Expiratory and inspiratory forced vital capacity and one-second forced volume in asymptomatic never-smokers in Norway

The objectives of this study were to examine within and between individual variation detected during forced expiratory (FE) and forced inspiratory (FI) manoeuvers in a general population and to investigate the dependence of these variables on age, body size, and gender. A random sample of asymptomatic never smokers who had never been exposed occupationally to quartz or asbestos and who were living on the south-western coast of Norway were examined by spirometry; 81% of the individuals invited to attend did so. Of the 488 subjects between 18 and 73 years of age, 98% contributed three acceptable recordings for forced expiratory vital capacity (FVC) and one-second forced expiratory volume (FEV1), 94% contributed three acceptable recordings for forced inspiratory vital capacity (FIVC) and 85% contributed three acceptable recordings for one-second forced inspiratory volume (FIV(1)). The within-subject variation increased with body height and was considerably larger for FIV(1) than for FVC, FEV(1) or FIVC. A four-parameter model of pulmonary function measurement divided by height squared, including a gender term and a linear and quadratic term of age, fit the median of the observed values well. The residuals had a close-to-normal distribution, and the fifth-percentile values were estimated as the lower limit of normal. The peak value of dynamic lung volumes was observed into the middle of the fourth decade of life, and the decline thereafter did not differ greatly between the genders or among the different indices. The forced inspiratory volumes are the first reported in any reference population.