POSTEXERCISE OXYGEN-UPTAKE KINETICS IN PATIENTS WITH LEFT-VENTRICULAR DYSFUNCTION

We assessed the kinetics of oxygen uptake (VO2) after symptom-limited maximal exercise by use of cardiopulmonary exercise testing with a bicycle ergometer in normal subjects and patients with left ventricular dysfunction due to dilated cardiomyopathy. During the first few minutes after the cessation of exercise, the VO2-time relationship showed an exponential-like decrease. A monoexponential curve was fitted to this relationship of the first 3 min after exercise to obtain the time constant of the decrease in VO2 (T(VO2)). The results of exercise testing in 37 normal subjects (25 male and 12 female) revealed that T(VO2) was relatively independent of age and gender. Then, 30 male patients with dilated cardiomyopathy (10 in New York Heart Association functional class I, 12 in class II, and 8 in class III) were evaluated and the results were compared with those of 16 age-matched male control normal subjects. Although the amount of the estimated oxygen debt was smaller in the patient group, the time constant T(VO2) was 117 +/- 8 s for the controls as compared with 130 +/- 14 s for the patients in class I, 153 +/- 13 s for those in class II, and 219 +/- 49 s for those in class III. There were significant correlations between T(VO2) and anaerobic threshold (r = -0.68, p < 0.001), peak VO2 (r = -0.74, p < 0.001), and the increase in VO2 per work rate (r = -0.88, p < 0.001). T(VO2) also correlated with the ventilatory equivalent for carbon dioxide output (VE/VCO2) at peak exercise (r = 0.70, p < 0.001) and the time course of minute ventilation during the early phase of the post-exercise period (r = 0.67, p < 0.001). Thus, the time course of VO2 decrease after symptom-limited exercise is considered to be closely related to exercise capacity and also to the degree of exercise-induced hyperpnea in patients with left ventricular dysfunction.