A High Degree of Dyspnea Is Associated With Poor Maximum Exercise Capacity in Subjects With COPD With the Same Severity of Air-Flow Obstruction

BACKGROUND: In patients with COPD, limited data have been reported concerning the association between dyspnea perception and exercise tests. Moreover, the perception of dyspnea has not been analyzed in patients with the same severity of air-flow obstruction. The aim of our study was to evaluate the relationship between the degree of dyspnea and exercise capacity in subjects with COPD who had the same severity of air-flow obstruction.

METHODS: We assessed dyspnea perception and maximum exercise capacity by using the modified Medical Research Council dyspnea scale (mMRC) questionnaire and by using the symptom-limited incremental cardiopulmonary exercise test, respectively. A propensity score matching was used to obtain the balance between the subjects with COPD and with an mMRC questionnaire score <2 and ≥2 (mMRC score) according to the severity of air-flow obstruction.

RESULTS: A total of 249 ambulatory adult patients with stable COPD (mean age, 68 y) were considered in the full cohort. After propensity score analysis, 160 subjects (65% men; mean ± SD FEV₁, 47.5 ± 12.8% of predicted) were included in our study cohort. The subjects with an mMRC questionnaire score ≥2 in comparison with those with an mMRC questionnaire score <2 showed lower values in oxygen uptake at peak (V_O2 max) (P = .002) and in maximum work load (P < .001). In the regression models, the mMRC questionnaire score was able to predict oxygen uptake at peak (P < .001) and at maximum work load (P < .001).

CONCLUSIONS: In subjects with COPD and with the same severity of air-flow obstruction, a high score in dyspnea was related to a poor maximum exercise capacity. Our results support the view that, in COPD, the severity of air-flow obstruction was less informative than symptoms in the combined assessment of the disease.