Estimated peak functional capacity: an accurate method for assessing change in peak oxygen consumption after cardiac...

Cardiopulmonary exercise testing (CPET) is the 'gold standard' method of determining VO_2peak . When CPET is unavailable, VO_2peak may be estimated from treadmill or cycle ergometer workloads and expressed as estimated metabolic equivalents (METs). Cardiac rehabilitation (CR) programmes use estimated VO_2peak (METs) to report changes in cardiorespiratory fitness (CRF). However, the accuracy of determining changes in VO_2peak based on estimated functional capacity is not known.

A total of 27 patients with coronary heart disease (88·9% male; age 59·5 ± 10·0 years, body mass index 29·6 ± 3·8 kg m^-2 ) performed maximal CPET before and after an exercise-based CR intervention. VO_2peak 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 VO_2peak and estimated VO_2peak was evaluated using Bland-Altman limits of agreement (LoA) and intraclass correlation coefficients.

Directly determined VO_2peak did not increase following CR (0·5 ml kg^-1 min^-1 (2·7%); P = 0·332). Estimated VO_2peak increased significantly (0·4 METs; 1·4 ml kg^-1  min^-1 ; 6·7%; P = 0·006). The mean bias for estimated VO_2peak versus directly determined VO_2peak was 0·7 ml kg^-1  min^-1 (LoA -4·7 to 5·9 ml  kg^-1  min^-1 ). Aerobic efficiency (ΔVO₂ /ΔWR slope) was significantly associated with estimated VO_2peak measurement error.

Change in estimated VO_2peak derived from the ACSM leg cycling equation is not an accurate surrogate for directly determined changes in VO_2peak . Our findings show poor agreement between estimates of VO_2peak and directly determined VO_2peak . Applying estimates of VO_2peak to determine CRF change may over-estimate the efficacy of CR and lead to a different interpretation of study findings.