Preschool oscillometry and lung function at adolescence in asthmatic children

Reduced lung function in early childhood is associated with persistent symptoms and low lung function later in life. Impulse oscillometry (IOS) is feasible for assessing lung function also in preschool children, and some of the parameters, such as respiratory resistance at 5 Hz (Rrs5) and the frequency dependence of resistance (dRrs/df), have been suggested to reflect small airway dysfunction. Whether changes in preschool IOS predict later lung function remains unknown.

The medical data of 154 asthmatic children with IOS performed at 2-7 years and spirometry at 12-18 years were analyzed. IOS and post-bronchodilator spirometry parameters were compared, and the association was estimated in a multivariate model.

Measured at preschool age, particularly Rrs5 and dRrs/df were significantly correlated with post-bronchodilator forced expiratory volume in 1 sec (FEV1) at adolescence (Rrs5: r = -0.223, P = 0.005; dRrs/df: r = 0.234, P = 0.004). Although the number of children with decreased FEV1 was low, associations of increased Rrs5 (odds ratio (OR) 5.9, 95% confidence interval (CI) 1.7; 20.9) and decreased dRrs/df (OR 8.2, 95% CI 1.7; 39.6) with decreased FEV1 remained significant in multivariate analyses. Similar findings were observed also with other spirometric parameters.

In asthmatic children, preschool IOS is associated with spirometric lung function at adolescence, but the scatter is wide. Normal preschool IOS seems to indicate favourable lung function outcome, whereas in some individuals IOS could potentially be of clinical use, at a younger age than spirometry, to screen lung function deficits and increased risk for later lung function impairment.