Airflow limitation and airway dimensions in chronic obstructive pulmonary disease

A Novel Spirometric Measure Identifies Mild COPD Unidentified by Standard Criteria

BACKGROUND

In chronic obstructive pulmonary disease, both smaller and larger airways are affected. FEV₁ mainly reflects large airways obstruction, while the later fraction of forced exhalation reflects reduction in terminal expiratory flow. In this study, the objective was to evaluate the relationship between spirometric ratios, including the ratio of forced expiratory volume in 3 and 6 seconds (FEV₃/FEV₆), and small airways measures and gas trapping at quantitative chest CT scanning, and clinical outcomes in the Genetic Epidemiology of COPD (COPDGene) cohort.

METHODS

Seven thousand eight hundred fifty-three current and ex-smokers were evaluated for airflow obstruction by using recently defined linear iteratively derived equations of Hansen et al to determine lower limit of normal (LLN) equations for prebronchodilator FEV₁/FVC, FEV₁/FEV₆, FEV₃/FEV₆, and FEV₃/FVC. General linear and ordinal regression models were applied to the relationship between prebronchodilator spirometric and radiologic and clinical data.

RESULTS

Of the 10,311 participants included in the COPDGene phase I study, participants with incomplete quantitative CT scanning or relevant spirometric data were excluded, resulting in 7,853 participants in the present study. Of 4,386 participants with FEV₁/FVC greater than or equal to the LLN, 15.4% had abnormal FEV₃/FEV₆. Compared with normal FEV₃/FEV₆ and FEV₁/FVC, abnormal FEV₃/FEV₆ was associated with significantly greater gas trapping; St. George's Respiratory Questionnaire score; modified Medical Research Council dyspnea score; and BMI, airflow obstruction, dyspnea, and exercise index and with shorter 6-min walking distance (all P < .0001) but not with CT scanning evidence of emphysema.

CONCLUSIONS

Current and ex-smokers with prebronchodilator FEV₃/FEV₆ less than the LLN as the sole abnormality identifies a distinct population with evidence of small airways disease in quantitative CT scanning, impaired indexes of physical function and quality of life otherwise deemed normal by using the current spirometric definition.

Sex differences of COPD phenotypes in nonsmoking patients

BACKGROUND

There is growing evidence about sex-related phenotypes of COPD. However, the sex differences in COPD mainly result from smokers. This study evaluated the sex differences in nonsmoking patients with COPD, focusing on structural changes in the lungs in airway diseases and emphysema.

METHODS

Ninety-seven nonsmoking patients, defined as having <1 pack-year of lifetime cigarette smoking, diagnosed with COPD were selected from a Korean COPD cohort. Emphysema extent and mean wall area percentage (WA%) on computed tomography were compared between the male and female groups.

RESULTS

The 97 patients with COPD included 62 females and 35 males. Emphysema index was significantly lower (3.5±4.2 vs 6.2±5.7, P<0.01) and mean WA% on computed tomography was significantly higher (71.8%±5% vs 69.4%±5%, P<0.01) in females than in males, after adjusting for age, body mass index, history of biomass exposure, and postbronchodilator forced expiratory volume in 1 second (% of predicted).

CONCLUSION

WA% was higher and emphysema extent was lower in nonsmoking females with COPD than in nonsmoking males with COPD. These findings suggest that males may be predisposed to an emphysema phenotype and females may be predisposed to an airway phenotype of COPD.

COPD immunopathology

The immunopathology of chronic obstructive pulmonary disease (COPD) is based on the innate and adaptive inflammatory immune responses to the chronic inhalation of cigarette smoking. In the last quarter of the century, the analysis of specimens obtained from the lower airways of COPD patients compared with those from a control group of age-matched smokers with normal lung function has provided novel insights on the potential pathogenetic role of the different cells of the innate and acquired immune responses and their pro/anti-inflammatory mediators and intracellular signalling pathways, contributing to a better knowledge of the immunopathology of COPD both during its stable phase and during its exacerbations. This also has provided a scientific rationale for new drugs discovery and targeting to the lower airways. This review summarises and discusses the immunopathology of COPD patients, of different severity, compared with control smokers with normal lung function.

Differences of airway dimensions between patients with and without bronchiolitis obliterans syndrome after lung transplantation-Computer-assisted quantification of computed tomography

BACKGROUND

The aim of our retrospective study was to determine whether a dedicated software for assessment of airway morphology can detect differences in airway dimensions between patients with and without bronchiolitis obliterans syndrome (BOS), regarded as the clinical correlate of chronic lung allograft rejection.

METHODS

12 patients with and 14 patients without diagnosis of BOS were enrolled in the study. Evaluation of bronchial wall area percentage (WA%) and bronchial wall thickness (WT) in all follow-up CT scans was performed using a semiautomatic airway assessment tool. We assessed temporal changes (ΔWA%, ΔWT) and compared these morphological parameters with forced expiratory volume in one second (ΔFEV1).

RESULTS

In patients with and without BOS, the temporal changes over the entire follow-up were 26.6% versus 16.2% for ΔFEV1 (p=0.034), 14.2% versus 5.4% for ΔWA% (p=0.003) and 0.212mm versus 0.064mm for ΔWT (p=0.011).

CONCLUSIONS

We detected significant differences of the temporal changes of airway dimensions (ΔWA%, ΔWT) between lung transplant recipients with and without BOS. We conclude that computer-assisted bronchial wall measurements in CT scans might complement the information from pulmonary function tests and establish as a non-invasive method to confirm BOS in lung transplant recipients in the future.

A mixed phenotype of airway wall thickening and emphysema is associated with dyspnea and hospitalization for chronic obstructive pulmonary disease

RATIONALE

Quantitative computed tomography (CT) has been used to phenotype patients with chronic obstructive pulmonary disease (COPD). A mixed phenotype is defined as the presence of both airway wall thickening and emphysema on quantitative CT. Little is known about patients with COPD with the mixed phenotype.

OBJECTIVES

To propose a method of phenotyping COPD based on quantitative CT and to compare clinically relevant outcomes between patients with COPD with the mixed phenotype and those with other CT-based phenotypes.

METHODS

Each of 427 male smokers (187 without COPD, 240 with COPD) underwent a complete medical interview, pulmonary function testing, and whole-lung CT on the same day. The percentage of low-attenuation volume at the threshold of -950 Hounsfield units (%LAV) and the square root of wall area of a hypothetical airway with an internal perimeter of 10 mm (Pi10) were measured. Patients with COPD were classified into four distinct phenotypes based on the upper limits of normal for %LAV and Pi10, which were derived from the data of smokers without COPD by using quantile regression.

MEASUREMENTS AND MAIN RESULTS

Of 240 patients with COPD, 52 (21.7%) were classified as CT-normal phenotype, 39 (16.3%) as airway-dominant phenotype, 103 (42.9%) as emphysema-dominant phenotype, and 46 (19.2%) as mixed phenotype. Patients with COPD with the mixed phenotype were associated with more severe dyspnea than those with each of the remaining CT-based phenotypes (P < 0.01 for all comparisons). The number of hospitalizations for COPD exacerbations during the preceding year was 2.0 to 3.6 times higher in patients with the mixed phenotype than in those with each of the remaining CT-based phenotypes (P < 0.05 for all comparisons). Findings persisted after adjustment for age, pack-years of smoking, smoking status, body mass index, and FEV1.

CONCLUSIONS

Patients with COPD with the mixed phenotype are associated with more severe dyspnea and more frequent hospitalizations than those with each of the remaining CT-based phenotypes. Thus, patients with COPD with the mixed phenotype may need more attention and interventions.

