NOX4 and chronic obstructive pulmonary disease: In order to evaluate whether smoking has an impact on the expression of NOX4 and TGF-β, as well as ASM remodeling, parameters including SMA-WT% and SMA-WA% (as indexes of ASM mass for ASM remodeling), and the expression of NOX4 and TGF-β between the control non-COPD group, current smokers with COPD, ex-smoker with COPD, and never smokers with COPD.