Prediction of oxygen uptake () during exercise from relations established in normal subjects between and work load in watts (W) may be inaccurate in patients with chronic heart failure because these patients could manifest delayed kinetics at final stages of exercise. To test the hypothesis that even at low levels of work, patients exhibit a lower 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. (ml/min per kg) was measured every 15 s. The 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 uptake, or both; accordingly, indirect estimates of requirements derived from intensity or duration of exercise in such patients are overestimated.
This work was supported by grants from the Société Française de Cardiologie, the Federation Française de Cardiologie and the Institut National des Sciences et de la Recherche Médicale, Paris.