Application Study Of Laser Irradiation In Reducing Nerve Injury Induced By High Frequency Electrical Stimulation

Nerve conduction block based on high frequency biphasic (HFB)(kHz) electrical currents could potentially be used to relieve muscle spasms, selectively activate nerve fibers, and improve voiding efficiency, etc, and would have great values in relevant scientific researches and clinical applications. However, safety problem of this technique has become one of the key issues while implementing nerve conduction block efficaciously. Compared with the previous electrophysiologic study, conduction velocity distribution (CVD) could provide more detailed information about the state of nerve fibers, thus giving more explicit evidence for test of nerve conductibility. This study implemented the algorithm of calculating CVD based on deconvolution, and verified and analyzed it both in a model simulation and with the in vitro experimental data. This study explored the effects of HFB electrical currents on nerve conductibility by analyzing the differences between the CVDs before and following HFB elctrical stimulation (differential CVD, dCVD). Also, this study proposed a method of utilizing laser irradiation to optimize nerve conduction block by HFB electrical stimulation according to our previously obtained research results and potential nerve injury mechanism, to reduce the electrical stimulation induced nerve injury.First, this study investigated nerve injuries induced by HFB electrical currents stimulation with different parameters (amplitudes, frequencies and durations). High frequency current amplitude varied within the range of0.125-8times blocking threshold. With increasing of HFB current amplitudes, nerve injuring rates (IR) were observed to increase at first and then decrease, and then increase eventually. During the first phase of IR becoming increased, the blocking rates (BR) changed linearly accordingly. When HFB electrical current amplitude was at the blocking threshold, IR reached its local maximum; while as HFB amplitudes continued to increase (until at about2.25times blocking threshold), IR decreased gradually until its local minimum; further increasing HFB amplitudes would resulted in continuously increased IR. At HFB amplitudes large enough, nerve would be damaged completely. Following experiments performed nerve stimulation with HFB electrical currents of different frequencies (1kHz,2.5kHz,5kHz, and10kHz) while maintaining balanced anodal and cathodal phases. The result showed that nerve injury became less with higher HFB current frequencies. In experiments employing various HFB electrical stimulation durations, longer durations of HFB stimulation caused more severe nerve damage and slower recovering speed.This study also explored the application of laser irradiation in reducing nerve injuries induced by HFB electrical current stimulus. It was found that laser irradiation with a certain parameters successfully relieved nerve injuries and promoted neural recovering speeds after injury occurred. The statistical results showed that effecting rate (ER) of laser irradiation in reducing nerve injuries was significant (P<0.0001); the effecting rates of laser irradiation were depending upon its parameters. Laser irradiation of650nm was observed to be superior to850nm in promoting neural recovery speeds, and the corresponding ratio of averaged ER was1.76. Effectiveness of laser irradiation of different powers exhibited phase dependent during neural60s post stimulus recovering. Laser irradiation with relative low power acted with shorter latency and longer sustained periods, while laser irradiation of relative high power exhibited relatively apparent delay to become effective. In this study, laser irradiation with650nm wavelength and50mW power exhibited significant performance.This study performed data acquisition and analysis on isolated bull frog’s sciatic nerves. The results displayed that, nerve injuries were introduced while employing HFB electrical current to implement conduction block; to reduce the nerve injuries, optimized parameters (2.25times blocking threshold amplitudes, higher frequency, and shorter duration) may exist for HFB electrical currents. Also, laser irradiation with650nm wavelength and50mW power could significantly decrease the nerve injuries induced by HFB electrical current. This study also discussed the probable mechanisms underlying nerve injury induced by HFB electrical current and reduces of nerve injury by laser irradiation.This study demonstrated that laser irradiation could be used as an auxiliary method to relieve nerve injuries induced by HFB electrical current. This study results also provided some thoughts for implementing safe nerve conduction block by HFB electrical current stimulation.