What Is Bioelectricity

Many applications such as defibrillation or electroporation are performed in the nonlinear range. Defibrillation is a life-saving procedure electroporation is used for a very short opening of cells. Surgery and ablation are performed using high-frequency currents (electrosurgery). 

Bioelectricity experiments are performed in vivo or ex vivo wifli pickup electrodes and stimulation electrodes. Electrotherapeutical methods use electricity controlled by current or voltage, charge, energy, waveform, and time. 

Bioimmittance is measured in vivo or in vitro. The tissue may be kept alive and perfused under ex vivo conditions. Bioimmittance can be measured with two-, three- or four-electrode systems. With four electrodes, one electrode pair is current carrying and the other pair picks up the corresponding potential difference somewhere else in the tissue. If the measured voltage is divided by the applied current, the transfer impedance is calculated. If no voltage is measured, the transfer impedance is zero. This is equivalent to the bioelectricity case in which a signal from the source, such as the heart, is transferred to the skin surface electrodes. Zero transfer impedance does not mean the tissue conducts well, only that no signal transfer occurs. With the bioimpedance two-electrode technique, the transfer factor is eliminated because current application and signal pickup occur at the same site, which means that measured impedance reflects tissue electrical properties more directly. 

Single cells are measured with microelectrodes and clamp and patch techniques (see Chapters 7 and 10). 

Exogenic current is usually applied with electrodes in galvanic contact with tissue. It is also possible to apply it by a magnetic field without making physical contact with the tissue. Biopotential is difficult but not impossible to measure without galvanic contact. 

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