Stress action on biological tissue and tissue models detected by the Py value.

The Py value, a fast measurable combination of the conductivity at the corner frequencies of the beta-dispersion, is a measure of the relative cell volume concentration in tissue. In many cases, if the biological object is stressed, for instance, by mechanical deformation, shortage of oxygen, electric field strength, temperature rise, or ischemia, Py increases. Depending on the object and the kind of stress, Py plateaus for minutes up to hours and then it decreases continuously. Values of passive electrical parameters of biological tissues are often given without information about the time following a stimulation or stress situation, for example, death, surgery, field application, etc. However, since the passive electrical properties change with time, information about their history, for example, time after death, should be given.