Evaluation of Reversibility of Cerebral Infarction by Somatosensory Evoked Potentials in Experimental Focal Cerebral Ischemia

Park, Chun Kun; Baik, Won Hyun; Kim, Young Bae; Kang, Joon Ki; Song, Jin Un; Choi, Chang Rak

Abstract

Somatosensory evoked potentials(SSEP's) are commonly employed to monitor cerebral and spinal cord function in patients with various lesions in the nervous system. In this study, we evaluated SSEP's as a means of measuring not only neurophysiological function but also the alteration of blood folw in the territory of cerebral ischemia. We examined SSEP's and regional cerebral blood flow(rCBF) in the bilateral suprasy1vian gyri following unilateral middle cerebral artery(MCA) occlusion in 15 cats(Group II). The duration of arterial occlusion was 30 minutes followed by 1 hour of recirculation. Five additional cats served as sham-operated groups(Group I). The animals in Group II were divided into 2 subgroups according to the change of the observed rCBF in the ipsilateral hemisphere. Immediately after MCA occlusion, rCBF decreased from around 50 to 14mg/100g/min. Decreased rCBF was remained below 20ml/100g/min throughout the ischemic period in 6 cats(Group IIb), and in the remaining 9 cats, the decreased rCBF was increasing during ischemia although the blood flow was subnormal(Group IIa). The recovery of rCBF during recirculation was faster in Group IIa than in Group IIb. In Group IIa and IIb, there was a significant slowing of the interpeak latency between dorsal column nuclei(Fz) and the major negative deflection(MN) (P<0.05) in the ipsilateral hemisphere and a precipitous decrease in the amplitude of the ipsilateral P1-MN complex immediately after occlusion(P<0.05). In Group IIb the suppressed SSEP's did not show any recovery during ischemia, and recovered late during recirculation. In Group IIa the suppressed SSEP's tended to recover during recirculation. In Group IIa the suppressed SSEP's tended to recover during ischemia and recovered early during recirculation. SSEP's were not completely abolished throughout the experiment in any experimental grup. The relationship between the changes in rCBF and amplitude of SSEP's in the ipsilateral hemisphere was significant(r=0.943, P<0.05) during occlusion of the middle cerebral artery in Group IIa. However there was not any other relationship in the other groups or among other wave components. These results indicate that the suppression of SSEP's and their failure to recover during focal cerebral ischemia correlate with the lack of collateral circulation. Furthermore, SSEP's can be useful means to evaluate the reversibility of cerebral ischemia, which may be decided by existence of collateral circulation. And it appers that the time threshold for abolition of SSEP's is more than 30 minutes in focal cerebral ischemia in the cat.