Predictors in routine practice of 6-min walking distance and oxygen desaturation in patients with COPD: impact of comorbidities

Figures & data

Table 1 Clinical and lung function data

Variable	N=440
Comorbidities (present)
Sex male/female	72.7% (320)/ 27.3% (120)
Age	62 [56–70]
Low BMI ≤18.5 kg/m^2	9.1% (40)
Obesity BMI >30 kg/m^2	18.9% (83)
Smoking history (pack-years) Current/ex smokers	38.0 [23.8–55.0] 31.2% (135)/65.8% (285)
Hypertension	36.4% (160)
Ischemic heart disease	13.4% (59)
Chronic heart failure	12.5% (55)
Diabetes	10.2% (45)
Mechanical limitation	20.9% (92)
Sleep apnea	8.4% (37)
FEV1 (L)	1.41 [0.97–1.87]
FEV1% pred	51 [36–68]
GOLD 2007 severity
1 2 3 4	8.4% (37) 42.5% (187) 32.7% (144) 16.4% (72)
FEV1/FVC	0.51 [0.42–0.61]
FVC % pred	86 [71–102]
RV % pred	167 [131–208]
TLC % pred	114 [103–128]
RV/TLC %	55 [47–64]
mMRC (0–4)	2 [1–2]
Chronic bronchitis	66.6% (293)
Exacerbations/year	1 [0–3]
BODE score	3 [1–4]
ADO score	3 [2–5]

Note: Data reported as numbers (percentages) or median [IQRQ1–Q3].

Abbreviations: BMI, body mass index; RV, residual volume; TLC, total lung capacity; mMRC, modified Medical Research Council scale for dyspnea; BODE, body mass index, obstruction, dyspnea and exercise score; ADO, age, dyspnea and obstruction score.

Figure 1 Distribution of the 6MWD (m).

Abbreviations: 6MWD, 6-min walking distance; m, meters.

Figure 2 Relationship between 6MWD and EID (SpO2 min).

Abbreviations: 6MWD, 6-min walking distance; EID, exercise induced desaturation.

Table 2 Univariate comparisons for low vs high 6MWD

Variable	6MWD ≤350 m N=146	6MWD >350 m N=294	p	Desaturation N=155	No desaturation N=285	p
Sex male/female	70.5% (103)/29.5% (43)	73.8% (217)/26.2% (77)	0.469	69.0% (107)/31.0% (48)	74.7% (213)/25.3% (72)	0.199
Age	65 [58–74]	60 [54–67]	<0.0001	60 [54–67]	62 [56–71]	0.0410
BMI ≤18.5	10.3% (15)	8.5% (25)	0.543	11.6% (18)	7.7% (22)	0.175
Obesity BMI >30	23.3% (34)	16.7% (49)	0.095	13.5% (21)	21.8% (62)	0.036
Hypertension	41.8% (61)	33.7% (99)	0.096	40.0% (62)	34.4% (98)	0.242
Chronic heart failure	16.4% (24)	10.5% (31)	0.078	11.0% (17)	13.3% (38)	0.474
Ischemic heart disease	16.4% (24)	11.9% (35)	0.189	10.3% (16)	15.1% (43)	0.161
Diabetes	11.0% (16)	9.9% (29)	0.721	9.0% (14)	10.9% (31)	0.542
Exacerbations/year	2 [0–3]	1 [0–2]	0.0021	1 [0–3]	1 [0–2]	0.0235
mMRC stage	2 [1–3]	1 [1–2]	<0.0001	2 [1–3]	1 [1–2]	<0.0001
SGRQ global score	53 [42–64] missing 19	39 [27–53] missing 46	<0.0001	49 [35–59] missing 20	42 [28–56] missing 45	0.0066
BODE	5 [3–6]	2 [1–3]	<0.0001	4 [2–5]	2 [1–4]	<0.0001
ADO	5 [4–6]	3 [2–4]	<0.0001	4 [3–5]	3 [2–4]	<0.0001
HAD anxiety ≥10	26.7% (39) missing 18	23.8% (70) missing 50	0.414	25.2% (39) missing 22	24.6% (70) missing 46	0.864
HAD depression ≥10	20.5% (30) missing 20	13.6% (40) missing 46	0.169	18.1% (28) missing 22	14.7% (42) missing 44	0.649
FEV1% pred	42 [31–54]	56 [41–71]	<0.0001	38 [29–52]	57 [43–71]	<0.0001
FVC % pred	74 [61–89]	90 [76–106]	<0.0001	76 [62–91]	89 [75–106]	<0.0001
RV % pred	175 [137–223]	161 [131–199]	0.0364	189 [147–238]	156 [127–187]	<0.0001
TLC % pred	113 [98–127]	115 [104–128]	0.3958	118 [106–132]	112 [100–124]	0.0012
RV/TLC %	60 [52–67]	53 [44–61]	<0.0001	61 [51–66]	53 [46–61]	<0.0001
SpO2 at rest	95 [92–96]	96 [94–97]	<0.0001	94 [92–96]	96 [95–98]	<0.0001

Notes: Data reported as percentages (numbers) or median [IQR Q1–Q3]. Significant (P< 0.05) shown in bold.

Abbreviations: 6MWD, 6-min walking distance; ADO, age, dyspnea and obstruction score; BMI, body mass index; BODE, obstruction, dyspnea and exercise score; HAD, Hospital anxiety and depression scale; mMRC, modified Medical Research Council scale for dyspnea; RV, residual volume; SGRQ, Saint George's Respiratory Questionnaire; SpO2, transcutaneous oxygen saturation; TLC, total lung capacity.

