Exhaled nitric oxide as a marker of chlorine exposure in young asthmatic swimmers

Swimming is recommended for people with asthma. However, the inevitable exposure to chlorine and its disinfectant byproducts in indoor swimming pools could be responsible for bronchial inflammation and asthma development. Fractional exhaled nitric oxide (FeNO) is a noninvasive marker of airway inflammation that predicts asthma exacerbations.

To evaluate pretraining and posttraining FeNO levels in young swimmers with asthma attending an indoor chlorinated pool compared with a set of healthy swimmers and to examine the potential risk of exposure to chlorine as a factor associated with bronchial inflammation.

A total of 146 children (8-18 years old) constantly attending an indoor chlorinated swimming pool were enrolled. Spirometry and FeNO measurements were performed 30 minutes after their arrival at the pool and immediately after exercise. Pre-exercise and postexercise spirometric and FeNO levels were assessed in a random subgroup of 14 swimmers (10 with asthma and 4 without) who performed cardiopulmonary exercise testing.

Asthma was detected in 23 swimmers. In swimmers with asthma, preswimming FeNO values were significantly elevated compared with swimmers without asthma and their FeNO values measured before cardiopulmonary exercise testing. Postexercise FeNO values were significantly decreased by approximately one-third in healthy children and children with asthma in all sporting backgrounds. However, postswimming FeNO values remained significantly higher in swimmers with asthma compared with those without asthma. Forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and FEV₁/FVC ratio values showed no significant difference before and after 2 types of activity.

Elevated FeNO levels before and after swimming were recorded in swimmers with asthma not observed in a different exercise field. The presence of chlorine in the indoor swimming pool seems to explain this finding.