Modified Medical Research Council scale vs Baseline Dyspnea Index to evaluate dyspnea in chronic obstructive pulmonary disease

Figures & data

Table 1 Description of patients characteristics by GOLD grade of airflow obstruction

	GOLD 1 (N=15)	GOLD 2 (N=98)	GOLD 3 (N=79)	GOLD 4 (N=47)
Age (years)	74.0 [47.0; 77.0]	65.0 [56.0; 72.0]	64.0 [57.0; 72.0]	64.0 [57.0; 73]
BMI	25.0 [22.2; 29.7]	25.5 [23.3; 29.3]	24.5 [20.1; 28.3]	22.4 [18.8; 25.7]
FEV1 (% pred)	85.2 [83.7; 90.4]	66.1 [58.8; 72.7]	40.9 [35.0; 44.9]	25.0 [20.6; 29.3]
FVC% pred	118 [109.7; 124.1]	95 [87.4; 103.9]	81.5 [68.6; 92.7]	75.9 [62.9; 123.4]
FRC% pred	128.6 [100.8; 150.5]	122.1 [97.4; 139.9]	153.7 [125.7; 176.4]	179.5 [152.1; 212.7]
RV% pred	148.8 [106.7; 179.8]	132.9 [104.6; 165.4]	183.1 [154.6; 209.6]	223.3 [184.9; 261.7]
IC/TLC	0.37 [0.35; 0.45]	0.39 [0.33; 0.45]	0.28 [0.22; 0.33]	0.23 [0.17; 0.26]
HAD anxiety	6.0 [4.0; 10.0]	7.0 [4.0; 11.0]	7.0 [5.0; 10.0]	8.0 [4.0; 11.0]
HAD depression	6.0 [2.0; 10.0]	5.0 [3.0; 8.0]	6.0 [3.0; 9.0]	7.0 [3.0; 10.0]
BDI	6 [4; 10]	7 [6; 9]	6 [4; 7]	4 [3; 6]
mMRC	1 [0; 3]	1 [1; 2]	2 [1; 3]	3 [2; 3]
mMRC
Grade 0 (%)	4 (27%)	24 (24%)	8 (10%)	1 (2%)
Grade 1 (%)	6 (40%)	48 (49%)	23 (29%)	6 (13%)
Grade 2 (%)	1 (7%)	15 (15%)	24 (30%)	12 (26%)
Grade 3 (%)	3 (20%)	7 (7%)	17 (22%)	18 (38%)
Grade 4 (%)	1 (7%)	4 (4%)	7 (9%)	10 (21%)
Heart failure (%)	1 (7%)	17 (17%)	12 (15%)	8 (17%)
Venous thromboembolic history (%)	1 (7%)	9 (9%)	6 (8%)	3 (6%)
BMI
≤18.5 kg/m^2	0	1 (1%)	11 (14%)	10 (21%)
>30 kg/m^2	3 (20%)	21 (21%)	16 (20%)	5 (11%)

Note: Data are shown as median [IQR] or n (%).

Abbreviations: BDI, Baseline Dyspnea Index; BMI, body mass index; GOLD, Global initiative for chronic Obstructive Lung Disease; HAD, Hospital Anxiety-Depression; FEV₁, forced expiratory volume in 1 second; FRC, functional residual capacity; FVC, forced vital capacity; IC, inspiratory capacity; IQR, interquartile range; mMRC, modified Medical Research Council; RV, residual volume; TLC, total lung capacity.

Figure 1 Distribution of the BDI score.

Abbreviation: BDI, Baseline Dyspnea Index.

Figure 2 Relationships between BDI and mMRC scores in COPD patients. The median value and interquartile range of BDI are indicated for each mMRC level.

Abbreviations: BDI, Baseline Dyspnea Index; COPD, chronic obstructive pulmonary disease; mMRC, modified Medical Research Council.

Table 2 Univariate analysis of categorical variables associated with mMRC/BDI

Variables	Index	Median [IQR]		Wilcoxon P-value
		Men	Women
Sex	BDI	6 [5; 8]	6 [3; 8]	0.238
	mMRC	1 [1; 3]	2 [1; 3]	0.036
		Yes	No
Chronic bronchitis	BDI	6 [5; 8]	6 [4; 8]	0.699
	mMRC	2 [1; 3]	1 [1; 3]	0.567
Venous thromboembolic history	BDI	6 [2; 7]	6 [4.5; 8]	0.268
	mMRC	3 [1; 3]	1 [1; 3]	0.019
Heart failure	BDI	5.5 [3; 7]	6 [5; 8]	0.087
	mMRC	2 [1; 3]	1 [1; 3]	0.024
Low BMI ≤18.5 kg/m^2	BDI	4 [3; 6]	7 [5; 8]	<0.0001
	mMRC	2 [1; 3]	1 [1; 3]	0.3431
Obesity	BDI	6 [5; 8]	6 [4; 8]	0.8822
	mMRC	2 [1; 3]	1 [1; 3]	0.5864
		HAD <10	HAD ≥10
Anxiety	BDI	7 [5; 8]	5.5 [3; 7]	0.003
	mMRC	1 [1; 2]	2 [1; 3]	0.001
Depression	BDI	7 [5; 8]	4 [3; 6]	<0.0001
	mMRC	1 [1; 2]	3 [1; 3]	0.00014
		<25%	≥25%
IC/TLC	BDI	5 [3; 6]	7 [5; 8]	<0.0001
	mMRC	3 [2; 3]	1 [1; 2]	<0.0001

Abbreviations: BDI, Baseline Dyspnea Index; BMI, body mass index; HAD, Hospital Anxiety–Depression; IC, inspiratory capacity; IQR, interquartile range; mMRC, modified Medical Research Council; TLC, total lung capacity.

