Figure 1. Lung function trajectories to chronic obstructive pulmonary disease (COPD).

The figure represents four lung function trajectories identified in the study by Lange et al. ⁷ based on levels of forced expiratory volume in one second (FEV ₁) before the age of 40 years (below or above 80% of predicted value) and the presence or absence of Global initiative for chronic Obstructive Lung Disease (GOLD) grade of at least 2 COPD at the end of follow-up. The y-axis represents the percentage of expected maximally attained FEV ₁. Modified from 7.