Oxygen uptake efficiency slope as a useful measure of cardiorespiratory functional reserve in adult cardiac patients

In this study we aimed to elucidate the validity and usefulness of the oxyg en uptake efficiency slope (OUES) in the evaluation of adult cardiac patien ts. Cardiopulmonary exercise tests were performed on a treadmill by 50 adul t patients with chronic heart failure. The OUES was calculated from data fo r the first 75%, 90%, and 100% of exercise duration. The OUES is derived fr om the following equation: (V) over dotO(2)=ax log(V) over dot(E) + b, wher e (V) over dot O-2 is oxygen uptake (ml/kg/min), (V) over dot(E) is minute ventilation (1/kg/min), and the constant "a" represents OUES. We also deter mined the ventilatory anaerobic threshold (VAT). The correlation coefficien t of the logarithmic curve-fitting model was [mean (SD)I 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Asso ciation functional classes (P < 0.001). OUES and maximum (V) over dot O-2 w ere significantly correlated (r=0.78, P < 0.01) Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intr aclass correlation coefficient = 0.99). Our results suggest that OUES is ap plicable to adult cardiac patients as an objective, effort-independent esti mation of cardiorespiratory functional reserve.