Smoking Duration and Cessation in Relation to DLCO Among Patients with Stable COPD

Abstract

Smoking contributes to airway, parenchymal, and pulmonary vascular abnormalities in chronic obstructive pulmonary disease (COPD). Diffusing capacity of the lung for carbon monoxide (DLCO) provides complementary information on alveolar–capillary gas transfer beyond conventional spirometry. This cross-sectional study compared DLCO between current and former smokers with stable COPD and evaluated the relationships of smoking duration and smoking cessation duration with DLCO % predicted. Fifty patients with stable COPD were included, comprising 25 current smokers and 25 former smokers. Demographic characteristics, smoking history, hemoglobin concentration, spirometry, and DLCO were assessed. Absolute DLCO values were compared between groups using an independent-samples t-test, while Pearson correlation was used to assess relationships with DLCO % predicted. Mean absolute DLCO was significantly lower in current smokers than in former smokers (14.27 ± 4.36 vs 16.78 ± 4.09 mL/min/mmHg; p=0.041). Among current smokers, smoking duration showed a moderate negative correlation with DLCO % predicted (r=−0.445; p=0.026), whereas among former smokers, smoking cessation duration showed a strong positive correlation with DLCO % predicted (r=0.608; p=0.001). Former smokers with stable COPD had higher absolute DLCO than current smokers, while longer smoking duration and longer smoking cessation duration showed opposite associations with DLCO % predicted. These findings highlight the relationship between smoking history and pulmonary gas-transfer capacity in stable COPD.