Bronchial lability in cystic fibrosis.

Bronchial lability was studied in 52 children with cystic fibrosis (CF) and assessed by changes in the peak expiratory flow measured before, during, and after running. The findings are discussed in relation to the severity of pulmonary involvement assessed clinically and radiologically, and with those found in asthmatic children and those with a history of wheezy bronchitis in early childhood. In patients with CF, bronchial lability was found even in those with minimal pulmonary involvement. The lability was due not only to bronchoconstriction but to a dilatation which was greater than occurs in normal and asthmatic children; this dilatation increased with the severity of the disease. Only 14 of 52 children with CF had results within the normal range for all indices; 50% had abnormal bronchodilatation during exercise and 46% had abnormal bronchoconstriction after exercise.