Abstract
Cardiopulmonary exercise testing (CPET) is the 'gold standard' method of determining VO2peak . When CPET is unavailable, VO2peak may be estimated from treadmill or cycle ergometer workloads and expressed as estimated metabolic equivalents (METs). Cardiac rehabilitation (CR) programmes use estimated VO2peak (METs) to report changes in cardiorespiratory fitness (CRF). However, the accuracy of determining changes in VO2peak based on estimated functional capacity is not known. A total of 27 patients with coronary heart disease (88·9% male; age 59·5±10·0years, body mass index 29·6±3·8kgm-2 ) performed maximal CPET before and after an exercise-based CR intervention. VO2peak was directly determined using ventilatory gas exchange data and was also estimated using the American College of Sports Medicine (ACSM) leg cycling equation. Agreement between changes in directly determined VO2peak and estimated VO2peak was evaluated using Bland-Altman limits of agreement (LoA) and intraclass correlation coefficients. Directly determined VO2peak did not increase following CR (0·5mlkg-1 min-1 (2·7%); P=0·332). Estimated VO2peak increased significantly (0·4 METs; 1·4mlkg-1 min-1 ; 6·7%; P=0·006). The mean bias for estimated VO2peak versus directly determined VO2peak was 0·7mlkg-1 min-1 (LoA -4·7 to 5·9ml kg-1 min-1 ). Aerobic efficiency (ΔVO2 /ΔWR slope) was significantly associated with estimated VO2peak measurement error. Change in estimated VO2peak derived from the ACSM leg cycling equationis not an accurate surrogate for directly determined changes in VO2peak . Our findings show poor agreement between estimates of VO2peak and directly determined VO2peak . Applying estimates of VO2peak to determine CRF change may over-estimate the efficacy of CR and lead to a different interpretation of study findings.
Highlights
Structured exercise training is a core component of most cardiac rehabilitation (CR) programmes 1-4
Reporting mean cardiorespiratory fitness (CRF) changes using estimated metabolic equivalents (METs) may over-estimate the efficacy of CR and lead to a different interpretation of study findings compared to directly determined VO2peak
Patient characteristics and medications at baseline are reported in Table 1. n=44 patients conducted a baseline maximal cardiopulmonary exercise testing (CPET). n=17 were lost to follow-up. n=27 were included for analysis. (88.9% male; age 59.5 ± 10.0 years, body mass index [BMI] 29.6 ± 3.8 kg.m-2)
Summary
Structured exercise training is a core component of most cardiac rehabilitation (CR) programmes 1-4. Information obtained during CPET provides some of the most accurate data on which to base an exercise prescription and to determine changes in CRF following the completion of a CR programme. Recently challenged 8 equations for estimating VO2peak and METs are traditionally based on an assumed linear relationship between VO2 and work rate 7. Increases in estimated functional capacity during an exercise test are commonly expressed in multiples of resting metabolic rate. Peak estimated METs achieved during maximal exercise testing are used to risk-stratify patients, prescribe individual exercise intensities for exercise training, and to determine changes in CRF following exercise interventions 10. Whilst the limitations of estimating VO2peak from a single exercise test are known, the accuracy of estimated changes in VO2peak following an exercise training intervention is unclear
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