Epidemiology of the origins of airflow limitation in asthma

Abstract

There is now conclusive evidence that, as a group, subjects with asthma have lower levels of lung function as compared with their peers and that a significant proportion of subjects with persistent asthma are at risk of developing non-fully reversible airflow limitation, the clinical hallmark of chronic obstructive pulmonary disease. Although at the population level the most conspicuous form of airflow limitation in asthma seems to be that of subjects who wheeze during the first years of life and whose symptoms persist into adult life, asthma-related lung deficits can be related to both acquired deficits in growth of lung function in childhood and steeper decline of lung function in adult life. These trajectories of lung function are likely to differ across subgroups of individuals with asthma, suggesting that different windows of opportunity may exist to modify the natural course of the disease before irreversible deficits are established. These observations indicate the importance of identifying biomarkers that can be used to target children and adults with asthma at increased risk for airflow limitation and determining whether pharmacological interventions can protect these patients from the development of chronic obstructive pulmonary disease.

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 .

Figure 2.

Decline of FEV₁ over the span of adult life in male participants in the Busselton Health Study derived from linear mixed effects models. The continuous line refers to nonsmoking males without asthma; the dotted line to nonsmoking with asthma; the dashed and dotted line to smoking without asthma; and the dashed line to smoking with asthma. Reprinted by Reference 17.