The likelihood of improving physical activity after pulmonary rehabilitation is increased in patients with COPD who have better exercise tolerance

Figures & data

Table 1 Baseline demographic characteristics of participants with valid PA assessments (by site)

Participant characteristics	N	Total (n=236)	N	Leuven (n=149)	N	Athens (n=87)	P-value
Age, years	236	65±8	149	65±7	87	65±9	0.66
Gender (male/female), n	236	178/58	149	103/46	87	75/12	0.003
BMI, kg/m^2	236	25 [22–29]	149	25 [21–29]	87	27 [24–30]	<0.001
BMI ≥30, n (%)	236	56 (23.7)	149	34 (22.8)	87	22 (25.3)	0.67
FEV1, L	236	1.21 [0.89–1.65]	149	1.10 [0.88–1.48]	87	1.45 [0.98–1.89]	0.002
FEV1, % predicted	236	44.3 [33.0–59.0]	149	41.5 [32.6–54.0]	87	51 [33–64]	0.06
GOLD stage (I/II/III/IV), n	236	10/83/100/43	149	7/43/70/29	87	3/40/30/14	0.07
TLCO, % predicted	220	50.0 [39.0–65.2]	133	45.5 [37.1–58.9]	87	57 [43–73]	<0.001
MRC score	185	3 [2–4]	98	3 [2–4]	87	3 [2–4]	0.12
CRDQtotal	216	81 [69–94]	129	78 [67–88]	87	88 [76–108]	<0.001
6MWDi group ≥350 m, n (%)	236	169 (71%)	149	110 (74%)	87	59 (68%)	0.32
6MWD, m	236	416 [332–486]	149	426 [333–500]	87	392 [332–454]	0.04
VO2 peak, mL/kg/min	235	15.1 [12.6–17.9]	148	15.5 [12.1–19.8]	87	15.0 [13.8–17.6]	0.45
Physical activity, steps/day	236	3,920 [2,295–5,804]	149	3,902 [2,326–5,493]	87	4,014 [2,287–6,260]	0.70
Physical activity >7,000 m (n, %)	236	32 (13.6%)	149	21 (14.1%)	87	11 (12.6%)	0.75
Quadriceps force, Nm	228	116.2±40.6	141	110.0±33.9	87	126.2±48.2	0.05

Notes: Data are median [IQR] or mean ± SD unless otherwise stated. P-values refer to comparisons between Leuven and Athens sites. Bold values denote statistical significance.

Abbreviations: 6MWD, Six-minute walk distance; 6MWDi, initial six-minute walk distance; BMI, body mass index; CRDQ, Chronic Respiratory Disease Questionnaire; FEV₁, forced expiratory volume in the first second; GOLD, Global burden Of Lung Disease; MRC, Medical Research Council dyspnea scale (score range 1–5); Nm, newton-meters; PA, physical activity; TLCO, transfer factor for carbon monoxide.

Figure 1 CONSORT diagram of patient flow through the study.

Abbreviations: n, number of participants; PA, physical activity; PR, pulmonary rehabilitation.

Table 2 Characteristics of “PA responders” (>1,000 steps/day) vs “nonresponders”

Participant characteristics	N	“PA responder”	N	“PA nonresponder”	P-value
Age	75	64.4±7.3	161	65.5±8.0	0.29
BMI	75	25 [22–28]	161	25 [22–30]	0.73
FEV1, % predicted	75	50.8±15.9	160	44.8±17.6	0.012
TLC, % predicted	75	112.4±16.9	157	119.8±22.7	0.013
FRC, % predicted	75	150.9±39.1	155	164.8±41.9	0.017
TLCO, % predicted	74	54.8±19.2	146	52.3±18.0	0.35
MRC score	59	3 [2–3]	126	3 [3–4]	0.024
CRDQtotal	72	87.6±21.4	151	79.5±18.5	0.004
Physical activity, steps/day	75	4,210±2,488	161	4,222±2,526	0.97
6MWDi group (<350 m/≥350 m), n	75	11/64	161	56/105	0.001
6MWDi, m	75	444±103	161	382±115	<0.001
VO2 peak (mL/kg/min)	75	16.8±3.9	160	14.8±3.9	<0.001
Wmax	75	70.7±27.2	160	58.2±23.6	<0.001
Quadriceps force, Nm	71	126.1±40.1	157	111.7±40.1	0.012
Δ FEV1, % predicted	75	-0.02±5.94	156	0.21±5.55	0.78
Δ CRDQdyspnea	72	5.7±5.2	142	4.9±5.1	0.27
Δ CRDQtotal	65	15.9±11.5	135	14.3±11.9	0.37
Δ 6MWD, m	75	57.2±67.6	156	41.4±47.7	0.042
6MWD responders >30 m (n, %)	75	52 (69.3%)	156	98 (62.8%)	0.33
Δ VO2peak (mL/kg/min)	74	1.13±3.00	146	1.37±2.75	0.55
Δ Quadriceps force (Nm)	71	16.5±23.9	153	13.5±15.1	0.27

Notes: Data are median [IQR] or mean ± SD. Bold font denotes statistical significance; Dashed line separates baseline and change (Δ) variables.

Abbreviations: 6MWD, six-minute walk distance; 6MWDi, initial six-minute walk distance; BMI, body mass index; CRDQ, Chronic Respiratory Disease Questionnaire; FEV₁, forced expiratory volume in the first second; FRC, functional residual capacity; MRC, Medical Research Council dyspnea scale (score range 1–5); Nm, newton-meters; PA, physical activity; TLC, total lung capacity; TLCO, transfer factor of carbon monoxide.

Figure 2 Changes in PA levels and six-minute walk distance, according to group.

