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 FEV(1) 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 FEV(1) 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.