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George E. Carvell, PhD, PT   University of Pittsburgh
PERIPHERAL NERVE CONDUCTION:Sensory Nerve Conduction Block
Sensory Nerve Conduction Block
Nerve conduction block can result from axonal degeneration, severe demyelination, or a transient physiologic conduction block due to nerve compression (neuropraxia). If all fibers are involved no evoked waveforms will result from nerve stimulation anywhere proximal to the lesion. If partial conduction block occurs, the waveforms have reduced amplitude but normal conduction time (surviving axons conducting at normal velocity). Partial conduction block may be found with a partial (1st, 2nd or 3rd degree) nerve injury or with certain peripheral neuropathies. Waveforms have short durations, and low amplitude (averaging required).
GMOMM  2001
  Antidromic Sensory Nerve Conduction Studies record responses from digital nerves or superficial cutaneous nerves. Stimuli are delivered at several locations along the course of the nerve. Brief (0.1 msec monophasic DC pulses at 1/sec) but strong (supramaximal strength) stimuli are used. Responses are recorded as simulated digital oscilloscope traces in these animations. A ground electrode is placed over non-contractile tissue (not shown). The example shown here is antidromic sensory nerve conduction for the Median Nerve. Ring recording electrodes are placed around the proximal and middle phalanges of the index finger. Proximal and distal stimuli & stimulation sites are the same as for median motor nerve conduction. Sensory compound action potentials are small (mV range) and high amplifier gain is required. If peripheral nerve disease is present the signal to noise ratio may require waveform averaging to reveal tiny responses buried within the background noise (note calibration scale on scope).