Effect of sympathectomy on spinal blood flow autoregulation and posttraumatic ischemia.

Abstract

✓ The hypothesis that the paravertebral sympathetic ganglia play a role in spinal blood flow regulation was tested in cats. Five cats were subjected to paravertebral sympathectomy, two to combined sympathectomy-adrenalectomy, three to adrenalectomy alone, and five controls received no treatment. Laminectomy was carried out to expose the T4–10 cord, and autoregulation was tested by measuring blood flow from the lateral columns with the hydrogen clearance technique during manipulation of systemic pressure with intravenous saline infusion and nitroprusside administration. The cord was then contused at T-7 with a 400 gm-cm impact injury. Posttraumatic blood flow was recorded, and neurophysiological function was assessed with somatosensory evoked potential (SEP) monitoring. Before injury, blood flow in the untreated (control) group had no consistent relationship with mean systemic pressure over the range 80 to 160 mm Hg. In contrast, in all cats with paravertebral sympathectomy, whether accompanied by adrenalectomy or not, blood flows increased with systemic pressure (correlation coefficient 0.86, p < 0.01). After injury, the control and adrenalectomized cats showed blood flow decreases of > 60% to 4 to 6 ml/100 gm/min (p < 0.01) by 2 to 3 hours. However, cats with paravertebral sympathectomy maintained blood flow above 9 ml/100 gm/min for up to 3 hours after injury. All the sympathectomized cats recovered their SEP by the 3rd hour after injury, compared with none of the controls. Thus, in the absence of the paravertebral sympathetic ganglia, spinal blood flow autoregulation was impaired and the typical posttraumatic loss in blood flow did not occur. The sympathectomy also protected the spinal cords from the neurophysiological loss usually seen in 400 gm-cm injury. The data suggest the need for caution in using acetylcholine blocking agents to paralyze animals in experimental spinal injury, since these agents alter sympathetic activity and may influence the injury process. The spinal cord is an excellent model in which to investigate sympathetic regulation of central nervous system blood flow.