Comparison of oxygen uptake during bicycle exercise in patients with chronic heart failure and in normal subjects

Abstract

Prediction of oxygen uptake (V̇O2) during exercise from relations established in normal subjects between V̇O2 and work load in watts (W) may be inaccurate in patients with chronic heart failure because these patients could manifest delayed V̇O2 kinetics at final stages of exercise. To test the hypothesis that even at low levels of work, patients exhibit a lower V̇O2 than do normal subjects, 77 patients with heart failure and 27 control subjects with a normal heart or with disease other than heart failure underwent bicycle exercise with respiratory gas analysis. Work load was increased by 10 W/min from an initial 20 W. V̇O2 (ml/min per kg) was measured every 15 s. The Δ V ̇O2 ΔW ratio was significantly reduced only in the most severely impaired patients in heart failure class C-D (8.75 ± 2.14 versus 11.05 ± 0.38, p < 0.05). Class B patients showed a lower ratio at a work load of ≥80 W, whereas class C-D patients manifested a lower ratio at ≥20 W. Even with a low incremental work rate protocol, compared with sedentary normal subjects or patients without heart failure, patients with heart failure demonstrate impaired oxygen uptake. This observation suggests the presence of anaerobic metabolism or delayed V̇O2 uptake, or both; accordingly, indirect estimates of V̇O2 requirements derived from intensity or duration of exercise in such patients are overestimated. © 1990.