MPO and chronic obstructive pulmonary disease: The results for MPO were very similar (Figure 4b) smokers vs. non-smokers p = 0.01 (%), p = 0.003 (total), never smokers vs. ex smokers p = 0.536 (%), p = 0.09 (total), healthy smokers vs. stage 0 COPD p = 0.114 (%), p = 0.610 (total).