LUNG-FUNCTION, AIRWAY RESPONSIVENESS, AND RESPIRATORY SYMPTOMS BEFOREAND AFTER BRONCHIOLITIS

Acute viral respiratory illness during infancy has been implicated as a precursor for subsequent lower respiratory morbidity in childhood. A prospective, longitudinal study of respiratory function, airway respo nsiveness, and lower respiratory illness during early childhood was pe rformed in a cohort of 253 healthy infants to characterise those who e xperienced bronchiolitis. Seventeen infants (7% of the cohort), were g iven a diagnosis of bronchiolitis during the first two years of Life w ith two (1%) requiring hospital admission. Seventy one per cent of tho se infants with bronchiolitis had a family history of atopy, 53% of as thma, and 29% had a mother who smoked cigarettes. These family history characteristics in this group with bronchiolitis were not different f rom the rest of the cohort. There were also no differences in the numb er of older siblings, the number breast fed, the duration of breast fe eding, or socioeconomic status of the families between those that did and did not get bronchiolitis. Respiratory function was assessed at 1, 6, and 12 months of age. Maximum flow at functional residual capacity (V(max)FRC) was measured using the rapid thoracic compression techniq ue. Resistance (Rrs) and size corrected compliance (Crs/kg) were obtai ned from a single brief occlusion at end inspiration. Airway responsiv eness was assessed by histamine inhalation challenge and the provocati on concentration of histamine resulting in a 40% fall on V(max)FRC fro m baseline (PC40) was determined. Respiratory measurements were ranked into terciles to assess the distribution of infants who developed bro nchiolitis through the cohort. At the age of 5 weeks, a significant tr end was observed for infants who subsequently developed bronchiolitis during the first year of life to have baseline V(max)FRC values in the lowest tercile (odds ratio 3.16, 95% confidence interval 0.87 to 11.6 ). Rrs, Crs/kg, and PC40 were not different at any age between the bro nchiolitics and the cohort. Cough and wheeze were noted to be frequent before the episode of bronchiolitis. This study has demonstrated that infants who develop bronchiolitis have evidence of pre-existing reduc ed respiratory function and lower respiratory symptoms. It is proposed that bronchiolitis, although potentially contributory, is not usually causative of subsequent lower respiratory morbidity.