Blood flow dynamics in heart failure

Background-Exercise intolerance in heart failure (HF) may be due to inadequ ate vasodilation, augmented vasoconstriction, and/or altered muscle metabol ic responses that lead to fatigue. Methods and Results-Vascular and metabolic responses to rhythmic forearm ex orcise were tested in 9 HF patients and 9 control subjects (CTL) during 2 p rotocols designed to examine the effect of HF on the time course of oxygen delivery versus uptake (protocol 1) and on vasoconstriction during exercise with 50 mm Hg pressure about the forearm to evoke a metaboreflex (protocol 2). In protocol 1, venous lactate and H+ were greater at 4 minutes of exer cise in HF versus CTL (P<0.05) despite similar blood flow and oxygen uptake responses. In protocol 2, mean arterial pressure increased similarly in ea ch group during ischemic exercise. In CTL, forearm blood flow and vascular conductance were similar at the end of ischemic and ambient exercise. In HF , forearm blood flow and vascular conductance were reduced during ischemic exercise compared with the ambient trial. Conclusions-Intrinsic differences in skeletal muscle metabolism, not vasodi latory dynamics, must account for the augmented glycolytic metabolic respon ses to moderate-intensity exercise in class IT and III HF. The inability to increase forearm vascular conductance during ischemic handgrip exercise, d espite a normal pressor response, suggests that enhanced vasoconstriction o f strenuously exercising skeletal muscle contributes to exertional fatigue in HF.