Lung cancer screening: promise and pitfalls

The results of the National Lung Screening Trial (NLST) have provided the medical community and American public with considerable optimism about the potential to reduce lung cancer mortality with imaging-based screening. Designed as a randomized trial, the NLST has provided the first evidence of screening benefit by showing a 20% reduction in lung cancer mortality and a 6.7% reduction in all-cause mortality with low dose helical computed tomography (LDCT) screening relative to chest X-ray. The major harms of LDCT screening include the potential for radiation-induced carcinogenesis; high false-positivity rates in individuals without lung cancer, and overdiagnosis. Following the results of the NLST, the National Comprehensive Cancer Network (NCCN) published the first of multiple lung cancer screening guidelines under development by major medical organizations. These recommendations amalgamated screening cohorts, practices, interpretations, and diagnostic follow-up based on the NLST and other published studies to provide guidance for the implementation of LDCT screening. There are major areas of opportunity to optimize implementation. These include standardizing practices in the screening setting, optimizing risk profiles for screening and for managing diagnostic evaluation in individuals with indeterminate nodules, developing interdisciplinary screening programs in conjunction with smoking cessation, and approaching all stakeholders systematically to ensure the broadest education and dissemination of screening benefits relative to risks. The incorporation of validated biomarkers of risk and preclinical lung cancer can substantially enhance the effectiveness screening programs.

Continuous quantitative measurement of the proximal airway dimensions and lung density on four-dimensional dynamic-ventilation CT in smokers

Purpose

Four-dimensional dynamic-ventilation computed tomography (CT) imaging demonstrates continuous movement of the airways and lungs, which cannot be depicted with conventional CT. We aimed to investigate continuous changes in lung density and airway dimensions and to assess the correlation with spirometric values in smokers.

Materials and methods

This retrospective study was approved by the Institutional Review Board, and informed consent was waived. Twenty-one smokers including six patients with COPD underwent four-dimensional dynamic-ventilation CT during free breathing (160 mm in length). The mean lung density (MLD) of the scanned lung and luminal areas (Ai) of fixed points in the trachea and the right proximal bronchi (main bronchus, upper bronchus, bronchus intermedius, and lower bronchus) were continuously measured. Concordance between the time curve of the MLD and that of the airway Ai values was expressed by cross-correlation coefficients. The associations between these quantitative measurements and the forced expiratory volume in 1 second/forced vital capacity (FEV₁/FVC) values were assessed by Spearman’s rank correlation analysis.

Results

On the time curve for the MLD, the Δ-MLD1.05 values between the peak inspiratory frame to the later third frame (1.05 seconds later) were strongly correlated with the FEV₁/FVC (ρ=0.76, P<0.0001). The cross-correlation coefficients between the airway Ai and MLD values were significantly correlated with the FEV₁/FVC (ρ=−0.56 to −0.66, P<0.01), except for the right upper bronchus. This suggested that the synchrony between the airway and lung movement was lost in patients with severe airflow limitation.

Conclusion

Respiratory changes in the MLD and synchrony between the airway Ai and the MLD measured with dynamic-ventilation CT were correlated with patient’s spirometric values.

Computed tomography manifestation of acute exacerbation of chronic obstructive pulmonary disease: A pilot study

Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is an acute event characterized by the worsening of a patient's respiratory symptoms. To the best of our knowledge, few studies have investigated the computed tomography (CT) manifestation of AECOPD. Thus, the aim of the present study was to examine the CT manifestations during AECOPD. In total, 40 patients with AECOPD admitted to the emergency department were enrolled. CT images obtained at the time of exacerbation and at the 3-month follow-up were paired. Clinical characteristics and routine blood test results were also recorded. Airway dimensions and attenuation per patient were quantified from the 3rd to the 6th generation of four bronchi by Airway Inspector Slicer 2.8. The emphysema extent was also quantified and lung infiltration was detected, classified and measured. The CT images showed an increased wall area percentage (WA%) and increased mean and peak wall attenuation during the AECOPD; however, the extent of emphysema did not change significantly. In total, 60% of AECOPD patients presented with lung infiltration, compared with those at the follow-up CT scanning. The presence and extent of segmental distribution consolidation was correlated with the neutrophil percentage (N%), with a statistically significant difference observed. The total volume of lung parenchymal infiltration was correlated with the white blood cell (WBC) count and N%; however, no significant correlations were detected between the presence or extent of acinar shadow, air space consolidation with lobular distribution, ground-glass attenuation with lobular distribution, thickening of the interlobular septa and signs of infection (including the number of main symptoms, body temperature, WBC count and N%). The WA%, mean wall attenuation and peak wall attenuation increased during AECOPD, but the emphysema extent was unchanged. Lung infiltration existed frequently; however, only consolidation with segmental distribution appeared to be associated with bacterial infection.

Computed Tomographic Airway Morphology in Chronic Obstructive Pulmonary Disease. Remodeling or Innate Anatomy?

Computed tomographic measures of central airway morphology have been used in clinical, epidemiologic, and genetic investigation as an inference of the presence and severity of small-airway disease in smokers. Although several association studies have brought us to believe that these computed tomographic measures reflect airway remodeling, a careful review of such data and more recent evidence may reveal underappreciated complexity to these measures and limitations that prompt us to question that belief. This Perspective offers a review of seminal papers and alternative explanations of their data in the light of more recent evidence. The relationships between airway morphology and lung function are observed in subjects who never smoked, implying that native airway structure indeed contributes to lung function; computed tomographic measures of central airways such as wall area, lumen area, and total bronchial area are smaller in smokers with chronic obstructive pulmonary disease versus those without chronic obstructive pulmonary disease; and the airways are smaller as disease severity increases. The observations suggest that (1) native airway morphology likely contributes to the relationships between computed tomographic measures of airways and lung function; and (2) the presence of smaller airways in those with chronic obstructive pulmonary disease versus those without chronic obstructive pulmonary disease as well as their decrease with disease severity suggests that smokers with chronic obstructive pulmonary disease may simply have smaller airways to begin with, which put them at greater risk for the development of smoking-related disease.

Quantitative computed tomography imaging in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease having small airway inflammation, emphysema, and pulmonary hypertension. It is now clear that spirometry alone cannot differentiate each component. Quantitative computed tomography (QCT) is increasingly used to quantify the amount of emphysema and small airway involvement in COPD. Inspiratory CT guides in assessing emphysema while expiratory CT identifies areas of air trapping which is a surrogate of small airway inflammation. By constructing a three-dimensional model of airways, we can also measure the airway wall thickness of segmental and subsegmental airways. The aim of this review is to present the current knowledge and methodologies in QCT of the lung that aid in identifying discrete COPD phenotypes.

Airway Segmentation and Centerline Extraction from Thoracic CT - Comparison of a New Method to State of the Art Commercialized Methods

INTRODUCTION

Our motivation is increased bronchoscopic diagnostic yield and optimized preparation, for navigated bronchoscopy. In navigated bronchoscopy, virtual 3D airway visualization is often used to guide a bronchoscopic tool to peripheral lesions, synchronized with the real time video bronchoscopy. Visualization during navigated bronchoscopy, the segmentation time and methods, differs. Time consumption and logistics are two essential aspects that need to be optimized when integrating such technologies in the interventional room. We compared three different approaches to obtain airway centerlines and surface.

METHOD

CT lung dataset of 17 patients were processed in Mimics (Materialize, Leuven, Belgium), which provides a Basic module and a Pulmonology module (beta version) (MPM), OsiriX (Pixmeo, Geneva, Switzerland) and our Tube Segmentation Framework (TSF) method. Both MPM and TSF were evaluated with reference segmentation. Automatic and manual settings allowed us to segment the airways and obtain 3D models as well as the centrelines in all datasets. We compared the different procedures by user interactions such as number of clicks needed to process the data and quantitative measures concerning the quality of the segmentation and centrelines such as total length of the branches, number of branches, number of generations, and volume of the 3D model.

RESULTS

The TSF method was the most automatic, while the Mimics Pulmonology Module (MPM) and the Mimics Basic Module (MBM) resulted in the highest number of branches. MPM is the software which demands the least number of clicks to process the data. We found that the freely available OsiriX was less accurate compared to the other methods regarding segmentation results. However, the TSF method provided results fastest regarding number of clicks. The MPM was able to find the highest number of branches and generations. On the other hand, the TSF is fully automatic and it provides the user with both segmentation of the airways and the centerlines. Reference segmentation comparison averages and standard deviations for MPM and TSF correspond to literature.

CONCLUSION

The TSF is able to segment the airways and extract the centerlines in one single step. The number of branches found is lower for the TSF method than in Mimics. OsiriX demands the highest number of clicks to process the data, the segmentation is often sparse and extracting the centerline requires the use of another software system. Two of the software systems performed satisfactory with respect to be used in preprocessing CT images for navigated bronchoscopy, i.e. the TSF method and the MPM. According to reference segmentation both TSF and MPM are comparable with other segmentation methods. The level of automaticity and the resulting high number of branches plus the fact that both centerline and the surface of the airways were extracted, are requirements we considered particularly important. The in house method has the advantage of being an integrated part of a navigation platform for bronchoscopy, whilst the other methods can be considered preprocessing tools to a navigation system.

