Zhao Yajun, Zheng Shuang, Beitel-White Natalie, Liu Hongmei, Yao Chenguo, Davalos Rafael V
Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA, United States.
Bioelectromechanical Systems Laboratory, Virginia Tech, Blacksburg, VA, United States.
Front Bioeng Biotechnol. 2020 May 19;8:396. doi: 10.3389/fbioe.2020.00396. eCollection 2020.
Pulsed electric field treatment modalities typically utilize multiple pulses to permeabilize biological tissue. This electroporation process induces conductivity changes in the tissue, which are indicative of the extent of electroporation. In this study, we characterized the electroporation-induced conductivity changes using all treatment pulses instead of solely the first pulse as in conventional conductivity models. Rabbit liver tissue was employed to study the tissue conductivity changes caused by multiple, 100 μs pulses delivered through flat plate electrodes. Voltage and current data were recorded during treatment and used to calculate the tissue conductivity during the entire pulsing process. Temperature data were also recorded to quantify the contribution of Joule heating to the conductivity according to the tissue temperature coefficient. By fitting all these data to a modified Heaviside function, where the two turning points ( , ) and the increase factor () are the main parameters, we calculated the conductivity as a function of the electric field (), where the parameters of the Heaviside function ( and ) were functions of pulse number (). With the resulting multi-factor conductivity model, a numerical electroporation simulation can predict the electrical current for multiple pulses more accurately than existing conductivity models. Moreover, the saturating behavior caused by electroporation can be explained by the saturation trends of the increase factor in this model. The conductivity change induced by electroporation has a significant increase at about the first 30 pulses, then tends to saturate at 0.465 S/m. The proposed conductivity model can simulate the electroporation process more accurately than the conventional conductivity model. The electric field distribution computed using this model is essential for treatment planning in biomedical applications utilizing multiple pulsed electric fields, and the method proposed here, relating the pulse number to the conductivity through the variables in the Heaviside function, may be adapted to investigate the effect of other parameters, like pulse frequency and pulse width, on electroporation.
脉冲电场治疗方式通常利用多个脉冲使生物组织通透化。这种电穿孔过程会引起组织电导率变化，而这种变化可指示电穿孔的程度。在本研究中，我们使用所有治疗脉冲来表征电穿孔引起的电导率变化，而不是像传统电导率模型那样仅使用第一个脉冲。采用兔肝组织来研究通过平板电极施加的多个100微秒脉冲所引起的组织电导率变化。在治疗过程中记录电压和电流数据，并用于计算整个脉冲过程中的组织电导率。还记录温度数据，以根据组织温度系数量化焦耳热对电导率的贡献。通过将所有这些数据拟合到一个修正的阶跃函数，其中两个转折点（ ， ）和增加因子（）是主要参数，我们计算了作为电场（）函数的电导率，其中阶跃函数的参数（ 和 ）是脉冲数（）的函数。利用所得的多因素电导率模型，数值电穿孔模拟能够比现有电导率模型更准确地预测多个脉冲的电流。此外，该模型中增加因子 的饱和趋势可以解释电穿孔引起的饱和行为。电穿孔引起的电导率变化在前约30个脉冲时显著增加，然后趋于在0.465 S/m处饱和。所提出的电导率模型比传统电导率模型能更准确地模拟电穿孔过程。利用该模型计算的电场分布对于利用多个脉冲电场的生物医学应用中的治疗规划至关重要，并且这里提出的通过阶跃函数中的变量将脉冲数与电导率相关联的方法，可能适用于研究其他参数，如脉冲频率和脉冲宽度，对电穿孔的影响。