Table 3 (A) Multivariate analysis for low vs high 6MWD. (B) Multivariate analysis for the presence of desaturations

OR estimates
Effect	Point estimate	95% Wald confidence limits
A
Age/10 years	1.953	1.510	2.527
FVC/10% pred	0.794	0.707	0.890
mMRC	1.954	1.541	2.477
SpO2 at rest	0.857	0.787	0.933
B
Age/10 years	0.661	0.507	0.861
Obesity yes vs no	0.457	0.242	0.864
Hypertension yes vs no	1.690	1.020	2.800
FEV1/10% pred	0.674	0.590	0.770
SpO2 at rest	0.701	0.632	0.778

Abbreviations: 6MWD, 6-min walking distance; mMRC, modified Medical Research Council scale for dyspnea; SpO2, transcutaneous oxygen saturation.

Table 4 Multivariate analysis for 6MWD in absolute value (m)

Parameter	DF	Parameter estimate	SE	t value	Pr > |t|
Intercept	1	100.46004	168.52394	0.60	0.5514
Age	1	−3.22696	0.46779	−6.90	<0.0001
Obesity	1	−24.05947	11.73060	−2.05	0.0409
Hypertension	1	−20.54332	9.78203	−2.10	0.0363
Diabetes	1	33.89135	15.15119	2.24	0.0258
FEV1% pred	1	1.25108	0.25561	4.89	<0.0001
mMRC	1	−31.07953	4.65525	−6.68	<0.0001
SpO2 at rest	1	5.17758	1.73057	2.99	0.0029

Note: Significant (P< 0.05) shown in bold.

Abbreviations: 6MWD, 6-min walking distance; mMRC, modified Medical Research Council scale for dyspnea; SpO2, transcutaneous oxygen saturation.

Table S1 Univariate logistic analysis for low 6MWD

Effect	OR estimates	95% Wald confidence limits		Wald Chi-square	Pr > ChiSq
Female vs male	1.177	0.757	1.828	0.5227	0.4697
Age	1.056	1.034	1.079	24.4536	<0.0001
Low BMI yes vs no	1.232	0.628	2.416	0.3690	0.5435
Obesity yes vs no	1.518	0.929	2.481	2.7719	0.0959
Hypertension yes vs No	1.414	0.940	2.126	2.7609	0.0966
Ischemic heart disease yes vs No	1.456	0.830	2.554	1.7137	0.1905
Heart failure yes vs No	1.669	0.940	2.965	3.0538	0.0805
Diabetes yes vs No	1.125	0.590	2.145	0.1273	0.7213
OSAS yes vs No	0.840	0.403	1.751	0.2167	0.6416
Chronic bronchitis yes vs No	1.192	0.779	1.825	0.6567	0.4177
FEV1% pred	0.966	0.955	0.977	35.1247	<0.0001
FEV/FVC	0.073	0.015	0.360	10.3363	0.0013
FVC % pred	0.971	0.961	0.981	33.2866	<0.0001
RV (L)	1.214	1.047	1.409	6.5540	0.0105
TLC % pred	1.004	0.990	1.019	0.3466	0.5560
mMRC	2.234	1.798	2.776	52.6517	<0.0001
Exacerbations/patient/year	1.148	1.038	1.270	7.2482	0.0071

Note: Significant P-values shown in bold.

Abbreviations: BMI, body mass index; OSAS, obstructive sleep apnea syndrome; FEV1 % pred, forced expiratory volume in one second, percentage of predicted; FVC % pred, forced vital capacity, percentage of predicted; RV (L), residual volume in liters; TLC (L), total lung capacity in liters; TLC % pred, total lung capacity, percentage of predicted; mMRC, modified Medical Research Council dyspnea scale; 6MWD, 6-min walking distance.

Table S2 Univariate logistic analysis for the presence of significant desaturations

Effect	OR estimates	95% Wald confidence limits		Wald Chi-square	Pr > ChiSq
Sex female vs male	1.327	0.861	2.046	1.6424	0.2000
Age/10 years	0.840	0.690	1.024	2.9788	0.0844
Low BMI yes vs no	1.571	0.815	3.028	1.8185	0.1775
Obesity yes vs no	0.564	0.329	0.967	4.3370	0.0373
Hypertension yes vs no	1.272	0.850	1.905	1.3651	0.2427
Ischemic heart disease yes vs no	0.648	0.352	1.193	1.9404	0.1636
Heart failure yes vs no	0.801	0.436	1.472	0.5121	0.4742
Diabetes yes vs no	0.814	0.419	1.580	0.3712	0.5424
OSAS yes vs no	0.480	0.214	1.078	3.1579	0.0756
Chronic bronchitis yes vs no	1.084	0.714	1.643	0.1425	0.7058
FEV1% pred	0.952	0.940	0.964	58.3708	<0.0001
FEV1/FVC	0.003	<0.001	0.018	41.5437	<0.0001
FVC % pred	0.973	0.964	0.983	29.4992	<0.0001
RV (L)	1.346	1.158	1.563	15.0655	0.0001
TLC (L)	1.001	0.999	1.004	1.1197	0.2900
RV/TLC %	1.008	0.997	1.019	1.8886	0.1694
mMRC	1.490	1.231	1.804	16.7205	<0.0001
Exacerbations/patient/year	1.110	1.005	1.226	4.2674	0.0388

Note: Significant P-values shown in bold.

Abbreviations: BMI, body mass index; OSAS, obstructive sleep apnea syndrome; FEV1 % pred, forced expiratory volume in one second, percentage of predicted; FVC % pred, forced vital capacity, percentage of predicted; RV (L), residual volume in liters; TLC (L), total lung capacity in liters; mMRC, modified Medical Research Council dyspnea scale.