SPIROMETRY IN THE LUNG HEALTH STUDY .2. DETERMINANTS OF SHORT-TERM INTRAINDIVIDUAL VARIABILITY

The Lung Health Study (LHS) is a randomized clinical trial designed to determine whether a smoking intervention program and use of an inhale d bronchodilator (ED) can reduce the rate of decline of FEV(1) in ciga rette smokers with airflow limitation. During recruitment, spirometry was performed at second and third screening visits, a mean of 21 d apa rt. A total of 5,887 smokers, 35 to 60 yr of age and of whom 63% were men, met the study eligibility requirements. Smokers taking physician- prescribed BDs or with an FEV(1) < 50% or > 90% predicted were exclude d, as were those whose FEV(1)/FVC ratio was greater than 70%. Two inha lations of isoproterenol were given to determine ED response during th e second visit. A serial dilution methacholine challenge test was done during the third visit to determine nonspecific airway reactivity. Ni nety-five percent of the differences between FEV(1) measured at the tw o visits were within 240 ml for women and within 320 ml for men (coeff icients of repeatability). The best independent predictors of the mean shortterm (between visit) intraindividual FEV(1) variability were fac tors indicating intrinsic airway reactivity of the participants: bronc hodilator response, methacholine reactivity, and the presence of wheez ing; as well as factors influenced by the quality of spirometry testin g: the difference between the highest and second highest FEV(1)s and p eak flows during baseline spirometry, and the time to reach peak flow (PEFT).