Reproducibility of Borg scale measurements of dyspnea during exercise in patients with COPD

The purpose of this study was to evaluate the moderate term (5 weeks) reproducibility of Borg scale ratings of the effort to breathe (Borg(e)) and the degree of discomfort evoked by breathing (Borg(d)) in patients with COPD during exercise. Six subjects with moderately severe COPD (FEV₁, 1.42 ± 0.50 L) underwent progressive incremental exercise (15 W/min) on a cycle ergometer to a symptom-limited maximum every week for 6 weeks (first week used as practice session). Minute ventilation (V̇E), oxygen consumption (V̇O₂), and Borg ratings were obtained every minute during exercise. Borg(e) and Borg(d) were highly correlated in each subject (r=-0.99 ± 0.01). Borg scores were not significantly different across study days during both maximal and submaximal exercise. The within-subject coefficient of variation (CV) for Borg(e) during maximal exercise was 13.9 ± 9.0% (range, 6 to 31%) which was not significantly different from that observed for the physiological indices: 8.2 ± 4.1% (range, 4 to 15%) for V̇E and 5.2 ± 3.4% (range, 1 to 10%) for V̇O₂. In contrast, at 66% of the maximum workload, the within-subject CV for Borg(e) was 25.0 ± 13.6% (range, 12 to 50%) which was significantly greater than that observed for the physiologic indices: 5.8 ± 2.0% (range, 3 to 9%) for V̇E and 4.6 ± 1.1% (range, 3 to 6%) for V̇O₂. In every subject, Borg(e) was linearly correlated with V̇E, V̇O₂, and workload. However, within an individual subject, the slope of these relationships varied between trials; within-subject CV for the slope of the Borg(e)/V̇E relationship was 20.2 ± 8.0% (range, 12 to 32%). In conclusion, during incremental exercise Borg ratings of dyspnea are not as reproducible as physiologic indices in patients with COPD.