A correction procedure for the volume conductor effect in the compound action potential recorded from isolated nerve trunk.

The shape and magnitude of the compound action potential (CAP), which is the linear summation of the single fiber action potentials, depend strongly on the recording conditions. Volume conductor effect should be eliminated or corrected in order to get reliable information about the functional state of the nerve trunk. In the case of monophasic extracellular recordings, the integral of CAP recorded extracellularly tends to decrease with the distance, because the extracellular resistance between the stimulating and recording electrodes changes. To compensate for this effect, we took into account the spatial deviation of the integral of CAP versus distance and defined a spatial correcting factor, g(x). By applying g(x) to all CAPs, we get corrected CAP (cCAP) data for further evaluations. It is well known that the slope of the maximum derivative of CAP versus distance curve would be a measure of conduction velocity distribution for the fast conducting nerves in a nerve trunk. The slopes of these curves for extracellular and suction techniques on the same nerves are compared; we concluded that the difference between the two techniques was not important for the correction procedure on extracellular records.