Study objective: To investigate the ability of patients with COPD to reproduce an exercise intensity accurately on the treadmill using dyspnea ratings obtained during incremental exercise on the cycle ergometer (cross-modal exercise prescription).
Design: Five visits over an 8-week period.
Patients: Thirteen symptomatic patients with stable COPD. Age was 67±6 years (mean±SD). FEV1 was 1.15±0.22 L (45±7% predicted).
Interventions: At each visit, patients performed spirometry and exercise. Visit 1 was a practice incremental exercise test on the cycle ergometer. At visit 2 (1 week later), patients estimated the intensity of dyspnea using the 0 to 10 category-ratio scale during an incremental exercise test on the cycle ergometer (cycle estimation trial). Visit 3, 5 weeks later, was a practice session on the treadmill. At visit 4, 1 week later, patients were instructed to produce specific intensities of dyspnea (ie, dyspnea targets) at 50% and at anaerobic threshold (AT) or 80% of peak oxygen consumption (VO2) as calculated from results at visit 2 (treadmill production trial). Visit 5, 1 week later, was the treadmill estimation trial.
Measurements and results: Lung function was stable at all visits. Dyspnea ratings were 1.9±0.9 at 50% of VO2 and 5.6±1.5 at AT/80% of peak VO2 (17.5±3.3 mL/kg/min). The VO2 at the treadmill production trial (761±185 mL/min) was significantly higher than at the cycle estimation trial (612±159 mL/min) at the low dyspnea target (p<0.0002; upward bias, 26±16%). In contrast, there was no significant difference in VO2 values (929±176 mL/min vs 948±259 mL/min) at the high dyspnea target (p>0.5; 0±11% bias).
Conclusions: Patients with COPD can use dyspnea ratings from an incremental cycle ergometry test to regulate exercise on the treadmill without systematic bias at an intensity of 80% of peak VO2, but exceed the desired VO2 when using the dyspnea rating at an intensity of 50% of peak VO2.