Exercise-induced bronchoconstriction is associated with air humidity and particulate matter concentration in preschool children

Abstract

<p>Background: Long-term exposure to air pollution is connected to asthma morbidity in children. Exercise-induced bronchoconstriction (EIB) is common in asthma, and the free running test outdoors is an important method for diagnosing asthma in children. It is not known whether momentary air pollution exposure affects the results of outdoor exercise tests in children. Methods: We analyzed all reliable exercise challenge tests with impulse oscillometry in children (n = 868) performed between January 2012 and April 2015 at Tampere University Hospital. Pollutant concentrations (PM<sub>2.5</sub>, NO<sub>2</sub>, and O<sub>3</sub>) at the time of the exercise test were collected from public registers. We compared the pollutant concentrations with the proportion and severity of EIB and adjusted the analyses for air humidity and pollen counts. Results: Pollution levels were rarely high (median PM<sub>2.5</sub> 6.0 µg/m<sup>3</sup>, NO<sub>2</sub> 12.0 µg/m<sup>3</sup>, and O<sub>3</sub> 47.0 µg/m<sup>3</sup>). The relative change in resistance at 5 Hz after exercise did not correlate with O<sub>3</sub>, NO<sub>2</sub> or PM<sub>2.5</sub> concentrations (p values 0.065−0.884). In multivariate logistic regression, we compared the effects of PM<sub>2.5</sub> over 10 µg/m³, absolute humidity (AH) over 10 g/m³ and alder or birch pollen concentration over 10 grains/m³. High (over 10 g/m<sup>3</sup>) AH was associated with decreased incidence (OR 0.31, p value 0.004), and PM<sub>2.5</sub> over 10 µg/m³ was associated with increased incidence (OR 1.69, p value 0.036) of EIB. Conclusions: Even low PM<sub>2.5</sub> levels may have an effect on EIB in children. Of the other properties of air, only AH was associated with the incidence of EIB.</p>