On adjusting measurements of airway responsiveness for lung size and airway caliber

It has been suggested that during bronchial challenge with a pharmacologic agent, subjects with small lungs receive a proportionally greater dose of agonist than do those with larger lungs. This infers that measurements of airway hyperresponsiveness (AHR) between different age and gender groups may not be comparable. To examine this, we analyzed data from population samples of 1,613 children 7 to 12 yr of age and 1,484 adults 25 to 50 yr of age in whom we measured airway responsiveness by histamine inhalation test. We used FVC as a surrogate measurement for lung size and FEV(1)/FVC as surrogate measurement for airway caliber. When AHR was adjusted for FVC, FEV(1)/FVC, and gender, the differences in prevalence between age groups was reduced. The prevalence of AHR in those between 7 and 9 yr of age decreased from 20.2% (95% Cl, 17.7 to 22.7) to 15.7% (95% CI, 13.4 to 18.0), but the prevalence of AHR in those 35 to 44 yr of age remained the same at 7.6% (95% CI, 5.9 to 9.3). We conclude that FVC and FEV(1)/FVC have a small but significant effect on the measurement of airway responsiveness and that more precise measurements of the prevalence of AHR can be obtained by standardization for these parameters.