A reversible electrical block of the pudendal nerves may provide a valuable method for restoration of urinary voiding in individuals with bladder-sphincter dyssynergia. This study quantified the stimulus parameters and effectiveness of high frequency (HFAC) sinusoidal waveforms on the pudendal nerves to produce block of the external urethral sphincter (EUS). A proximal electrode on the pudendal nerve after its exit from the sciatic notch was used to apply low frequency stimuli to evoke EUS contractions. HFAC at frequencies from 1 to 30 kHz with amplitudes from 1 to 10 V were applied through a conforming tripolar nerve cuff electrode implanted distally. Sphincter responses were recorded with a catheter mounted micro-transducer. A fast onset and reversible motor block was obtained over this range of frequencies. The HFAC block showed three phases: a high onset response, often a period of repetitive firing and usually a steady state of complete or partial block. A complete EUS block was obtained in all animals. The block thresholds showed a linear relationship with frequency. HFAC pudendal nerve stimulation effectively produced a quickly reversible block of evoked urethral sphincter contractions. The HFAC pudendal block could be a valuable tool in the rehabilitation of bladder-sphincter dyssynergia.

Many medical conditions are characterized by undesired or pathological peripheral neurological activity. The local delivery of high-frequency alternating currents (HFAC) has been shown to be a fast acting and quickly reversible method of blocking neural conduction and may provide a treatment alternative for eliminating pathological neural activity in these conditions. This work represents the first formal study of electrode design for high-frequency nerve block, and demonstrates that the interpolar separation distance for a bipolar electrode influences the current amplitudes required to achieve conduction block in both computer simulations and mammalian whole nerve experiments. The minimal current required to achieve block is also dependent on the diameter of the fibers being blocked and the electrode–fiber distance. Single fiber simulations suggest that minimizing the block threshold can be achieved by maximizing both the bipolar activating function (by adjusting the bipolar electrode contact separation distance) and a synergistic addition of membrane sodium currents generated by each of the two bipolar electrode contacts. For a rat sciatic nerve, 1.0–2.0 mm represented the optimal interpolar distance for minimizing current delivery.

These results demonstrate that bilateral HFAC block of the PN can produce effective voiding. Neural prostheses using this approach may provide an alternative method for producing micturition for people with spinal cord injury.

In this chapter we focus on technology to activate electrically peripheral motor nerves. Two important concepts are stressed; 1) the closer the electrode is to the target tissue the easier it is to isolate the applied electric field to a smaller region and 2) the affect of the applied electric field is, generally speaking, always the greatest on the largest myelinated axons experiencing the applied electric field.. These concepts are applicable to other neural systems. Motor nerves can be activated through electrodes placed on the surface of the skin, on the surface of the muscle, in the muscle, on the motor nerve or in the motor nerve. All electrodes must satisfy the requirements of material compatibility, mechanical compatibility and the ability to transfer the required electrical charges without tissue or material deterioration. The choice of electrode materials and geometric design are determined by these factors and by the intended location on the nerve or muscle. Specific designs, tissue reactions and applications are described herein. Electrodes placed on muscles produce single muscle activation. Nerve electrodes can have the advantage of activating multiple muscles. Selective stimulation of peripheral nerve fibers for effecting specific muscle activation or specific motor function is discussed in the section on nerve electrodes.