Inspiratory airflow limitation after exercise challenge in cold air in asthmatic children.

Methacholine and histamine can lead to inspiratory flow limitation in asthmatic children and adults. This has not been analyzed after indirect airway stimuli, such as exercise. The aim of the study was to analyze airflow limitation after exercise in cold, dry air. 72 asthmatic children with mild to moderate asthma (mean age 13.2 ± 2.2 yrs) performed a treadmill exercise challenge. A fall of >10% in FEV(1) was the threshold for expiratory flow limitation and a fall of >25% of MIF(50) was the threshold for inspiratory flow limitation. The occurrence of wheeze, stridor and cough were quantified before and after exercise. After exercise, the mean fall in FEV(1) was 17.7 ± 14.6%, while the mean fall in MIF(50) was 25.4 ± 15.8%; no correlation was found between fall in FEV(1) and MIF(50) (R(2): 0.04; p = 0.717). 53 of the 72 children showed an inspiratory and/or expiratory airflow limitation. 38% (20/53) of these children showed an isolated expiratory flow limitation, 45% (24/53) showed both expiratory and inspiratory flow limitation and 17% (9/53) showed an isolated inspiratory flow limitation. The fall in FEV(1) peaked 9 min after exercise and correlated to expiratory wheeze. The fall in MIF(50) peaked 15 min after exercise and correlated to inspiratory stridor. The time difference in peak fall between FEV(1) and MIF(50) was statistically significant (5.9 min; p < 0.001, 99% CI: 2.3-9.5 min). In conclusion, this study shows that an exercise challenge in asthmatic children can give rise to inspiratory airflow limitation, which may give rise to asthma like symptoms.