Modeling study of activation and propagation delays during stimulation of peripheral nerve fibers with a tripolar cuff electrode

Computer simulations were performed to investigate the timing of action potential production and propagation in nerve fibers ranging in diameter from 5 to 15 μm during stimulation with a tripolar cuff electrode. The influence of stimulus pulse amplitude and duration on size selective excitation and blocking was considered. Because the stimulus duration required to produce anodal blocking depends on the time at which the action potential arrives at the blocking anode, delays in fiber activation and action potential propagation were investigated. They were found to be dependent on fiber diameter as well as stimulus amplitude and duration. The total delay associated with events occurring at the cuff electrode could be expressed as the sum of the activation delay and the propagation delay. Simple exponential equations were proposed for calculating activation and propagation delay as functions of fiber diameter and stimulus amplitude. Estimates of delays in action potential production and propagation may be useful for the design of electrodes and selection of stimuli for producing selective blocking of nerve fibers, and also for the analysis of compound neural signals elicited by electrical stimulation