Lung function deficits in children born very preterm versus at
term
Children born very preterm had more airway obstruction, higher airway
resistance, lower diffusion capacity and more ventilation inhomogeneity
at 12 years of age than their term born controls. This was most evident
before bronchodilator inhalation and was seen in a majority of the tests
performed and both as absolute values and as percent of predicted normal
values (Figure 1 and Tables 2 and 3).
Spirometry showed significantly more airway obstruction, measured as
reductions in FEV1, FEV1/FVC and
FEF25-75, in children born very preterm compared to
term, both as absolute values and as percent of predicted (Figure 1A-C,
Table 2). FEV1 below the lower limit of normal occurred
in 23.5% of children born very preterm but only in 3.6% of children
born at term (p=0.001). The corresponding proportions for
FEV1/FVC were 25.0% versus 9.1% (p=0.014) and for
FEF25-75 39.7% versus 10.9% (p<0.001).
Dysanapsis ratio was lower in children born very preterm than in
children born at term (p=0.004, Table 2).
Measurement of static lung volumes showed lower VC and higher RV as
percent of predicted in very preterm infants, and also higher RV/TLC
(Table 2 and 3). However, TLC and alveolar volume were not significantly
different between children born preterm or at term.
Inspiratory, expiratory, and total airway resistance, as measured by
body plethysmography, were higher in children born preterm (Table 3).
Impulse oscillometry similarly showed a higher total resistance
(R5, Figure 1D), frequency dependence of resistance
(R5-R20) and resonant frequency
(Fres), a lower reactance at 5 Hz (more negative
X5), and an increased area under the reactance curve
(AX; all p<0.001, Table 3), all indicating dysfunction of
peripheral airways.
Diffusion capacity (DLCO) and the diffusion coefficient
for CO (KCO) were significantly lower in preterm- than
in term-born children (Table 3 and Figure 1E). However, the proportion
of preterm-born children with measurements below the lower limit of
normal was much smaller for DLCO (5.7% for children
born preterm and 0% for term born controls, E-table 2) than for
expiratory flows.
During N2 washout, children born very preterm had a
significantly higher lung clearance index (both LCI2.5and LCI5.0) than children born at term (Table 3 and
Figure 1F). This was most prominent for LCI2.5,
indicating an increased ventilation inhomogeneity most evident in the
peripheral airways.
Within the whole study population, children with
FEV1/FVC or FEF25-75 below the lower
limit of normal had significantly more often experienced wheezing,
disturbed sleep or at least one of the symptoms listed in Table 1 (all
p<0.05). A previous diagnosis of asthma was almost twice as
common in children found to have FEF25-75 below the
lower limit of normal than in those with a normal
FEF25-75 (42.4% vs. 22.0%, p=0.004).