Identifying Abnormal Exertional Breathlessness in COPD: Comparing Modified Medical Research Council and COPD Assessment Test With Cardiopulmonary Exercise Testing

Abstract

Background: COPD management is guided by the respiratory symptom burden, assessed using the modified Medical Research Council (mMRC) scale, the COPD Assessment Test (CAT), or both.

Research question: What are the abilities of mMRC and CAT to detect abnormally high exertional breathlessness on incremental cardiopulmonary cycle exercise testing (CPET) in people with COPD?

Study design and methods: Analysis of people aged ≥ 40 years with FEV₁ to FVC ratio of < 0.70 after bronchodilator administration and ≥ 10 pack-years of smoking from the Canadian Cohort Obstructive Lung Disease study. Abnormal exertional breathlessness was defined as a breathlessness (Borg scale 0-10) intensity rating more than the upper limit of normal at the symptom-limited peak of CPET using normative reference equations.

Results: We included 318 people with COPD (40% female) with a mean (SD) age of 66.5 (9.3) years and FEV₁ of 79.5% predicted (19.0% predicted); 26% showed abnormally low exercise capacity (peak oxygen uptake less than the lower limit of normal). Abnormally high exertional breathlessness was present in 24%, including 9% and 11% of people with mMRC score of 0 and CAT score of < 10, respectively. An mMRC score of ≥ 2 and CAT score of ≥ 10 was most specific (95%) to detect abnormal exertional breathlessness, but showed low sensitivity of only 12%. Accuracy for all scale cutoffs or combinations was < 65%. Compared with people with true-negatives findings, people with abnormal exertional breathlessness but low mMRC score, low CAT scores (false-negatives findings), or both showed worse self-reported and physiologic outcomes during CPET, were more likely to have physician-diagnosed COPD, but were not more likely to be taking any respiratory medication (37% vs 30%; mean difference, 6.1%; 95% CI, -7.2 to 19.4; P= .36).

Interpretation: In COPD, mMRC and CAT showed low concordance with CPET and failed to identify many people with abnormally high exertional breathlessness.

Clinical trial registry: ClinicalTrials.gov; No.: NCT00920348; URL: www.

Clinicaltrials: gov.

Keywords: dyspnea; exercise capacity; exercise test; reference values.

Figure 1

Participant flow diagram. CanCOLD = Canadian Cohort Obstructive Lung Disease; CAT = COPD Assessment Test; CPET = cardiopulmonary exercise testing; mMRC = modified Medical Research Council; $\dot{\mathrm{V}}$o₂ = oxygen uptake.

Figure 2

A-D, Bar graphs showing the prevalence of abnormally high exertional breathlessness by mMRC breathlessness rating (A), CAT total score (B), and (C, D) combinations of the scales. CAT = COPD Assessment Test; mMRC = modified Medical Research Council.

Figure 3

A-D, Line graphs showing detection of abnormally high exertional breathlessness at the symptom-limited peak of incremental cardiopulmonary cycle exercise testing in people with COPD using mMRC breathlessness ratings (A), CAT total scores (B), and combinations of the scales (C, D). The discriminative ability for the variable(s) was assessed as the AUC, where 1.0 is optimal and 0.5 is no better than chance. AUC = area under the receiver operating characteristic curve; CAT = COPD Assessment Test; mMRC = modified Medical Research Council.