Chronic obstructive pulmonary disease exacerbations in the COPDGene study: associated radiologic phenotypes

Abstract

Purpose: To test the hypothesis-given the increasing emphasis on quantitative computed tomographic (CT) phenotypes of chronic obstructive pulmonary disease (COPD)-that a relationship exists between COPD exacerbation frequency and quantitative CT measures of emphysema and airway disease.

Materials and methods: This research protocol was approved by the institutional review board of each participating institution, and all participants provided written informed consent. One thousand two subjects who were enrolled in the COPDGene Study and met the GOLD (Global Initiative for Chronic Obstructive Lung Disease) criteria for COPD with quantitative CT analysis were included. Total lung emphysema percentage was measured by using the attenuation mask technique with a -950-HU threshold. An automated program measured the mean wall thickness and mean wall area percentage in six segmental bronchi. The frequency of COPD exacerbation in the prior year was determined by using a questionnaire. Statistical analysis was performed to examine the relationship of exacerbation frequency with lung function and quantitative CT measurements.

Results: In a multivariate analysis adjusted for lung function, bronchial wall thickness and total lung emphysema percentage were associated with COPD exacerbation frequency. Each 1-mm increase in bronchial wall thickness was associated with a 1.84-fold increase in annual exacerbation rate (P = .004). For patients with 35% or greater total emphysema, each 5% increase in emphysema was associated with a 1.18-fold increase in this rate (P = .047).

Conclusion: Greater lung emphysema and airway wall thickness were associated with COPD exacerbations, independent of the severity of airflow obstruction. Quantitative CT can help identify subgroups of patients with COPD who experience exacerbations for targeted research and therapy development for individual phenotypes.

Figure 1a:

Three-dimensional surface plots demonstrate relationships between emphysema percentage, wall thickness, and COPD exacerbation frequency (vertical axis). Different panels show the plot rotated to allow appreciation of different aspects. (a) Surface view of entire relationship shows the largely independent effects of emphysema percentage and segmental wall thickness. (b) Horizontal view emphasizes the increased exacerbation frequency at greater levels of emphysema. Also note the very strong effect of bronchial wall thickness at low levels of emphysema. (c) Depth view emphasizes relationship between increasing wall thickness and exacerbation frequency at low levels of emphysema.

Figure 1b:

Three-dimensional surface plots demonstrate relationships between emphysema percentage, wall thickness, and COPD exacerbation frequency (vertical axis). Different panels show the plot rotated to allow appreciation of different aspects. (a) Surface view of entire relationship shows the largely independent effects of emphysema percentage and segmental wall thickness. (b) Horizontal view emphasizes the increased exacerbation frequency at greater levels of emphysema. Also note the very strong effect of bronchial wall thickness at low levels of emphysema. (c) Depth view emphasizes relationship between increasing wall thickness and exacerbation frequency at low levels of emphysema.

Figure 1c:

Three-dimensional surface plots demonstrate relationships between emphysema percentage, wall thickness, and COPD exacerbation frequency (vertical axis). Different panels show the plot rotated to allow appreciation of different aspects. (a) Surface view of entire relationship shows the largely independent effects of emphysema percentage and segmental wall thickness. (b) Horizontal view emphasizes the increased exacerbation frequency at greater levels of emphysema. Also note the very strong effect of bronchial wall thickness at low levels of emphysema. (c) Depth view emphasizes relationship between increasing wall thickness and exacerbation frequency at low levels of emphysema.

Figure 2:

Axial CT scans in two subjects with different COPD phenotypes (Table 2): emphysema-predominant COPD (≥35% emphysema, <1.75-mm segmental bronchial wall thickness) (left) and airway-predominant COPD (<35% emphysema, ≥1.75-mm segmental bronchial wall thickness) (right).