Effects of spinal cord compression on repetitive impulse conduction of the ascending fibers of the dorsal column.

The effects of spinal cord compression on conduction of compound action potentials (CAPs) in the dorsal column fibers at various stimulus frequencies were analysed in pentobarbital anesthetised cats. The L 6 posterior root was given 1 to 500 Hz stimuli, and the CAPs were recorded from the L 2 posterior column. The 100th CAP was recorded at 100, 200 and 500 Hz. The L 4 cord segment was compressed by stepped increments (0.5 mm/5 min.) with a plastic plate (4 x 10 mm) until the responses at 1 Hz disappeared, then the compression was released. Before compression, each CAP at all frequencies showed almost uniform amplitudes and latencies. During compression, the CAPs were not altered significantly at any frequency until the spinal cord was compressed 2.5-4.0 mm. Further compression produced a progressive decrease in amplitude and increase in latency of the CAPs. At 500 Hz, however, the conduction block (amplitude loss, latency increase) was much severer than that produced at lower frequencies. After release of compression, the CAPs at all frequencies recovered progressively, and became almost stable after about 1 hour. The recovery rate of amplitude was only about 30% compared to the amplitude before compression at 500 Hz, and about 50% at 1 and 200 Hz. However, the recovery rate of amplitude at 100 Hz (65%) exceeded those at 1 and 200 Hz. To observe the difference in recovery rates among them, all the trains of CAPs were analyzed. Before compression, the amplitudes were almost uniform at stimulus frequencies as high as 500 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)