TABLE 4

Generated reference equations for adjusted forced expiratory flow (FEF) values

EquationsExplained variance for the FEF/FVC equations %
Reference equationRSDTrainingInternal validationExternal validation
Males
 FEF25/FVC s−13.56+0.001A+0.003W−0.013H0.2866.796.4813.16
 FEF50/FVC s−12.02−0.004A+0.001W–0.006H0.2056.174.764.04
 FEF75/FVC s−10.68−0.005A–0.0009W–0.0005H0.08435.932.137.8
 FEF25–75/FVC s−11.70−0.007A+0.0005W−0.004H0.16916.613.814.9
Females
 FEF25/FVC s−13.52−0.0005A+0.003W−0.013H0.2786.215.824.56
 FEF50/FVC s−12.05−0.005A+0.001W−0.006H0.2018.649.549.32
 FEF75/FVC s−10.73−0.006A−0.001W−0.0004H0.09541.041.546.0
 FEF25–75/FVC s−11.76−0.008A+0.00009W−0.004H0.17023.624.125.2

FVC: forced vital capacity; RSD: residual standard deviation; FEFx: forced expiratory flow at 25%, 50%, 75% and 25–75% of FVC; A: age (years); W: weight (kg); H: height (cm). Lower limit of normal=value−1.64×RSD; upper limit of normal=value+1.64×RSD.