A Comparison of Regional Blood Flow and Oxygen Utilization During Dynamic Forearm Exercise in Normal Subjects and Patients with Congestive Heart Failure

Patients with severe congestive heart failure (CHF) have been found to have a diminished response to the metabolic arteriolar dilator stimulus of ischemia. In order to evaluate a more physiologic stimulus and the possible metabolic consequences of this vascular abnormality, 22 normal subjects (N) and seven patients with severe CHF performed rhythmic forearm exercise by squeezing a rubber bulb to 25, 50, or 100 mm Hg for 5 sec, four times/min, for 5 min. During the last half of the 10 sec relaxation phases, forearm blood flow (FBF) was measured plethysmographically. Not only was FBF reduced at rest in CHF (CHF:2.00 ± 0.31; N: 3.10 ± 0.27 ml/min·100 ml, P < 0.02) but it was reduced at each level of exercise as well (CHF: 4.05 ± 0.71, 5.57 ± 0.71, 6.68 ± 3.09; N: 7.10 ± 0.76, 11.15 ± 1.24, 20.32 ± 1.93 ml/min·100 ml, P < 0.01). Forearm oxygen extraction, calculated from brachial venous and systemic arterial blood, was consistently increased in CHF and was sufficient to maintain a normal forearm oxygen consumption at rest (CHF: 0.14 ± 0.04; N: 0.12 ± 0.01 ml O 2 /min · 100 ml, P < 0.5). During exercise the calculated index of oxygen consumption was reduced at all levels of exercise (CHF: 0.30 ± 0.04, 0.48 ± 0.09, 0.54 ± 0.14; N: 0.51 ± 0.05, 0.89 ± 0.08, 1.63 ± 0.13 ml O 2 /min · 100 ml, P < 0.01). These differences persisted despite alpha-adrenergic blockade with phentolamine and suppression of skin flow in N by epinephrine iontophoresis. Therefore, at comparable levels of dynamic forearm exercise patients with CHF have an inadequate arteriolar dilation and their augmented oxygen extraction is not sufficient to prevent them from shifting more completely to anaerobic metabolism.