The prediction of small airway dimensions using computed tomography

Airflow limitation and airway dimensions in chronic obstructive pulmonary disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation caused by emphysema and/or airway narrowing. Computed tomography has been widely used to assess emphysema severity, but less attention has been paid to the assessment of airway disease using computed tomography.

OBJECTIVES

To obtain longitudinal images and accurately analyze short axis images of airways with an inner diameter>or=2 mm located anywhere in the lung with new software for measuring airway dimensions using curved multiplanar reconstruction.

METHODS

In 52 patients with clinically stable COPD (stage I, 14; stage II, 22; stage III, 14; stage IV, 2), we used the software to analyze the relationship of the airflow limitation index (FEV1, % predicted) with the airway dimensions from the third to the sixth generations of the apical bronchus (B1) of the right upper lobe and the anterior basal bronchus (B8) of the right lower lobe.

MEASUREMENTS AND MAIN RESULTS

Airway luminal area (Ai) and wall area percent (WA%) were significantly correlated with FEV1 (% predicted). More importantly, the correlation coefficients (r) improved as the airways became smaller in size from the third (segmental) to sixth generations in both bronchi (Ai: r=0.26, 0.37, 0.58, and 0.64 for B1; r=0.60, 0.65, 0.63, and 0.73 for B8).

CONCLUSIONS

We are the first to use three-dimensional computed tomography to demonstrate that airflow limitation in COPD is more closely related to the dimensions of the distal (small) airways than proximal (large) airways.

Characteristics of COPD phenotypes classified according to the findings of HRCT

The present study was performed to clarify the clinical characteristics of chronic obstructive pulmonary disease (COPD) patients classified into phenotypes according to the dominancy of emphysema and the presence of bronchial wall thickening evaluated by chest high-resolution computed tomography (HRCT). Eighty-five patients with stable COPD (FEV1 < or = 80%) were examined by chest HRCT. Emphysematous changes and bronchial wall thickening were evaluated visually, and COPD patients were classified into three phenotypes: absence of emphysema, with little emphysema with or without bronchial wall thickening (A phenotype), emphysema without bronchial wall thickening (E phenotype), and emphysema with bronchial wall thickening phenotype (M phenotype). Clinical characteristics were compared among the three phenotypes. The A phenotype group showed a higher prevalence of subjects who had never smoked and patients with wheezing, higher values of body mass index (BMI) and DLco, milder lung hyperinflation, and greater reversibility of airflow limitation responsive to inhaled beta2-agonist as compared with the other phenotypes. The degree of emphysema was significantly associated with Brinkman index, lower BMI, decrease in DLco, lower FEV1/FVC. The presence of bronchial wall thickening in A- and M- phenotype was significantly associated with reversibility responsive to treatment with inhaled corticosteroid and sputum eosinophilia. These findings suggest that the morphological phenotypes of COPD show several clinical characteristics and different responsiveness to treatment with bronchodilators and inhaled corticosteroids.

Antiinflammatory effects of salmeterol/fluticasone propionate in chronic obstructive lung disease

RATIONALE

No currently available treatment is reported to reduce the exaggerated airway wall inflammation of chronic obstructive pulmonary disease.

OBJECTIVES

We tested the hypothesis that inhaled combined long-acting beta2-agonist (salmeterol) and corticosteroid (fluticasone propionate) will reduce inflammation.

METHODS

Bronchial biopsies and induced sputum were taken from 140 current and former smokers (mean age, 64 yr) with moderate to severe disease, randomized in a 13-wk double-blind study to placebo (n = 73) or salmeterol/fluticasone propionate 50/500 microg (n = 67) twice daily. Biopsies were repeated at 12 wk and sputa at 8 and 13 wk. After adjustment for multiplicity, comparisons between active and placebo were made for median change from baseline in the numbers of biopsy CD8+ and CD68+ cells/mm2 and sputum neutrophils.

