Changes in the FEV₁/FVC Ratio During Childhood and Adolescence: an Intercontinental Study

In children, the ratio of forced expiratory volume in 1 s (FEV₁) to forced vital capacity (FVC) is reportedly constant or falls linearly with age, whereas the ratio of residual volume (RV) to total lung capacity (TLC) remains constant. This seems counter-intuitive given the changes in airway properties, body proportions, thoracic shape and respiratory muscle function that occur during growth. The age dependence of lung volumes, FEV₁/FVC and RV/TLC were studied in children worldwide. Spirometric data were available for 22,412 healthy youths (51.4% male) aged 4-20 yrs from 15 centres, and RV and TLC data for 2,253 youths (56.7% male) from four centres; three sets included sitting height (SH). Data were fitted as a function of age, height and SH. In childhood, FVC outgrows TLC and FEV₁, leading to falls in FEV₁/FVC and RV/TLC; these trends are reversed in adolescence. Taking into account SH materially reduces differences in pulmonary function within and between ethnic groups. The highest FEV₁/FVC ratios occur in those shortest for their age. When interpreting lung function test results, the changing pattern in FEV₁/FVC and RV/TLC should be considered. Prediction equations for children and adolescents should take into account sex, height, age, ethnic group, and, ideally, also SH.