Reference equations for spirometry from a general population sample in central Italy

Aim of this study was to derive new lung function reference equations and compare the predicted values with those from three sets of existing reference equations: one derived from a Northern Italy population and the two others widely used in European (ECCS) and American (NHANES III) clinical practice. Reference equations for flow-volume curve indexes and VC were derived on 497 normal subjects, aged 8-74, from the epidemiological survey in Pisa, Central Italy (1991-1993). By applying natural cubic splines, one single smooth and continuous equation for the entire age range was provided for each index, separately by gender. Along with age and height, reference values also depended on BMI. Differences among the four reference equations for FEV1, FVC, VC were quantified for average subjects. The magnitude largely varied over the age range in both genders, reaching up to half litre of air volume at specific ages.