Figure 1.

Hypothetical mechanisms that may lead to a critically low level of lung function in adult life and to chronic airway obstruction (horizontal line): line a, normal growth and decline; line b, impaired lung growth with a lower plateau phase but a normal rate of decline compared with line a; line c, normal plateau with rapid initial decline in lung function and a subsequent normal rate of decline; line d, normal plateau with normal initial rate of decline but a subsequent accelerated loss in lung function. Reprinted by permission from Reference 46.