[Cortical somatosensory evoked potential associated with experimental chronic cord compression by epidural neoplasm in rabbits].

An experimental model of spinal cord compression was developed in rabbits by epidural neoplasms which were injected anterior to the T 13 vertebral body and grew into the spinal canal through the intervertebral foramina. With this experimental model, the neurological condition of the animals was monitored using a scale and changes of somatosensory evoked potentials (SEPs) were studied to evaluate the neurophysiological effect of experimental chronic cord compression. The animals were immobilized with pancuronium bromide and artificial respiration was maintained through a tracheostomy. SEPs were recorded by silver ball electrodes which were positioned epidurally over the somatosensory cortex through small burr holes. A subcutaneous needle placed at the nose served as a reference electrode. Right hind paw was stimulated via two percutaneous needles with 0.1 msec rectangular impulses sufficiently strong to produce motor responses, ranging from 10 to 20 volt in control rabbits. Electrical stimuli were delivered at a rate of 1 Hz. The intensity of electrical stimulation was raised up to 300 volt, when no consistent SEP was observed in the rabbit with spinal neoplasm. The SEP was summated by averaging 50 successive cortical transients with the analysis time of 200 and 500 msec. The cortical SEPs in the rabbit normally consisted of a positive-negative sequence, which we labelled P1, N1, P2, N2 and so on. Early peaks, P1 and N1, were observed constantly with average latencies of 30.1 and 53.3 msec respectively in normal rabbits. The variability of amplitudes seen even in control animals made them a less useful measure of function than latencies. Normal SEPs were preserved until the animals demonstrated moderate paraparesis.(ABSTRACT TRUNCATED AT 250 WORDS)