Table 4.

Association of prebronchodilator and postbronchodilator spirometric measures with number of exacerbations and severe exacerbations per year, change in FEV₁, dyspnoea scores and distance covered in 6 min walk test from phase 1 to phase 2 visit (5-year interval)

	Prebronchodilator FEV1/FVC <0.7 (PREO)			Postbronchodilator FEV1/FVC <0.7 (POSTO)
	Coef (95% CI)	P value	AIC	Coef (95% CI)	P value	AIC
Exacerbations per year	0.35 (0.31 to 0.4)	<0.001	−893	0.38 (0.34 to 0.43)	<0.001	−929
Severe exacerbations per year	0.14 (0.11 to 0.16)	<0.001	−11608	0.14 (0.12 to 0.16)	<0.001	−11614
Change in FEV1, mL	−2.25 (−20.3 to 15.8)	0.81	54 317	10 (−7.26 to 29.3)	0.24	54 315
Change in MMRC	0.2 (0.12 to 0.27)	<0.001	1978	0.21 (0.13 to 0.29)	<0.001	1974
Change in SGRQ	1.92 (0.99 to 2.85)	<0.001	26 399	2.56 (1.62 to 3.5)	<0.001	26 387
Change in 6-MWD, feet	−22.2 (−44.3 to 0.05)	0.049	55 763	−33.2 (−55.6 to 10.8)	0.004	55 758

	Postbronchodilator FEV1% predicted			Postbronchodilator FEV1% predicted
	Coef (95% CI)	P value	AIC	Coef (95% CI)	P value	AIC
Exacerbations	−0.011 (−0.012 to 0.01)	<0.001	−1233	−0.011 (−0.01 to 0.0097)	<0.001	−1222
Severe exacerbations	−0.004 (−0.0045 to 0.0036)	<0.001	−11787	−0.004 (−0.0045 to 0.0036)	<0.001	−11777
Change in FEV1, mL	−1.91 (−2.28 to 1.53)	<0.001	54 218	−2.76 (−3.13 to 2.39)	<0.001	54 112
Change in MMRC	−0.002 (−0.0038 to 0.00065)	0.006	1996	−0.02 (−0.0036 to 0.00037)	0.016	1998
Change in SGRQ	−0.01 (−0.03 to 0.0095)	0.32	26 415	−0.01 (−0.029 to 0.01)	0.34	26 415
Change in 6-MWD, feet	0.99 (0.53 to 1.46)	<0.001	55 749	0.9 (0.43 to 1.37)	<0.001	55 753

All regression models included the following covariates: age, sex, race, smoking status, pack per years, history (per questionnaire) of asthma, diabetes, high blood pressure, stroke and sleep apnoea.

6-MWD, 6 min walk distance; AIC, Akaike information criterion; FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity; MMRC, modified Medical Research Council dyspnoea score; SGRQ, St. George’s Respiratory Questionnaire score.