Application of the collision technique and development of fast-recovery preamplifier for detecting conduction delicits in lumbar spinal stenosis.

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Clinically recorded lumbosacral evoked potentials after peripheral nerve stimulation are less sensitive than might be expected for a single radicular lesion. Direct nerve root stimulation, despite its potential advantage, is not practical because of an overloading stimulus artifact. A collision technique should circumvent these problems. For a single L-5 radicular lesion produced in rats by constant, localized compression, sequential changes of epidurally recorded potentials after sciatic nerve stimulation (Group 1) or direct L-5 root stimulation (Group 2) were compared to those after a combination of L-6 root and sciatic nerve stimulation (Group 3). At every step of recording, the N1 peak amplitude was significantly smaller in group 2 and 3 than in group 1, whereas there was no significant difference between group 2 and 3. Thus, the collision technique in gourp 3 achieved nearly the same diagnostic yield as the direct L5 root stimulation in group 2 by blocking the unwanted impulses transmitted via the L6 root.In clinical practice, unlike animal experiments, it is difficult to control the stimulus artifact by shielding the stimulator from the surrounding tissues and thereby reducing spread of stimulus current. To circumvent this problem, we developed a fast-recovery preamplifier. This preamplifier interposed between the recording electrodes and the amplifier allows opening the conduction path at the moment of large stimulus input and closing the path with the wane of its magnitude. The printed circuit plate of the preamplifier was made of glass epoxy because of an excellent high frequency specificity of the material. It was shielded from the outside electric noise by being doubly encased in two aluminum boxes. In addition, the electric noise occurring when the switch closes and opens was minimized by using the MCD-5221 switch.