Localized Electrical Nerve Blocking

Abstract

Localized electrical nerve blocking was investigated in computer simulation and in vivo trials for sinusoidal frequencies between 5 and 20 kHz. Computer simulations indicated that a localized transmission block of the axons could occur in each of the axon models. An approximation of nerve stimulation was derived from individual axon simulations conducted over axon diameters of 5-15 microm and electrode to axon distances of 0.25 to 2.0 mm. Examination of the membrane voltage and ionic gate potentials indicated that the block could be attributed to an elevated membrane voltage. The elevated membrane voltage could prevent conduction of action potentials through the region of the sinusoidal currents. At lower amplitudes, the sinusoidal current could stimulate the axon and generate a continuous series of action potentials. In vivo trials demonstrated that the sinusoidal frequencies of greater than 10 kHz would cause a localized block in rats. Sinusoidal frequencies below 5 kHz would lead to a reduction in muscle force that appeared to be caused by depletion of transmitter at the neuromuscular junction. As indicated by the computer models of rat nerves, the endplate depletion block occurred at a lower frequency (below 5 kHz) than the block (above 10 kHz). A partial block of the axon was demonstrated, suggesting that sinusoidal currents could be used to provide selective stimulation if they are combined with distal electrical stimulation.

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 blocking method using biphasic electrical current is more useful than uniphasic current in chronic applications, since the biphasic stimulation causes less tissue damage due to electro-chemical reactions (Agnew and McCreery, 1990). Therefore, recent studies have focused on high-frequency biphasic electrical stimulation (Bhadra and Kilgore, 2005;Bhadra et al, 2006;Tai et al, 2005a,b,c;Williamson and Andrews, 2005;Zhang et al, 2006a,b).…”

“…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. In one of these studies (Williamson and Andrews, 2005) each rat was warmed during the tests by radiant heat from above and a heating pad below.…”

“…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. In one of these studies (Williamson and Andrews, 2005) each rat was warmed during the tests by radiant heat from above and a heating pad below. A recent study (Bhadra et al, 2006) using cat pudendal nerve found that nerve block could be observed between 1 kHz and 30 kHz, but the frequency range to induce a complete block varied significantly between animals.…”