Ottawa scale and the Grading of Recommendations Assessment, Development and Evaluation working group methodology. Narrative synthesis will be conducted for all included studies. Meta-analysis will also be conducted for prevalence estimates and associated risk factors where data quality and availability allow. Random effects models will be used to conduct the meta-analysis and I² statistics will be used to assess heterogeneity across studies. Where appropriate subgroup analysis will be conducted to explore heterogeneity.

ETHICS AND DISSEMINATION

There is no requirement for ethical approval for this project. Findings will be disseminated via peer-reviewed publications and other formats, for example, conferences, congresses or symposia.

PROSPERO REGISTRATION NUMBER

CRD42021250206.

Prediction of COPD by the single-breath nitrogen test and various respiratory symptoms

Early identification of subjects running an increased risk of contracting COPD enables focus on individual preventive measures. The slope of the alveolar plateau of the single-breath nitrogen washout test (N2-slope) is a sensitive measure of small-airway dysfunction. However, its role remains unexplored in predicting hospital admission or death related to COPD, i.e. incident COPD events, in relation to the presence of various respiratory symptoms. A random population sample of 625 men, aged 50 (n=218) or 60 years (n=407), was followed for 38 years for incident COPD events. At baseline, a questionnaire on respiratory symptoms and smoking habits was collected, spirometry and the single-breath nitrogen test were performed, and the N2-slope was determined. Proportional hazard regression (Cox regression) analysis was used for the prediction model. The N2-slope improved the prediction of COPD events significantly beyond that of respiratory symptoms weighted all together and other covariates (hazard ratio 1.63, 95% CI 1.20-2.22; p<0.005), a prediction applicable to subjects without (p=0.001) and with (p<0.05) airway obstruction. Dyspnoea and wheezing were the most predictive symptoms. The combination of the N2-slope and number of respiratory symptoms notably resulted in an effective prediction of incident COPD events even in nonobstructive subjects, as evidenced by a predicted incidence of ∼70% and ∼90% for a very steep N2-slope combined with many respiratory symptoms in subject without and with airway obstruction, respectively. The alveolar N2-slope should be considered in the critical need for further research on early diagnosis of COPD.

Seven Pillars of Small Airways Disease in Asthma and COPD: Supporting Opportunities for Novel Therapies

Identification of pathologic changes in early and mild obstructive lung disease has shown the importance of the small airways and their contribution to symptoms. Indeed, significant small airways dysfunction has been found prior to any overt airway obstruction being detectable by conventional spirometry techniques. However, most therapies for the treatment of obstructive lung disease target the physiological changes and associated symptoms that result from chronic lung disease, rather than directly targeting the specific underlying causes of airflow disruption or the drivers of disease progression. In addition, although spirometry is the current standard for diagnosis and monitoring of response to therapy, the most widely used measure, FEV1 , does not align with the pathologic changes in early or mild disease and may not align with symptoms or exacerbation frequency in the individual patient. Newer functional and imaging techniques allow more effective assessment of small airways dysfunction; however, significant gaps in our understanding remain. Improving our knowledge of the role of small airways dysfunction in early disease in the airways, along with the identification of novel end points to measure subclinical changes in this region (ie, those not captured as symptoms or identified through standard FEV1), may lead to the development of novel therapies that directly combat early airways disease processes with a view to slowing disease progression and reversing damage. This expert opinion paper discusses small airways disease in the context of asthma and COPD and highlights gaps in current knowledge that impede earlier identification of obstructive lung disease and the development and standardization of novel small airways-specific end points for use in clinical trials.

Interrelationships Among Small Airways Dysfunction, Neutrophilic Inflammation, and Exacerbation Frequency in COPD

BACKGROUND

Small airways disease (SAD) is a key component of COPD and is a main contributing factor to lung function decline.

RESEARCH QUESTION

Is SAD a key feature of frequent COPD exacerbators and is this related to airway inflammation?

STUDY DESIGN AND METHODS

Thirty-nine COPD patients defined as either frequent exacerbator (FE) group (≥ 2 exacerbations/y; n = 17) and infrequent exacerbator (IFE) group (≤ 1 exacerbation/y; n = 22) underwent the forced oscillation technique (resistance at 5 Hz minus 19 Hz [R5-R19], area of reactance [AX]), multiple breath nitrogen washout (conducting airways ventilation heterogeneity, acinar ventilation heterogeneity [S_acin]), plethysmography (ratio of residual volume to total lung capacity), single-breath transfer factor of the lung for carbon monoxide, spirometry (FEV₁, FEV₁/FVC), and paired inspiratory-expiratory CT scans to ascertain SAD. A subpopulation underwent bronchoscopy to enable enumeration of BAL cell proportions.

RESULTS

S_acin was significantly higher in the COPD FE group compared with the IFE group (P = .027). In the FE group, markers of SAD were associated strongly with BAL neutrophil proportions, R5-R19 (P = .001, r = 0.795), AX (P = .049, ρ = 0.560), residual volume to total lung capacity ratio (P = .004, r = 0.730), and the mean lung density of the paired CT scans (P = .018, r = 0.639).

INTERPRETATION

Increased S_acin may be a consequence of previous exacerbations or may highlight a group of patients prone to exacerbations. Measures of SAD were associated strongly with neutrophilic inflammation in the small airways of FE patients, supporting the hypothesis that frequent exacerbations are associated with SAD related to increased cellular inflammation.

Early COPD: current evidence for diagnosis and management

Chronic obstructive pulmonary disease (COPD) affects one-tenth of the world's population and has been identified as a major global unmet health need by the World Health Organisation, which predicts that within 10 years, COPD will become the third leading cause of death. Despite active research, there have been no recent major strides in terms of disease modifying treatment for COPD; smoking cessation remains the only intervention known to alter disease progression and improve mortality. As established COPD is a key driver of disease burden, earlier diagnosis coupled with disease-modifying intervention carries promise as a route to address this global health priority. The concept of early COPD is emerging as an area of focus for research and consideration of new treatment modalities, as it has been hypothesised that intervention at this stage may potentially halt or reverse the disease process. However, at present, a globally accepted criteria for defining early COPD does not exist. Several studies propose small airways disease as the earliest stage in the development of COPD, and this has been demonstrated to be a precursor to development of emphysema and to correlate with subsequent development of airflow obstruction. However, treatment strategies for early disease, which pre-date the development of airflow obstruction, remain uncertain. This review addresses the rationale and current evidence base for the diagnosis and treatment of early COPD and highlights the challenges of implementing trials and clinical pathways to address COPD earlier in the life course, particularly in the absence of a universally accepted definition of COPD.The reviews of this paper are available via the supplemental material section.