Effect of bronchodilator inhalation on lung function
Reversibility, here meaning an improvement in lung function after inhalation of 200 µg salbutamol, occurred both in children born at term and in children born very preterm (Figure 1), but the effect was generally larger in the very preterm group, so that after bronchodilator the difference between the two groups was, for some parameters, no longer significant. Table 4 shows % of predicted values, E-table 3 shows absolute values, and E-table 4 proportion of children with values outside the normal range before versus after bronchodilator. E-table 5 shows reversibility in percent and E-table 6 absolute reversibility, also in relation to BPD.
Children born preterm were more reversible in FEV1/FVC and FEF25-75 compared to full term controls (E-table 5 and 6), but after bronchodilator, there remained a significant difference between children born preterm versus at term for FEV1 and FEF25-75, but not for FEV1/FVC (Tables 4 and E-table 3). After bronchodilator, the proportion of children born very preterm with FEV1below the lower limit of normal fell from 23.5% to 7.6% (p=0.001). For FEV1/FVC, the similar proportions were 25.0% versus 7.6%, and for FEF25-75 they were 39.7 % versus 16.3% (both p<0.001, Table 4).
Bronchodilator inhalation caused no significant change in lung volumes,i.e. FVC, TLC, RV or alveolar volume in children born very preterm (Table 4).
Children born very preterm were more reversible than children born at term in total airway resistance, as measured by body plethysmography, and frequency dependence of resistance (R5-20) and airway reactance (X5, AX and Fres) as measured by IOS (E-table 6). Total airway resistance (measured by body plethysmography and as R5 by impulse oscillometry) decreased significantly after bronchodilator inhalation, so that no difference remained in comparison with children born at term. Small airway dysfunction measured by impulse oscillometry also improved after bronchodilator (all p<0.001) but remained significantly higher than in children born at term (Tables 4 and E-table 3).
In children born preterm, DLCO and KCOincreased after bronchodilator inhalation but remained significantly lower than in term infants (Tables 4 and E-table 3). However, after bronchodilator inhalation, almost all children had values within a normal range (E-table 4).
Multiple breath wash-out in children born preterm showed a significant fall in Scond and Sacin after bronchodilator (Table 4 and E-table 3). Notably, the proportion of children born very preterm with Scond above the 95th centile fell from 17.3% to 4.4% (p=0.035, E-table 4).
In a subgroup analysis of children born very preterm with or without BPD, the bronchodilator response was found to be similar with the same significance levels in both subgroups for measurements made during spirometry, body plethysmography and diffusion capacity (E-tables 5 and 6).