Distribution of Forced Expiratory Volume in One Second and Forced Vital Capacity in Healthy, White, Adult Never-Smokers in Six U.S. Cities

Abstract

As part of a longitudinal study of the respiratory health effects of air pollution, the lung function of 2454 white adults 25-74 yr of age who had never smoked and who reported no respiratory symptoms was measured. These measurements were analyzed to develop a simple model for the cross-sectional dependence of pulmonary function on height, sex and age. Both forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were effectively standardized for body size by dividing each pulmonary function measurement by the square of the standing height (HT2). The age-specific distribution of these standardized measurements was approximately Gaussian, with variance that was independent of age. Plots of FEV1/HT2 and FVC/HT2 against age showed a nonlinear relationship consistent with an increase in the rate of pulmonary function loss with age. On the basis of these graphic analyses, both pulmonary function measurements were fitted to a 4-parameter normative model including sex and linear and quadratic terms in age as dependent variables. This model gave predictions that were very close to those from more complicated models currently in use. Predicted percentile levels were calculated for each sex and age, and described the observations well. The estimated annual change in height-standardized lung function based on the cross-sectional model was compared with the observed change between the 1st and 2nd examinations of these adults 3 yr later. The observed changes were close to predicted values, except for subjects younger than 35 yr of age at their 1st examination. The observed change was larger for men than for women. Such simple longitudinal comparisons were subject to selection bias. Subjects in the lowest quartile of FEV1/HT2 for their age and sex at the 1st examination had a lower probability of providing a lung function measurement 3 yr later.