The third subdivision of bioelectromagnetism discusses the measurement of intrinsic electric and magnetic properties of biological tissue. Part VIII briefly discusses, for example, the measurement of tissue impedance and of the electrodermal response.
The measurement of tissue impedance was first applied to impedance plethysmography. The most successful application of this technique, however, is impedance cardiography, which can be used for the noninvasive measurement of the stroke volume. Impedance plethysmography has also other applications - for example, measurement of the amount of fluid in the pleural cavities or detection of thromboses in the veins of the legs. Impedance plethysmography has also been used successfully in detecting the gastric activity in small babies.
A new application of the impedance technique is impedance tomography, an attempt to image the electric conductivity of the body. Unlike x-ray tomography (CT scanning) and nuclear magnetic resonance imaging (NMRI), impedance tomography has not been very successful clinically. The reason for this is that the resolution of impedance measurements, even in two dimensions where most work has been performed, has been poor.
The electrodermal response has wide applications in psychophysiology. On this subject there is a large body of literature. For the sake of completenes of this book, the electrodermal response is briefly discussed.
Part VIII could have included a discussion of applications where magnetic properties of the tissue are measured: for example, magnetic susceptibility plethysmography and nuclear magnetic resonance imaging, NMRI. These are, however, not included to avoid an increase of the number of pages. It should also be noted that the first of these two techniques is not in clinical use, and the second, which involves the magnetic properties of the tissue on a nuclear level, is essentially outside the scope of this book. Because NMRI has been succesfully applied in clinical use there is also a very large literature on this subject elsewhere.