Minimal important difference and responsiveness of 2-minute walk test performance in people with COPD undergoing pulmonary rehabilitation

Figures & data

Figure 1 Process flow of measures recorded.

Abbreviation: PR, pulmonary rehabilitation.

Table 1 Pre-PR assessment characteristics of participants included in reliability and validity analyses (n=59)

Characteristics	Mean (SD) or frequency (%)
Age (years)	68.4 (9.8)
Males	28 (48%)
Body mass index (kg/m^2)	26.7 (5.9)
Number of pharmacologically managed comorbidities	3 (2)
Living arrangements
Home alone	25 (42%)
Home with spouse/partner	22 (37%)
Home with child/grandchild	8 (14%)
Home with friend/other	3 (5%)
Residential care	1 (2%)
FEV1%pred	47.8 (20.2)
FEV1/FVC	45.0 (15.0)
Smoking status
Never smoked	5 (9%)
Current smoker	12 (20%)
Exsmoker	42 (71%)
Long-term oxygen therapy	7 (12%)
Gait aid used during walking tests	6 (10%)
6MWD (m)	330.5 (96.0)
Best 2MWD (m)	132.5 (27.3)
CRQ n=55
CRQ-dyspnea	3.31 (1.23)
CRQ-emotional function	4.44 (1.35)
CRQ-mastery, median (IQR)	4.50 (2.5)
CRQ-fatigue	3.65 (1.31)
mMRC scale n=57
Grade 0	3 (5%)
Grade 1	16 (28%)
Grade 2	21 (37%)
Grade 3	12 (21%)
Grade 4	5 (9%)

Notes: Grade 0, I only get breathless with strenuous exercise; Grade 1, I get short of breath when hurrying on level ground or walking up a slight hill; Grade 2, on level ground, I walk slower than people of the same age because of breathlessness, or I have to stop for breath when walking at my own pace on the level; Grade 3, I stop for breath after walking ~100 m or after a few minutes on level ground; Grade 4, I am too breathless to leave the house or I am breathless when dressing or undressing.

Abbreviations: CRQ, Chronic Respiratory Questionnaire; FEV₁, forced expiratory volume in 1 second; FEV₁%pred, percentage predicted FEV₁; FVC, forced vital capacity; IQR, interquartile range; 2MWD, 2-minute walk distance; 6MWD, 6-minute walk distance; mMRC, modified Medical Research Council; PR, pulmonary rehabilitation.

Figure 2 Bland–Altman plot for test–retest reliability of 2MWD, with difference between measurements (y-axis) plotted against mean of the measurements (x-axis).

Notes: The central horizontal line represents the mean bias (2.4 m); the lower and upper dashed horizontal lines represent the 95% limits of agreement (−10.1 and 14.8 m).
Abbreviations: 2MWD, 2-minute walk distance; PR, pulmonary rehabilitation.

Table 2 Outcome measure responses to PR, n=41a

Measure	Pre-PR, mean (SD)	Post-PR, mean (SD)	Change post–pre-PR (95% CI)	Effect size	P-value
2MWD (m)	125.4 (32.3)	134.2 (28.5)	8.8 (3.6 to 14.0)	0.3	0.001
6MWD (m)	324.8 (97)	350.9 (107)	26.0 (0.6 to 51)	0.3	0.045
CRQ-D	3.40 (1.37)	3.57 (1.23)	0.17 (−0.22 to 0.56)	0.1	0.39
CRQ-EF	4.76 (1.27)	5.24 (1.40)	0.47 (0.06 to 0.87)	0.4	0.03
CRQ-M	5.11 (2.38)	5.20 (1.31)	0.08 (−0.65 to 0.81)	0.1	0.82
CRQ-F	3.97 (1.26)	4.60 (1.44)	0.64 (0.23 to 1.04)	0.5	0.003

Notes: Significant at P<0.05 level.

a n=41 for 2MWD; n=40 for 6MWD, n=37 for CRQ domains.

Abbreviations: CI, confidence interval; CRQ-D, Chronic Respiratory Questionnaire dyspnea domain; CRQ-EF, Chronic Respiratory Questionnaire emotional function domain; CRQ-M, Chronic Respiratory Questionnaire mastery domain; CRQ-F, Chronic Respiratory Questionnaire fatigue domain; 2MWD, 2-minute walk distance; 6MWD, 6-minute walk distance; PR, pulmonary rehabilitation.

Table S1 Baseline characteristics of recruited participants who did and did not complete valid post-PR testing

Characteristics	Valid post PR data available (n=41), mean (SD) or frequency	No valid post PR data available (n=31), mean (SD) or frequency	P-value, test for between group differencea
Age, years	70.5 (8.2)	66.9 (12.2)	0.17
Male gender	22	17	0.92
Smoking status
Never smoked	5	0	0.001
Current smoker	3	12
Exsmoker	33	19
LTOT
Yes	5	5	0.63
No	36	26
FEV1%pred	51.8 (21.0)	41.9 (16.7) n=29	0.04
mMRC
0	2	2	0.96
1	11	6
2	13	10
3	10	9
4	4	3
Pre-PR 2MWD (test 1)	125.4 (32.3)	124.3 (25)	0.89
Pre-PR 6MWD	327.7 (97.9)	298.8 (99.4)	0.22

Note:

a Independent sample t-test (continuous data) or chi square test (categorical data).

Abbreviations: FEV₁%pred, percentage predicted forced expiratory volume in 1 second; LTOT, long-term oxygen therapy; 2MWD, 2-minute walk distance; 6MWD, 6-minute walk distance; mMRC, modified Medical Research Council; PR, pulmonary rehabilitation.