Two 6-minute Walk Tests Are Required During Hospitalisation for Acute Exacerbation of COPD

Figures & data

Table 1. Participant characteristics, according to total cohort, region and 6MWD change status

	Total	Australia	Brazil	‘Improvers’ A	‘Decliners’	‘Improvers’ B	‘Others’
Participant characteristics	(n = 46)	(n = 17)	(n = 29)	(n = 32)	(n = 14)	(n = 14)	(n = 32)
Age, years	67.2 (11.1)	69.4 (11.3)	65.9 (11.0)	68.1 (10.9)	65.0 (11.7)	65.1 (12.3)	68.1 (10.7)
Gender, male:female	25:21	7:10	18:11	19:13	6:8	8:6	17:15
Body mass index, kg/m^2	23.3 (4.6)	24.4 (4.2)	22.7 (4.7)	23.3 (5.0)	23.4 (3.4)	24.2 (5.0)	23.0 (4.4)
Smoking pack-years	45.2 [34 – 60]	43.8 [30 – 67.5]	47.4 [36.7 – 55.4]	46.2 [34.6 – 63.8]	44.6 [33.1 – 54.3]	48.0 [38.5 – 60.3]	48.0 [38.5 – 60.3]
FEV1, % predicted	43.0 (16.2)	41.9 (20.4)	43.5 (14.1)	43.0 (17.8)	43.1 (12.5)	42.8 (15.9)	43.1 (16.6)
Home oxygen, n (%)	6 (13)	2 (12)	4 (14)	4 (13)	2 (14)	0 (0)	6 (19)
Respiratory comorbidity, n (%)	13 (28)	9 (53)	4 (14)^*	7 (22)	6 (43)	5 (36)	8 (25)
Cardiac comorbidity, n (%)	26 (57)	8 (47)	18 (62)	18 (56)	8 (57)	6 (43)	20 (63)
Anthonisen AECOPD type:
- Type 1, n (%)	27 (59)	12 (71)	15 (52)	17 (53)	10 (71)	6 (43)	21 (66)
- Type 2, n (%)	15 (33)	4 (24)	11 (38)	13 (41)	2 (14)	7 (50)	8 (25)
- Type 3, n (%)	4 (9)	1 (6)	3 (10)	2 (6)	2 (14)	1 (7)	3 (9)
NIV use in first 48 hours, n (%)	20 (43)	3 (18)	17 (59)^*	12 (38)	8 (57)	5 (36)	15 (47)
Baseline SGRQ:
- Total score	59.9 (19.8)	47.3 (17.2)	67.2 (17.1)^*	59.0 (19.8)	61.8 (19.7)	53.2 (21.4)	62.8 (18.3)
- Symptom domain	69.3 (17.6)	67.9 (16.4)	70.2 (18.5)	68.5 (17.1)	71.2 (19.2)	63.7 (18.4)	71.8 (17.0)
- Activity domain	73.4 (25.2)	50.9 (20.7)	86.6 (16.9)^*	73.5 (26.0)	73.3 (24.2)	67.3 (27.0)	76.1 (24.3)
- Impact domain	49.4 (20.8)	39.0 (18.2)	55.6 (19.9)^*	48.2 (20.8)	52.3 (21.1)	42.5 (22.9)	52.4 (19.4)
Hospital length of stay, days	7.6 (3.7)	5.5 (4.2)	8.8 (2.8)^*	7.1 (3.4)	8.6 (4.4)	6.8 (4.1)	7.9 (3.5)
mMRC dyspnoea scale	3 [1 – 3]	2 [1 – 3]	3 [1 – 3]	2.5 [1 – 3.5]	3 [1 – 3]	3 [1 – 3]	3 [1 – 3]
BODE index	5 [3 – 6]	5 [3 – 6]	5 [2 – 6]	5 [3 – 6.5]	4.5 [2 – 6]	5 [2 – 6]	5 [2 – 6]

Data are presented as mean (standard deviation) or median [interquartile range] where data not normally distributed (indicated via significant Shapiro–Wilk statistic, p < 0.05) for relevant outcome. AECOPD = acute exacerbation of chronic obstructive pulmonary disease; FEV₁ = forced expiratory volume in the first second; SGRQ = St. George's Respiratory Questionnaire. AECOPD type defined according to Anthonisen criteria (13).

* Denotes statistically significant difference compared to Australian cohort (p < 0.01).

Figure 1. Bland-Altman plot of agreement between repeated performance of the 6-minute walk test. Black circles represent data from Australia; open circles represent data from Brazil. T1 = test one; T2 = test two.

