Smoking cessation affects the natural history of COPD

Figures & data

Table 1 Clinical characteristics of patients in the death group and survival group

Parameter	Both groups	Death groups	Survival groups	P-value
Subjects, n	204	113	91
Sex (M/F), n	201/3	110/3	91/0	0.083
Age, years	67.9±9.4	71.0±8.5	64.0±8.9	<0.001
Pack-year	45.3±34.5	45.1±36.5	45.7±32.0	0.897
Smoking time, years	38.2±11.5	40.3±12.7	35.7±9.3	0.003
Cigarettes smoked in 1 day, n	23.0±13.0	22.5±14.0	23.6±11.6	0.539
Age of onset of smoking, years	25.9±8.3	27.0±8.8	25.7±7.4	0.059
Quitting smoking	92	40	52	0.001
Time of quitting smoking, years	4.4±7.0	3.6±6.4	5.3±7.7	0.083
Age of quitting smoking, years	58.8±10.4	62.8±10.8	55.6±8.9	0.001
Course of disease, years	12.7±10.8	13.5±12.5	10.7±7.9	0.054
Onset of symptoms, years	55.6±12.5	57.5±13.4	53.3±10.9	0.017
Smoking time before disease, years	29.5±11.8	30.8±13.0	28.1±10.0	0.088
Pack-year before disease	34.0±26.0	33.9±28.2	34.2±23.1	0.935
FVC% predicted	71.5±19.4	73.4±20.1	69.1±18.1	0.113
FEV1% predicted	43.3±19.1	39.6±17.8	46.5±19.6	0.010
FEV1/FVC	46.7±11.3	44.4±11.3	48.5±11.0	0.009
RV% predicted	207.5±66.7	216.7±69.2	200.1±63.9	0.077
RV/TLC	66.0±10.8	65.0±11.4	67.4±10.0	0.117
DLCO % predicted	72.9±45.5	68.0±27.3	76.9±55.8	0.163
R% predicted	256.6±133.0	254.6±129.4	259.1±138.0	0.806
PO2, mmHg	81.1±23.7	81.4±25.3	80.8±21.7	0.867
PCO2, mmHg	45.0±14.2	45.8±13.8	44.1±14.6	0.406

Notes: Statistically significant values are shown in bold. Data shown as mean ± standard deviation.

Abbreviations: DLCO, single-breath diffusing capacity of carbon monoxide; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; PCO₂, partial pressure of carbon dioxide; PO₂, partial pressure of oxygen; R, airway resistance; RV, residual volume; TLC, total lung capacity.

Table 2 Variables associated with all-cause mortality of COPD in a Cox proportional hazard regression model

Variable	Unadjusted		Fully adjusted
	HR (95% CI)	P-value	HR (95% CI)	P-value
Age	1.093 (1.056–1.132)	<0.001	1.139 (1.077–1.204)	<0.001
Years of smoking	1.043 (1.015–1.071)	0.002	0.984 (0.950–1.020)	0.389
Age of quitting smoking	1.091 (1.057–1.126)	<0.001	1.078 (1.025–1.113)	0.003
Onset of symptoms	1.036 (1.011–1.062)	0.005	0.975 (0.940–1.011)	0.166
FEV1% predicted	1.020 (1.004–1.036)	0.028	1.020 (1.002–1.038)	0.025

Note: Statistically significant values are shown in bold.

Abbreviations: CI, confidence interval; FEV₁, forced expiratory volume in one second; HR, Hazard ratio.

Table 3 Differences in clinical characteristics between patients of smoking-cessation group and continuing-smoking group

Parameter	Both groups	Quitting smoking	Continuing smoking	P-value
Subjects, n	204	92	112
Sex (M/F), n	201/3	90/2	111/1	0.452
Age, years	67.9±9.4	68.4±9.3	67.4±9.4	0.425
Age of quitting smoking, years		58.8±10.4
Pack-year	45.3±34.5	44.6±29.4	45.9±38.3	0.791
Years of smoking, years	38.2±11.5	35.5±10.8	41.6±11.6	0.001
Cigarettes smoked in 1 day, n	23.0±13.0	23.9±11.9	22.2±13.8	0.353
Age of onset of smoking, years	25.9±8.3	25.1±8.2	26.8±8.2	0.131
Death	113	40	73	0.002
Exacerbations in past 12 months	1.3±1.4	1.1±1.9	1.2±1.7	0.286
Course of disease, years	12.7±10.8	13.9±10.5	10.8±10.9	0.040
Onset of symptoms, years	55.6±12.5	54.4±10.8	57.5±10.9	0.043
FVC% predicted	71.5±19.4	73.1±19.7	70.2±19.1	0.290
FEV1% predicted	43.3±19.1	44.5±19.3	42.6±19.0	0.486
FEV1/FVC	46.7±11.3	46.8±10.5	46.6±12.0	0.895
RV% predicted	207.5±66.7	197.3±54.7	215.9±74.2	0.041
RV/TLC	66.0±10.8	65.1±10.0	66.8±11.5	0.272
DLCO % predicted	72.9±45.5	69.3±27.1	75.9±56.2	0.307
R% predicted	256.6±133.0	255.3±126.5	257.7±138.6	0.897
PO2, mmHg	81.1±23.7	81.2±24.3	81.1±23.3	0.983
PCO2, mmHg	45.0±14.2	44.8±13.3	45.2±14.9	0.812

Notes: Statistically significant values are shown in bold. Data shown as mean ± standard deviation.

Abbreviations: DLCO, single-breath diffusing capacity of carbon monoxide; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; PCO₂, partial pressure of carbon dioxide; PO₂, partial pressure of oxygen; R, airway resistance; RV, residual volume; TLC, total lung capacity.

Table 4 Causes of patient death in smoking-cessation group and continuing-smoking group

Causes of death	Both groups, n	Quitting smoking, n (%)	Continuing smoking, n (%)	P-value
AECOPD	60	21 (52.5)	39 (53.4)	0.926
Cardiovascular disease	17	6 (15)	11 (15.1)	0.992
Lung cancer	15	6 (15)	9 (12.3)	0.692
Pulmonary infection	9	3 (7.5)	6 (8.2)	0.894
Other diseases	12	4 (10)	8 (11.0)	0.876
Total	113	40	73	0.002

Note: Statistically significant values are shown in bold.

Abbreviation: AECOPD, acute exacerbation Chronic Obstructive Pulmonary Disease.

Figure 1 Kaplan–Meier survival curves for COPD patients in the quitting-smoking group (n=92; 40 deaths) and continuing-smoking group (n=112; 73 deaths).

Notes: Patients in the quitting-smoking group had lower survival than those in the continuing-smoking group. There was a significant difference between the two groups (log-rank test, 13.59; P=0.0002).