Reduced lung function in early infancy has been associated with later obstructive airway diseases. We assessed whether reduced lung function shortly after birth predicts asthma 10 years later.

We conducted a prospective birth cohort study of healthy infants in which we measured lung function shortly after birth with the use of tidal breathing flow-volume loops (the fraction of expiratory time to peak tidal expiratory flow to total expiratory time [t _PTEF/t _E]) in 802 infants and passive respiratory mechanics, including respiratory-system compliance, in 664 infants. At 10 years of age, 616 children (77%) were reassessed by measuring lung function, exercise-induced bronchoconstriction, and bronchial hyperresponsiveness (by means of a methacholine challenge) and by conducting a structured interview to determine whether there was a history of asthma or current asthma.

As compared with children whose t _PTEF/t _E shortly after birth was above the median, children whose t _PTEF/t _E was at or below the median were more likely at 10 years of age to have a history of asthma (24.3% vs. 16.2%, P=0.01), to have current asthma (14.6% vs. 7.5%, P=0.005), and to have severe bronchial hyperresponsiveness, defined as a methacholine dose of less than 1.0 μmol causing a 20% fall in the forced expiratory volume in 1 second (FEV₁) (9.1% vs. 4.9%, P=0.05). As compared with children whose respiratory-system compliance was above the median, children with respiratory compliance at or below the median more often had a history of asthma (27.4% vs. 14.8%; P=0.001) and current asthma (15.0% vs. 7.7%, P=0.009), although this measure was not associated with later measurements of lung function. At 10 years of age, t _PTEF/t _E at birth correlated weakly with the maximal midexpiratory flow rate (r=0.10, P=0.01) but not with FEV₁ or forced vital capacity.

Reduced lung function at birth is associated with an increased risk of asthma by 10 years of age.