MEASUREMENTS AND MAIN RESULTS

Combination therapy was associated with a reduction in biopsy CD8+ cells of -118 cells/mm2 (95% confidence interval [CI], -209 to -42; p = 0.02), a reduction of 36% over placebo (p = 0.001). CD68+ cells were unaffected by combination treatment. Sputum differential (but not total) neutrophils reduced progressively and, at Week 13, significantly with combination treatment (median treatment difference, 8.5%; 95% CI, 1.75%-15.25%; p = 0.04). The combination also significantly reduced biopsy CD45+ and CD4+ cells and cells expressing genes for tumor necrosis factor-alpha and IFN-gamma and sputum total eosinophils (all p < or = 0.03). These antiinflammatory effects were accompanied by a 173-ml (95% CI, 104-242; p < 0.001) improvement in prebronchodilator FEV1.

CONCLUSIONS

The combination of salmeterol and fluticasone propionate has a broad spectrum of antiinflammatory effects in both current and former smokers with chronic obstructive pulmonary disease, which may contribute to clinical efficacy.

High-resolution computed tomography imaging of airway disease in infants with cystic fibrosis

RATIONALE

The development of early lung disease in patients with cystic fibrosis (CF) remains poorly defined.

OBJECTIVE

Determine whether asymptomatic infants with CF have evidence for changes in airway structure when assessed by high-resolution computed tomography, and whether airway structure correlates with airway function in this age group.

METHODS

Thirteen infants with CF (8-33 mo) and 13 control infants (7-25 mo) were evaluated. Airway wall and lumen areas were measured from three 1-mm-thick cross-sectional images obtained from upper, middle, and lower lobes during a respiratory pause with the lungs inflated to an airway pressure of 20 cm H2O. Lung tissue density was measured from images obtained during a respiratory pause at FRC. Forced expiratory flows were measured by the rapid thoracic compression technique in 11 infants with CF.

RESULTS

Airway wall area increased more per unit increase in airway size, whereas airway lumen area increased less per unit increase in airway size in the CF than in the control group. Among infants with CF, a greater ratio of wall to lumen area correlated with lower airway function. In addition, lung density at relaxed (passive) FRC was lower for infants with CF than for control infants (0.38 vs. 0.43 g/ml; p < 0.02).

CONCLUSIONS

Our results indicate that infants with CF have thickened airway walls, narrowed airway lumens, and air trapping, when assessed by high-resolution computed tomography, and measurements of airway structure correlated with airway function.

Quantitative computed tomography of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is described as airflow limitation that is not fully reversible. Quantitative assessment of structural changes within the lung that are responsible for this airflow limitation has relied on the examination of tissue obtained from surgical or postmortem specimens. However, in the past two decades, researchers have developed novel and robust tools to measure the structure of the lung parenchyma and airway wall by using computed tomographic (CT) scans, which do not require the removal of lung tissue. These techniques are extremely important because they allow longitudinal studies of the pathogenesis of COPD and the assessment of therapeutic interventions. Another application of this approach is that it potentially allows phenotyping of individuals who predominately have emphysema or small-airway disease, which may be important for the evaluation of pathogenesis and prescription of treatment options. This review describes some of these CT techniques for quantitative assessment of lung structure.

Structural changes in the airways in asthma: observations and consequences

Structural changes reported in the airways of asthmatics include epithelial fragility, goblet cell hyperplasia, enlarged submucosal mucus glands, angiogenesis, increased matrix deposition in the airway wall, increased airway smooth muscle mass, wall thickening and abnormalities in elastin. Genetic influences, as well as fetal and early life exposures, may contribute to structural changes such as subepithelial fibrosis from an early age. Other structural alterations are related to duration of disease and/or long-term uncontrolled inflammation. The increase in smooth muscle mass in both large and small airways probably occurs via multiple mechanisms, and there are probably changes in the phenotype of smooth muscle cells, some showing enhanced synthetic capacity, others enhanced proliferation or contractility. Fixed airflow limitation is probably due to remodelling, whereas the importance of structural changes to the phenomenon of airways hyperresponsiveness may be dependent on the specific clinical phenotype of asthma evaluated. Reduced compliance of the airway wall secondary to enhanced matrix deposition may protect against airway narrowing. Conversely, in severe asthma, disruption of alveolar attachments and adventitial thickening may augment airway narrowing. The encroachment upon luminal area by submucosal thickening may be disadvantageous by increasing the risk of airway closure in the presence of the intraluminal cellular and mucus exudate associated with asthma exacerbations. Structural changes may increase airway narrowing by alteration of smooth muscle dynamics through limitation of the ability of the smooth muscle to periodically lengthen.