Table 6– Associations between spirometric outcomes and specific airway resistance with extremely preterm birth and other factors
zFEV1zFEF25–75%zFEV1/FVCZsReff
Subjects n949494100
Variability explained# %41362013
Constant-0.11-0.430.280.34
EP-1.31 (-1.73– -0.89)***-1.14 (-1.59– -0.69)***-0.58 (-0.99– -0.17)**0.45 (0.12–0.78)**
Wheeze ever-0.71 (-1.16– -0.26)**-0.84 (-1.32– -0.36)**-0.66 (-1.09– -0.22)**0.38 (0.04–0.73)*
Other variables of interest+
 BPD-0.47 (-1.10– -0.15)-0.38 (-1.05–0.29)-0.08 (-0.69–0.53)0.30 (-0.20–0.81)
 White mother0.43 (-0.19–1.05)NA§NA§NA§
  • Data presented as coefficient (95% CI), unless otherwise stated. FEV1: forced expiratory volume in 1 s; FEF25–75%: forced expiratory flow between 25–75% forced vital capacity (FVC); sReff: specific effective airway resistance; EP: extreme pre-term; BPD: bronchopulmonary dysplasia; NA: not applicable. #: adjusted r2 derived from multiple linear regression using the whole dataset (EP + controls). : most significantly associated with these lung function outcomes. +: not significantly associated with the lung function outcomes after adjusting for the above variables. §: factor not included in the model as it was not significantly associated with the lung function variable. With the exception of sReff, once accounted for this variable, additional symptoms and current asthma did not add significantly to the models. Current asthma status was significantly associated with a further increase in sReff by an average of 0.48 Z-score (95% CI 0.07–0.90) (p = 0.02) while the contribution from the “wheeze: ever” variable was no longer significant (mean Z-score (95% CI) 0.26 (-0.10–0.61)). Although the univariate associations of BPD with lung function and of ethnicity with FEV1 (but not FEF25–75%, FEV1/FVC or sReff) (supplementary table E1) were no longer significant during multiple linear regression, they are reported as additional variables of interest since they show identical trends to those found when analysing the entire cohort 11. *: p<0.05; **: p<0.01; ***: p<0.0001.