How do dyspnoea scales compare with measurement of functional capacity in patients with COPD and at risk of COPD?

BACKGROUND: In primary care, formal functional capacity testing is not always feasible. Guidelines for family practitioners suggest the use of dyspnoea scales to assess exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). AIMS: To examine whether the use of activity-based dyspnoea scales can substitute for actual functional capacity testing. METHODS: 128 subjects (49% at risk of COPD, 24% GOLD stage I, 17% GOLD stage II, 9% GOLD stage III) performed an Incremental Shuttle Walk Test (ISWT) and completed the Medical Research Council dyspnoea scale (MRC), Baseline Dyspnoea Index (BDI), Oxygen Cost Diagram (OCD), Clinical COPD Questionnaire (CCQ), and St George's Respiratory Questionnaire (SGRQ). RESULTS: Analysis of variance showed that the relationship between the ISWT and the MRC dyspnoea scale was statistically significant but moderate (p < 0.001, R2 = 0.166). Correlations between the ISWT and the other dyspnoea scales were also moderate (correlation coefficients 0.34-0.42). Combining the dyspnoea scales in one analysis resulted in a proportion of explained variance of the ISWT of 21.4% (R2 = 0.214). CONCLUSIONS: Dyspnoea scales cannot substitute for formal functional capacity testing. Authors of COPD guidelines should consider stating more specifically that the MRC and similar scales measure (self-reported) activity-related dyspnoea but cannot replace objectively measured functional capacity