Association of air humidity with incidence of exercise‐induced bronchoconstriction in children

Abstract Background The effects of humidity and temperature on results of free running test in children are not known. Objective Assess the relation of outdoor air temperature, relative humidity (RH), and absolute humidity (AH) to airway obstruction in children after free running exercise test. Methods We analyzed all exercise challenge tests with impulse oscillometry in children between January 2012 and April 2015 in the Tampere University Hospital. The associations of AH, RH, and temperature of outdoor air with change in airway resistance were studied using regression analysis and by comparing the frequency of exercise‐induced bronchoconstriction (increase ≥40% in resistance at 5 Hz) at different levels of temperature and humidity. Results Overall, 868 children with reliable results were included (mean age: 5.4 years; range: 3.0‐14.1). In regression analysis, the relative change in resistance at 5 Hz after exercise was related to temperature (regression coefficient = −0.223, P = .020) and AH (regression coefficient = −0.893, P = .002), but not to RH. If absolute air humidity was <5 g/m 3 , exercise‐induced bronchoconstriction (EIB) occurred in 17.6% of study subjects and at AH levels ≥10 g/m 3 , it occurred in 5.9% of study subjects ( P = .008). In multiple regression analysis comparing the effects of temperature and humidity and adjusting for covariates, only AH was independently associated with change in airway resistance ( P = .009). Conclusion High AH of air is associated with lower incidence of EIB after outdoor exercise test in children. A negative test result at AH ≥10 g/m 3 should be interpreted with caution.