Effects of waveform shape and electrode material on KiloHertz frequency alternating current block of mammalian peripheral nerve

Abstract

Objectives KiloHertz frequency alternating current waveforms produce conduction block in peripheral nerves. It is not clearly known how the waveform shape affects block outcomes, and if waveform effects are frequency dependent. We determined the effects of waveform shape using two types of electrodes. Materials and methods Acute in-vivo experiments were performed on 12 rats. Bipolar electrodes were used to electrically block motor nerve impulses in the sciatic nerve, as measured using force output from the gastrocnemius muscle. Three blocking waveforms were delivered (sinusoidal, square and triangular) at 6 frequencies (10–60 kHz). Bare platinum electrodes were compared with carbon black coated electrodes. We determined the minimum amplitude that could completely block motor nerve conduction (block threshold), and measured properties of the onset response, which is a transient period of nerve activation at the start of block. In-vivo results were compared with computational modeling conducted using the NEURON simulation environment using a nerve membrane model modified for stimulation in the kilohertz frequency range. Results For the majority of parameters, in-vivo testing and simulations showed similar results: Block thresholds increased linearly with frequency for all three waveforms. Block thresholds were significantly different between waveforms; lowest for the square waveform and highest for triangular waveform. When converted to charge per cycle, square waveforms required the maximum charge per phase, and triangular waveforms the least. Onset parameters were affected by blocking frequency but not by waveform shape. Electrode comparisons were performed only in-vivo. Electrodes with carbon black coatings gave significantly lower block thresholds and reduced onset responses across all blocking frequencies. For 10 and 20 kHz, carbon black coating significantly reduced the charge required for nerve block. Conclusions We conclude that both sinusoidal and square waveforms at frequencies of 20 kHz or higher would be optimal. Future investigation of carbon black or other high charge capacity electrodes may be useful in achieving block with lower BTs and onsets. These findings will be of importance for designing clinical nerve block systems.

Spatiotemporal parameters for energy efficient kilohertz-frequency nerve block with low onset response

“…We supported this theory by demonstrating that thresholds of non-sinusoidal waveforms were explained by the rms of the signal after lowpass filtering, and that this rms depended largely on the amplitude of the fundamental frequency component resulting from Fourier analysis. This theory explains the observation that square waveforms—with first harmonic amplitude of ~ 1.3 (4/π)—have lower block thresholds than sinusoids [ 4 , 6 ], as well as the observation that triangular waveforms—with first harmonic amplitude of ~ 0.8 (8/π 2 )—have higher block thresholds compared to sinusoids [ 6 ]. However, this theory assumed that lowpass filtering of waveforms was the sole determinant of block threshold, despite the known nonlinear axonal membrane dynamics.…”

“…Importantly, these findings were dependent on the electrode geometry: most of the monopolar and tripolar tests with composite signals showed an effect of waveform shape on block threshold and onset response, while most bipolar tests did not. This may explain why previous studies investigating waveform effects—which used only bipolar cuffs—observed waveform effects only on block threshold but not on onset response [ 4 , 6 ].…”

“…Higher frequencies had lower onset response and higher block thresholds [ 2 – 5 ]. Waveform shape had no clear effect on onset response, although block thresholds were lowest for square waves and highest for triangular waves or low duty cycle rectangular waves [ 4 – 6 ]. Inter-contact spacing and contact circumferential lengths could influence block threshold and onset response, although only bipolar cuffs parameters were considered [ 7 – 9 ].…”

“…Further, an infinite number of periodic waveforms are possible beyond the previously explored square, rectangular, and triangular waveforms; thus, the ability of alternative waveform shapes to modify KHF nerve block characteristics remains underexplored. Finally, although a number of different cuff geometries were used in prior literature (for overview tables, see [ 6 , 7 , 9 ]), those studies did not investigate the effects of the number of contacts nor, crucially, the interaction between temporal parameters (i.e., frequency, waveform shape) and electrode geometry.…”

Bioelectronic modulation of carotid sinus nerve to treat type 2 diabetes: current knowledge and future perspectives

“…These materials have been tested to evaluate the block threshold (BT) and the onset response (BR); the two main parameters involved in KHFAC. Both of them should be minimized: the block threshold can be defined as the amplitude value completely blocking the nerve conduction, while the onset response as the initial nerve activity starting after the block is imposed (Green et al, 2022). Patel et al (2018) evaluated different electrode materials among the most commonly used, without identifying any significant difference in BT and OR.…”