Spinal Cord Stimulation and Cerebral Blood Flow: An Experimental Study

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Abstract
Spinal cord stimulation (SCS) affects peripheral, coronary and cerebral blood flow (CBF) in humans. In 1986 Meglio et al. [Appl Neurophysiol 1986;49:139–146] advocated a functional reversible sympathectomy as one of the mechanisms of SCS in man. An experimental animal model was developed to study SCS effects on CBF and to investigate the possible mechanisms. Twenty-one white New Zealand rabbits were anesthetized with FIuo-thane; spontaneous ventilation was permitted. A steady hemodynamic and metabolic state was maintained. A small cervical laminectomy was performed and an electrode (Medtronic Sigma 3483) was placed in the epidural space over the posterior spinal cord. Both common carotid arteries were exposed and external carotid arteries were ligated. In 3 animals, the cervical symapthetic trunk (CST) was exposed and wrapped with bipolar hook-stimulating electrodes. SCS was performed for 20 min with electrical square waves of 210 µs duration, 80 cycles/s, at 2/3 motor threshold itensity. CST stimulation was delivered for 1 min with the following parameters: 10 V, 10 cycles/s, 0.5 ms duration. CBF velocities of both internal carotid arteries were measured by using a CW Doppler (in all the animals) and electromagnetic flowmeter (in 2 animals), at rest, during sympathetic trunk stimulation, during SCS, during simultaneous SCS and CST stimulation. During SCS, an increase of CBF was detected in 11 rabbits (52.4%); a decrease was observed in two cases (9.5%). No change was detected in the remaining 8 animals (38%). CST stimulation induced a decrease of CBF in all animals. Electromagnetic flowmetry confirmed velocitometric findings in the 2 cases studied. In 2 rabbits showing an increase of CBF during SCS, simultaneous CST and SCS stimulation was followed by a decrease of CBF, which was significantly less than the one obtained with CST stimulation alone. In the remaining animal presenting no change of CBF during SCS, CST stimulation produced the same decrease of CBF when delivered during SCS. Our data strongly support the hypothesis that a reversible functional sympathectomy occurs during SCS.

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