The role of cardiac output response in blood flow distribution during exercise in patients with chronic heart failure.

The relationship between blood flow in the working leg and cardiac output (Q) response was determined for patients with chronic heart failure. The ratio of leg blood flow (LBF) to Q (LBF/Q) at the same workload during submaximal exercise was significantly different in three groups of patients classified by peak cardiac index: it was 0.22 +/- 0.08 in the 'satisfactory' Q group vs 0.33 +/- 0.09 in the moderate Q group, and 0.38 +/- 0.08 in the poor Q group (P < 0.01) in the first stage of exercise. delta LBF/delta Q, the slope of change in leg blood flow to Q from rest to peak exercise, was significantly larger in the poor Q group than in the satisfactory Q group (P < 0.01). The intergroup arteriovenous oxygen difference (AVO2D) in organs other than the leg was large, while that in the working leg was small. Leg vascular resistance at submaximal workload was similar in the three groups, but vascular resistance in other organs was significantly higher in the poor Q group than in the satisfactory Q group (P < 0.001). These findings suggested that metabolic vasodilating stimuli in the working leg attenuated excessive vasoconstriction and caused a shift in blood flow from other organs to the working leg under conditions of severely reduced Q response.