Optimal threshold of subtraction method for quantification of air-trapping on coregistered CT in COPD patients

OBJECTIVES

To investigate the optimal threshold of subtraction method for quantification of air trapping on co-registered CT in COPD patients in correlation with pulmonary function parameters.

METHODS

From June 2005 to October 2010, 174 patients were included in our study. Inspiration and expiration CT were performed followed by non-rigid registration using in-house software. The subtraction value per voxel between inspiration and registered expiration CT was obtained, and volume fraction of air trapping (air trapping index, ATI), using variable thresholds was calculated. ATI, expiration/inspiration ratio of mean lung density (E/I MLD) and the percentage of lung voxels below -856 HU on expiration CT (Exp-856) were correlated with FEF25-75% and RV/TLC.

RESULTS

The highest correlation coefficient with FEF25-75% was -0.656, using the threshold of 80 HU. As for RV/TLC, the highest correlation coefficient was 0.664, using the threshold of 30 HU. When plotting the relationship between subtraction thresholds and FEF25-75% and RV/TLC, the threshold of 60 HU was most suitable (r = -0.649 and 0.651). Those correlation coefficients were comparable to the results with E/I MLD (r = -0.670 and 0.657) and Exp-856 (r = -0.604 and 0.565).

CONCLUSIONS

The optimal threshold for quantification of air trapping was 60 HU and showed comparable correlations with pulmonary function parameters.

KEY POINTS

• The optimal CT threshold of subtraction method for air trapping was 60 HU. • ATI with 60 HU threshold was comparable to E/I MLD and Exp -856 . • Emphysema may substantially contribute to air trapping with statistical significance (P < 0.001).

Automated continuous quantitative measurement of proximal airways on dynamic ventilation CT: initial experience using an ex vivo porcine lung phantom

Background

The purpose of this study was to evaluate the feasibility of continuous quantitative measurement of the proximal airways, using dynamic ventilation computed tomography (CT) and our research software.

Methods

A porcine lung that was removed during meat processing was ventilated inside a chest phantom by a negative pressure cylinder (eight times per minute). This chest phantom with imitated respiratory movement was scanned by a 320-row area-detector CT scanner for approximately 9 seconds as dynamic ventilatory scanning. Obtained volume data were reconstructed every 0.35 seconds (total 8.4 seconds with 24 frames) as three-dimensional images and stored in our research software. The software automatically traced a designated airway point in all frames and measured the cross-sectional luminal area and wall area percent (WA%). The cross-sectional luminal area and WA% of the trachea and right main bronchus (RMB) were measured for this study. Two radiologists evaluated the traceability of all measurable airway points of the trachea and RMB using a three-point scale.

Results

It was judged that the software satisfactorily traced airway points throughout the dynamic ventilation CT (mean score, 2.64 at the trachea and 2.84 at the RMB). From the maximum inspiratory frame to the maximum expiratory frame, the cross-sectional luminal area of the trachea decreased 17.7% and that of the RMB 29.0%, whereas the WA% of the trachea increased 6.6% and that of the RMB 11.1%.

Conclusion

It is feasible to measure airway dimensions automatically at designated points on dynamic ventilation CT using research software. This technique can be applied to various airway and obstructive diseases.

How Common Is Airflow Limitation in Patients With Emphysema on CT Scan of the Chest?

BACKGROUND

COPD has traditionally been defined by the presence of irreversible airflow limitation on spirometry using either the GOLD (Global Initiative for Chronic Obstructive Lung Disease) or American Thoracic Society/European Respiratory Society criteria (lower limit of normal [LLN]). We have observed that some patients with clinical COPD and emphysema on chest CT scan have no obstruction on spirometry. The purpose of this study was to assess the prevalence of obstruction by GOLD and LLN criteria in patients with emphysema on CT scan and determine which radiographic criteria were associated with a clinical diagnosis of COPD.

METHODS

We retrospectively analyzed the clinical records and spirometry of all patients who had radiographically defined emphysema on chest CT scans completed at the University of Vermont in 2011. We compared spirometric criteria and CT scan factors with the presence of clinical COPD based on chart review.

RESULTS

We identified 274 patients with CT scan-defined emphysema. GOLD criteria detected obstruction in 228 patients (83%), and LLN detected obstruction in 206 patients (75%). However, GOLD failed to correctly identify 19 patients (6.9%) and LLN failed to identify 38 patients (13.9%) (average 10.4%) who had radiographic emphysema and a clinical diagnosis of COPD. Obese patients had a lower prevalence of obstruction whether classified by LLN or GOLD. Among patients with spirometric obstruction, there were greater degrees of emphysema and more severely increased airway wall thickness. Factors that were independently associated with clinical COPD were lower FVC % predicted, lower FEV1/FVC ratio, and increasing airway wall thickness.

CONCLUSIONS

Spirometry missed 10.4% of patients with clinical COPD who have significant emphysema on chest CT scan.

Comparison of a New Integral-Based Half-Band Method for CT Measurement of Peripheral Airways in COPD With a Conventional Full-Width Half-Maximum Method Using Both Phantom and Clinical CT Images

OBJECTIVES

To compare a new integral-based half-band method (IBHB) and a conventional full-width half-maximum (FWHM) method in measuring peripheral airway dimensions at airway phantoms and thin-section computed tomography of chronic obstructive pulmonary disease (COPD).

METHODS

The IBHB was validated and compared using airway phantoms and 50 patients with COPD. Airway parameters (wall area percentage [WA%], mean lumen radius, and mean wall thickness) were measured at fourth to sixth generations of the right apical bronchus. Matched results from 2 methods were compared and correlated with forced expiratory volume (FEV) in 1 second (FEV1), FEV1 / forced vital capacity (FVC), and global initiative for chronic obstructive lung disease (GOLD) stage. Linear regression analysis was performed using airway dimensions and emphysema index.

RESULTS

The IBHB generated more accurate measurements at phantom study. Measured airway parameters by both methods at thin-section computed tomography study were significantly different (all P < 0.05, paired t test). The IBHB method-measured WA% and wall thickness were significantly smaller. Mean WA% with IBHB also showed better correlation than that with FWHM (FEV1, r = -0.52 vs -0.28; FEV1 / FVC, r = -0.41 vs r = -0.20; GOLD, 0.52 vs 0.33, respectively). Linear regression analysis revealed fifth-generation WA% measured by IBHB was an independent variable, and addition to emphysema index increased predictability (FEV1, r = 0.63; FEV1 / FVC, r = 0.61; GOLD, r = 0.70).

CONCLUSIONS

The new IBHB measured peripheral airway dimensions differently than FWHM and showed better correlations with functional parameters in COPD.

Childhood-onset asthma in smokers. association between CT measures of airway size, lung function, and chronic airflow obstruction

RATIONALE AND OBJECTIVES

Asthma is associated with chronic airflow obstruction. Our goal was to assess the association of computed tomographic measures of airway wall volume and lumen volume with the FEV1 and chronic airflow obstruction in smokers with childhood-onset asthma.

METHODS

We analyzed clinical, lung function, and volumetric computed tomographic airway volume data from 7,266 smokers, including 590 with childhood-onset asthma. Small wall volume and small lumen volume of segmental airways were defined as measures 1 SD below the mean. We assessed the association between small wall volume, small lumen volume, FEV1, and chronic airflow obstruction (post-bronchodilator FEV1/FVC ratio < 0.7) using linear and logistic models.

MEASUREMENTS AND MAIN RESULTS

Compared with subjects without childhood-onset asthma, those with childhood-onset asthma had smaller wall volume and lumen volume (P < 0.0001) of segmental airways. Among subjects with childhood-onset asthma, those with the smallest wall volume and lumen volume had the lowest FEV1 and greatest odds of chronic airflow obstruction. A similar tendency was seen in those without childhood-onset asthma. When comparing these two groups, both small wall volume and small lumen volume were more strongly associated with FEV1 and chronic airflow obstruction among subjects with childhood-asthma in multivariate models.

