On mechanisms of interaction in electrosurgery
On mechanisms of interaction in electrosurgery
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DOI：
10.1088/1367-2630/10/12/123022
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发表时间：
2008-12-16
影响因子：
3.3
通讯作者：
Jayaraman, Pradeep
中科院分区：
文献类型：
--
作者：
Palanker, Daniel;Vankov, Alexander;Jayaraman, Pradeep
电外科手术广泛应用于各种外科手术，但其潜在的相互作用机制尚不清楚。自20世纪30年代以来，电外科手术的基本原理并没有发生太大变化——切割仍然使用连续的射频波形进行，在深度上留下数百微米的附带损伤区。可变占空比的脉冲波形主要用于组织凝固。最近，我们已经证明，通过微电极应用微秒爆发的电外科手术可以在软组织解剖中提供细胞精度。本文研究了导电介质中脉冲放电的动力学，以及伴随的汽化、空化和电离现象。结果表明，电极周围蒸汽腔的电离对于超过汽化阈值的能量传递是必不可少的。等离子体介导放电的电离阈值电压和电阻值在放电的负相比正相要低得多。交流波形与电极的电容耦合通过移动电极上的介质电压来补偿这种不对称性，从而增加正幅值并减少负幅值，从而在相反的相位实现电荷平衡。平面绝缘电极的暴露边缘宽度为12.5 μ m，持续时间为40 μ s，即使是坚硬的生物组织也可以以细胞精度解剖。例如，在叶片每毫米长度2.2 mJ的脉冲能量下实现软骨剥离，并且只留下5-20 μ m宽的热损伤区。
Electrosurgery is broadly used in a wide variety of surgical procedures, yet its underlying mechanisms of interaction are poorly characterized. Fundamentals of electrosurgery have not changed much since the 1930s-cutting is still performed using continuous RF waveforms, leaving a collateral damage zone of hundreds of micrometers in depth. Pulsed waveforms with variable duty cycle are used mostly for tissue coagulation. Recently, we have demonstrated that electrosurgery with microsecond bursts applied via microelectrodes can provide cellular precision in soft tissue dissection. This paper examines dynamics of pulsed electrical discharges in conductive medium, and accompanying phenomena, such as vaporization, cavitation and ionization. It is demonstrated that ionization of the vapor cavity around the electrode is essential for energy delivery beyond the vaporization threshold. It is also shown that the ionization threshold voltage and resistance of the plasma-mediated discharge are much lower in the negative phase of the discharge than in the positive one. Capacitive coupling of the ac waveform to the electrode compensates for this asymmetry by shifting the medium voltage on the electrode, thus increasing the positive and decreasing the negative amplitudes to achieve charge balance in the opposite phases. With planar insulated electrodes having exposed edges of 12.5 mu m in width and bursts of 40 mu s in duration even tough biological tissues can be dissected with cellular precision. For example, cartilage dissection is achieved with pulse energy of 2.2 mJ per millimeter of length of the blade, and leaves a thermal damage zone of only 5-20 mu m in width.