Notes: Green arrows denote improvement in PA ≥1,000 steps/day; red arrows denote change in PA <1,000 steps/day. Arrow tails reflect baseline function; arrow heads reflect function at 3 months. Vertical dashed line denotes 350 m cutoff for groups defined according to 6MWDi.
Abbreviations: PA, physical activity; 6MWDi, initial six-minute walk distance.

Figure 3 Change in physical activity (mean steps/day) over initial six-minute walk distance groups.

Note: Horizontal bars denote mean group values.

Table 3 Logistic regression analysis to predict physical activity “responders” (Δ1,000 steps/day) at 3 months

Predictors	Univariate		Multivariate
	OR (95% CI)	P-value	OR (95% CI)	P-value
6MWDi <350 m (reference)	–	–	–	–
6MWDi ≥350 m	3.10 (1.51–6.36)	0.002	3.25 (1.12–9.40)	0.030
CRDQtotal	1.02 (1.01–1.04)	0.005	1.02 (1.00–1.03)	0.080
FEV1, % predicted	1.02 (1.00–1.04)	0.013	1.02 (0.99–1.04)	0.198
MRC dyspnea	0.67 (0.49–0.93)	0.015	1.00 (0.66–1.51)	0.990
Quadriceps force, Nm	1.01 (1.00–1.02)	0.015	1.01 (1.00–1.01)	0.189
FRC, % predicted	0.99 (0.98–1.00)	0.019	0.99 (0.98–1.00)	0.218
Body mass index	0.97 (0.93–1.03)	0.388
Baseline physical activity (steps/day)	1.00 (1.00–1.00)	0.973
Δ daylight hours	1.00 (1.00–1.00)	0.009	1.00 (1.00–1.00)	0.018
Site: Leuven (reference)	–	–
Athens	1.12 (0.64–1.97)	0.695
PA monitor: DynaPort (reference)	–	–
Actigraph	0.97 (0.48–1.96)	0.928
SenseWear	1.35 (0.61–3.00)	0.462

Notes: Bold font denotes statistical significance; – denotes reference group.

Abbreviations: 6MWDi, initial six-minute walk distance; BMI, body mass index; CRDQtotal, Chronic Respiratory Disease Questionnaire Total score; FEV₁, forced expiratory volume in the first second; FRC, functional residual capacity; MRC, Medical Research Council dyspnea scale (score range 1–5); PA, physical activity.

Table S1 Pulmonary rehabilitation responses

Participant characteristics	Total (n=236)	Leuven (n=149)	Athens (n=87)	P-value
Δ FEV1, % predicted	0 [−1.6–1.36]	0.0 [−4.0–4.0]	0.0 [0.0–0.0]	0.82
Δ CRDQ total	13 [7–21]	18 [10–25]	10 [6–14]	<0.001
Δ 6MWD, m	41 [23–72]	48 [20–83]	38 [25–52]	0.15
6MWD responders (Δ>30 m), n (%)	150 (65)*	92 (64)*	58 (67)	0.67
Δ VO2peak, mL/kg/min	1.23 [0.19–2.38]	0.92 [−0.83–2.77]	1.33 [0.93–1.89]	0.03
Δ Quadriceps force, Nm	14.4±18.4	13.3±21.1	16.3±12.9	0.09
Δ Physical activity, mean steps/day	551±1,770	592±1,861	480±1,612	0.64
PA responders (Δ>1,000 steps/day), n (%)	75 (32)	46 (31)	29 (33)	0.70

Notes: Data are median [IQR] or mean ± SD. Bold font denotes statistical significance between the two sites.

* 3-month 6MWD data unavailable for five participants at Leuven site.

Abbreviations: Δ, change; 6MWD, six-minute walk test distance; BMI, body mass index; CRDQ, Chronic Respiratory Disease Questionnaire; FEV₁, forced expiratory volume in the first second; m, meters; Nm, newton-meters; PA, physical activity.

Figure S1 Pearson correlation between 6MWDi and change in PA (steps/day).

Notes: Proportion of PA responders, according to 6MWDi groups (vertical dashed line), denoted by the ratio of dots above vs below the horizontal dashed line. The horizontal dashed line represents a change in PA of more than 1,000 steps/day.

Abbreviations: 6MWDi, initial 6-minute walk distance; PA, physical activity.

Figure S2 Pearson correlation between changes in PA levels and changes in exercise tolerance at 3 months.

Notes: Closed circles represent patients with 6MWDi of <350 m; open circles represent patients with 6MWDi of at least 350 m. Horizontal dashed line represents the proposed minimally important difference threshold for improvement in PA after PR (1,000 steps/day).

Abbreviations: 6MWDi, initial 6-minute walk distance; PA, physical activity; PR, pulmonary rehabilitation.

Figure S3 ROC curve of 6MWDi cutoff to identify PA responder.

Notes: Arrow denotes 350 m cutoff reference value corresponding with 85.33% sensitivity; 34.78% specificity; 50.85% correctly classified; +ve likelihood ratio 1.308; -ve likelihood ratio 0.422.

Abbreviations: 6MWDi, initial 6-minute walk distance; PA, physical activity; ROC, receiver operator curve.

Figure S4 Changes in physical activity across the two 6MWDi groups, expressed as percent change from baseline.

Notes: Horizontal bars denote group means. Percentage change derived from mean steps/day weekly count. Horizontal dashed lines represent the point of zero change.

Abbreviation: 6MWDi, initial 6-minute walk distance.

Figure S5 Changes in physical activity across 6MWDi quartiles.

Notes: (A) Change in physical activity expressed as steps/day. (B) Change in physical activity expressed as percent change from baseline, derived from mean steps/day weekly count. Horizontal dashed lines represent the point of zero change. P-value denotes result from one-way ANOVA test.

Abbreviation: 6MWDi, initial 6-minute walk distance.