Objectives: To investigate cardiorespiratory and dyspnea responses to incremental and self-paced exercise tests in patients with COPD.
Design: A prospective within-subject design was used.
Patients: Twenty stable subjects (15 men), with a mean (± SD) age of 64.0 ± 7.5 years and moderate-to-severe COPD (ie, mean FEV1, 0.8 ± 0.3 L and 28.9 ± 7.9% predicted) were studied.
Methods: Each subject completed a 6-min walk test (6MWT), an incremental shuttle walking test (ISWT), and a cycle ergometer test (CET), within a 2-week period. The tests were performed at least 24 h apart. Standardized encouragement was utilized in each test with the aim of maximizing performance. Heart rate (HR) and dyspnea were measured each minute throughout the tests, and pulse oximetric saturation (Spo2) was measured before and immediately after each test. The distances walked in the 6MWT and ISWT were compared to peak oxygen uptake (V̇o2) values from the CET.
Results: HR increased linearly with increasing workload during the CET and ISWT, but increased alinearly with a disproportionate increase early in the 6MWT. In contrast, dyspnea scores increased linearly during the 6MWT, but increased alinearly with a disproportionate increase late during the CET and ISWT. Peak HR and dyspnea were not significantly different between tests. Spo2 was significantly lower at the end of both walking tests compared to that at the end of the CET (p < 0.001). The distance walked in both the ISWT and 6MWT were related to peak V̇o2 values on the CET (for both tests, r = 0.73; p < 0.001).
Conclusions: The patterns of response in HR and dyspnea seen during the 6MWT suggest that patients with COPD titrate exertion against dyspnea to achieve a peak tolerable intensity. This strategy is not possible in an externally paced ISWT or CET. However, it is a limited strategy, with performance converging at higher workloads. Similar peak exercise responses were achieved in the 6MWT, ISWT, and CET. Greater oxygen desaturation was observed during the field walking tests, suggesting that both the ISWT and 6MWT are more sensitive than the CET in detecting exercise-induced hypoxemia and in assessing ambulatory oxygen therapy needs.