The effects of limb suction during arterial occlusion on arterial baroreflex in humans

Peripheral venous distension evokes a reflex sympathetic activation [venous distension reflex (VDR)]. Previous study showed that venous distension in a forearm with a volume infusion raised sympathetic baroreflex sensitivity (SBRS). However, the effects of venous distension on baroreflex sensitivity (BRS) in the lower limb have not been examined. We hypothesized that the venous distension in an upper or lower limb by the negative pressure would alter BRS. In 20 healthy subjects, one arm or one leg of the subjects was placed into an airtight pressure tank, although a cuff was placed proximally on the limb. A negative pressure of 100 mmHg was applied for 2 min, although the limb was arterially occluded [occlusion and suction (O&S)]. Arm- or leg-occlusions without negative pressure were performed for 2 min as control trials. Beat-by-beat blood pressure (BP), heart rate, and muscle sympathetic nerve activity (MSNA) were recorded. SBRS and the cardiovagal BRS (CBRS) were calculated. BP and MSNA were significantly increased by arm-O&S and leg-O&S (all, P < 0.05), although limb occlusion alone did not raise MSNA. Arm-O&S and leg-O&S significantly raised SBRS and rightward shifted the midpoints of the SBRS curve (T50) (all, P < 0.05). Leg-occlusion did not alter SBRS. None of the interventions altered CBRS. The results suggest that venous distension in either a forearm or a leg induces similar effects on BRS. The increased SBRS slope and rightward shift of the midpoint may contribute to heightened sympathetic activity observed during venous distension.