Lung hyperinflation and functional exercise capacity in patients with COPD – a three-year longitudinal study

BMC Pulmonary Medicine

Table 2 Predictors for mean 6MWD estimated with GEE regression analysis

Predictors	Bivariate		Multivariate^a
Predictors	Beta	p	Beta	95% CI	p
Time		< 0.001			< 0.001^b
1 year vs. baseline	8.1	0.052	6.0	- 1.9 – 13.4	0.134
3 years vs. baseline	- 21.0	< 0.001	- 24.1	- 35.1 – - 13.9	< 0.001
Sex, (male vs. female)	35.1	0.002	- 28.8	- 60.1 – 2.5	0.072
Age (years)	- 5.3	< 0.001	- 1.8	- 3.4 – - 0.3	0.019
FEV₁ (L)	107.3	< 0.001	47.5	21.7–73.2	< 0.001
FVC (L)	57.1	< 0.001	20.9	5.2–36.7	0.009
IC/TLC ratio (at 0.35)	489.4	< 0.001			< 0.001^c
At baseline			116.3	−10.0 – 242.7	0.071
At 1 year			175.2	25.1–325.4	0.022
At 3 years			454.2	263.3–645.2	< 0.001
FMI (kg/m²)	- 8.2	< 0.001	- 8.3	- 12.2 – - 4.4	< 0.001
FFMI (kg/m²)	5.2	0.008	1.3	- 3.6 – 6.3	0.592
Pack years	- 0.2	0.577	- 0.2	- 0.7 – 0.3	0.421
Experienced > 2 exacerbations last year	- 66.4	< 0.001	- 32.1	- 53.5 – - 10.7	0.003
Charlson comorbidity index; score		0.001			0.006^b
2 vs. 1	- 30.6	0.025	- 12.1	- 33.5 – 9.2	0.266
3 vs. 1	- 56.6	0.003	- 37.4	- 68.7 – - 6.1	0.019
4 vs. 1	- 58.9	0.016	- 54.8	- 91.6 – - 18.0	0.004
Light physical activity ≥1 h/week	69.9	< 0.001	34.2	7.5–60.8	0.012
Hard physical activity ≥1 h/week	66.4	< 0.001	37.0	18.6–55.4	< 0.001

Beta estimated regression coefficient, P p-value, CI confidence interval, 6MWD 6-min walk distance, GEE generalized estimated equation, FEV₁ forced expiratory volume in one second, FVC forced vital capacity, IC/TLC ratio inspiratory-to-total lung capacity ratio, FMI fat mass index, FFMI fat free mass index
^a The model included all predictors and interaction terms for time x IC/TLC ratio centered at mean value (0.35). ^b Test for overall effect. ^c Test for time as effect modifier (test of interaction)

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