Figure 2. Six-minute walk distance performance on tests 1 and 2. “Decliner” denotes test worsening on repeat testing; “Improver” (method A) denotes improvement by any distance on repeat testing.

Table 2. Intraclass correlation coefficients (ICC_2,1) and 95% confidence intervals for 6-minute walk test outcomes

	Total	Australia	Brazil	‘Improvers’ A	‘Decliners’	‘Improvers’ B	‘Others’
Participant characteristics	(n = 46)	(n = 17)	(n = 29)	(n = 32)	(n = 14)	(n = 14)	(n = 32)
6MWD, m	0.885 (0.801 – 0.934)	0.783 (0.494 – 0.916)	0.917 (0.832 – 0.960)	0.923 (0.664 – 0.972)	0.798 (0.261 – 0.940)	0.802 (−0.033 – 0.953)	0.917 (0.836 – 0.959)
Nadir SpO2, %	0.910 (0.844 – 0.949)	0.893 (0.696 – 0.962)	0.904 (0.807 – 0.954)	0.915 (0.834 – 0.957)	0.840 (0.571 – 0.946)	0.898 (0.702 – 0.966)	0.901 (0.808 – 0.951)
End-test heart rate	0.670 (0.472 – 0.803)	0.559 (0.123 – 0.814)	0.867 (0.738 – 0.935)	0.641 (0.378 – 0.808)	0.684 (0.261 – 0.886)	0.408 (−0.164 – 0.766)	0.814 (0.652 – 0.905)
End-test dyspnoea	0.908 (0.837 – 0.949)	0.904 (0.737 – 0.967)	0.910 (0.817 – 0.957)	0.923 (0.848 – 0.962)	0.881 (0.662 – 0.962)	0.924 (0.740 – 0.976)	0.904 (0.810 – 0.953)

6MWD = six-minute walk distance; SpO₂ = oxyhaemoglobin saturation; m = metres.

Table 3. Six-minute walk test performance.

	Total	Australia	Brazil	‘Improvers’ A	Decliners	‘Improvers’ B	Others
Participant characteristics	(n = 46)	(n = 17)	(n = 29)	(n = 32)	(n = 14)	(n = 14)	(n = 32)
Test one
6MWD, m	302.7 (99.8)	300.7 (66.1)	303.9 (116.2)	292.4 (101.4)	326.4 (95.5)	277.3 (85.2)	313.8 (104.9)
Nadir SpO2, %	90 [84 – 93]	87 [81 – 90]	92 [89 – 94]	91 [83 – 94]	90 [85 – 92]	88 [75 – 93]	91 [86 – 94]
End-test heart rate	110 (15)	107 (18)	111 (12)	111 (15)	107 (13)	108 (17)	110 (14)
End-test dyspnoea	3.7 (1.7)	3.5 (1.3)	3.8 (1.9)	3.7 (1.6)	3.6 (1.9)	3.7 (1.5)	3.6 (1.8)
Need for rest, n (%)	17 (37)	10 (59)	7 (24)^*	13 (41)	4 (29)	7 (50)	10 (31)
Use of oxygen, n (%)	9 (20)	2 (12)	7 (24)	7 (22)	2 (14)	2 (14)	7 (22)
Test two
6MWD, m	308.9 (104.3)	305.6 (93.6)	303.9 (116.2)	324.1 (104.6)	274.1 (98.4)	333.2 (95.2)	298.3 (107.7)
Nadir SpO2, %	91 [84 – 93]	88 [82 – 91]	92 [88 – 93]	91 [84 – 93]	91 [85 – 93]	89 [78 – 92]	91 [85 – 93]
End-test heart rate	109 (19)	103 (26)	111 (12)	111 (19)	103 (19)	114 (18)	106 (20)
End-test dyspnoea	3.7 (1.7)	3.5 (1.4)	3.8 (1.9)	3.8 (1.8)	4.5 (1.7)	3.8 (1.8)	3.7 (1.7)
Need for rest, n (%)	12 (26)	7 (41)	5 (17)	7 (22)	5 (36)	2 (14)	10 (31)
Use of oxygen, n (%)	9 (20)	2 (12)	7 (24)	6 (19)	3 (21)	3 (21)	6 (19)

Data are mean (standard deviation) or median [interquartile range] unless otherwise stated; 6MWD = six-minute walk distance; SpO₂ = oxyhaemoglobin saturation; m = metres; T1 = test one; T2 = test two.

* ^*denotes statistically significant difference compared to Australian cohort (p < 0.05).

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