Specific airway resistance in 3-year-old children: a prospective cohort study.

The development of a method to assess lung function in young children may provide new insight into asthma development. Plethysmographic measurement of specific airway resistance (sR(aw)) is feasible in this age group. We aimed to identify risk factors associated with low lung function in early childhood in a prospective birth cohort. Children were prenatally assigned to risk group according to parental atopic status (high risk, both parents atopic; medium risk, one parent atopic; low risk, neither parent atopic) and followed prospectively until age 3 years. We measured sR(aw) in 503 symptom-free children using whole-body plethysmography during tidal breathing. 803 of 868 children attended the clinic, of whom 503 obtained satisfactory sR(aw) readings. 200 who wheezed at least once during first 3 years of life had significantly higher sR(aw) than the 303 who had never wheezed (mean difference 5.8%, 95% CI 2.2-9.3, p=0.002). For children who had never wheezed there were significant differences in sR(aw) between risk groups (p<0.001). Children at high risk (n=87) had a higher sR(aw) (geometric mean 1.17 kPa/s, 1.12-1.22) than children at medium risk (n=162; 1.02 kPa/s, 1.00-1.05) and at low risk (54; 1.04 kPa/s, 0.99-1.11). Atopic children (n=62) had significantly higher sR(aw) (1.15 kPa/s, 1.09-1.21) than those who were not atopic (232; 1.05 kPa/s, 1.02-1.07, p=0.002). For non-atopic children, those at high risk (58) had higher sR(aw) (1.13kPa/s, 1.07-1.18) than those at medium risk (125, 1.01kPa/s, 0.98-1.05) or at low risk (49, 1.04 kPa/s, 0.97-1.10, p=0.003). We showed a significant interaction between history of maternal asthma and child's atopic status (p=0.006). Even in the absence of respiratory symptoms, children of atopic parents and those with personal atopy have impaired lung function in early life.