The change in the impedance of biological tissue under the influence of voltage is used in the diagnosis and treatment of various diseases. Mathematical models describing physical and biological processes in biological objects are based on electrical substitution schemes. The subject of research of this work was the study of the change in the impedance of biological tissue in the transient process of ionization under the action of DC voltage. An analysis of the known substitution schemes was carried out, the shortcomings of their application were identified when the transient processes of ionization in the tissue under the action of direct current voltage were studied, and the substitution scheme with the introduction of additional resistance was substantiated, both analytically and experimentally. In the work, the bioimpedance method is applied when direct current voltage is applied to biological tissue, taking into account the law of commutation in transient ionization processes. An invasive measurement of the change in impedance with needle electrodes was carried out, and it was proved that the active component proportionally depends on the distance between the electrodes, while the capacitive component remains unchanged. It is shown that the ionization time constant is a criterion parameter and can be used in the diagnosis of the development of ischemic disease of muscle tissue, the change in the state of biological tissue when blood flow is stopped during the application of a tourniquet. It has been proven that the ionization time constant does not change with an unchanged ionic composition of the tissue and can be used in the analysis of the composition of the intercellular space. A simultaneous invasive measurement was performed in two identical places of different limbs, on one of which a hemostatic tourniquet was applied. The obtained results made it possible to conclude that a change in the constant time from 15% to 50% compared to two constant times allows for rapid diagnosis, within 2 minutes, of the state of biological tissue and can be used in the study of the development of diseases associated with ischemia. The results of the study can be used for rapid diagnosis of the state of a biological object and the creation of an inexpensive device for its use in surgery and research laboratories