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A7058 - Comparison of Calculated and Measured Peak Oxygen Uptake in COPD
Author Block: M. Tornatore1, R. J. Perez2, D. Datta3, R. Wu4; 1Internal medicine residency program, University of Connecticut, Farmington, CT, United States, 2Pulmonary/Critical Care fellowship program, UCONN, Farmington, CT, United States, 3Pulmonary/Critical Care Program, University of Connecticut, Farmington, CT, United States, 4Statistics, University of Connecticut, Farmington, CT, United States.
Purpose: Peak oxygen uptake (VO2pk) measured by cardiopulmonary exercise testing (CPET), the gold standard for assessing functional capacity, is not utilized commonly due to its cost and complicated mode of performance. The six-minute walk distance (6MWD) estimated by the 6-minute walk test (6MWT) is commonly used in the follow-up of COPD patients. 6MWT is a submaximal test and hence, 6MWD is not felt to represent an accurate substitute of VO2pk. A predictive equation to calculate VO2pk from mean 6MWD for patients with moderate-to-severe cardiopulmonary disease, has been reported to show significant correlation between calculated and measured values of VO2pk. The objective of this study was to determine the accuracy of the VO2pk estimated by a predictive equation using 6MWD by comparing it with measured VO2pk in patients with COPD. Methods: Patients with COPD who had a 6MWT and CPET performed prior to starting pulmonary rehabilitation were studied. Retrospective review of medical records was performed to obtain the following data: patient’s age, gender, mean FEV1, 6MWD, and measured VO2 peak. VO2 peak was calculated by using a predictive equation: Mean VO2peak (ml kg/ min) = 4.948 + 0.023 X 6 MWD meters. Correlation analysis was used to determine the correlation between the calculated and measured VO2peak. Standard error of estimate was determined to assess agreement between measured and calculated values of VO2pk. Results: Of 60 patients studied, 43% were female; the mean age was 70.7± 8 years. Mean FEV1 was51± 17%; mean 6MWD was 307 + 70 meters; mean measured VO2peak was 13.8 + 4.4ml/kg/min; mean calculated VO2peak using 6MWD was 12 + 1.3 6ml/kg/min. The individual and mean values of measured and calculated VO2pk did not show a large variation. On correlation analysis, a significant correlation between the two values were noted (r=0.367, p= 0.005), was noted. Standard error of estimate of measured and calculated values was 0.53, which is quite low and indicates that the calculated VO2peak is an accurate representation of measured VO2peak in COPD patients. Conclusions: VO2pk calculated from 6MWD approximates measured values with fair accuracy compared to actual measured VO2pk. Studies on larger groups of patients are needed to confirm that there is agreement between these the two parameters and if the calculated value can be used as a substitute for the measured VO2pk. Clinical Implication: Calculated VO2pk derived from 6MWD is an accurate measure of functional capacity.