Predicting the rate of oxygen consumption during the 3-minute constant-rate stair stepping and shuttle tests in people with COPD

Background: The 3-minute constant-rate stair stepping (3-min CRSST) and constant-speed shuttle tests (3-min CSST) were developed to assess breathlessness in response to a standardized exercise stimulus. Estimating the rate of oxygen consumption (V'O-2) during these tests would assist clinicians to relate the stepping/shuttle speeds that elicit breathlessness to daily physical activities with a similar metabolic demand. This study: (I) developed equations to estimate the V'O-2 of these tests in people with chronic obstructive pulmonary disease (COPD); and (II) compared the newly developed and American College of Sports Medicine (ACSM) metabolic equations for estimating the V'O-2 of these tests. Methods: This study was a retrospective analysis of people with COPD who completed a 3-min CRSST (n=98) or 3-min CSST (n=69). Multivariate linear regression estimated predictors (alpha <0.05) of V'O-2 to construct COPD-specific metabolic equations. The mean squared error (MSE) of the COPD-specific and ACSM equations was calculated and compared. Bland Altman analyses evaluated level of agreement between measured and predicted V'O-2 using each equation; limits of agreement (LoA) and patterns of bias were compared. Results: Stepping rate/shuttle speed and body mass were identified as significant predictors of V'O-2. The MSE of the COPD-specific equations was 0.05 L.min(-1) for both tests. Mean difference between measured and predicted V'O-2 was 0.00 L.min(-1) (95% LoA -0.46, 0.46) and 0.00 L.min(-1) (95% LoA -0.44, 0.44) for the 3-min CRSST and 3-min CSST, respectively. For the ACSM metabolic equations, the MSE was 0.10 L.min(-1) and 0.18 L.min(-1) for the 3-min CRSST and 3-min CSST, respectively. The ACSMM, metabolic equations underestimated V'O-2 of the 3-min CRSST by -0.18 L.min(-1) (95% LoA -0.68, 0.32), and overestimated V'O-2 of the 3-min CSST by 0.35 L.min(-1) (95% LoA -0.14, 0.84). Conclusions: This study presents metabolic equations to predict V'O-2 of the 3-min CRSST and 3-min CSST for people with COPD that are more accurate than the ACSM metabolic equations.