CONCLUSION

In smokers with childhood-onset asthma, smaller airways are associated with reduced lung function and chronic airflow obstruction. Clinical trial registered with www.clinicaltrials.gov (NCT00608764).

Three dimensional imaging of paraffin embedded human lung tissue samples by micro-computed tomography

Background

Understanding the three-dimensional (3-D) micro-architecture of lung tissue can provide insights into the pathology of lung disease. Micro computed tomography (µCT) has previously been used to elucidate lung 3D histology and morphometry in fixed samples that have been stained with contrast agents or air inflated and dried. However, non-destructive microstructural 3D imaging of formalin-fixed paraffin embedded (FFPE) tissues would facilitate retrospective analysis of extensive tissue archives of lung FFPE lung samples with linked clinical data.

Methods

FFPE human lung tissue samples (n = 4) were scanned using a Nikon metrology µCT scanner. Semi-automatic techniques were used to segment the 3D structure of airways and blood vessels. Airspace size (mean linear intercept, Lm) was measured on µCT images and on matched histological sections from the same FFPE samples imaged by light microscopy to validate µCT imaging.

Results

The µCT imaging protocol provided contrast between tissue and paraffin in FFPE samples (15mm x 7mm). Resolution (voxel size 6.7 µm) in the reconstructed images was sufficient for semi-automatic image segmentation of airways and blood vessels as well as quantitative airspace analysis. The scans were also used to scout for regions of interest, enabling time-efficient preparation of conventional histological sections. The Lm measurements from µCT images were not significantly different to those from matched histological sections.

Conclusion

We demonstrated how non-destructive imaging of routinely prepared FFPE samples by laboratory µCT can be used to visualize and assess the 3D morphology of the lung including by morphometric analysis.

Geodesic Atlas-Based Labeling of Anatomical Trees: Application and Evaluation on Airways Extracted From CT

We present a fast and robust atlas-based algorithm for labeling airway trees, using geodesic distances in a geometric tree-space. Possible branch label configurations for an unlabeled airway tree are evaluated using distances to a training set of labeled airway trees. In tree-space, airway tree topology and geometry change continuously, giving a natural automatic handling of anatomical differences and noise. A hierarchical approach makes the algorithm efficient, assigning labels from the trachea and downwards. Only the airway centerline tree is used, which is relatively unaffected by pathology. The algorithm is evaluated on 80 segmented airway trees from 40 subjects at two time points, labeled by three medical experts each, testing accuracy, reproducibility and robustness in patients with chronic obstructive pulmonary disease (COPD). The accuracy of the algorithm is statistically similar to that of the experts and not significantly correlated with COPD severity. The reproducibility of the algorithm is significantly better than that of the experts, and negatively correlated with COPD severity. Evaluation of the algorithm on a longitudinal set of 8724 trees from a lung cancer screening trial shows that the algorithm can be used in large scale studies with high reproducibility, and that the negative correlation of reproducibility with COPD severity can be explained by missing branches, for instance due to segmentation problems in COPD patients. We conclude that the algorithm is robust to COPD severity given equally complete airway trees, and comparable in performance to that of experts in pulmonary medicine, emphasizing the suitability of the labeling algorithm for clinical use.

Longitudinal shape irregularity of airway lumen assessed by CT in patients with bronchial asthma and COPD

BACKGROUND

Airway remodelling in bronchial asthma (BA) and COPD has been quantitatively assessed by analysing the airway wall area and the luminal area on cross-sectional CT images. To date, there have been no reports on assessment of the longitudinal structure of the airway lumen.

METHODS

Quantitative airway analysis using CT was performed on three groups consisting of 29 patients with BA, 58 patients with COPD and 59 healthy controls. To assess the longitudinal shape irregularity of the airway lumen, new quantitative CT parameters, validated by a phantom study, were established. The internal radii of imaginary inscribed spheres in the airway lumen were measured as a function of distance from the level of the carina to the fifth-order branches of the right posterior basal bronchus. The gaps of these radii from the regression line were calculated as parameters to reflect the longitudinal airway lumen shape irregularity. These new parameters were compared among the study groups as well as with the conventional parameters of airway wall thickening and luminal area.

RESULTS

Longitudinal airway lumen shape irregularity was significantly greater in patients with COPD than in those with BA and healthy controls. Wall thickening was significantly greater, and luminal area smaller, in patients with BA than in those with COPD and healthy controls. These results were consistent even among the BA and COPD subgroups with similar airflow limitation.

CONCLUSIONS

The combination of cross-sectional and longitudinal airway structure analyses using CT images may suggest differences in the characteristics of airway remodelling between COPD and asthma.

Optical coherence tomography in respiratory science and medicine: from airways to alveoli

Optical coherence tomography is a rapidly maturing optical imaging technology, enabling study of the in vivo structure of lung tissue at a scale of tens of micrometers. It has been used to assess the layered structure of airway walls, quantify both airway lumen caliber and compliance, and image individual alveoli. This article provides an overview of the technology and reviews its capability to provide new insights into respiratory disease.

Chronic Obstructive Pulmonary Disease: CT Quantification of Airway Dimensions, Numbers of Airways to Measure, and Effect of Bronchodilation

PURPOSE

To determine the effect of bronchodilation on airway indexes reflecting airway disease in patients with chronic obstructive pulmonary disease (COPD) and to determine the minimum number of segmental and subsegmental airways required.

MATERIALS AND METHODS

This study was approved by the local ethical committee, and written informed consent was obtained from all subjects. Twenty patients with COPD who had undergone pre- and postbronchodilator pulmonary function tests and computed tomographic (CT) examinations were prospectively included. Eight healthy volunteers underwent two CT examinations. Luminal area and wall thickness (WT) of third- and fourth-generation airways were measured twice by three readers. The percentage of total airway area occupied by the wall and the square root of wall area at an internal perimeter of 10 mm (√WAPi10) were calculated. The effects of pathologic status, session, reader, bronchodilation, and CT examination were assessed by using mixed linear model analyses. The number of airways to measure for a definite percentage error of √WAPi10 was computed by using a bootstrap method.

RESULTS

There were no significant session, reader, or bronchodilation effects on WT in third-generation airways and √WAPi10 in patients with COPD (P values ranging from .187 to >.999). WT in third-generation airways and √WAPi10 were significantly different in patients with COPD and control subjects (P = .018 and <.001, respectively). Measuring 12 third- or fourth-generation airways ensured a maximal 10% error of √WAPi10.

CONCLUSION

WT in third-generation airways and √WAPi10 are not significantly different before and after bronchodilation and are different in patients with COPD and control subjects. Twelve is the minimum number of third- or fourth-generation airways required to ensure a maximal 10% error of √WAPi10. (©) RSNA, 2015 Clinical trial registration no. NCT01142531 Online supplemental material is available for this article.

CT-Definable Subtypes of Chronic Obstructive Pulmonary Disease: A Statement of the Fleischner Society

The purpose of this statement is to describe and define the phenotypic abnormalities that can be identified on visual and quantitative evaluation of computed tomographic (CT) images in subjects with chronic obstructive pulmonary disease (COPD), with the goal of contributing to a personalized approach to the treatment of patients with COPD. Quantitative CT is useful for identifying and sequentially evaluating the extent of emphysematous lung destruction, changes in airway walls, and expiratory air trapping. However, visual assessment of CT scans remains important to describe patterns of altered lung structure in COPD. The classification system proposed and illustrated in this article provides a structured approach to visual and quantitative assessment of COPD. Emphysema is classified as centrilobular (subclassified as trace, mild, moderate, confluent, and advanced destructive emphysema), panlobular, and paraseptal (subclassified as mild or substantial). Additional important visual features include airway wall thickening, inflammatory small airways disease, tracheal abnormalities, interstitial lung abnormalities, pulmonary arterial enlargement, and bronchiectasis.

Assessment of Small Airways with Computed Tomography: Mosaic Attenuation or Lung Density?

BACKGROUND

Computed tomography (CT) assessment of air trapping has been considered useful as a measure of small airway disease. Mean lung density (MLD) and the percentage of the lung field occupied by low attenuation area (LAA%) can be evaluated automatically, and their expiratory/inspiratory (E/I) ratios correlate with asthma severity and spirometry parameters. However, mosaic attenuation, another indicator of air trapping, has been assessed visually, and its functional relevance remains controversial.

