Fig. 2From: Biomarkers of early chronic obstructive pulmonary disease (COPD) in smokers and former smokers. Protocol of a longitudinal studyLung function and GOLD stages of the participants currently enrolled in the study. The y-axis represents the FEV1/FVC ratio from the spirometry test and the x-axis shows patient classification in the following groups: healthy, at risk and COPD participants GOLD stage 1–3Back to article page