Pliquett Uwe, Nuccitelli Richard
Institut für Bioprozeβ- und Analysenmeβtechnik e.V., Heilbad Heiligenstadt Germany.
BioElectroMed Corp., Burlingame, CA 94010, USA.
Bioelectrochemistry. 2014 Dec;100:62-8. doi: 10.1016/j.bioelechem.2014.03.001. Epub 2014 Mar 12.
Experimental evidence shows that nanosecond pulsed electric fields (nsPEF) trigger apoptosis in skin tumors. We have postulated that the energy delivered by nsPEF is insufficient to impart significant heating to the treated tissue. Here we use both direct measurements and theoretical modeling of the Joule heating in order to validate this assumption. For the temperature measurement, thermo-sensitive liquid crystals (TLC) were used to determine the surface temperature while a micro-thermocouple (made from 30 μm wires) was used for measuring the temperature inside the tissue. The calculation of the temperature distribution used an asymptotic approach with the repeated calculation of the electric field, Joule heating and heat transfer, and the subsequent readjustment of the electrical tissue conductivity. This yields a temperature distribution both in space and time. It can be shown that for the measured increase in temperature an unexpectedly high electrical conductivity of the tissue would be required, which was indeed found by using voltage and current monitoring during the experiment. Using impedance measurements within t(after)=50 μs after the pulse revealed a fast decline of the high conductivity state when the electric field ceases. The experimentally measured high conductance of a skin fold (mouse) between plate electrodes was about 5 times higher than those of the maximally expected conductance due to fully electroporated membrane structures (G(max)/G(electroporated))≈5. Fully electroporated membrane structure assumes that 100% of the membranes are conductive which is estimated from an impedance measurement at 10 MHz where membranes are capacitively shorted. Since the temperature rise in B-16 mouse melanoma tumors due to equally spaced (Δt=2 s) 300 ns-pulses with E=40 kV/cm usually does not exceed ΔΤ=3 K at all parts of the skin fold between the electrodes, a hyperthermic effect on the tissue can be excluded.
实验证据表明，纳秒级脉冲电场（nsPEF）可引发皮肤肿瘤细胞凋亡。我们推测，nsPEF传递的能量不足以使被处理组织产生显著的发热。在此，我们通过焦耳热的直接测量和理论建模来验证这一假设。对于温度测量，使用热敏液晶（TLC）来确定表面温度，同时使用微型热电偶（由30μm的导线制成）测量组织内部温度。温度分布的计算采用渐近方法，反复计算电场、焦耳热和热传递，并随后重新调整组织电导率。这得出了空间和时间上的温度分布。可以证明，对于所测量的温度升高，需要组织具有出乎意料的高电导率，这在实验过程中通过电压和电流监测确实得到了证实。在脉冲后50μs内进行阻抗测量表明，当电场停止时，高电导率状态迅速下降。实验测量的平板电极之间皮肤褶皱（小鼠）的高电导率比由于完全电穿孔膜结构而最大预期电导率高约5倍（G(max)/G(电穿孔)）≈5。完全电穿孔膜结构假设100%的膜是导电的，这是根据在10MHz下膜电容短路时的阻抗测量估计得出的。由于在B - 16小鼠黑色素瘤肿瘤中，由于等间距（Δt = 2 s）的300 ns脉冲且电场强度E = 40 kV/cm，电极之间皮肤褶皱所有部位的温度升高通常不超过ΔΤ = 3 K，因此可以排除对组织的热疗效应。
