Nerve conduction block utilising high-frequency alternating current

Abstract

High-frequency alternating current (AC) waveforms have been shown to produce a quickly reversible nerve block in animal models, but the parameters and mechanism of this block are not well understood. A frog sciatic nerve/gastrocnemius muscle preparation was used to examine the parameters for nerve conduction block in vivo, and a computer simulation of the nerve membrane was used to identify the mechanism for block. The results indicated that a 100% block of motor activity can be accomplished with a variety of waveform parameters, including sinusoidal and rectangular waveforms at frequencies from 2 kHz to 20 kHz. A complete and reversible block was achieved in 34 out of 34 nerve preparations tested. The most efficient waveform for conduction block was a 3-5 kHz constant-current biphasic sinusoid, where block could be achieved with stimulus levels as low as 0.01 microCphase(-1). It was demonstrated that the block was not produced indirectly through fatigue. Computer simulation of high-frequency AC demonstrated a steady-state depolarisation of the nerve membrane, and it is hypothesised that the conduction block was due to this tonic depolarisation. The precise relationship between the steady-state depolarisation and the conduction block requires further analysis. The results of this study demonstrated that high-frequency AC can be used to produce a fast-acting, and quickly reversible nerve conduction block that may have multiple applications in the treatment of unwanted neural activity.

Influence of frequency and temperature on the mechanisms of nerve conduction block induced by high-frequency biphasic electrical current

“…11). However, previous studies using animals (Bhadra et al, 2006;Bhadra and Kilgore, 2005;Bowman and McNeal, 1986;Kilgore and Bhadra, 2004;Rehoul and Rosenblueth, 1939;Rosenblueth and Rehoul, 1939;Tai et al, 2004;2005c;Tanner, 1962;Williamson and Andrews, 2005) showed that the minimal blocking frequency varied between 1 kHz and 10 kHz in different nerves of various species using different electrode geometries. Therefore, the temperature might be one of the factors that could influence the minimal blocking frequency.…”

“…The block of spontaneous neuronal activity was always coincident with a stimulus-induced rise in extracelluar potassium concentration, suggesting that a constant potassium outflow from the neurons was induced by the stimulation. The stimulation frequency to block the hippocampal neuron is relatively low (<500 Hz) compared to the minimal stimulation frequency required to block the axonal conduction (1-10 kHz) (Bhadra et al, 2006;Bhadra and Kilgore, 2005;Bowman and McNeal, 1986;Kilgore and Bhadra, 2004;Rehoul and Rosenblueth, 1939;Rosenblueth and Rehoul, 1939;Tai et al, 2004;2005c;Tanner, 1962;Williamson and Andrews, 2005). However, this frequency discrepancy might be caused by the slow membrane dynamics of the neuron and the longer duration action potential.…”

“…A reversible nerve conduction block method will find many applications in both clinical medicine and basic neuroscience (Kilgore and Bhadra, 2004;Nashold et al, 1982;Tai et al, 2004). Understanding the biophysics and mechanisms underlying the nerve conduction block induced by high-frequency biphasic electrical current could promote its clinical application and possibly the design of new stimulation waveforms of a lower frequency to block nerve conduction.…”

“…For example, blocking peripheral nerves could help alleviate chronic pain of peripheral origin (Nashold et al, 1982) or stop unwanted motor effects such as muscle spasms and spasticity (Kilgore and Bhadra, 2004). Blocking pudendal nerve conduction in spinal cord injured people during micturition could reduce urethral sphincter contraction and urethral outlet resistance, and improve voiding efficiency (Tai et al, 2004).…”

“…Previous studies indicated that temperature might play a role in this difference in minimal blocking frequency. For example, a study using isolated frog sciatic nerve (Kilgore and Bhadra, 2004) reported that nerve block could be observed at a stimulation frequency as low as 1 kHz at room temperature. Studies using rat sciatic nerves (Bhadra and Kilgore, 2005;Williamson and Andrews, 2005) showed that consistent nerve block could be achieved at stimulation frequencies greater than 10 kHz which was presumably at body temperature near 37 °C.…”