Robustness of the oxygen uptake efficiency slope to exercise intensity in patients with coronary artery disease

Oxygen uptake efficiency slope (OUES) and ventilatory efficiency (VE/VCO2 slope) are widely used as submaximal measurements of cardiopulmonary exercise testing as the evaluator or prognosticator of cardiac diseases. However, very few studies have compared the effects of submaximal exercise on these measurements. A total of 58 patients with coronary artery disease underwent maximal cardiopulmonary exercise testing on a treadmill. We compared the values obtained from the first 75% (VE/VCO2 slope75 and OUES75) and 90% (VE/VCO2 slope90 and OUES90) of the exercise period with the entire duration (VE/ VCO2 slope100 and OUES100). Although OUES100, OUES90 and OUES75 were virtually identical, submaximal calculations of VE/VCO2 slope underestimated the measurements. The Bland-Altman method revealed that submaximal measurements of OUES agreed very well with maximal OUES (limits of agreement -5.0% to +6.0% for OUES90, and -11.5% to +12.9% for OUES75). However, the submaximal calculations of VE/ VCO2 slope showed rather poor agreement with the maximal calculations (limit of agreement -11.8% to +3.1% for VE/VCO2 slope90, and -20.8% to +5.3%% for VE/VCO2 slope75). These results revealed that both the OUES and the VE/VCO2 slopes are not overly influenced by exercise.