Fig. 6.

Relationship between hindlimb blood flow and HR during mild and moderate exercise (Ex) before (solid lines) and after (dashed lines) induction of heart failure. Hindlimb blood flow was reduced via transient vascular occlusion of the terminal aorta. During mild exercise, a clear threshold exists for metaboreflex activation both before and after induction of heart failure as hindlimb blood flow must be reduced below threshold from the free flow (no occlusion) levels before tachycardia occurs. However, during moderate exercise in heart failure, the free flow level of hindlimb blood flow (indicated by vertical dashed lines) is now below the threshold seen in control experiments, indicating that the reflex is now tonically active [modified from Hammond et al. (35)].