Changing relationships between stature and lung volumes during puberty

In a follow-up study the relationship between growth in body dimensions and in lung volumes during the adolescent growth spurt was studied in 149 girls and 477 boys, aged 11.5-14.0 years at the start of the study. Total lung capacity (TLC), residual volume, vital capacity (VC) and series dead space were measured twice a year for 6 years. When analyzed cross-sectionally lung volumes can be described by a power function of stature, both for each set of half-yearly measurements and when all data are pooled. The powers were close to 3, increasing at each time of measurement in boys and decreasing in girls. These trends reflect that in each subject the growth spurt does not start at the same age, and that individual growth occurs non-linearly along a steeper line than found in the cross-section. Using simple allometric relationships between stature and lung volumes, volume predictions are too high in the youngest age group, and too low in the oldest adolescents. Including age in the regression equation removes this trend in the cross-sectional data, and for VC and TLC also in the longitudinal data.