Modelling the lung function of Caucasians during adolescence as a basis for reference values

BACKGROUND: In childhood the relationship between lung size and stature changes during the adolescent growth spurt. This is not allowed for in models of lung function based on stature alone. For spirometric indices inclusion of an age x stature interaction (A x St) can overcome the difficulty. AIM: The study tested the hypothesis that this simple, interactive model might also be effective for total lung capacity and its subdivisions and the single breath transfer factor for carbon monoxide. SUBJECTS AND METHODS: Data were available for 695 asymptomatic non-smokers (Caucasians) aged 7-20 years (440 boys, 255 girls). Each lung function index was described using the above model and the fit was compared with that from a linear, power or polynomial model based on stature alone. RESULTS: After allowing for stature, the A x St interaction term was significant for almost all indices. The improved fit was most apparent for the lung function of older adolescent boys. Reference values using the model are reported. CONCLUSIONS: A simple model based on stature and an interaction between stature and age can account for the changing relationship between body habitus during the growth spurt and lung size and transfer factor in a single equation encompassing children and adolescents. Its use is recommended for deriving reference values when the explanatory variables are limited to stature and age.