Distribution of Forced Vital Capacity and Forced Expiratory Volume in One Second in Children 6 to 11 Years of Age

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Abstract
We analyzed 44,664 annual measurements of forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) in 12,258 white children and 1,041 black children between 6 and 11 yr of age in 6 communities. Sex- and race-specific lung function development is described for this sample of preadolescent children. For both races, girls have lower median values of FVC and FEV1 than do boys of the same height. However, for the same level of FVC, girls have a higher FEV1/FVC ratio. Blacks have median levels of lung function lower by approximately 13% than whites of the same sex and standing height. Regression analysis showed that height, race, and sex are the most important predictors of lung function. Lung function also increases with weight and age, but the effect of these two variables on predicted lung function is small. The residuals from the regression model, which describe the distribution of lung function values, follow a Gaussian distribution in the logarithmic scale. A simple model is presented for calculating percentiles of the distribution of FVC and FEV1 as a function of height, race, and sex. In a subset of children with at least 5 annual observations, observed growth was compared with the constant percentile curves of the pulmonary function for height distributions. These children track along constant percentile curves (growth curves) of FVC and FEV1 given height, much as they track along growth curves of height given age, once the larger proportional measurement error of lung function is taken into account. The proposed growth curves can therefore be applied clinically to evaluate a child's lung function, not only at a single examination but also longitudinally over a series of observations.