The Forward Problem in Electroneurography I: A Generalized Volume Conductor Model

We describe a generalized volume conductor model for the compound action potential (CAP) of a peripheral nerve in situ. The extracellular single fiber action potentials (SFAP´s), the constituting elements of the CAP, are expressed in terms of the intracellular action potentials and of the effect of volume conduction using a convolution formulation. The model incorporates variations in the intracellular action potential duration over the fiber population. Volume conduction is described in a generalized formalism for a class of cylinder symmetrical configurations. The CAP is finally formulated as a linear sumation of the SFAP´s, with incorporation of the distribution of propagaytion velocities over the fiber population. We show that the final expressions for SFAP´s and CAP can be given in a mathematically transparent form, which gives a clear insight into the mechanisms involved in the genesis of different potential waveshapes.