Effects of compression and ischemia on spinal cord evoked potentials.

Ascending and descending spinal cord potentials were recorded during conduction block produced by compression and ischemia to the spinal cord of cats. Dorsally and ventrally applied compression produced proportional changes in both ascending and descending potentials. Results for induced ischemia were much more variable. Although both systems were significantly affected by extreme ischemia, loss of descending activity was not always accompanied by a loss of ascending activity for lesser ischemic insults. This finding was attributed to the variability of the spinal cord vascular supply. It is concluded that monitoring of ascending evoked activity (e.g., somatosensory evoked potentials) would reflect changes in descending spinal cord conduction for compressive and higher magnitude ischemic spinal cord insult. It is also pointed out that lesser degrees of spinal cord ischemia can produce dysfunction in descending systems which may not be detected by monitoring of somatosensory evoked potentials. The significance of the observed relationship between ascending spinal cord and cortical evoked potentials is also discussed.