OBJECTIVES

This retrospective study was conducted to correlate mosaic attenuation, which was assessed visually and automatically, and the E/I ratios of MLD and LAA% (defined as areas <-960 Hounsfield units) with clinical and physiological variables, including impulse oscillometry (IOS) indices.

MATERIAL AND METHODS

In 36 nonsmoking patients with stable asthma, the lungs were scanned at full inspiration and full expiration. Mosaic attenuation was measured visually and automatically, by counting areas with CT values higher than the surrounding areas. MLD and LAA% were measured using our validated method. Spirometry, IOS, exhaled NO and the sputum eosinophil count were evaluated.

RESULTS

The automatic results and visual scores of mosaic attenuation correlated well on expiratory scans (r = 0.894) and to a lesser degree on inspiratory scans (r = 0.629; p < 0.0001 for both). However, only the E/I ratios of MLD and LAA% correlated with forced expiratory volume in 1 s/forced vital capacity of spirometry and the IOS indices of resistance from 5 to 20 Hz and the integrated area of low-frequency reactance.

CONCLUSIONS

Our automatic method for analysis of mosaic attenuation is likely useful, but the results themselves may not be reflecting small airway involvement of asthma, unlike the E/I ratios of MLD and LAA%.

Effect of threshold on the correlation between airflow obstruction and low attenuation volume in smokers assessed by inspiratory and expiratory MDCT

BACKGROUND

The estimation of emphysematous changes is very sensitive to computed tomography (CT) threshold level. In clinical practice, the predetermined threshold is usually set at -950 Hounsfield units (HU) for the detection of low attenuation volume (LAV). However, threshold levels that are tightly connected to pulmonary function abnormalities have not been determined.

PURPOSE

To determine the threshold level for calculating an LAV that closely reflects airflow limitation in patients with chronic obstructive pulmonary disease (COPD).

MATERIAL AND METHODS

Seventy-six consecutive non-COPD smokers and COPD patients underwent paired inspiratory and expiratory multidetector CT (MDCT). LAV% was segmented every 10 HU between -1000 and -750 HU to examine the correlation between LAV% and indexes of obstructive impairment.

RESULTS

LAV% gradually increased as the threshold level increased on both inspiratory and expiratory images. LAV% on inspiratory images was higher than that on expiratory images at all threshold levels between -1000 and -750 HU. The threshold level that correlated with obstructive impairment differed between the two images: -930 HU on inspiratory and -870 or -880 HU on expiratory images.

CONCLUSION

LAV% dramatically changed according to the threshold level on both inspiratory and expiratory images, indicating that LAV% is dependent on the attenuation threshold level in patients with COPD. The threshold linking LAV% to airflow limitation was higher on expiratory than on inspiratory images.

Regional bronchodilator response assessed by computed tomography in chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

The reliability of CT assessment of regional bronchodilation is not universally accepted. In this study, using our proprietary 3D-CT software, we first examined airway inner luminal area (Ai) before and after inhalation of SFC in a group of COPD patients and then evaluated the same parameters for two sets of CT data obtained from clinically stable subjects with no intervention.

METHODS

We conducted CT at deep inspiration and pulmonary function tests before and one week after inhalation of SFC in 23 COPD patients. As a non-intervention group, we used two sets of CT data obtained with one-year interval in another group of subjects who demonstrated stable pulmonary function (n=8). We measured Ai at the mid-portions of 3rd to 6th generation in 8 bronchi of the right lung, a total of 32 identical sites before and after intervention.

RESULTS

The average bronchodilation at all sites (ΔAi%: 28.2 ± 4.1 (SE)%) (r=0.65, p<0.001) and that of each generation significantly correlated with % improvement of FEV1 (ΔFEV1%), which increased from 1.40 ± 0.10 L to 1.58 ± 0.10 L. When subjects were classified into two groups in terms of mean ΔFEV1%, even the poor responders (ΔFEV1% <14% above baseline, n=13) displayed significantly larger ΔAi% compared with the non-intervention group (19.1 ± 4.6% versus 2.1 ± 3.9%). Inter-observer variability for overall ΔAi% was within acceptable levels.

CONCLUSIONS

CT can reliably detect the regional bronchodilation in 3rd to 6th generation airways when ΔFEV1 is as small as 180 ml on average. This study was registered in the UMIN Clinical Trials Registry (UMIN-CTR) system (http://www.umin.ac.jp/. No. UMIN 000002668).

Understanding the contribution of native tracheobronchial structure to lung function: CT assessment of airway morphology in never smokers

Background

Computed tomographic (CT) airway lumen narrowing is associated with lower lung function. Although volumetric CT measures of airways (wall volume [WV] and lumen volume [LV]) compared to cross sectional measures can more accurately reflect bronchial morphology, data of their use in never smokers is scarce. We hypothesize that native tracheobronchial tree morphology as assessed by volumetric CT metrics play a significant role in determining lung function in normal subjects. We aimed to assess the relationships between airway size, the projected branching generation number (BGN) to reach airways of <2mm lumen diameter –the site for airflow obstruction in smokers- and measures of lung function including forced expiratory volume in 1 second (FEV₁) and forced expiratory flow between 25% and 75% of vital capacity (FEF 25–75).

Methods

We assessed WV and LV of segmental and subsegmental airways from six bronchial paths as well as lung volume on CT scans from 106 never smokers. We calculated the lumen area ratio of the subsegmental to segmental airways and estimated the projected BGN to reach a <2mm-lumen-diameter airway assuming a dichotomized tracheobronchial tree model. Regression analysis was used to assess the relationships between airway size, BGN, FEF 25–75, and FEV₁.

Results

We found that in models adjusted for demographics, LV and WV of segmental and subsegmental airways were directly related to FEV₁ (P <0.05 for all the models). In adjusted models for age, sex, race, LV and lung volume or height, the projected BGN was directly associated with FEF 25–75 and FEV₁ (P = 0.001) where subjects with lower FEV₁ had fewer calculated branch generations between the subsegmental bronchus and small airways. There was no association between airway lumen area ratio and lung volume.

Conclusion

We conclude that in never smokers, those with smaller central airways had lower airflow and those with lower airflow had less parallel airway pathways independent of lung size. These findings suggest that variability in the structure of the tracheobronchial tree may influence the risk of developing clinically relevant smoking related airway obstruction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0181-y) contains supplementary material, which is available to authorized users.

Inflammation and pathological damage to the lungs of mice are only partially reversed following smoking cessation on subacute exposure to cigarette smoke

The present study aimed to observe the level of inflammation and the number of lesions in the airways and parenchyma of mouse lungs subsequent to smoking cessation following 4 weeks exposure to cigarette smoke. Enlargement of the regional airspaces, deposition of peribronchial collagen fibers and macrophage infiltration were assessed. In addition, the expression levels of matrix metalloproteinase (MMP)‑12 and transforming growth factor (TGF)‑β1 were detected in the airways and lung parenchyma of C57BL/6 J mice. Mice, which were exposed to filtered air for 4 weeks or cigarette smoke for 8 weeks were used as control groups. A 4 week duration of smoke exposure induced the expansion of alveolar spaces ~100 µm from the terminal bronchioles, but without increased deposition of collagen around the small airways, which was not reversed following smoking cessation. Pulmonary infiltration of macrophages and the protein expression levels of MMP‑12 and TGF‑β1 increased in the airways following 4 weeks smoke exposure, however, there was no further increase at 8 weeks, and the expression levels of TGF‑β1 in the lung parenchyma decreased. At 4 weeks post‑smoking cessation, the expression levels of TGF‑β1 in the airways and lung parenchyma returned to normal; whereas, 1 week after smoking cessation, the expression levels of MMP‑12 were higher compared with the normal control group. Subacute exposure to cigarette smoke induced an inflammatory response and regional damage to the lung parenchyma, prior to deposition of collagen around the airways. Following smoking cessation, the pulmonary inflammatory reaction was partially reversed, however, macrophage infiltration and the expression levels of MMP‑12 remained significantly higher compared with the control mice. These results suggested that regulation of the expression of MMP‑12 and TGF‑β1, particularly in the distribution in the airways and lung parenchyma, may be a strategy for the early treatment of chronic obstructive pulmonary disease.

