Figure 1. Longitudinal Lung-Function Trajectories.

Possible lung-function trajectories during the first three decades of life are shown; the lung function plotted for each age is the percentage of the maximum forced expiratory volume in 1 second (FEV₁) in a person without lung disease; the maximum value is usually attained at the age of 18 to 30 years. A normal pattern of lung-function growth and decline is characterized by a steep increase during adolescence, a plateau in early adulthood, and a gradual decline into old age. Abnormal trajectories include reduced growth, normal growth and an early decline, and reduced growth and an early decline. The red brackets indicate FEV₁ criteria according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 2 (FEV₁ ≥50% and <80%) and stage 3 (FEV₁ ≥30% and <50%) of chronic obstructive pulmonary disease (COPD), when accompanied by a ratio of FEV₁ to forced vital capacity that is less than 0.70. The figure is adapted from Speizer and Tager.¹