Measure of the opposition to the flow of a sinusoidal alternating electric current.
Published in Chapter:
New Perspectives in Rheoencephalography
Juan J. Perez (University of Valencia, Spain), Enrique Guijarro (University of Valencia, Spain), Pedro Ortiz (Consorcio Hospital General Universitario de Valencia, Spain), and José M. Pons (Consorcio Hospital General Universitario de Valencia, Spain)
Copyright: © 2008
|Pages: 8
DOI: 10.4018/978-1-59904-889-5.ch123
Abstract
One of the most important advances in biomedical engineering has been the ability to inspect inside the body without opening it. In this sense, rheoencephalography (REG) is an electromedical technique used to assess the cerebral blood flow (CBF) by noninvasive electrical impedance methods, using electrodes attached to the scalp surface. This technique was first proposed by Polzer and Schuhfried (1950), and emerged as an extrapolation of impedance plethysmography applied to the head. An electric current flowing through a biological tissue causes a potential difference between any pair of electrodes that can be measured. This potential difference depends on the amplitude of the injected current, the shape of the conductor, the arrangement of the electrodes, and the electrical characteristics of the tissue. For instance, the electrical conductivity of the lung tissue is much lower than that of the cerebrospinal fluid (CSF), since alveolar sacs are nonconductive. Furthermore, the electrical conductivity depends on the frequency of the electric current, the orientation of the tissue fibers relative to the current flow, and the amount of extracellular fluid that surrounds the cells. For example, electrical conductivity is higher in the blood than in most tissues, since plasma acts as a truehighway for ions (Malmivuo & Plonsey, 1995).