Study objective: We evaluated the longitudinal changes in lung function and the factors associated with FEV1 changes over time in a sample of asthmatic subjects.
Setting: FEV1 measures were recorded every 3 months over a 5-year follow-up period. To compare all subjects independently of body size, FEV1 values were normalized for the subject’s height at the third power. We evaluated the possible effect of age, baseline FEV1, disease duration, and FEV1 variability on the rate of change of FEV1.
Patients: We studied 142 subjects with asthma diagnosed on the basis of validated clinical and functional criteria.
Results: FEV1 showed a linear decay with aging in each subject. For a subject 1.65 m in height, the median overall FEV1 decay was 40.9 mL/yr. FEV1 decay slopes were significantly influenced by age and sex, being steeper in younger male subjects. A significant interaction was found between age and baseline FEV1: the FEV1 decay was significantly higher among younger asthmatics with a poorer baseline functional condition. A longer disease duration was associated with a lower FEV1 slope. FEV1 variability was strongly associated with an increased rate of FEV1 decline.
Conclusions: FEV1 decline in patients with bronchial asthma is significantly influenced by baseline FEV1, disease duration, and FEV1 variability. Moreover, the rate of FEV1 decline seems to increase in younger subjects only when the baseline function is poorer.