Longitudinal change of FEV₁ and inspiratory capacity: clinical implication and relevance to exacerbation risk in patients with COPD

Figures & data

Table 1 Baseline characteristics of study participants

Characteristics	All patients (N=982)
Male sex, n (%)	958 (97.6)
Age, years	72.7±8.4
BMI, kg/m^2	23.0±3.3
Ever smokera	977 (99.8)
Smoking pack-years	45.4±24.0
mMRC dyspnea scale	1.4±0.9
CAT score	15.8±7.7
SGRQ score	35.1±19.0
6MWD, m	394.9±102.4
History of exacerbation in the past year
Exacerbation (yes, %)	210 (21.6)
Frequency of exacerbation (number/year)	2.2±2.3
Post-bronchodilator FEV1
Value, L	1.7±0.6
% of predicted value	62.7±19.3
Post-bronchodilator FVC
Value, L	3.4±0.8
% of predicted value	87.8±17.6
Post-bronchodilator FEV1/FVC, %	49.8±11.7
DLCO
Value, mL/mmHg/min	13.4±5.8
% of predicted value	74.3±23.0
GOLD stage, n (%)
I	173 (17.6)
II	547 (55.7)
III	230 (23.4)
IV	32 (3.3)

Notes: Data are presented as number (%) or mean ± SD.

a Ever smoker includes current or ex-smoker.

Abbreviations: BMI, body mass index; CAT, COPD assessment test; DLCO, diffusing capacity for carbon monoxide; SGRQ, St George’s Respiratory Disease Questionnaire.

Table 2 Lung volume measurement

Parameters	Value
VC
L	3.3±0.8
% of predicted value	92.5±51.9
IC
L	1.9±0.6
% of predicted value	74.6±22.9
RV
L	2.8±1.2
% of predicted value	126.6±56.2
FRC
L	3.8±0.9
% of predicted value	117.2±26.2
TLC
L	6.1±1.3
% of predicted value	109.6±23.1
RV/TLC ratio, %	44.1±11.7
IC/TLC ratio, %	31.3±9.9
VC/TLC ratio, %	55.3±12.2

Note: Data are presented as number (%) or mean ± SD.

Abbreviations: FRC, functional residual capacity; IC, inspiratory capacity; RV, residual volume; TLC, total lung capacity; VC, vital capacity.

Figure 1 Study population.

Abbreviation: PY, pack-years.

Figure 2 Correlation between IC, IC/TLC and (A, E) mMRC dyspnea scale, (B, F) SGRQ, (C, G) CAT, and (D, H) 6MWD in COPD patients.

Abbreviations: CAT, COPD assessment test; IC, inspiratory capacity; SGRQ, St George’s Respiratory Disease Questionnaire; TLC, total lung capacity.

Figure 3 Mean change of FEV₁ and IC from enrollment.

Note: The bars in this graph represents the mean value and 95% CI.
Abbreviations: BD, bronchodilator; IC, inspiratory capacity.

Table 3 Effect of exacerbation on the change in FEV₁, IC, and IC/TLC ratio

Characteristics	Adjusted annual rate of change in FEV1, mL/year	P-value	Adjusted annual rate of change in IC, mL/year	P-value	Adjusted annual rate of change in IC/TLC, %	P-value
FEV1 ≥50%
Exacerbation in the past year prior to enrollment		0.189		0.580		0.597
No	−22.28±6.26		−0.04±13.07		0.09±0.22
Yes	−3.0±12.92		−16.26±26.22		−0.17±0.43
Exacerbation during follow-up		0.935		0.546		0.520
Infrequent (<2/year)	−18.59±5.87		−5.90±12.14		0.01±0.20
Frequent (≥2/year)	−16.88±20.29		22.46±45.36		0.50±0.75
FEV1 <50%
Exacerbation in the past year prior to enrollment		0.900		0.189		0.676
No	8.28±10.82		−2.16±20.34		−0.01±0.34
Yes	6.12±13.35		−44.78±25.18		−0.23±0.40
Exacerbation during follow-up		0.213		0.056		0.105
Infrequent (<2/year)	12.29±9.24		−4.75±17.28		0.13±0.29
Frequent (≥2/year)	−14.46±19.40		−78.05±34.16		−0.95±0.50

Notes: Data are shown as mean ± standard error. Mixed-effects linear regression analysis was performed, which included the following covariates: age, sex, BMI, exacerbation before and after enrollment, inhaled bronchodilator use, and interaction of each covariate with time.

Abbreviations: BMI, body mass index; IC, inspiratory capacity; TLC, total lung capacity.

Table 4 Exacerbation risk during the follow-up period of 3 years according to FEV₁ and IC changesa and IC/TLC ratiob

Lung function changes	Crude HR	95% CI	P-value	Adjusted HRc	95% CI	P-value
1 year
IC change ≤150 mL	1.00	0.63–1.60	0.988	1.07	0.67–1.72	0.780
FEV1 change ≤100 mL	0.87	0.56–1.36	0.549	0.89	0.57–1.38	0.597
IC/TLC ≤25%	1.11	0.73–1.67	0.632	1.07	0.70–1.62	0.766
2 years
IC change ≤150 mL	0.68	0.51–1.13	0.133	0.77	0.45–1.32	0.345
FEV1 change ≤100 mL	0.94	0.59–1.50	0.797	1.08	0.67–1.75	0.743
IC/TLC ≤25%	1.16	0.73–1.85	0.526	1.04	0.65–1.67	0.870
3 years
IC change ≤150 mL	1.21	0.62–2.34	0.580	1.04	0.53–2.04	0.916
FEV1 change ≤100 mL	1.01	0.59–1.70	0.980	1.08	0.67–1.75	0.743
IC/TLC ≤25%	1.53	0.92–2.54	0.104	1.26	0.74–2.15	0.397

Notes:

a Based on the minimal clinically important difference, the absolute value of the change was <150 mL for the IC, and 100 mL for the FEV₁ was regarded as reference value.

b The IC/TLC ratio was divided into low (IC/TLC ratio ≦25%) and high groups (IC/TLC ratio >25%)

c adjusted for age, sex, body mass index, smoking pack-years, and previous history of exacerbation in the past year.

Abbreviations: IC, inspiratory capacity; TLC, total lung capacity.

Figure S1 Correlation between (A) IC and (B) IC/TLC ratio with post-bronchodilator FEV₁.

Abbreviations: BD, bronchodilator; IC, inspiratory capacity; TLC, total lung capacity.

Figure S2 Longitudinal change of annual (A) FEV₁ and (B) IC (mL) in COPD patients during 3-year follow-up according to history of exacerbation.

Abbreviation: IC, inspiratory capacity.