Figure 1.

Examples of lung function trajectories from birth to death. The red shaded area highlights the population of young adults with chronic obstructive pulmonary disease to be included in treatment trials. Gray shaded areas indicate that these age limits are somewhat arbitrary (based on normal peak + plateau lung function), and therefore some age variability may be acceptable. Note also that this age range includes trajectories with normal peak lung function (100% reference) as well as those with reduced peak lung function (<80% reference) and that both can have a normal or an enhanced decline with time. For further explanations, see the main text.