[Study on prevention of paraplegia during occlusion blockade of the thoracic aorta--examination of the evoked potential in the motor nerve induced by stimulation of the motor area of cerebral cortex].

In an attempt to trace the motor neurons in the descending tract of the motor system of the spinal cord and anterior horn, we have succeeded in inducing a potential in the peripheral motor nerve (evoked motor nerve action potential: EMNAP) by stimulating the motor area of the cerebral cortex in dogs, we have examined the characteristics of this potential. Besides the EMNAP, we have induced the conventional somatosensory evoked potential (SSEP) and evoked spinal cord potential (ESCP) during spinal ischemia. These are compared with each other, with theoretical predictions and with pathological findings. EMNAP possessed a biphasic negative potential (N1, N2) and subsequent multiphasic potential (N3+n) during the latency 10-18 msec. The stimulation threshold of EMNAP in the lower limbs was the lowest near the longitudinal fissure in the anterior part of the cerebral crucial groove. The amplitude of N2 and N3+n of EMNAP decreased under the condition of frequent stimulation. N2 and N3+n did not disappear after the dorsal root was severed. When the three potentials of EMNAP, SSEP, and ESCP were simultaneously induced, the left subclavian artery was occluded, the descending aorta was partially occluded immediately under the bifurcation of this artery, and the pressure of the partially occluded periphery was gradually reduced, EMNAP alone disappeared at 45.2 +/- 6.2 mmHg. Although ESCP and SSEP did not disappear even when partial occluding was continued for 90 minutes under this condition, histopathological findings obtained by formalin perfusion fixation showed ischemic disorder of the anterior horn cells when compared with the normal group fixed in the same way. EMNAP was considered to be induced through the alpha-motoneuron in the anterior horn of the spinal cord, and disappeared under the critical ischemia in which ESCP and SSEP do not disappear. Disorder of the anterior horn cells were also observed histopathologically. Direct monitoring of the alpha-motoneuron in the anterior horn, which is most susceptible to disorders, seems appropriate as a method for preventing paraplegia. EMNAP may be useful for monitoring motor function of the spinal cord not only during chest surgery but also for other types of diagnosis and treatment.