A novel method for characterization of peripheral nerve fiber size distributions by group delay measurements and simulated annealing optimization

The ability to determine the characteristics of peripheral nerve fiber size distributions would provide additional information to clinicians for the diagnosis of specific pathologies of the peripheral nervous system. Investigation of these conditions, using electro-diagnostic techniques, is advantageous in the sense that such techniques tend to be minimally invasive yet provide valuable diagnostic information. One of the principal electro-diagnostic tools available to the clinician is the nerve conduction velocity test. While the peripheral nerve conduction velocity test can provide useful information to the clinician regarding the viability of the nerve under study, it is a single parameter test that yields no detailed information about the characteristics of the functioning nerve fibers within the nerve trunk. In this study we present a technique based on a decomposition of the maximal compound evoked potential and subsequent determination of the group delay of the contributing nerve fibers. The fiber group delay is then utilized as an initial estimation of the nerve fiber size distribution and the concomitant temporal propagation delays of the associated single fiber evoked potentials to a reference electrode. Subsequently the estimated single fiber evoked potentials are optimized against the template maximal compound evoked potential using a simulated annealing algorithm. Simulation studies, based on deterministic single fiber action potential functions, are used to demonstrate the robustness of the proposed technique in the presence of noise associated with variations in distance between the nerve fibers and the recording electrodes between the two recording sites.