Figure 1).

Data adapted from Fletcher and Peto (3) on the natural history of chronic obstructinve pulmonary disease (COPD) in relation to the four Global initiative for chronic Obstructive Lung Disease (GOLD) categories of COPD severity. It is postulated that the slow rates of decline in forced expiratory volume in 1 s (FEV₁) observed in nonsmokers and in the majority of those who either smoke or have stopped smoking is caused by a slow rate of loss of terminal bronchioles. It is further postulated that the rapid decline in FEV₁ observed in the susceptible minority and in those who fail to reach to reach the maximum expected FEV₁ at 25 years of age is caused by a significantly more rapid rate of terminal bronchiolar loss in this group of individuals