Intra- and inter-rater reproducibility of the 6-minute walk test and the 30-second sit-to-stand test in patients with severe and very severe COPD

Figures & data

Figure 1 Assessment procedures at day 1 (T1) and day 2 (T2 reassessment).

Abbreviations: Dyspnea, perceived dyspnea; end-, measure taken immediately after test completion; 6MWT, six-minute walk test; 30sec-STS, 30-second sit-to-stand test; SpO₂, arterial oxygen saturation as measured by pulse oximetry.

Table 1 Characteristics

Variables	Patients with COPD	Not included
Sex, men/women (n)	28/22	21/37
Age, years (SD)	66.6±9.0	69.4±9.1
Body mass index, kg/m^2, mean (SD)	25.4±5.6	25.8±5.6
FEV1 % predicted, mean (SD)	32.3±9.0	35.1±9.4
FEV1/FVC, mean (SD)	41.4±10.6	45.1±11.8
GOLD I/II/III/IV, %	0/0/54/46	0/0/67/33
A/B/C/D,^Citation36 %	0/36/0/64	3/33/7/57
MRC dyspnea scale, median (range)	3.5 (3–5)	3.0 (2–5)
CAT symptoms, mean (SD)	20.8±6.1	18.7±7.6
BODE index points, median (range)	5 (3–9)	5 (3–8)
Charlson index 1/2/≥3, %	52/30/18	28/47/26
LTOT, n (%)	4 (8)	9 (16)
Walking aid, stick/walker, n (%)	1/8 (18)	4/17 (36)
Highest 6MWD (SD)	347 (102)	330 (103)
Highest 30sec-STS (SD)	10.8 (4.1)	9.8 (4.8)

Notes: Data are presented as mean ± SD, median (range), or percentage in non-normally distributed variables.

Abbreviations: A/B/C/D, risk stratification; BODE index, body mass index, airflow obstruction, dyspnea, and exercise capacity; CAT, COPD assessment test; LTOT, long-term oxygen therapy; MRC, Medical Research Council; 6MWD, six-minute walk distance; 30sec-STS, 30 second sit-to-stand test.

Table 2 Intra-rater reproducibility test-day 1 (T1)

Variables	Test one	Test two	Difference	ICC1.1 (LL95)	SEM (SEM%)	SRD95% (SRD%)
6MWD	329.5±100.9	330.9±109.8	1.4 [−5.3; 8.1]	0.98 (0.96)	14.84 (5)	41.13 (13)
End SpO2	90.6±7.9	90.6±7.9	0.0 [−1.1; 1.1]	0.87 (0.78)	2.82 (3)	7.82 (7)
End HR	104.0±19.6	106.5±18.9	2.5 [0.4; 4.7]*	0.91 (0.85)	5.75 (5)	15.94 (15)
End dyspnea	5.7±2.7	6.5±2.6	0.8 [0.5; 1.1]*	0.88 (0.81)	0.93 (15)	2.58 (42)
30sec-STS	9.9±3.9	9.7±4.1	−0.2 [−0.5; 0.3]	0.94 (0.90)	0.97 (10)	2.68 (27)

Notes: Test one and two and difference are presented as mean ± SD or delta difference [SE 95% CI]. Significant difference between tests is denoted as

* P<0.05.

Abbreviations: Dyspnea, perceived dyspnea (Borg cr-10); HR, heart rate (beats per minute); ICC_1.1, intraclass correlation coefficient model 1.1; LL₉₅, lower 95% confidence limit; 6MWD, six-minute walk distance (meters); SEM, standard error of measurement; SEM%, standard error of measurement expressed as a percentage of the mean; 30sec-STS, 30 second sit-to-stand test (repetitions); SpO₂, arterial oxygen saturation as measured by pulse oximetry (%); SRD95%, smallest real difference at the 95% confidence level; SRD%, smallest real difference as a percentage of the mean.

Figure 2 Bland–Altman plots of the 6MWD and 30sec-STS.

Notes: Mean difference between tests/or raters (dotted line) with limits of agreement 95% CI (black lines). The dashed line is the regression of change against the mean value. (A) 6MWD scores against 6MWD difference from a single rater at test-day 1 (T1). (B) 30sec-STS scores against 30sec-STS difference from a single rater at test-day 1 (T1). (C) 6MWD score difference obtained by two different raters on two separate test-days (T2 vs T1). (D) 30sec-STS score difference obtained by two different raters on two separate test-days (T2 vs T1).
Abbreviations: 30sec-STS, 30-second sit-to-stand test; 6MWD, 6-minute walk distance.

