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).