Compound action potential reconstructions and predicted fiber diameter distributions.

Electrophysiologic and anatomic studies on cat saphenous nerve were combined with CAP modelling and computer analysis. Myelinated nerve FD histograms were compiled from transverse section photomicrographs using various estimates of diameter, primarily those based on fiber cross-section area. The FD histogram and biophysical parameters were more important in the CAP reconstruction model than the SFAP parameters. The biophysical parameters were optimized to obtain best fits between recorded and reconstructed CAPs. Finally, the inverse of the CAP reconstruction model was used to predict FD histograms from optimized biophysical parameters and recorded CAP waveforms under carefully controlled experimental conditions. The results of these studies provide an empirical basis for relating volume conducted CAPs to the anatomic and physiologic characteristics of nerve fiber bundles. More accurate histologic methods and procedures for estimating biophysical parameters are needed before this approach to the inverse problem can be pursued further. The major advantage of estimating FD distributions rather than CV distributions is that the anatomic data are truly independent reference standards for evaluating the results.