Table 3 Inter-rater reproducibility (highest value T1 vs highest value T2)

Variables	Rater T1	Rater T2	Difference	ICC1.1 (LL95)	SEM (SEM%)	SRD95% (SRD%)
6MWD	339.3±103.7	347.2±101.7	7.9 [0.02; 15.8]*	0.96 (0.94)	20.46 (6)	56.70 (16)
End SpO2	90.6±8.1	89.8±7.6	−0.8 [−0.3; 2.0]	0.86 (0.77)	2.94 (3)	8.15 (9)
End HR	105.4±19.1	110.7±17.7	5.3 [2.2; 8.4]*	0.79 (0.66)	8.48 (8)	23.50 (22)
End dyspnea	6.2±2.6	6.4±2.7	0.2 [−0.1; 0.6]	0.85 (0.75)	1.01 (16)	2.80 (45)
30sec-STS	10.2±3.9	10.8±4.1	0.6 [0.2; 1.1]*	0.92 (0.86)	1.14 (11)	3.15 (30)

Notes: Rater T1, T2, and difference are presented as mean ± SD or delta difference [SE 95% CI]. Significant difference between raters is denoted

* P<0.05.

Abbreviations: Dyspnea, perceived dyspnea (Borg cr-10); HR, heart rate (beats per minute); ICC_1.1, intraclass correlation coefficient model 1.1; LL₉₅, lower 95% confidence limit; 6MWD, six-minute walk distance (meters); 30sec-STS, 30 second sit-to-stand test (repetitions); SEM, standard error of measurement; SEM%, standard error of measurement expressed as a percentage of the mean; SpO₂, arterial oxygen saturation as measured by pulse oximetry (%); SRD95%, smallest real difference at the 95% confidence level; SRD%, smallest real difference as a percentage of the mean.

Table 4 Explorative results for 6MWD

	Intra-rater test-day 1 (T1)			Inter-rater (highest value T1 vs highest value T2)
	Improvers (n)	Non-improvers (n)	Total count (n)	Improvers (n)	Non-improvers (n)	Total count (n)
≥350 m	16	6	22a	14	10	24c
<350 m	12	16	28b	17	9	26d
Total count (n)	28	22	50	31	19	50

Notes: Number of improvers and non-improvers with a BODE index³⁸ cut off for the 6MWD.

a 18% (4/22) who walked ≥350 m improved their second 6MWD by ≥30 m and none showed a decrease by ≥30 m.

b 17% (2/28) who walked <350 m improved their second 6MWD by ≥30 m while 18% (5/28) decreased their walking distance by ≥30 m.

c 8% (2/24) who walked ≥350 m improved their 6MWD by ≥30 m from T1 to T2 while 4% (1/24) decreased their walking distance by ≥30 m.

d 19% (5/26) who walked <350 m improved their 6MWD by ≥30 m from T1 to T2 while 8% (2/26) decreased their walking distance with ≥30 m.

Abbreviations: 6MWD, six-minute walk distance; intra-rater, values obtained by the same rater on the same day; inter-rater, highest values obtained by two different raters on two separate test-days (T1 vs T2); BODE index, body mass index, airflow obstruction, dyspnea, and exercise capacity.

Table 5 Explorative results for 30sec-STS

	Intra-rater test-day 1 (T1)			Inter-rater (highest value T1 vs highest value T2)
	Improver (n)	Non-improver (n)	Total count (n)	Improver (n)	Non-improver (n)	Total count (n)
>8 repetitions	8	27	35	16	20	36
≤8 repetitions	4	11	15	5	9	14
Total count (n)	12	38	50	21	29	50

Note: Number of improvers and non-improvers with a criterion-based cut off^16,17,43 for the 30sec-STS.

Abbreviations: 30sec-STS, 30 second sit-to-stand test (repetitions); intra-rater, values obtained by the same rater on the same day; inter-rater, highest values obtained by two different raters on two separate test-days (T1 vs T2).

Figure S1 Recruitment flowchart.

COSMINCosmin checklist Available from: https://www.cosmin.nl/tools/checklists-assessing-methodological-study-qualities/Accessed October 05, 2018

 Google Scholar

AgustiAHurdSJonesPFabbriLMMartinezFVogelmeierCGlobal Initiative for Chronic Obstructive Lung Disease2017 Available from: https://goldcopd.org/wp-content/uploads/2017/11/GOLD-2018-v6.0-FINAL-revised-20-Nov_WMS.pdfAccessed October 05, 2018

 Google Scholar

GuralnikJMSimonsickEMFerrucciLA short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admissionJ Gerontol1994492M85M948126356

 PubMedGoogle Scholar

ButcherSJPikalukBJChuraRLWalknerMJFarthingJPMarciniukDDAssociations between isokinetic muscle strength, high-level functional performance, and physiological parameters in patients with chronic obstructive pulmonary diseaseInt J Chron Obstruct Pulmon Dis2012753754222973094

 PubMed Web of Science ®Google Scholar

BlandJMAltmanDGStatistical methods for assessing agreement between two methods of clinical measurementLancet1986184763073102868172

 PubMed Web of Science ®Google Scholar