Reference values for lung function tests in females. Regression equations with smoking variables.

Prediction formulas for static and dynamic spirometry, gas distribution, static lung mechanics and transfer test were derived from measurements in healthy females. The measurements included total lung capacity, residual volume, airway resistance, static elastic recoil pressure of the lung, static compliance, closing volume, slope of the alveolar plateau (phase III), flow-volume variables (including mean transit time) during breathing of air or a helium/oxygen mixture, and conventional spirometric indices. The results from 86 smokers and 100 never-smokers were evaluated separately and combined. For all lung function tests, a single regression equation including time-related smoking variables, valid for both smokers and never-smokers, was obtained. For many lung function tests, a nonlinear age coefficient resulted in a significant reduction in variance compared with simple linear models. Heavy tobacco smoking influenced most lung function tests less than ageing from 20 to 70 years, but for airway resistance, volumic airway conductance, closing volume, phase III, FEV1/VC, volume of isoflow and mean transit time the opposite was found.