PATHOPHYSIOLOGY AND NATURAL HISTORY CONGESTIVE HEART FAILURE Exercise intolerance in patients with chronic heart failure: role of impaired nutritive flow to skeletal muscle

The maximal exercise capacity of patients with chronic heart failure is frequently reduced. To investigate whether this exercise intolerance is caused by inadequate nutritive flow to skeletal muscle, we compared cardiac outputs, leg blood flow, and leg metabolism during maximal bicycle exercise in seven patients with normal maximal oxygen uptake (V02) (>20 ml/min/kg; group A), eight patients with heart failure and moderately reduced maximal V02 (15 to 18 ml/min/kg; group B), and eight patients with heart failure and markedly reduced maximal V02 (<14 ml/min/kg; group C). As the severity of exercise intolerance increased from group A to group C there was a progressive decline in cardiac output and leg blood flow at any given workload accompanied by a progressive decline in maximal cardiac output (liters/min) (A, 12.4 + 1.0; B, 8.7 ± 0.9; C, 5.5 ± 0.7), maximal leg flow (liters/min) (A, 4.0 0.3; B, 2.6 + 0.4; C, 1.4 + 0.2), and maximal leg V02 (ml/min) (A, 564 + 49; B, 403 + 41; C, 213 ± 35 ml/min). All patients terminated exercise because of severe leg fatigue. At termination of exercise, all three groups exhibited similar marked levels of leg 02 extraction (%) (A, 80 ± 2; B, 83 + 3; C, 89 + 1) and high femoral-arterial lactate gradients (mg/dl) (A, 15.4 + 2.6; B, 18.3 ± 3.5; C, 19.2 ± 3.6), suggesting that exercise was limited when a critical level of muscle underperfusion was reached. These data suggest that the reduced maximal exercise capacity of patients with chronic heart failure is primarily due to impaired nutritive flow to skeletal muscle and resultant muscular fatigue. Circulation 69, No. 6, 1079-1087, 1984. THE MAXIMAL exercise capacity of patients with chronic heart failure is frequently reduced.'-1 It has recently been suggested that this exercise intolerance is primarily caused by inadequate blood flow to working skeletal muscle,3'4 since patients with heart failure have reduced cardiac outputs, early increases in lactate concentration, and augmented limb 02 extraction during exercise.3 6 However, it has yet to be directly demonstrated that perfusion of working skeletal muscle is impaired during upright maximal exercise in such patients. Accordingly, this study was undertaken to determine whether blood flow in skeletal muscle is reduced during maximal exercise in patients with chronic heart From the Cardiovascular Section, Department of Medicine, University of Pennsylvania, Philadelphia. Supported in part by NIH Clinical Research Grant 5-MO 1-RROO040. Address for correspondence: John R. Wilson, M.D., Cardiovascular Section, 943 W. Gates, Hospital of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104. Received Oct. 6, 1983; revision accepted March 8, 1984. Dr. Wilson was supported in part by a Special Investigatorship from the American Heart Association. He currently holds New Investigatorship No. HL 30665 from the NIH. Vol. 69, No. 6, June 1984 failure and to investigate whether maximal exercise capacity in such patients correlates with the adequacy of flow to skeletal muscle.