Muscular blood flow response to submaximal leg exercise in normal subjects and in patients with heart failure

Blood flow to working skeletal muscle is usually reduced during exercise in patients with congestive heart failure. An intrinsic impairment of skeletal muscle vasodilatory capacity has been suspected as a mechanism of this muscle underperfusion during maximal exercise, but its role during submaximal exercise remains unclear. Therefore, we studied by transcutaneous Doppler ultrasonography the arterial blood flow in the common femoral artery at rest and during a submaximal bicycle exercise in 12 normal subjects and in 30 patients with heart failure. Leg blood flow was lower in patients than in control subjects at rest [0.29 +/- 0.14 (SD) vs. 0.45 +/- 0.14 l/min, P < 0.01], at absolute powers and at the same relative power (2.17 +/- 1.06 vs. 4.39 +/- 1.4 l/min, P < 0.001). Because mean arterial pressure was maintained, leg vascular resistance was higher in patients than in control subjects at rest (407 +/- 187 vs. 247 +/- 71 mmHg.l-1.min, P < 0.01) and at the same relative power (73 +/- 49 vs. 31 +/- 13 mmHg.l-1.min, P < 0.01) but not at absolute powers. Although the magnitude of increase in leg blood flow corrected for power was similar in both groups (31 +/- 10 vs. 34 +/- 10 ml.min-1.W-1), the magnitude of decrease of leg vascular resistance corrected for power was higher in patients than in control subjects (5.9 +/- 3.3 vs. 1.9 +/- 0.94 mmHg.l-1.min.W-1, P < 0.001). These results suggest that the ability of skeletal muscle vascular resistance to decrease is not impaired and that intrinsic vascular abnormalities do not limit vasodilator response to submaximal exercise in patients with heart failure.