Correlation of a decline in aerobic capacity with development of emphysema in patients with chronic obstructive pulmonary disease: a prospective observational study

In patients with COPD, CT assessment of emphysema and airway disease is known to be associated with lung function and 6-minute walk distance. However, it remains to be determined whether low attenuation area (LAA) on CT is associated with aerobic capacity assessed using cardiopulmonary exercise testing (CPET). In this prospective observational study, we repeatedly conducted high-resolution CT and CPET using a treadmill in 81 COPD patients over a median interval of 3.5 years. Two investigators independently scored LAA on images obtained at the aortic arch level, tracheal bifurcation level, and supradiaphragmatic level. Grades for the images of each lung were added to yield the total LAA score. Total LAA score was negatively correlated with peak aerobic capacity ([Formula: see text]) (p<0.001, r = -0.485). LAA scores of the upper (aortic arch level) and the lower (supradiaphragmatic level) lungs were both significantly associated with peak [Formula: see text]. There was a significant correlation between total LAA score and peak CO2 output ([Formula: see text]) (p<0.001, r = -0.433). Total LAA score was correlated with oxygen saturation at peak exercise (p<0.001, r = -0.634) and the estimated dead space fraction (p<0.001, r = 0.416). The mean annual change in total LAA score was significantly correlated with those in peak [Formula: see text] (p<0.001, r = -0.546) and peak [Formula: see text] (p<0.001, r = -0.488). The extent of emphysema measured by CT was associated with the results of CPET. The time-dependent changes in CPET data were also correlated with that in total LAA score. CT assessment could be a non-invasive tool to predict aerobic capacity in patients with COPD.

OSCILLATORY FLOW OF HFV DISTRIBUTED IN LEFT AND RIGHT LUNGS: A MODEL-BASED EXPERIMENT AND INVESTIGATION

The human respiratory system is not entirely symmetric, and regional respiratory diseases can further enlarge this difference in most cases. Therefore, the lungs perform differently. This paper explored the possibilities of suppressing and enhancing the performance of a diseased lung with different high-frequency ventilation (HFV) frequencies by experimenting, as well as modeling, the oscillatory airflow distribution between the left and right lungs. The experimental setup mainly consisted of a physical respiratory model, a signal acquisition device, and a high-frequency oscillation ventilator. This ventilator outputs a positive sinusoidal air-pressure during inspiration. On these bases, a series of experiments were also conducted with different compliances and resistances in the left and the right lungs. The experiments demonstrated that the oscillatory flow distribution is primarily correlated with the oscillation frequency and the regional lung compliance.

Chronic obstructive pulmonary disease

COPD is characterized by airflow limitation that is not fully reversible. The morphological basis for airflow obstruction results from a varying combination of obstructive changes in peripheral conducting airways and destructive changes in respiratory bronchioles, alveolar ducts, and alveoli. A reduction of vascularity within the alveolar septa has been reported in emphysema. Typical physiological changes reflect these structural abnormalities. Spirometry documents airflow obstruction when the FEV1/FVC ratio is reduced below the lower limit of normality, although in early disease stages FEV1 and airway conductance are not affected. Current guidelines recommend testing for bronchoreversibility at least once and the postbronchodilator FEV1/FVC be used for COPD diagnosis; the nature of bronchodilator response remains controversial, however. One major functional consequence of altered lung mechanics is lung hyperinflation. FRC may increase as a result of static or dynamic mechanisms, or both. The link between dynamic lung hyperinflation and expiratory flow limitation during tidal breathing has been demonstrated. Hyperinflation may increase the load on inspiratory muscles, with resulting length adaptation of diaphragm. Reduction of exercise tolerance is frequently noted, with compelling evidence that breathlessness and altered lung mechanics play a major role. Lung function measurements have been traditionally used as prognostic indices and to monitor disease progression; FEV1 has been most widely used. An increase in FVC is also considered as proof of bronchodilatation. Decades of work has provided insight into the histological, functional, and biological features of COPD. This has provided a clearer understanding of important pathobiological processes and has provided additional therapeutic options.

Advanced imaging in COPD: insights into pulmonary pathophysiology

Chronic obstructive pulmonary disease (COPD) involves a complex interaction of structural and functional abnormalities. The two have long been studied in isolation. However, advanced imaging techniques allow us to simultaneously assess pathological processes and their physiological consequences. This review gives a comprehensive account of the various advanced imaging modalities used to study COPD, including computed tomography (CT), magnetic resonance imaging (MRI), and the nuclear medicine techniques positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Some more recent developments in imaging technology, including micro-CT, synchrotron imaging, optical coherence tomography (OCT) and electrical impedance tomography (EIT), are also described. The authors identify the pathophysiological insights gained from these techniques, and speculate on the future role of advanced imaging in both clinical and research settings.

Chronic respiratory symptoms associated with airway wall thickening measured by thin-slice low-dose CT

OBJECTIVE

In lung cancer screening, the prevalence of chronic respiratory symptoms is high among heavy smokers. The purpose of this study was to compare CT-derived airway wall measurements between male smokers with and those without chronic respiratory symptoms.

MATERIALS AND METHODS

Fifty male heavy smokers with chronic respiratory symptoms (cough, excessive mucus secretion, dyspnea, and wheezing) and 50 without any respiratory symptom were randomly selected from the Dutch-Belgian Randomized Lung Cancer Screening Trial. Thin-slice low-dose CT images were evaluated with dedicated software for airway measurements. Wall area percentage and airway wall thickness were measured from trachea to bronchi in five different pulmonary lobes of airways with a luminal diameter of 5 mm or greater. Association between airway wall measurements and respiratory symptoms was analyzed by multiple linear regression adjusted for age, body mass index, smoking status, emphysema, and pulmonary function.

RESULTS

After adjustment for relevant factors, a significant positive association between airway wall measurements and respiratory symptoms was found in airways with a luminal diameter between 5 to 10 mm (p < 0.01), but not in airways measuring 10 mm or greater (p > 0.05). At the airway level between 5 to 10 mm, the mean wall area percentages were 51.5% ± 7.9%. Airway wall thicknesses were 1.54 ± 0.39 mm and 1.37 ± 0.35 mm (p < 0.001).

CONCLUSION

Male heavy smokers with chronic respiratory symptoms in lung cancer screening, who are at high-risk of chronic bronchitis, have bronchial wall thickening in airways with a luminal diameter of 5-10 mm but not in larger airways.

Not all measures of hyperinflation are created equal: lung structure and clinical correlates of gas trapping and hyperexpansion in COPD: the Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

BACKGROUND

Hyperinflation refers to a nonspecific increase in absolute lung volumes and has a poor prognosis in COPD. The relative contribution of increased airways resistance and increased parenchymal compliance to hyperinflation of each absolute lung volume is poorly understood. We hypothesized that increased residual volume (RV) and RV/total lung capacity (TLC) would be associated with reduced airway lumen dimensions, whereas increased functional residual capacity (FRC), TLC, and reduced inspiratory capacity (IC)/TLC would be associated with emphysema on CT scan. We examined whether clinical characteristics differed accordingly.

METHODS

The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study recruited smokers aged 50 to 79 years who were free of clinical cardiovascular disease. Gas trapping was defined as RV or RV/TLC greater than the upper limit of normal and hyperexpansion as FRC or TLC greater than the upper limit of normal or IC/TLC less than the lower limit of normal. Airway lumen diameters and percent emphysema &lt; -950 Hounsfield units were quantified on CT images. Analyses were adjusted for age, sex, body size, race/ethnicity, education, and smoking.

RESULTS

Among 116 participants completing plethysmography, 15% had gas trapping, 18% has hyperexpansion, and 22% had both. Gas trapping was associated with smaller airway lumen diameters (P = .001), greater dyspnea (P = .01), and chronic bronchitis (P = .03). Hyperexpansion was associated with percent emphysema (P &lt; .001), lower BMI (P = .04), and higher hemoglobin concentration (P = .001).

CONCLUSIONS

Gas trapping and hyperexpansion on plethysmography were associated with distinct differences in lung structure and clinical characteristics. Absolute lung volumes should not be considered equivalent in their estimation of hyperinflation and provide insight into the extent of airway and parenchymal abnormalities in COPD.

