CC16 in tracheal aspirate | IL-1β in tracheal aspirate | TNFα in tracheal aspirate | IL-1β/CC16 ratio in tracheal aspirate | TNF-α/CC16 ratio in tracheal aspirate | |

Spirometry | (n=20) | (n=18) | (n=18) | (n=18) | (n=18) |

FEV1, L | r=0.03, p=0.90 | r=−0.47, p=0.048 | r=−0.55, p=0.019 | r=−0.52, p=0.028 | r=−0.51, p=0.029 |

FEV1, z-score | r=0.27, p=0.26 | r=−0.13, p=0.60 | r=−0.21, p=0.41 | r=−0.21, p=0.41 | r=−0.37, p=0.13 |

FEV1/FVC | r=0.51, p=0.021 | r=−0.17, p=0.49 | r=−0.09, p=0.74 | r=−0.63, p=0.005 | r=−0.68, p=0.002 |

FEV1/FVC, z-score | r=0.50, p=0.025 | r=−0.22, p=0.39 | r=−0.18, p=0.47 | r=−0.62, p=0.006 | r=−0.71, p=0.001 |

FEF_{25–75}, L/s | r=0.33, p=0.16 | r=−0.39, p=0.11 | r=−0.36, p=0.15 | r=−0.73, p<0.001 | r=−0.73, p<0.001 |

FEF_{25–75}, z-score | r=0.39, p=0.094 | r=−0.25, p=0.32 | r=−0.21, p=0.40 | r=−0.51, p=0.031 | r=−0.58, p=0.011 |

Impulse oscillometry | (n=20) | (n=18) | (n=18) | (n=18) | (n=18) |

R_{5}, kPa×s/L | r=−0.19, p=0.43 | r=0.09, p=0.71 | r=−0.23, p=0.36 | r=0.18, p=0.47 | r=0.001, p=1.00 |

R_{20}, kPa×s/L | r=−0.02, p=0.93 | r=0.18, p=0.49 | r=−0.12, p=0.64 | r=−0.01, p=0.97 | r=−0.16, p=0.53 |

R_{5}–R_{20}, kPa×s/L | r=−0.49, p=0.028 | r=0.14, p=0.58 | r=0.09, p=0.72 | r=0.57, p=0.013 | r=0.62, p=0.006 |

X_{5}, kPa×s/L | r=0.37, p=0.11 | r=−0.29, p=0.24 | r=−0.18, p=0.48 | r=−0.61, p=0.008 | r=−0.53, p=0.023 |

F_{res}, 1 /s | r=−0.65, p=0.002 | r=0.02, p=0.95 | r=0.02, p=0.95 | r=0.54, p=0.022 | r=0.69, p=0.002 |

AX, kPa/L | r=−0.57, p=0.008 | r=0.26, p=0.31 | r=0.16, p=0.53 | r=0.72, p<0.001 | r=0.73, p<0.001 |

Body plethysmography | (n=18) | (n=17) | (n=17) | (n=17) | (n=17) |

R_{insp}, kPa×s/L | r=−0.27, p=0.27 | r=0.17, p=0.52 | r=0.19, p=0.47 | r=0.36, p=0.15 | r=0.53, p=0.029 |

R_{exp}, kPa×s/L | r=−0.26, p=0.30 | r=0.30, p=0.25 | r=0.25, p=0.34 | r=0.60, p=0.012 | r=0.60, p=0.011 |

R_{tot}, kPa×s/L | r=−0.31, p=0.21 | r=0.27. p=0.30 | r=0.22, p=0.39 | r=0.55, p=0.023 | r=0.61, p=0.010 |

Diffusion capacity | (n=18) | (n=17) | (n=17) | (n=17) | (n=17) |

DL_{CO}, mmol/(min×kPa) | r=0.24, p=0.33 | r=−0.07, p=0.80 | r=−0.03, p=0.91 | r=−0.12, p=0.65 | r=−0.13, p=0.61 |

DL_{CO}, z-score | r=0.46, p=0.056 | r=0.36, p=0.16 | r=0.35, p=0.18 | r=0.15, p=0.57 | r=0.081, p=0.76 |

Alveolar volume, L | r=−0.24, p=0.34 | r=−0.28, p=0.28 | r=-041, p=0.10 | r=−0.29, p=0.26 | r=−0.15, p=0.58 |

Alveolar volume, z-score | r=0.09, p=0.72 | r=0.06, p=0.82 | r=0.17, p=0.52 | r=0.13, p=0.62 | r=0.26, p=0.31 |

K_{CO}, mmol/(min×kPa×L) | r=0.60, p=0.008 | r=0.27, p=0.30 | r=0.39, p=0.12 | r=0.028, p=0.91 | r=−0.083, p=0.75 |

K_{CO}, z-score | r=0.42, p=0.086 | r=0.28, p=0.27 | r=0.22, p=0.39 | r=0.020, p=0.94 | r=−0.15, p=0.58 |

Multiple breath washout | (n=19) | (n=17) | (n=17) | (n=17) | (n=17) |

LCI_{2.5} | r=−0.30, p=0.22 | r=−0.09, p=0.74 | r=−0.40, p=0.12 | r=0.21, p=0.43 | r=−0.037, p=0.89 |

LCI_{5.0} | r=−0.33, p=0.17 | r=−0.31, p=0.23 | r=−0.53, p=0.030 | r=0.022, p=0.93 | r=−0.15, p=0.58 |

S_{cond}×VT | r=−0.21, p=0.39 | r=−0.08, p=0.76 | r=0.07, p=0.79 | r=0.18, p=0.48 | r=0.26, p=0.31 |

S_{acin}×VT | r=−0.09, p=0.72 | r=−0.53, p=0.030 | r=−0.54, p=0.027 | r=−0.25, p=0.33 | r=−0.25, p=0.33 |

The table shows correlations (regression coefficients and p values) by Spearman's r between CC16, IL-1β, TNF-α, IL1-β/CC16 and TNFα/CC16 in tracheal aspirate and the various lung function measurements. The actual number (n) is given for the respective test, except for FEF

_{25–75}where data from one child are missing. P values <0.05 were considered significant and are marked as bold.AX, area under the reactance curve between 5 Hz and F

_{res}; CC16, club cell secretory protein; FEF_{25-75}, mean forced expiratory flow between 25% and 75% ; FEV_{1}, forced expiratory volume in 1 s; F_{res}, resonant frequency; FVC, forced vital capacity; IL-1β, interleukin-1β; LCI_{5.0}and LCI_{2.5}, lung clearance index, defined as the number of lung volume turnovers required to reach 5% and 2.5%; R_{exp}, expiratory flow resistance of the airways; R_{insp}, inspiratory flow resistance of the airways; R_{5,}R_{20}, respiratory resistance at 5 and 20 Hz, respectively; R_{5}-R_{20}, frequency dependence of resistance; R_{tot}, total flow resistance of the airways; S_{cond}x VT, an index of ventilation inhomogeneity in conductive airways; TNFα, tumour necrosis factor-α; X_{5}, respiratory reactance at 5 Hz.