Flow-volume curves in healthy non-smokers and in smokers

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Abstract
Maximum expiratory flow-volume curves were recorded in lung healthy nonsmokers and in smokers. Multiple linear regression analysis was performed with regard to sex, age, height and weight. The regressions for maximum expiratory flow at 50 and 25% of vital capacity (MEF50 and MEF25, respectively) on age were significantly different for nonsmokers and smokers, in males and females, but the large scatter around the regression line resulted in > 50% of smokers within 1 SD of the reference values for nonsmokers. A skew distribution of MEF25 around the mean was observed at ages > 60 yr and set an upper limit for linear regression. Avove 60 yr no linear age dependence was found for MEF25. There was a minor reduction (2%) in the residual SD of the peak expiratory flow (PEF), MEF50 and MEF25 regressions when height was added as an independent variable besides age, while the addition of weight did not reduce the scatter. The inter-individual variability in MEF150 and MEF25 was relatively large even when sex and age were accounted for and there was no further benefit in including height or weight in the regression equations. The discriminating ability of the MEF50 and MEF25 variables was small, indicated by considerable overlapping between nonsmokers and smokers.