Spinal cord responses to peripheral nerve stimulation in man.

Summated spinal evoked responses were recorded with surface electrodes in 11 normal subjects. Bipolar recordings were obtained from electrode pairs at the L4-L2 spinous process level and T12-T10 spinous process level via peroneal nerve stimulation at the popliteal fossa. Responses were recorded with a TECA-4 electromyograph machine interfaced with a Nicolet 1070 series signal averager. The stimulus rate was controlled by a gated circuit that avoids simultaneous recording of the volume conducted electrocardiogram signal. Bilateral recordings were obtained to compare symmetries of the evoked responses, and H-reflexes were performed with simultaneous recording of the spinal evoked responses. The spinal responses were analyzed with respect to latency, duration, amplitude, waveform and conduction velocity. Symmetries of the bilateral responses were demonstrated by the student's t statistic and the correlation coefficient. When the peroneal nerve was stimulated at the lateral border of the popliteal fossa and the response recorded at the L4-L2 spinous process levels, the mean and standard deviation of the latency and conduction velocity of the fastest afferent fibers were 9.09 +/- 0.75 msec and 67.8 +/- 4.70 m/sec, respectively. The corresponding values at the T12-T10 spinous process level were 9.83 +/- 0.74 msec and 70.64 +/- 4.95 m/sec respectively.