Asymptomatic bronchial hyperresponsiveness to exercise in childhood and the development of asthma related symptoms in young adulthood: the Odense Schoolchild Study

Background-Exercise testing may be of value in identifying a group of child ren at high risk of subsequently developing respiratory symptoms. As few lo ngitudinal studies have investigated this issue, the bronchial hyperrespons iveness to exercise in asymptomatic children was evaluated as a risk factor for developing asthma related symptoms in young adulthood. Methods-A community based sample of 1369 schoolchildren, first investigated in 1985 at a mean age of 9.7 years, was followed up after a mean of 10.5 y ears. Nine hundred and twenty children (67%) were asymptomatic in childhood and 777 (84.9%) of these were re-investigated at follow up. At the first e xamination a maximum progressive exercise test on a bicycle ergometer was u sed to induce airway narrowing. The forced expiratory volume in one second (FEV1) after exercise was considered abnormal if the percentage fall in FEV 1 was more than 5% of the highest fall in the reference subjects characteri sed by having no previous history of asthma or asthma related symptoms. The threshold for a positive test was 8.6% of pre-exercise FEV1. Results-One hundred and three subjects (13%) had wheeze within the last yea r at follow up and, of these, nine (9%) had been hyperresponsive to exercis e in 1985. One hundred and seventy subjects (22%) had non-infectious cough within the previous year, 11 of whom (6%) had been hyperresponsive to exerc ise in 1985. Multiple regression analysis showed that subjects with hyperre sponsiveness to exercise had an increased risk of developing wheeze compare d with subjects with a normal response to exercise when the fall in FEV1 af ter exercise was included as a variable (threshold odds ratio (OR) 2.3 (95% CI 1.1 to 5.5)). The trend was not significant when exercise induced bronc hospasm was included as a continuous variable (OR 1.02 (95% CI 0.97 to 1.06 )). Conclusions-Asymptomatic children who are hyperresponsive to exercise are a t increased risk of developing new symptoms related to wheezing but the pre dictive value of exercise testing for individuals is low.