Cardiorespiratory Response To Different Exercise Tests In Interstitial Lung Disease

Introduction: The 6-min stepper test (6MST) has been used as an alternative to the 6-min walk test (6MWT) to assess exercise tolerance in patients with interstitial lung disease (ILD). Recent data suggest that the tests may involve different energy pathways and cardiorespiratory responses. We thus aimed to compare the cardiorespiratory responses of ILD patients during the 6MWT and the 6MST. Methods: Thirty-one patients with ILD were randomized to perform both tests in the order 6MST -> 6MWT (n = 16) or 6MWT -> 6MST (n = 15). Gas exchange, HR, and pulse O-2 saturation (SpO(2)) were measured continuously, and dyspnoea, leg discomfort, and blood lactate concentration were assessed before and immediately after each test. Results: Oxygen uptake ((V) over dotO(2)) was lower (P = 0.002) and respiratory equivalent ratio for O-2 ((V) over dot(E)/(V) over dotO(2)) and RER were higher (both P < 0.001) during the 6MST compared with the 6MWT. The 6MST was also associated with higher blood lactate concentrations (6MST, 4.16 +/- 1.95 mmol.L-1; 6MWT, 2.84 +/- 1.17 mmol.L-1; P = 0.01), higher leg discomfort scores (6MST 5 +/- 3 points, 6MWT 3 +/- 2 points; P < 0.001), and smaller decreases in SpO(2) (6MST -5% +/- 5%, 6MWT -9% +/- 6%; P < 0.001). Conclusions: ILD patients exhibited greater ventilatory responses and lower arterial O-2 desaturation during the 6MST compared with the 6MWT. The higher lactate concentrations and perceived muscle fatigue observed during the 6MST may indicate the presence of intertest differences in active muscle metabolism that could contribute to the distinct cardiorespiratory responses.