Electrical Bioimpedance (EBI) is now a mature technology in medicine, with applications in clinical investigations, physiological research, and medical diagnosis (Schwan, 1999). The first monitoring application of bioimpedance techniques, impedance cardiography, date back to 1940. Since then, bioimpedance measurements have been used in several medical applications, from lung function monitoring and body composition, to skin cancer detection. A complete historical review is available in Malmivuo and Plonsey (1995). A medical imaging modality based on bioimpedance, Electrical Impedance Tomography (EIT) has also been developed (Bayford, 2006). EBI has been used to study the effect in the brain of spreading depression, seizure activity, asphyxia and cardiac arrest since 1950s and 1960s (Ochs & Van Harreveld, 1956), but the most important activities in electrical cerebral bioimpedance research has been during the last 20 years (Holder, 1987; Holder & Gardner-Medwin, 1988).
Key Terms in this Chapter
Seizure: Abnormal electrical activity in the brain tissue, which is usually accompanied by motor activity and/or sensory phenomena. Its origin can be epileptic or nonepileptic.
Brain Stroke: A cerebrovascular accident that occurs as a consequence of brain ischemia or cerebral haemorrhage; ischemic stroke and haemorrahagic stroke respectively.
Hypoxia: Reduction of oxygen supply to tissue below physiological level.
Ischemia: A low blood flow state leading to hypoxia in the tissue.
Electrical Bioimpedance: The physical magnitude that indicates the total impediment that a biomaterial offers to the flow of free electrical charges and the orientation of bounded electrical charges towards an existing electrical field.
Bioimpedance Tomography: Also known as Electrical Impedance Tomography, it is a medical imaging technique in which an image of the dielectric properties of biological tissue is inferred from surface electrical measurements.
Epilepsy: A neurological disorder in which abnormal electrical activity in the brain causes seizures.
Electrical Conductivity: A dielectric property that indicates the ability of a material to allow the flow of electrical charges.