D. Michael Ackermann

Conduction Block of Peripheral Nerve Using High Frequency Alternating Currents Delivered through an Intrafascicular Electrode

Many diseases are characterized by undesired or pathological neural activity. The local delivery of high‐frequency currents has been shown to be an effective method for blocking neural conduction in peripheral nerves and may provide a therapy for these conditions. To date, all studies of high‐frequency conduction block have utilized extraneural (cuff) electrodes to achieve conduction block. In this study we show that high‐frequency conduction block is feasible using intrafascicular electrodes. Muscle Nerve, 2010

Effect of Nerve Cuff Electrode Geometry on Onset Response Firing in High-Frequency Nerve Conduction Block

The delivery of high-frequency alternating currents has been shown to produce a focal and reversible conduction block in whole nerve and is a potential therapeutic option for various diseases and disorders involving pathological or undesired neurological activity. However, delivery of high-frequency alternating current to a nerve produces a finite burst of neuronal firing, called the onset response, before the nerve is blocked. Reduction or elimination of the onset response is very important to moving this type of nerve block into clinical applications since the onset response is likely to result in undesired muscle contraction and pain. This paper describes a study of the effect of nerve cuff electrode geometry (specifically, bipolar contact separation distance), and waveform amplitude on the magnitude and duration of the onset response. Electrode geometry and waveform amplitude were both found to affect these measures. The magnitude and duration of the onset response showed a monotonic relationship with bipolar separation distance and amplitude. The duration of the onset response varied by as much as 820% on average for combinations of different electrode geometries and waveform amplitudes. Bipolar electrodes with a contact separation distance of 0.5 mm resulted in the briefest onset response on average. Furthermore, the data presented in this study provide some insight into a biophysical explanation for the onset response. These data suggest that the onset response consists of two different phases: one phase which is responsive to experimental variables such as electrode geometry and waveform amplitude, and one which is not and appears to be inherent to the transition to the blocked state. This study has implications for nerve block electrode and stimulation parameter selection for clinical therapy systems and basic neurophysiology studies.

Electrical conduction block in large nerves: high-frequency current delivery in the nonhuman primate.

Recent studies have made significant progress toward the clinical implementation of high‐frequency conduction block (HFB) of peripheral nerves. However, these studies were performed in small nerves, and questions remain regarding the nature of HFB in large‐diameter nerves. This study in nonhuman primates shows reliable conduction block in large‐diameter nerves (up to 4.1 mm) with relatively low‐threshold current amplitude and only moderate nerve discharge prior to the onset of block. Muscle Nerve, 2011

Combined direct current and high frequency nerve block for elimination of the onset response

Nerve conduction in peripheral mammalian nerves can be blocked by high frequency alternating current (HFAC) waveforms. However, one of the disadvantages of HFAC block is that it produces an intense burst of firing in the nerve when the HFAC is first turned on. This is a significant obstacle to the clinical implementation of HFAC block. In this paper we present a method to produce HFAC block without the onset response, using a combination of direct current (DC) and HFAC block. This method was experimentally evaluated in an in-vivo mammalian model. Successful no-onset HFAC block was obtained using a DC block of 200 µA and an HFAC block of 30 kHz at 10 Vp-p. This may allow HFAC block to be used in clinical applications for pain relief.

Electrode design for high frequency block: Effect of bipolar separation on block thresholds and the onset response

The delivery of high frequency alternating currents (HFAC) to peripheral nerves has been shown to produce a rapid and reversible nerve conduction block at the site of the electrode, and holds therapeutic promise for diseases associated with undesired or pathological neural activity. It has been known since 1939 that the configuration of an electrode used for nerve block can impact the quality of the block, but to date no formal study of the impact of electrode design on high frequency nerve block has been performed. Using a mammalian small animal model, it is demonstrated that the contact separation distance for a bipolar nerve cuff electrode can impact two important factors related to high frequency nerve block: the amplitude of HFAC required to block the nerve (block threshold), and the degree to which the transient “onset response” which always occurs when HFAC is first applied to peripheral nerves, is present. This study suggests that a bipolar electrode with a separation distance of 1.0 mm minimizes current delivery while producing high frequency block with a minimal onset response in the rat sciatic nerve.

