Bioelectric sources

Plonsey, R. 1974. The formulation of bioelectric source-field relationship in terms of surface discontinuities. /. Frank Inst. 297 317. 

The positive lead of the single-fiber electrode (see Figure 25.6) is the end cap of a 25-/xm wire exposed through a side port on the cannula of a steel needle. Due to the small size of the positive lead, bioelectric sources, which are located more than about 300 /xm from the side port, will appear as common-mode signals and be suppressed by the differential amplifier. To further enhance the selectivity, the recorded signal is high-pass filtered at 500 Hz to remove low-frequency background activity from distant fibers. 

In electrophysiology, a body surface potential is often recorded, with the purpose of characterizing the unknown bioelectric source in position, size, and direction. To go from measured potentials in a known conductive medium and calculate back to the source properties is called an inverse problem. Usually there are infinitely many possible solutions to a posed problem (see Figure 8.11(c)). Important classical patient examination methods such as electrocardiogram and electroencephalogram are aimed at characterizing properties of the source organ, and are thus based upon more or less empirical solutions to the inverse problem. 

PU electrode situated on an inactive skin site. The other electrode is then situated on an active skin site. This constitutes a monopolar system. If both electrodes are situated on an active skin site, no signal (potential difference) is measured. Function is independent of surface area (as are all PU electrodes), but small electrodes pick up more noise. Not CC, current density J = 0. Indifferent electrode shall be situated far from bioelectric sources. Examples ECG right leg, other extremities, Wilson terminal. EEG ear flip, nose. Electrodermal activity elbow. 

Bioelectric sources are endogenous sources found in the body. At a short distance the signals may be dominated by the nervous parts of the organ, at larger distance by the muscle mass under nervous control. The signals are generated by the electrical activity of the cell membranes. 

Skin as an Endogenous Bioelectric Source, Skin Potential... 

From 1850 to 1900, we had a parallel development of important medical use of endogenic bioelectric sources in the body. 

Surface Potentials Generated by a Bioelectric Source in a Volume Conductor... 

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