Lung function

School children aged 7–13 years underwent an examination of the lung function by one of the two experienced operators, each using one of the two portable spirometers (EasyOne, NDD Medical Technologies, Zürich, Switzerland). Quality control assessment was done electronically (software spirometer) and manually. End-of-Test criteria, quality criteria and quality grading in EasyOne-PC were based upon published standards [14–17]. Lung function measurement that met the quality criterion of at least 2 acceptable tests and a difference between the best two FEV1 and FVC values equal to or less than 200 ml were selected.

The lung function tests were reviewed by a pulmonary function technician who made the final decision on acceptance or rejection. The following variables were obtained from the current analysis: forced vital capacity (FVC), 1-s forced expiratory volume (FEV1), peak expiratory flow (PEF), the maximum midexpiratory flow (MMEF) also known as forced expiratory flow between the 25th and 75th percent of FVC (FEF25–75) and the FEV1/FVC ratio, also called Tiffeneau-Pinelli index. To calculate the predicted lung function, the weight and height of the children were measured. Internal prediction formulas were developed. The natural logarithms of lung function variables were regressed on the logarithms of age and weight, and an interaction between sex and the logarithm of height [18]. In addition also low lung function, defined as < 85% of the internal predicted value, was calculated.

Lung function measurements were conducted only on days when the school had not been downwind from the industry for at least two days, to avoid acute effects of air pollutants on the days of the examinations.