Influence of radiant exposure and repetition rate in infrared neural stimulation with near-infrared lasers
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In this study, we combine heat diffusion equation and modified Hodgkin-Huxley axonal model to investigate how an action potential is generated during infrared neural stimulation. The effects of temporal and spatial distribution of heat induced by infrared pulsed lasers on variation of electrical membrane capacitance are investigated. These variations can lead to depolarize the membrane and generate an action potential. We estimate the threshold values of laser light parameters such as energy density, pulse duration, and repetition rate are needed to trigger an action potential. In order to do it, we present an analytic solution to heat diffusion equation. Then, the analytic results are verified by experimental results. Furthermore, the modified Hodgkin-Huxley axonal model is applied to simulate the generation of action potential during infrared neural stimulation by taking into account the temperature dependence of electrical membrane capacitance. Results show that the threshold temperature increase induced by a train infrared pulse laser can be smaller if repetition rate is higher. These results also indicate that temperature rise time and axon diameter influence on threshold temperature increase. To verify threshold values estimated by the presented method, we use a train infrared pulsed laser (λ = 1450 nm with repetition rate of 3.8 Hz, pulse duration of 18 ms and energy density of 5 J/cm2) to optically pace an adult rat heart, and we are able to successfully pace the rat heart during an open-heart surgery. The presented method can be used to estimate threshold values of laser parameters required for generating an action potential, and it can provide an insight to how the temperature changes lead to neural stimulation during INS.
KeywordsInfrared neural stimulation Axon Heat diffusion equation Optical pacing
Also, we would like very thank from Dr. Amir Darbandi-Azar, manager of experimental laboratory at Rajaie Cardiovascular Medical and Research Center, for helping us in animal model surgery.
This study has been supported by grant number D/1687/600 from Shahid Beheshti University.
Compliance with ethical standards
This experimental study (including animal study) was approved by the ethic committee of Rajaie Cardiovascular Medical and Research Center, Iran.
Conflict of interest
The authors declare that they have no conflict of interest.
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