[Measuring electric impedance of organs--methodologic principles]

Ischemia causes changes in organ tissue (e.g. during operation or transplantation) which may finally lead to irreversible injury, so that the organ can no longer be resuscitated. To the extent that these changes affect the electrical properties of the tissue they are manifested in the impedance spectrum. As an example, the course of impedance of a HTK-protected porcine liver is presented in the frequency range of 0.1 Hz to 10 MHz, which includes two dispersion--alpha- and beta-dispersion. Using a suitable electrical equivalent circuit analogue to the structure of the liver, the behavior of the alpha- and beta-dispersion is explained on the basis of gap junction closure and narrowing of the extracellular space due to cell swelling.