Effect of the polarization of tripolar electrodes on in-vivo electrical nerve block

Electrical nerve block is an emerging technique that has many potential advantages over other blocking methods and promise novel treatment opportunities for several medical problems such as acute and chronic pain, conditions associated with muscle spasticity, and heart failure. Applying DC current is one approach to produce nerve block through closing the inactivation gates of voltage gated sodium ion channels. However, DC current can cause damage both to the nerve and electrode, therefore it is crucial to use the lowest current possible for blocking. For this purpose, we used tripolar electrodes as it enables us to obtain larger contact surface area and we investigated the most effective combination of polarization. We used frog sciatic nerve/gastrocnemius preparation to examine nerve conduction block in-vivo. First we stimulated the nerve by applying AC current and recorded the contractions of the gastrocnemius muscle with the help of the force transducer. Then we applied incrementing DC current until reaching full blocking, the point where the muscle contractions stop. We, then, repeated the same procedure in different polarization combinations in order to determine the most effective configuration. Using this method, we observed (- + +) polarization, from proximal side to distal side of the sciatic nerve, enables us to block the action potential conduction most efficiently. (- - +), (- + -), (+ - +), (+ - -), (+ + -) configurations respectively give the subsequent efficient results. These findings can be explained by the direction of the blocking DC current created by the electrode. In (- + +) case, as current goes from positive to negative pole, the blocking current opposes the action potential current. This condition promotes the conduction blocking along with the inactivation of the sodium channels. In (+ + -) state, however;the direction of blocking current is same with the action potential, which makes it harder to achieve full blocking since blocking only depends on closure of inactivation gates. In conclusion, we find the (- + +) polarization is the most effective tripolar configuration for electrical nerve block with DC current. This technique can be used in future studies on nerve conduction blocking because it minimizes the blocking current, hence; nerve damage. Keywords: Direct current, Electrical nerve block, Polarization, Tripolar electrode.