WAVE-FORM ANALYSIS OF COMPOUND NERVE ACTION-POTENTIALS - A COMPUTER-SIMULATION

A compound nerve action potential (CNAP) recorded from surface of the skin is composed of single nerve fiber action potentials propagating a t various conduction velocities (CVs). Based on this assumption, we co nstructed two CNAPs simulating those at the digit elicited by stimulat ion of the median nerve at the wrist (CNAP-Wr) and the elbow (CNAP-EI) . Distribution of the nerve fiber CVs used for the simulation was esti mated from actual recordings of 12 healthy subjects. Mean ratio of the CNAP amplitude (CNAP-Wr/CNAP-EI) was 2.2, and that of the duration wa s 0.76. First, to analyze how CV distributions affect CNAP waveforms a rtificially in our computer program, we altered mean CV or standard de viation (SD) of the estimated distribution, and reconstructed CNAPs. R esults indicated that as the mean CV was made slower, the ratio of the CNAP amplitude increased and that of the duration decreased. Similar changes of the ratios were also shown when the SD of the CV distributi on was increased without changing the mean CV. Secondly, to make const ructed CNAPs more similar to actual recordings, we added artificial no ise to the constructed waves and had 11 electromyographers read onset and peak latencies. The average of maximum CVs calculated from the ons et latencies of CNAPs-Wr was 62m/sec, and that from the latency differ ence between CNAPs-Wr and -El was 70m/sec. Both CVs were slower than t he genuine maximum (77m/sec) given to the simulation program. The mean CV calculated from latency difference of the major positive peaks of the CNAPs was 62m/sec being close to the mode (62m/sec) or mean (60m/s ec) value of the given distribution. (C) 1994 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medic ine and Rehabilitation