Lower diffusing capacity with chronic bronchitis predicts higher risk of acute exacerbation in chronic obstructive lung disease

Background: This study was designed to evaluate the effect of chronic bronchitis (CB) symptoms and degree of emphysema in a multicenter Korean cohort. Methods: From April 2012 to May 2015, patients diagnosed with chronic obstructive lung disease (COPD) who were aged above 40 years at 46 hospitals throughout Korea were enrolled. All of the patients were classified according to CB symptoms and the diffusing capacity of the lung for carbon monoxide (DLCO); demographic data, symptom scores, and the result of lung function tests and exacerbations were then analyzed. Results: A total of 812 patients were enrolled. Among these patients, 285 (35.1%) had CB symptoms. A total of 51% of patients had high DLCO without CB symptoms [CB (-) high DLCO], 24.9% had CB symptoms only [CB (+) high DLCO], 14.2% had low DLCO only [CB (-) low DLCO], and 10.2% had both low DLCO and CB [CB (+) low DLCO]. Patients with CB (+) low DLCO showed a significantly lower postbronchodilator (BD) forced expiratory volume for 1 second (FEV₁) and more severe dyspnea than patients with CB (-) high DLCO. On multivariate analysis, the risk of acute exacerbation was two times higher [odds ratio (OR) 2.06; 95% confidence interval (CI): 1.18-3.62; P=0.01] in the CB (+) low DLCO group than in the CB (-) high DLCO group. Conclusions: In this COPD cohort, patients showed distinct clinical characteristics and outcomes according to the presence of CB and degree of DLCO. CB and low DLCO were associated with the risk of acute exacerbation.