Exercise-induced airway narrowing in army recruits with a history of childhood asthma.

The aim of this study was to determine whether the addition of cold, dry, inspired air to maximum heart rate (MHR) exercise increased the number of subjects demonstrating abnormal airway narrowing, when applied to symptom-free army recruits with a history of asthma in childhood. One hundred recruits with a history of asthma in childhood underwent two exercise challenges to maximum heart rate, breathing either room air or cold dry air in randomized order. The percentage fall index (%FI) was calculated for each challenge, a positive result being > or = 15%. A total of 29 subjects had a positive % fall index, 12 subjects were positive to both challenges, 7 to the room air alone and 10 to the cold air challenge alone. In these subjects (n = 29), the mean (SD) % fall index to the cold air challenge was 22.7 (11.0)% compared with 16.3 (9.5)% for the room air challenge. We conclude that when employed as a screening test for abnormal airway narrowing, the addition of cold, dry, inspired air during exercise does not increase the number of subjects with a positive response, but the magnitude of the response is increased.