Design of a high speed transcutaneous optical telemetry link.

In some neural prosthetic applications there is a need for high bandwidth communication between an implanted device and an external device. For example, transmitting 100 channels of neural waveform data for a cortical prosthetic control system may require up to 40 Mbps for a 100 channel array. Due to the high bandwidth required and its relative immunity from interference, optical telemetry is the most realistic method for achieving a clinically robust transcutaneous communication system capable of achieving these data rates. It is proposed that a transcutaneous optical telemetry link design can be optimized to system level design parameters (power consumption, implant location, etc.) by having a quantified understanding of the different link level design parameters (optical power, lens size, tissue effects, transmitter-receiver alignment, etc.) and an understanding as to how those parameters interact, and will allow for a design guided by an a priori assessment of these parameters. Some of these design factors and their interactions are identified and described. One of these parameters, the tissue optical spatial impulse response is measured empirically for several porcine dermal tissue configurations, and its implications for device design tradeoffs are discussed

Reduction of the onset response in high frequency nerve block with amplitude ramps from non-zero amplitudes

High frequency alternating current (HFAC) waveforms reversibly block conduction in mammalian peripheral nerves. The initiation of the HFAC produces an onset response in the nerve before complete block occurs. An amplitude ramp, starting from zero amplitude, is ineffective in eliminating this onset response. In fact, it makes the onset worse. We postulated that initiating the ramp from a non-zero amplitude would produce a different effect on the onset. This was tested in an in-vivo rat sciatic nerve model. HFAC was applied at supra block threshold amplitudes and then reduced to a lower amplitude (0%, 25% 50 %, 75% and 90% of the suprathreshold amplitude). The amplitude was then increased again to the original supra block threshold amplitude. This normally produces a second period of onset response if increased as a step. However, an amplitude ramp was successful in eliminating this onset. This was always possible for the ramps up from 50%, 75 % and 90% block threshold amplitude, but never from 0% or 25% of the block threshold amplitude. This maneuver can potentially be used to maintain complete nerve block, transition to partial block and then resume complete block without initiating another onset.

Implantable Neural Stimulators

Publisher Summary This chapter focuses on the implantable neural stimulators, which are used by the clinicians to execute the various and diverse neuromodulation therapies. Implantable neurostimulators have their technical roots in cardiac pacing, and their primary function is to activate or inhibit the nervous system to augment, improve or replace function lost to a neurological disease or disorder. The neurostimulator generates appropriate electric fields within neural tissues through the application of prescribed currents or voltages to electrodes in contact with the neural tissue. The physical form of the neurostimulator is designed based on constraints, requirements, and ideals from both the engineering and clinical realms. The device design must balance the need for a biocompatible, hermetically sealed, and mechanically robust package that is capable of housing all of the stimulator components and meeting the clinical demands for minimal invasiveness, conformation to anatomy, facilitation of surgical installment, and device cosmesis. The power is supplied by a source that is either internal to the implantable device or external to the body. Internal power sources are batteries whereas the external power sources include inductive radio-frequency (RF) coupling. Some of the other power sources include the use of nuclear powered cells and systems that harvest power from the body. Inductive and RF antenna-coupled links are the most commonly used means of transferring data to and from an implanted device, which are appropriate for low to moderate data rate applications.

Counted cycles method to quantify the onset response in high-frequency peripheral nerve block

The clinical use of high frequency alternating current (HFAC) to block nerve conduction in peripheral nerves is limited due to the large volley of nerve activity generated at the initiation of HFAC. This “onset response” must be characterized in order to determine if it is possible to eliminate it. In this study, preliminary experiments were conducted in an in-vivo animal model using counted cycles of HFAC to investigate and quantify the onset response. Using this method, it is possible to show quantitatively that the onset response has two phases with distinct characteristics. Eliminating the onset response is likely to require addressing each phase independently. It was also possible to show that HFAC establishes a complete block of nerve activity in 50–100 ms.