Table 3 Univariate analysis of mMRC/BDI correlates, using numerical variables

		Spearman correlation coefficients (rho)
		mMRC	BDI total	BDI functional impairment	BDI magnitude of task	BDI magnitude of effort
Age	rho	0.10816	−0.04967	−0.02118	−0.01477	−0.11339
	P-value	0.0953	0.4447	0.7446	0.8203	0.0802
BMI, kg/m^2	rho	−0.04476	0.19451	0.16882	0.21523	0.12184
	P-value	0.4910	0.0025	0.0089	0.0008	0.0600
SGRQ	rho	0.66602	−0.69067	−0.65152	−0.59262	−0.57354
	P-value	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
HAD anxiety	rho	0.19222	−0.21341	−0.24333	−0.17071	−0.09802
	P-value	0.0028	0.0009	0.0001	0.0082	0.1308
HAD depression	rho	0.30348	−0.40110	−0.41325	−0.36808	−0.25213
	P-value	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
FEV1 % pred	rho	−0.45100	0.40713	0.39529	0.34706	0.27785
	P-value	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
FVC% pred	rho	−0.26632	0.22602	0.22084	0.20309	0.13053
	P-value	<0.0001	0.0004	0.0006	0.0016	0.0438
IC/TLC%	rho	−0.37503	0.33243	0.32347	0.27679	0.20506
	P-value	<0.0001	<0.0001	<0.0001	<0.0001	0.0014

Abbreviations: BDI, Baseline Dyspnea Index; BMI, body mass index; HAD, Hospital Anxiety–Depression; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; IC, inspiratory capacity; TLC, total lung capacity; mMRC, modified Medical Research Council.

Table 4 Determinants of the mMRC scale in stepwise multivariate analysis

Analysis of maximum likelihood estimates
Parameter	Unit	DF	Estimate	Standard error	Wald χ^2	Pr > χ^2
BMI ≤18.5 kg/m^2	Yes	1	0.8422	0.4419	3.6326	0.0567
Obesity	Yes	1	−0.6220	0.3150	3.8985	0.0483
FEV1	%pred	1	0.0391	0.00785	24.7789	<0.0001
IC/TLC class	<25%	1	0.6994	0.3237	4.6689	0.0307
HAD depression	≥10	1	−0.8960	0.3008	8.8746	0.0029
Exacerbations rate	n/year	1	−0.1621	0.0547	8.7854	0.0030
Heart failure	Yes	1	−0.8884	0.3289	7.2974	0.0069
Venous thromboembolic history	Yes	1	−1.0541	0.4461	5.5819	0.0181

Abbreviations: BMI, body mass index; DF, degree of freedom; HAD, Hospital Anxiety–Depression; FEV₁, forced expiratory volume in 1 second; IC, inspiratory capacity; mMRC, modified Medical Research Council; TLC, total lung capacity.

Table 5 Determinants of the BDI total score in stepwise multivariate analysis

Analysis of maximum likelihood estimates
Parameter	Unit	DF	Estimate	Standard error	Wald χ^2	Pr > χ^2
Obesity	Yes	1	0.5180	0.3077	2.8352	0.0922
FEV1	% pred	1	−0.0252	0.00734	11.7574	0.0006
IC/TLC class	<25%	1	−0.5617	0.3177	3.1256	0.0771
HAD depression	≥10	1	1.2797	0.2997	18.2346	<0.0001
Exacerbation rate	n/year	1	0.1515	0.0537	7.9483	0.0048
Heart failure	Yes	1	0.7912	0.3243	5.9522	0.0147

Abbreviations: BDI, Baseline Dyspnea Index; DF, degree of freedom; HAD, Hospital Anxiety–Depression; FEV₁, forced expiratory volume in 1 second; IC, inspiratory capacity; TLC, total lung capacity.

Figure 3 Determinants of the mMRC grade (stepwise logistic regression).

Abbreviations: BDI, Baseline Dyspnea Index; FEV₁, forced expiratory volume in 1 second; IC, inspiratory capacity; mMRC, modified Medical Research Council; TLC, total lung capacity.

Figure 4 Determinants of the BDI score (stepwise logistic regression).

Abbreviations: BDI, Baseline Dyspnea Index; FEV₁, forced expiratory volume in 1 second; IC, inspiratory capacity; TLC, total lung capacity.