Failure of dobutamine to increase exercise capacity despite hemodynamic improvement in severe chronic heart failure

The acute hemodynamic and metabolic effects of dobutamine administered during exercise were studied in 8 patients with severe chronic heart failure. Exercise was performed on an upright bicycle ergometer using a graded protocol. During exercise performed without administration of dobutamine, exhaustion occurred after 4.5 ± 1.2 minutes of exercise. The cardiac index increased from 1.61 ± 0.25 to 2.67 ± 0.59 liters/min/m² (p <0.001), the arteriovenous oxygen difference from 7.8 ± 1.7 to 12.5 ± 2.4 ml/100 ml (p <0.001), and oxygen uptake from 7.9 ± 3.0 to 41.2 ± 15.7 mg/100 ml (p <0.001). During exercise performed with the administration of dobutamine, the cardiac index was significantly greater than during the control state, 3.23 ± 0.78 versus 2.67 ± 0.59 liters/min/m² (p <0.001), while the arteriovenous oxygen difference was significantly lower, 11.2 ± 2.1 vs 12.5 ± 2.4 ml/100 ml (p <0.01). The arterial lactate level was not significantly changed, 45.3 ± 17.6 versus 41.2 ± 15.7 mg/100 ml. Although the dobutamine level tended to increase maximal oxygen uptake compared with the control period of exercise, 9.1 ± 1.2 versus 8.5 ± 1.4 ml/kg/min (p <0.05), it did not significantly increase exercise capacity, 4.8 ± 1.5 versus 4.5 ± 1.2 min. Thus administration of dobutamine in patients with severe chronic heart failure increased the cardiac index during maximal exercise but failed to increase exercise capacity. Since arteriovenous oxygen difference is reduced, dobutamine probably increases blood flow to the nonexercising tissues and not to the actively metabolizing muscles.