Comparison of spatially matched airways reveals thinner airway walls in COPD. The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study and the Subpopulations and Intermediate Outcomes in COPD Study (SPIROMICS)

BACKGROUND

COPD is characterised by reduced airway lumen dimensions and fewer peripheral airways. Most studies of airway properties sample airways based upon lumen dimension or at random, which may bias comparisons given reduced airway lumen dimensions and number in COPD. We sought to compare central airway wall dimensions on CT in COPD and controls using spatially matched airways, thereby avoiding selection bias of airways in the lung.

METHODS

The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study and Subpopulations and Intermediate Outcomes in COPD Study (SPIROMICS) recruited smokers with COPD and controls aged 50-79 years and 40-80 years, respectively. COPD was defined by current guidelines. Using CT image data, airway dimensions were measured for all central airway segments (generations 0-6) following 5 standardised paths into the lungs. Case-control airway comparisons were spatially matched by generation and adjusted for demographics, body size, smoking, CT dose, per cent emphysema, airway length and lung volume.

RESULTS

Among 311 MESA COPD participants, airway wall areas at generations 3-6 were smaller in COPD compared with controls (all p<0.001). Among 1248 SPIROMICS participants, airway wall areas at generations 1-6 were smaller (all p<0.001), and this reduction was monotonic with increasing COPD severity (p<0.001). In both studies, sampling airways by lumen diameter or randomly resulted in a comparison of more proximal airways in COPD to more peripheral airways in controls (p<0.001) resulting in the appearance of thicker walls in COPD (p<0.02).

CONCLUSIONS

Airway walls are thinner in COPD when comparing spatially matched central airways. Other approaches to airway sampling result in comparisons of more proximal to more distal airways and potentially biased assessment of airway properties in COPD.

Techniques of assessing small airways dysfunction

The small airways are defined as those less than 2 mm in diameter. They are a major site of pathology in many lung diseases, not least chronic obstructive pulmonary disease (COPD) and asthma. The small airways are frequently involved early in the course of these diseases, with significant pathology demonstrable often before the onset of symptoms or changes in spirometry and imaging. Despite their importance, they have proven relatively difficult to study. This is in part due to their relative inaccessibility to biopsy and their small size which makes their imaging difficult. Traditional lung function tests may only become abnormal once there is a significant burden of disease within them. This has led to the term 'the quiet zone' of the lung. In recent years, more specialised tests have been developed which may detect these changes earlier, perhaps offering the possibility of earlier diagnosis and intervention. These tests are now moving from the realms of clinical research laboratories into routine clinical practice and are increasingly useful in the diagnosis and monitoring of respiratory diseases. This article gives an overview of small airways physiology and some of the routine and more advanced tests of airway function.

Detailed analysis of the density change on chest CT of COPD using non-rigid registration of inspiration/expiration CT scans

OBJECTIVES

One objective was to evaluate the air trapping index (ATI), measured by inspiration/expiration CT, in COPD patients and nonsmokers. Another objective was to assess the association between the pulmonary function test (PFT) and CT parameters such as ATI or other indices, separately in the whole lung, in emphysema, and in hyperinflated and normal lung areas.

METHODS

One hundred and thirty-eight COPD patients and 29 nonsmokers were included in our study. The ATI, the emphysema index (EI), the gas trapping index (Exp -856) and expiration/inspiration ratio of mean lung density (E/Iratio of MLD) were measured on CT. The values of the whole lung, of emphysema, and of hyperinflated and normal lung areas were compared and then correlated with various PFT parameters.

RESULTS

Compared with nonsmokers, COPD patients showed a higher ATI in the whole lung and in each lung lesion (all P < 0.05). The ATI showed a higher correlation than EI with FEF25-75%, RV and RV/TLC, and was comparable to Exp -856 and the E/I ratio of MLD. The ATI of emphysema and hyperinflated areas on CT showed better correlation than the normal lung area with PFT parameters.

CONCLUSIONS

Detailed analysis of density change at inspiration and expiration CT of COPD can provide new insights into pulmonary functional impairment in each lung area.

KEY POINTS

• COPD patients show significant air trapping in the lung. • The air trapping index is a comparable parameter to other CT indices. • Air trapping of emphysema and hyperinflated lung areas relates to functional loss. • The emphysema area changes more, with less air trapping than other areas.

Central airways remodeling in COPD patients

BACKGROUND

The contribution to airflow obstruction by the remodeling of the peripheral airways in chronic obstructive pulmonary disease (COPD) patients has been well documented, but less is known about the role played by the large airways. Few studies have investigated the presence of histopathological changes due to remodeling in the large airways of COPD patients.

OBJECTIVES

The aim of this study was to verify the presence of airway remodeling in the central airways of COPD patients, quantifying the airway smooth muscle (ASM) area and the extracellular matrix (ECM) protein deposition, both in the subepithelial region and in the ASM, and to verify the possible contribution to airflow obstruction by the above mentioned histopathological changes.

METHODS

Biopsies of segmental bronchi spurs were performed in COPD patients and control smoker subjects and immunostained for collagen type I, versican, decorin, biglycan, and alpha-smooth muscle actin. ECM protein deposition was measured at both subepithelial, and ASM layers.

RESULTS

The staining for collagen I and versican was greater in the subepithelial layer of COPD patients than in control subjects. An inverse correlation was found between collagen I in the subepithelial layer and both forced expiratory volume in 1 second and ratio between forced expiratory volume in 1 second and forced vital capacity. A statistically significant increase of the ASM area was observed in the central airways of COPD patients versus controls.

CONCLUSION

These findings indicate that airway remodeling also affects the large airways in COPD patients who have greater deposition of ECM proteins in the subepithelial layer and a larger smooth muscle area than control smoker subjects. These changes may contribute to chronic airflow obstruction in COPD patients.

Comparison of airway dimensions with once daily tiotropium plus indacaterol versus twice daily Advair(®) in chronic obstructive pulmonary disease

BACKGROUND

Current guidelines recommend combining long-acting bronchodilators with different modes of action in patients with moderate-to-severe chronic obstructive pulmonary disease (COPD). We evaluated the effects of airway dimensions and pulmonary function with tiotropium plus indacaterol versus Advair(®).

METHODS

Subjects (n = 46) were randomized to receive tiotropium (18 μg once daily) plus indacaterol (150 μg once daily) or Advair(®) (50/250 μg twice daily) for 16 weeks. Airway geometry was determined by quantitative computed tomography (luminal area, Ai; total area of the airway, Ao; wall area, WA; and percentage wall area, WA/Ao and wall thickness, T). Spirometry (forced expiratory volume in 1 s, FEV1; forced vital capacity, FVC and inspiratory capacity, IC) and St. George's Respiratory Questionnaire (SGRQ) were evaluated.

RESULTS

Tiotropium plus indacaterol significantly increased CT-indices including Ai corrected for body surface area (Ai/BSA), and decreased WA/BSA, WA/Ao and T/√BSA compared with Advair(®) (p < 0.05, respectively). In physiological parameters, mean difference in IC was significantly higher under treatment with tiotropium plus indacaterol than Advair(®) (p < 0.05). The changes in Ai/BSA, WA/BSA, WA/Ao and T/√BSA were significantly correlated with changes in IC (r = 0.535, p = 0.011; r = -0.688, p < 0.001; r = -0.555, p = 0.002 and r = -0.542, p = 0.007; respectively). There were more significant improvements in SGRQ scores after treatment with tiotropium plus indacaterol than Advair(®).

CONCLUSIONS

These findings suggest that dual bronchodilation with tiotropium plus indacaterol is superior in airway geometry and lung function compared with Advair(®) in COPD.

Ratios of peripheral-to-central airway lumen area and percentage wall area as predictors of severity of chronic obstructive pulmonary disease

OBJECTIVE

The purpose of this study was to assess the ability of the ratios of peripheral-to-central airway lumen area (hereafter referred to as LA) and percentage wall area (hereafter referred to as %WA) to predict the severity of chronic obstructive pulmonary disease (COPD) according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines.

