Baseline lung function
Preterm participants had a lower FEV1 (MD= -0.87; 95% CI -0.56, -1.17; p<0.001) and FEV1/FVC z-score (MD= -0.85; 95% CI -0.57, -1.14; p<0.001), but not FVC z-score (Table 2) compared to term-born participants. Obstructive spirometry (defined as FEV1 or FEV1/FVC ≤−1·64 z-scores) was seen in 31.4% of preterm participants, compared to 8.6% of term born controls (X2= 14.8, p<0.001).
Preterm-born participants also had abnormal respiratory mechanics as assessed by oscillometry. Spectral oscillometry z-scores revealed significant differences in reactance at 5Hz (Xrs5) (MD= -0.52; 95% CI -0.26 to -0.79; p<0.001), area under the reactance curve (AX) (MD= 0.67; 95% CI 0.40 to 0.94; p<0.001) and resonant frequency (Fres) (MD= 0.62; 95% CI 0.33 to 0.91; p<0.001) for those born preterm, compared to term. Z-scores for respiratory resistance at 5Hz (Rrs5) were not different between term and preterm groups (Table 2, p>0.05), however the difference between respiratory resistance at 5 and 20 Hz (Rrs5-20) was greater in the preterm group (Table 2, p<0.001).
At 10Hz, inspiratory and expiratory resistance was higher and reactance was lower in the preterm group (Table 2), however the magnitude of the difference between inspiratory and expiratory reactance values (X10insp-exp) was not different in those born preterm compared to term born controls (Table 2, p>0.05).