Visualization of temporal increase in compound nerve action magnetic fields in the human median nerve during ischemia

We studied the variation in the human median nerve activity during ischemia by measuring compound nerve action magnetic fields (CAFs). Temporal increases in the CAF during ischemia were successfully visualized on isofield contour maps. Intense paresthesias were induced after 29 ± 5 s (mean ± SD) of ischemia, which consistently reached a maximum after 4 min 55 ± 12 s. The variations in CAFs were consistent with changes in sensory perception. The hyperexcitability in large myelinated axons can be visualized as temporary increases in CAF. These results are the first to demonstrate the efficacy of magnetic-recording techniques, which allow monitoring of changes in neural activity.