Utility of Equations to Estimate Peak Oxygen Uptake and Work Rate From a 6-Minute Walk Test in Patients With COPD in a Clinical Setting

PURPOSE: To determine the utility of equations that use the 6-minute walk test (6MWT) results to estimate peak oxygen uptake (V)over dotO(2)) and peak work rate with chronic obstructive pulmonary disease (COPD) patients in a clinical setting. METHODS: This study included a systematic review to identify published equations estimating peak (V)over dotO(2) and peak work rate in watts in COPD patients and a retrospective chart review of data from a hospital-based pulmonary rehabilitation program. The following variables were abstracted from the records of 42 consecutively enrolled COPD patients: measured peak V)over dotO(2) and peak work rate achieved during a cycle ergometer cardiopulmonary exercise test, 6MWT distance, age, sex, weight, height, forced expiratory volume in 1 second, forced vital capacity, and lung diffusion capacity. Estimated peak V)over dotO(2) and peak work rate were estimated from 6MWT distance using published equations. The error associated with using estimated peak (V)over dotO(2) or peak work to prescribe aerobic exercise intensities of 60% and 80% was calculated. RESULTS: Eleven equations from 6 studies were identified. Agreement between estimated and measured values was poor to moderate (intraclass correlation coefficients = 0.11-0.63). The error associated with using estimated peak (V)over dotO(2) or peak work rate to prescribe exercise intensities of 60% and 80% of measured values ranged from mean differences of 12 to 35 and 16 to 47 percentage points, respectively. CONCLUSIONS: There is poor to moderate agreement between measured peak (V)over dotO(2) and peak work rate and estimations from equations that use 6MWT distance, and the use of the estimated values for prescription of aerobic exercise intensity would result in large error. Equations estimating peak (V)over dotO(2) and peak work rate are of low utility for prescribing exercise intensity in pulmonary rehabilitation programs.