TABLE 1

Changes in forced expiratory volume in 1 s (FEV₁) and respiratory system reactance (X_rs) indices over a 5-year interval

	Total	GOLD classification				FEV₁/height² classification L·m⁻²
	Total	I	II	III	IV	>0.5	≤0.5 to >0.4	≤0.4 to >0.3	≤0.3
Subjects n	24	5	9	6	4	14	4	3	3
FEV₁ z-score
Baseline	−3.18	−0.55	−2.48	−4.52	−6.05	−1.82	−4.18	−5.22	−6.19
After 5 years	−3.56*	−0.96	−3.25*	−4.54	−6.03	−2.38*	−4.25	−5.45	−6.26
Change per year	−0.08	−0.08	−0.15	−0.05	0.004	−0.11	−0.01	−0.05	−0.02
X₅ z-score
Baseline	−1.06	−0.33	−0.45	−1.62	−2.48	−0.41	−1.55	−1.95	−2.50
After 5 years	−1.53*	−0.51	−1.28*	−2.08	−2.54	−1.01*	−1.91	−2.37	−2.59
Change per year	−0.09	−0.05	−0.16	−0.09	−0.01	−0.12	−0.07	−0.08	−0.02
F_res z-score
Baseline	1.18	0.45	0.42	1.81	2.87	0.45	1.52	2.41	2.94
After 5 years	1.89*	0.80	1.45*	2.56	3.23	1.25*	2.12	3.05	3.42
Change per year	0.14	0.07	0.21	0.15	0.07	0.16	0.12	0.13	0.10
AX z-score
Baseline	1.00	0.37	0.40	1.53	2.34	0.40	1.35	1.95	2.40
After 5 years	1.50*	0.59	1.17	2.01	2.60	1.00*	1.73	2.30	2.75
Change per year	0.10	0.04	0.16	0.10	0.05	0.12	0.08	0.07	0.07

Data are presented as mean, unless otherwise stated. GOLD: Global Initiative for Chronic Obstructive Lung Disease; X₅: X_rs at 5 Hz; F_res: resonant frequency; AX: low-frequency reactance area. *: p<0.05 versus baseline.