Association of temperature and absolute humidity with incidence of exercise-induced bronchoconstriction in children

Exercise test outdoors is widely used to diagnose asthma in children, but it is unclear how much outdoor air factors affect the results.

We analysed 321 outdoor exercise challenge tests with spirometry in children 6-16 years conducted due to suspicion of asthma or for assessing the effect of medication on asthma. We studied the association of FEV₁ decrease and incidence of exercise-induced bronchoconstriction (EIB) with temperature, relative humidity (RH) and absolute humidity (AH).

Asthma was diagnosed in 57% of the subjects. AH ≥5 g/m³, but not RH or temperature, was associated with the EIB incidence (p = 0.035). In multivariable logistic regression, AH ≥5 g/m³ was negatively associated (OR = 0.51, 95% CI [0.28─0.92], p = 0.026) while obstruction before exercise (OR = 2.11, 95% CI [1.16─3.86], p = 0.015) and IgE-mediated sensitisation were positively associated with EIB (OR = 2.24, 95% CI [1.11─4.51], p = 0.025). AH (r = -0.12, p = 0.028) and temperature (r = -0.13, p = 0.023) correlated with decrease in FEV₁. In multivariable linear regression, only AH was associated with FEV₁ decrease (coefficient = -0.044, 95% CI [-0.085 to -0.004], p = 0.033).

AH of outdoor air associates with occurrence and severity of EIB in outdoor exercise tests in children. Care should be taken when interpreting negative outdoor exercise test results if AH of air is high.