On the possible significance of the quadratic effect of age on lung-function measurements

The problem of interpreting lung-function measurements in industrial workers is examined. Two common lung-function measurements (FEV₁, and FVC) are described. The standard method currently used in the analysis of such cross-sectional survey data is discussed. The basic assumption of a linear decline with age is questioned on the basis of large sets of data from a variety of industries in British Columbia. It is shown that, while the linear assumption holds approximately in unexposed. healthy nonsmoking individuals, a quadratic age effect is often observed in smokers and/or in individuals who are industrially exposed to certain fumes or dusts. Recognizing this accelerated rate of deterioration in the lungs is of fundamental importance both to the identification of affected individuals and to the understanding of the process involved. An attempt is made to interpret the variety of nonlinear situations observed, by appealing to population selection mechanisms, individual variations in susceptibility, and the effects due to various levels of stimulus strength.