SUBJECTS AND METHODS

We examined 32 patients (27 men and five women; mean age ± SD, 70.0 ± 6.8 years; seven GOLD stage 0 [at risk for COPD], 19 GOLD stage 1-2 [mild to moderate airflow limitation], and six GOLD stage 3-4 [severe to very severe airflow limitation]) using inspiratory CT. Mean LA and %WA were measured for the first (main bronchi), third, and fifth generations of five bronchi in each lobe and the ratios of peripheral to central airways were calculated (third to first, fifth to first, and fifth to third) and statistically compared.

RESULTS

The fifth-generation LA, LA fifth to first, and LA fifth to third significantly decreased and fifth %WA, %WA fifth to first, and %WA fifth to third also increased with progression of GOLD stage (p < 0.05), but central measurements, including first and third generations, did not. There were significant differences between GOLD 0 and GOLD 1-2 for %WA fifth to third and LA fifth to third and between GOLD 0 and GOLD 3-4 for all six parameters (p < 0.05); %WA fifth to third had the best cutoff value of 1.02 (sensitivity, 92%; specificity, 86%) for diagnosis of COPD (GOLD 1-4). The %WA fifth to first of 1.51 (sensitivity, 83%; specificity, 89%) was best for diagnosis of GOLD 3-4.

CONCLUSION

Ratios of peripheral-to-central airway LA and %WA show improved correlation with COPD severity.

Phenotypic and genetic heterogeneity among subjects with mild airflow obstruction in COPDGene

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by marked phenotypic heterogeneity. Most previous studies have focused on COPD subjects with FEV1 < 80% predicted. We investigated the clinical and genetic heterogeneity in subjects with mild airflow limitation in spirometry grade 1 defined by the Global Initiative for chronic Obstructive Lung Disease (GOLD 1).

METHODS

Data from current and former smokers participating in the COPDGene Study (NCT00608764) were analyzed. K-means clustering was performed to explore subtypes within 794 GOLD 1 subjects. For all subjects with GOLD 1 and with each cluster, a genome-wide association study and candidate gene testing were performed using smokers with normal lung function as a control group. Combinations of COPD genome-wide significant single nucleotide polymorphisms (SNPs) were tested for association with FEV1 (% predicted) in GOLD 1 and in a combined group of GOLD 1 and smoking control subjects.

RESULTS

K-means clustering of GOLD 1 subjects identified putative "near-normal", "airway-predominant", "emphysema-predominant" and "lowest FEV1% predicted" subtypes. In non-Hispanic whites, the only SNP nominally associated with GOLD 1 status relative to smoking controls was rs7671167 (FAM13A) in logistic regression models with adjustment for age, sex, pack-years of smoking, and genetic ancestry. The emphysema-predominant GOLD 1 cluster was nominally associated with rs7671167 (FAM13A) and rs161976 (BICD1). The lowest FEV1% predicted cluster was nominally associated with rs1980057 (HHIP) and rs1051730 (CHRNA3). Combinations of COPD genome-wide significant SNPs were associated with FEV1 (% predicted) in a combined group of GOLD 1 and smoking control subjects.

CONCLUSIONS

Our results indicate that GOLD 1 subjects show substantial clinical heterogeneity, which is at least partially related to genetic heterogeneity.

Airway wall thickness is increased in COPD patients with bronchodilator responsiveness

RATIONALE

Bronchodilator responsiveness (BDR) is a common but variable phenomenon in COPD. The CT characteristics of airway dimensions that differentiate COPD subjects with BDR from those without BDR have not been well described. We aimed to assess airway dimensions in COPD subjects with and without BDR.

METHODS

We analyzed subjects with GOLD 1-4 disease in the COPDGene® study who had CT airway analysis. We divided patients into two groups: BDR + (post bronchodilator ΔFEV1 ≥ 10%) and BDR-(post bronchodilator ΔFEV1 < 10%). The mean wall area percent (WA%) of six segmental bronchi in each subject was quantified using VIDA. Using 3D SLICER, airway wall thickness was also expressed as the square root wall area of an airway of 10 mm (Pi10) and 15 mm (Pi15) diameter. %Emphysema and %gas trapping were also calculated.

RESULTS

2355 subjects in the BDR-group and 1306 in the BDR + group formed our analysis. The BDR + group had a greater Pi10, Pi15, and mean segmental WA% compared to the BDR-group. In multivariate logistic regression using gender, race, current smoking, history of asthma, %emphysema, %gas trapping, %predicted FEV1, and %predicted FVC, airway wall measures remained independent predictors of BDR. Using a threshold change in FEV1 ≥ 15% and FEV1 ≥ 12% and 200 mL to divide patients into groups, the results were similar.

CONCLUSION

BDR in COPD is independently associated with CT evidence of airway pathology. This study provides us with greater evidence of changes in lung structure that correlate with physiologic manifestations of airflow obstruction in COPD.

Asthma: comparison of dynamic oxygen-enhanced MR imaging and quantitative thin-section CT for evaluation of clinical treatment

PURPOSE

To compare the use of dynamic oxygen-enhanced magnetic resonance (MR) imaging with the use of quantitatively assessed computed tomography (CT) for assessment of clinical stage and evaluation of pulmonary functional change due to treatment in patients with asthma.

MATERIALS AND METHODS

The institutional review board of Kobe University Hospital approved this study, and written informed consent was obtained from each subject. Thirty consecutive patients with asthma (17 men and 13 women; age range, 27-78 years) underwent dynamic oxygen-enhanced MR imaging, multidetector CT, and assessment of forced expiratory volume in 1 second. All patients were classified as having one of four stages of asthma according to the guidelines of the National Asthma Education and Prevention Program. Relative enhancement ratio ( RER relative enhancement ratio ) and wash-in time maps were generated by means of pixel-by-pixel analyses. Regions of interest were placed on images of the lung in all sections, and all measurements were averaged to determine mean RER relative enhancement ratio and mean wash-in time for each subject. Percentage of airway wall area and mean lung density were determined at quantitative CT. For comparison of the modalities for assessment of clinical stage, indexes of subjects at all clinical stages were compared by means of the Tukey honestly significant difference test. Evaluation of pulmonary functional improvement was assessed by correlating improvement of each index with that of forced expiratory volume.

RESULTS

Mean wash-in time was significantly different among patients with asthma of different clinical stages (P < .05), but significant differences between mean RER relative enhancement ratio and percentage of airway wall area were observed for a limited number of clinical stages (P < .05). Improvement of mean RER relative enhancement ratio (r = 0.63, P = .0002) and mean wash-in time (r = -0.75, P < .0001) was significantly correlated with forced expiratory volume.

CONCLUSION

Dynamic oxygen-enhanced MR imaging has potential as a tool for assessment of clinical stage and evaluation of pulmonary functional change due to treatment in patients with asthma.

Emphysema progression is visually detectable in low-dose CT in continuous but not in former smokers

OBJECTIVES

To evaluate interobserver agreement and time-trend in chest CT assessment of emphysema, airways, and interstitial abnormalities in a lung cancer screening cohort.

METHODS

Visual assessment of baseline and fifth-year examination of 1990 participants was performed independently by two observers. Results were standardised by means of an electronic score sheet; kappa and time-trend analyses were performed.

RESULTS

Interobserver agreement was substantial in early emphysema diagnosis; highly significant (p < 0.001) time-trends in both emphysema presence and grading were found (higher prevalence and grade of emphysema in late CT examinations). Significant progression in emphysema was seen in continuous smokers, but not in former smokers. Agreement on centrilobular emphysema subtype was substantial; agreement on paraseptal subtype, moderate. Agreement on panlobular and mixed subtypes was only fair. Agreement was fair regarding airway analysis. Interstitial abnormalities were infrequent in the cohort, and agreement on these was fair to moderate. A highly significant time-trend was found regarding interstitial abnormalities, which were more frequent in late examinations.

CONCLUSIONS

Visual scoring of chest CT is able to characterise the presence, pattern, and progression of early emphysema. Continuous smokers progress; former smokers do not.

KEY POINTS

• Substantial interobserver consistency in determining early-stage emphysema in low-dose CT. • Longitudinal analyses show clear time-trends for emphysema presence and grading. • For continuous smokers, progression of emphysema was seen in all lung zones. • For former smokers, progression of emphysema was undetectable by visual assessment. • Onset and progression of interstitial abnormalities are visually detectable.