[Pulmonary function indices: variability, predicted values and discriminating power (author's transl)].

Flow/volume curves, single-breath N2 washout curves, single-breath and steady-state carbon monoxide diffusion tests were performed on 229 firemen (aged 20 to 55 years) and repeated one week later on 183 of them. According to a questionnaire, 58 were asymptomatic non-smokers, 130 were asymptomatic smokers and 34 were smokers with symptoms of cough with or without sputum. Intra-individual variability of indices determined from tests performed at a week interval is not always aleatory and it is different in the three groups. It is the same for inter-individual variability which is lowest in asymptomatic smokers and highest in symptomatic smokers. Age and height were the most important factors in inter-individual variability for spirometric indices but do not affect the variability of the slope of N2 curve (delta N2) or fractional uptakes of CO. The ratio of residual variance (adjusted for age and morphometric parameters) on intra-individual variance indicated the choice of "sensitive" functional indices. This choice may be reached in a different way by comparison of means of groups distinguished according to symptoms or smoking habits. Reference equations for indices derived from each test are proposed. The problem of the choice of "sensitive" indices and the problem of reference groups and reference values are discussed.