VIII Measurement of the Intrinsic Electric Properties of Biological Tissues



VIIIMeasurement of
the Intrinsic ElectricProperties of Biological Tissues


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.