Limb position affects magnitude of reactive hyperemia

Abstract

Several studies have reported a greater blood flow response to contractions when the limb is in the dependent compared to the independent position. These results have been interpreted as evidence for a skeletal muscle pump contribution to exercise hyperemia. An alternative explanation is that there are positional differences in myogenic tone and that a given stimulus has a greater effect when the myogenic tone is enhanced. We hypothesized that the magnitude of reactive hyperemia would be greater with the limb in the dependent position. Ten healthy volunteers of both sexes participated in the study. Brachial blood flow was measured by Doppler ultrasound and blood pressure measured by Finapres. The subjects lay supine with one arm supported in two different positions – above and below the heart. Reactive hyperemia was produced by occlusion of the arterial inflow with a blood pressure cuff inflated to 200mmHg for varying durations − 0.5 min, 1 min, 2 min, 5 min in randomized order.The peak increases in blood flow were 77±11,178±24, 291±25, 398±33 ml/min above the heart and 96±19, 279±62, 550±60, and 711±69 ml/min below the heart (p<0.01). These results show that a standard stimulus (reactive hyperemia) elicits different responses depending on limb position. Furthermore, the results suggest the need to reevaluate studies employing positional changes to examine muscle pump influences on exercise hyperemia.