Sensory potentials and sural nerve biopsy: a model evaluation

Compound action potentials (CAPs) were recorded from the sural nerve prior to nerve biopsy in patients with various kinds of polyneuropathy. A previously developed volume conductor model for the CAP is applied to analyze the recorded CAPs in close relation with the morphological findings in the biopsy. First, the fiber diameter histograms obtained from the biopsy are used to simulate CAPs, by assuming a linear relation between fiber diameter and propagation velocity. It is concluded that the simulated CAPs deviate systematically from the recorded CAPs. Next, the assumption of a linear diameter-velocity relation is left, and the assumed fiber velocity distribution is adapted to obtain optimal model reconstructions of the recorded CAPs. It is concluded that the model is capable of reconstructing the recorded CAPs, including slow components and small polyphasic potentials in the case of severe fiber loss. It is demonstrated how the diameter histogram and the optimal velocity distribution can be combined to an empirical estimate of the diameter-velocity relation.