Among current and former smokers with or without chronic obstructive pulmonary disease (COPD), expiratory central airway collapse develops in approximately 5% and is associated with a worse respiratory-related quality of life, greater dyspnea, and an increased rate of total and severe exacerbations of pulmonary problems, according to a report published online Feb. 2 in JAMA.
Until recently, expiratory central airway collapse (ECAC) could only be studied using bronchoscopy, so it was not very well characterized. For example, the estimated prevalence among patients with known respiratory problems ranged from 1% to 53%. With the increasing use of noninvasive imaging techniques, the condition is being recognized more often, especially in association with smoking and COPD, but it still remains poorly understood, said Dr. Surya P. Bhatt of the division of pulmonary, allergy, and critical care medicine, University of Alabama at Birmingham, and his associates.
To assess the prevalence and clinical significance of ECAC, the investigators analyzed paired CT images of inspiratory and expiratory scans collected in the multicenter COPDGene study, focusing on scans for 8,820 current and former smokers aged 45-80 years (mean age, 59.7 years) who enrolled from local communities across the United States at 21 participating medical centers. Approximately 57% of the study participants were men, 66% were white and 34% were African American, 52% were active smokers, and 44% had COPD.
A total of 443 cases of ECAC were identified, for a prevalence of 5%.
ECAC was more common in participants with COPD (5.9%) than in those without COPD (4.3%), and the prevalence increased with increasing severity of COPD. Study subjects with ECAC were older than those without the condition, with a mean age of 65 years, compared with 59 years. ECAC also was more frequent among women than men (7.2% vs 3.1%), and among whites than blacks (6.2% vs 2.5%). Participants with ECAC had a higher body-mass index, a higher prevalence of chronic bronchitis, and more pack-years of smoking than those without ECAC.
In the primary data analysis, adults with ECAC had a worse respiratory-related quality of life than those without the condition, as measured using the St. George’s Respiratory Questionnaire. This association remained robust, and was independent of the degree of airflow obstruction and the severity of COPD, after the data were adjusted to account for patient demographics, structural lung disease, and forced expiratory volume in 1 second. “We speculate that ECAC might explain some cases of dyspnea disproportionate to apparent obstructive airways disease measured by CT, spirometry, or both,” Dr. Bhatt and his associates said.
Participants with ECAC also had more severe dyspnea as measured by the modified Medical Research Council score but did not have a shorter walking distance on the 6-minute walk test (JAMA 2016 Feb 2. doi: 10.1001/jama.2015.19431).A subset of 7,456 study participants were assessed at 3- to 6-month intervals for a median of 4.3 years. Compared with participants who did not have ECAC, those who did developed more total exacerbations of pulmonary problems (35 vs. 58 events per 100 person-years) and more severe exacerbations requiring hospitalization (10 vs. 17 events per 100 person-years). Mortality, however, was not significantly different between participants who had ECAC (9.9%) and those who did not (9.6%).
“Whether some of these [exacerbations] represent decompensated ECAC or whether ECAC is a marker for future respiratory events needs to be investigated. Our results suggest that ECAC might contribute to symptoms independent of underlying disease and also may serve as a CT-based biomarker of poor respiratory outcomes,” the investigators said.
This study was supported by the National Heart, Lung, and Blood Institute. Dr. Bhatt reported having no relevant financial disclosures; his associates reported ties to numerous industry sources.