Reference values for vital capacity and flow-volume curves from a general population study.

A longitudinal epidemiological respiratory study has been started in the North of Italy to investigate the natural history of obstructive airways disease and the long-term effect of SO2 exposure. The first cross-sectional study was completed in this unpolluted area before the activation of a thermoelectric power plant (500 tons of SO2 produced daily). Follow-up surveys are planned after pollution emission starts for a period of ten years. A sample (n = 3289) representative of the general population was drawn from the villages of the area according to the different risks of pollution exposure. Subjects completed questionnaires and performed lung function tests, including forced expiratory (FVC) manoeuvres. For 801 'normal' subjects, prediction equations have been derived in age/sex groups for slow vital capacity (VC) and variables from the FVC manoeuvre. Comparisons with predictions of other studies are reported. Differences among FVC predictions were found, indicating that the use of different criteria for determination of the FVC manoeuvre end-point can affect results. In 'normals' VC was higher than FVC in older subjects. The difference between VC and FVC may be hypothesized as an epidemiological indication of the ageing effect on the mechanical properties of the ventilatory system.