Increased mortality in patients with severe COPD associated with high-intensity exercise: a preliminary cohort study

Figures & data

Table 1 Characteristics of participants in each group, and of participants who died during the observation period

Variable	Regular-intensity rehabilitation (n=15)	High-intensity rehabilitation		Group difference (regular vs high-intensity) mean (95% CI); P-value*
		All participants (n=16)	Of which died (n=5)
Female sex, n (%)	10 (67)	9 (56)	3 (60)	P=0.55**
Age, years	69.7 (8.7)	68.6 (8.7)	73.6 (7.3)	1.1 (−5.4 to 7.7); P=0.73
Height, cm	170.4 (8.3)	168.3 (9.6)	163.8 (6.7)	2.2 (−4.4 to 8.8); P=0.51
Body mass, kg	67.3 (15.5)	67.5 (19.6)	55.0 (12.7)	0.2 (−13.2 to 12.8); P=0.97
BMI, kg/m^2	23.2 (5.1)	23.8 (6.3)	20.5 (4.6)	−0.6 (−4.8 to 3.6); P=0.78
Smoking status				P=0.55**
Current smoker (%)	6 (40)	6 (38)	1 (20)
Former smoker (%)	8 (53)	10 (62)	4 (80)
Never smoked (%)	1 (7)	0 (0)	0 (0)
Cigarette package years	38.7 (17.9)	63.4 (39.7)	54.2 (28.8)	−24.6 (−47.4 to −1.9); P=0.035
FEV1	0.88 (0.30)	0.94 (0.40)	0.80 (0.29)	−0.06 (−0.31 to 0.19); P=0.63
FEV1 % predicted	35.4 (11.4)	36.2 (9.2)	34.6 (8.8)	−0.74 (−8.37 to 6.90); P=0.84
Estimated VO2 max, mL/min/kg	8.78 (3.06)	8.95 (3.45)	7.62 (1.51)	−0.17 (−2.65 to 2.31); P=0.89
Oxygen sat, at rest	94.6 (1.8)	94.5 (2.1)	94.3 (2.1)	0.10 (−1.40 to 1.60); P=0.89
Oxygen supplement, yes (%)	0 (0)	2 (13)	1 (20)	P=0.16**
CAT	19.8 (7.7)	20.6 (6.0)	19.0 (4.8)	−0.8 (−6.1 to 4.4); P=0.74
Number of previous exacerbations, median (first; third quartile)	2 (0; 3)	1 (0.25; 4)	1 (0; 7.5)	P=0.14**
MRC				P=0.82**
3, n (%)	5 (33)	5 (31)	1 (20)
4, n (%)	4 (27)	3 (19)	0 (0)
5, n (%)	6 (40)	8 (50)	4 (80)
COPD stage (GOLD)				P=0.87**
2, n (%)	1 (7)	1 (6)	0 (0)
3, n (%)	8 (53)	10 (63)	3 (60)
4, n (%)	6 (40)	5 (31)	2 (40)
Comorbid cardiovascular disease, n (%)	3 (20)	8 (50)	3 (60)	P=0.11**
Comorbid diabetes, n (%)	2 (13)	3 (19)	1 (20)	P=0.68**
Number of hospitalizations from rehabilitation end +18 months	1.20 (1.37)	1.62 (2.75)	2.20 (3.90)	−0.4 (−2.0 to 1.2); P=0.59

Notes: Data are mean (SD) unless otherwise stated.

* Based on t-test.

** Based on chi-square.

Abbreviations: BMI, body mass index; CAT, COPD assessment test; CI, confidence interval; FEV₁, forced expiratory volume in 1 second; GOLD, Global Initiative for Chronic Obstructive Lung Disease; MRC, Medical Research Council; SD, standard deviation.

Table 2 Individual participant data on the participants who died during the 18-month observation period

Variable	Participant 1	Participant 2	Participant 3	Participant 4	Participant 5
Sex	Female	Male	Female	Female	Male
Age, years	73	71	64	84	76
Height, cm	159	167	173	156	164
Body mass, kg	59	75.6	49.0	45.1	46.3
BMI, kg/m^2	23.3	27.1	16.4	18.5	17.2
Smoking status	Former	Former	Former	Former	Current
Cigarette package years	37	100	49	25	60
FEV1	0.51	1.20	0.64	0.64	1.00
FEV1 % predicted	25.7	44.5	25.1	37.3	40.4
Oxygen saturation at rest	92	93	96	n/a	96
Oxygen supplement	No	Yes	No	No	No
CAT, 0–40	12	17	19	23	24
Number of previous	1	5	0	10	0
exacerbations
MRC score, 1–5	5	5	5	5	3
COPD stage (GOLD classification, 1–4)	4	3	4	3	3
Comorbid cardiovascular disease	No	Yes, valve stenosis	No	Ischemic heart disease	Hypertension
Comorbid diabetes	No	Yes	No	No	No
Time to death from rehab stop, days	1	26	90	115	461
Cause of death	COPD exacerbation. Respiratory acidosis	COPD exacerbation. Respiratory arrest with cardiac arrest	COPD exacerbation. Respiratory acidosis	COPD exacerbation	Ruptured abdominal aortic aneurysm
Number of hospitalizations from rehabilitation end +18 months	0	0	0	9	2

Abbreviations: BMI, body mass index; CAT, COPD assessment test; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; GOLD, Global Initiative for Chronic Obstructive Lung Disease; MRC, Medical Research Council; n/a, not/available.

Figure 1 Kaplan–Meier curve for survival.

Table 3 Hazard ratios from univariable Cox regression analyses of baseline characteristics predicting death

Variable	Hazard ratio	95% CI lower limit	95% CI upper limit	P-value
Male sex	1.14	0.19	6.88	0.89
Age, years	1.06	0.96	1.17	0.26
Body mass, kg	0.94	0.88	1.01	0.11
BMI, kg/m^2	0.89	0.73	1.08	0.23
Smoking status	0.53	0.10	2.75	0.45
Cigarette package years	1.00	0.98	1.03	0.85
FEV1	0.19	0.00	11.64	0.43
FEV1 % predicted	0.98	0.90	1.08	0.71
Estimated VO2 max, mL/min/kg	0.85	0.57	1.28	0.45
Oxygen sat, at rest	0.93	0.55	1.56	0.78
Oxygen supplement, yes	2.53	0.81	7.95	0.11
CAT	0.97	0.84	1.11	0.64
Number of previous exacerbations	1.20	0.89	1.62	0.24
MRC	2.59	0.67	10.00	0.17
COPD stage (GOLD)	1.44	0.30	6.99	0.66
Comorbid cardiovascular disease	2.72	0.45	16.32	0.27
Comorbid diabetes	1.13	0.38	3.38	0.83
Number of hospitalizations from rehabilitation end +18 months	1.17	0.85	1.62	0.34

Abbreviations: BMI, body mass index; CAT, COPD assessment test; CI, confidence interval; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; GOLD, Global Initiative for Chronic Obstructive Lung Disease; MRC, Medical Research Council.