Sympathetic Reflex Control of Subcutaneous Blood Flow in Tetraplegic Man during Postural Changes

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Abstract
1. The effect of head-up tilt upon subcutaneous blood flow in the distal arm and leg was studied in 12 patients with complete traumatic spinal cord transection at the cervical level. 2. Blood flow was measured by the local 133Xe washout technique. 3. Leg lowering induced a 47% decrease in blood flow in the distal leg. During head-up tilt (45°) blood flow in the leg decreased by 48%. In the arm remaining at heart level blood flow decreased by 37% during tilt and this vasoconstriction could be prevented by nervous blockade with lignocaine injected subcutaneously 5 cm proximally to the labelled area. Leg blood flow was unaltered by proximal blockade but could be blocked by local infiltration in the labelled area with lignocaine in low doses. 4. Head-up tilt of tetraplegic patients induced vasoconstriction in the subcutaneous tissue of the forearm, which could be prevented by proximal blockade. Thus the vasoconstriction could be due to a spinal sympathetic reflex mechanism. This as well as local mechanisms including the veno-arteriolar reflex may play a role in recovery of arterial blood pressure during head-up tilt in the tetraplegic patient.