Assessment of the bronchodilator response
Oscillometry was more feasible than spirometry, with 95% of overall participants obtaining acceptable measures pre- and post-bronchodilator with oscillometry, compared to 85% for FEV1(p<0.001) and 69% for FVC (p<0.001). However, the feasibility of achieving a successful bronchodilator assessment with either test was similar in term and preterm groups (p>0.05, Table 3).
A greater bronchodilator response was observed in the preterm group compared to the term group via both spirometry and oscillometry (Table 3). A small but significant improvement in FEV1, but not FVC, was observed, relative to term born controls with a mean difference of 3.5% (95% CI 2.0 to 4.9; p<0.001). Similarly, improvements were observed in the oscillometry measures ΔRrs5 (MD= -4.9%, 95% CI -8.7 to -1.0, p=0.013), ΔRrs5-20 (MD= -0.39, 95% CI -0.56 to -0.23, p<0.001), ΔXrs5 (MD= 11.4%, 95% CI 5.8 to 17.0, p<0.001) and ΔAX (MD= -14.1%, 95% CI -22.6 to -5.7, p=0.001).
Using published cut-offs, we observed a bronchodilator response in 24.1% of those born ≤32 weeks gestation by spirometry compared to 7.6% of term-born controls (p=0.003). Oscillometry detected a bronchodilator response in 16.4% of those born preterm, compared to 4.3% of term-born controls (p=0.009).
Intrabreath oscillometry revealed that the magnitude of the change in inspiratory reactance (X10insp) and expiratory reactance (X10exp) following bronchodilator was greater in those born preterm (Table 3). The magnitude of this change was however proportional across the breath cycle, with negligible within breath differences in reactance (X10insp-exp) (MD= -0.01, 95% CI -0.1208 to 0.101, p=0.861) (Table 3). No significant bronchodilator induced decrease in inspiratory or expiratory resistance were observed in the preterm group, relative to the term-control group (Table 3).