Table 6

Spirometry variables at 8 and 18 years within the preterm cohort, comparing smokers with non-smokers at 18 years

8 years 18 years
VariableSmokers
n=34
Non-smokers
n=163
Mean difference (95% CI),
p value
Smokers
n=35
Non-smokers
n=170
Mean difference (95% CI),
p value
FEV1
 z-score−0.76 (1.08)−0.96 (1.05)0.20 (−0.20 to 0.59), 0.33−1.17 (0.98)−0.99 (1.10)*−0.18 (−0.58 to 0.22), 0.37
 % predicted90.9 (13.0)88.6 (12.7)2.3 (−2.4 to 7.0), 0.3486.2 (11.6)88.2 (13.1)*−2.1 (−6.8 to 2.7), 0.39
FVC
 z−score−0.62 (1.01)−0.92 (1.25)0.30 (−0.15 to 0.75), 0.19−0.35 (1.07)−0.49 (1.03)0.15 (−0.23 to 0.52), 0.45
 % predicted92.6 (12.1)89.2 (14.6)3.4 (−1.8 to 8.7), 0.2096.0 (12.5)94.2 (12.0)1.7 (−2.7 to 6.2), 0.45
FEV1/FVC
 z-score−0.07 (1.62)0.14 (1.51)−0.21 (−0.78 to 0.36), 0.46−1.16 (1.26)−0.79 (1.25)*−0.37 (−0.83 to 0.09), 0.11
 %87.1 (9.9)88.7 (9.1)−1.6 (−5.1 to 1.8), 0.3578.9 (10.3)82.0 (9.4)*−3.1 (−6.6 to 0.4), 0.08
FEF25%–75%
 z-score−1.41 (0.98)−1.31 (1.17)†−0.10 (−0.53 to −0.32), 0.64−1.68 (1.11)−1.30 (1.21)−0.38 (−0.81 to 0.06), 0.09
 % predicted69.9 (20.2)72.2 (25.0)†−2.3 (−11.4 to 6.7), 0.6167.0 (20.1)74.4 (23.4)−7.4 (−15.8 to 1.0), 0.08
FEF75%
 z-score−0.49 (1.02)‡−0.61 (1.25)§0.12 (−0.36 to 0.61), 0.62−1.28 (1.09)−0.88 (1.15)*−0.40 (−0.82 to 0.02), 0.06
 % predicted88.0 (29.2)‡86.2 (39.3)§1.7 (−13.4 to 16.9), 0.8267.4 (27.0)78.3 (31.5)*−10.9 (−22.2 to 0.4), 0.06
  • *n=1 missing data.

  • †n=6 missing data.

  • ‡n=5 missing data.

  • §n=12 missing data.

  • FEF25%–75%, forced expiratory flow at 25%–75% of FVC; FEF75%, forced expiratory flow at 75% of FVC expired.