What types of electrode should I use?
Our goal is generally to provide but not proscribe choices. As with electrode positioning, decisions about electrode type are best addressed via the literature and discussions with colleagues. That said, here are some general considerations.
Disposable vs. re-usable electrodes. Most electrodes used for biopotential recording are Ag/Ag-Cl. When the electrodes are applied, chemical reactions at the surface of the electrodes must occur to allow electrical currents to flow between the subject and the equipment. These reactions cause the electrode surface to slowly degrade over time. With proper cleaning and storage, reusable electrodes may last several years, but the electrode surface at the end of this period is certainly different from what it was at the start. Disposable electrodes effectively remove this source of variance as each subject uses electrodes with fresh surfaces.
These fresh surfaces may be even more important from the subject’s perspective. Although proper sterilization will minimize risk, re-usable electrodes may be a source of infection. Better signals are generally acquired from subjects whose skin has been abraded to remove the outer layer of dead (hence dry and electrically non-conductive) skin cells. This abrasion partially exposes the subjects’ blood allowing microbes to enter or leave the subject’s body.
These concerns combined with the relative ease of use generally make disposable electrodes the preferred option for human subjects.
All electrodes distributed by BIOPAC Systems are hypo-allergenic and, in particular, latex-free. Once a decision has been made to use disposable electrodes, more restrictive choices will be dictated by the geometry needed for the desired measurements and the adhesive properties of the electrodes. When subjects must be active as part of the experimental protocol, cleaner recordings may be obtained with electrodes that adhere more strongly to the skin.
Special cases. Electrodermal activity (skin conductance) should be measured using electrodes with a gel that mimics the salt content of sweat:
Boucsein, W., Fowles, D.C., Grimnes, S., Ben-Shakhar,G., Roth, W.T., Dawson, M.E., and Filion, D.L. (2012). “Publication Recommendations for Electrodermal Measurements”, Psychophysiology, 49:1017-1034.
Therefore EL507 disposable electrodes or GEL101 with re-usable electrodes are strongly recommended for this application. Note that the gel on EL507 is slightly different from GEL101, it is better to use the same electrode type for all participants in any given study.
For impedance cardiography (ICG), a variety of electrode configurations have been used. In general there is an electrode or set of electrodes near the top of the neck , and another lower down on the torso. These electrodes inject a high frequency AC current. Below the top and above the bottom set of electrodes is another pair of electrodes or sets of electrodes used to measure the changes in voltage as the current flows past them. Initial experiments used four electrodes in the form of bands that fully encircled the neck and torso. For convenience, many researchers use spot electrodes or groups of spot electrodes instead.
For some discussion, see, for example:
Boomsma, D.I., de Vries, J., and Orlebeke, J.F. (1989). “Comparison of Spot and Band Impedance Cardiogram Electrodes across Different Tasks”, Psychophysiology, 26(6):695-699.
Sherwood, A., Allen, M.T., Kelsey, R.M., Lovallo, W.R., and van Doornen, L.J.P. (1990). “Methodological Guidelines for Impedance Cardiography”, Psychophysiology, 27(1):1-23.
Woltjer, H.H., Bogaard, H.J., and de Vries, P.M.J.M. (1997). “The Technique of Impedance Cardiography, European Heart Journal, 18:1396-1403.
Bacon, S.L., Keller, A.J., Lavoie, K.L., and Campbell, T.S. (2012). “Comparison of a Three-Quarter Electrode Band Configuration with a Full Electrode Band Configuration for Impedance Cardiography”, Psychophysiology, 47(6):1087-1093.
Please note that the nature of the generators underlying the ICG signal is still open for discussion, so theoretical rationales for selecting one electrode geometry over another may lack strong support:
Patterson, R.P. (2010). “Impedance Cardiography: What Is the Source of the Signal?”, Journal of Physics: Conference Series, 224:.
Trakic, A., Akhand, M., Wang, H., Mason, D., Liu, F., Wilson, S., and Crozier, S. (2010). “Computational Modelling of Blood-Flow-Induced Changes in Blood Electrical Conductivity and Its Contribution to the Impedance Cardiogram”, Physiological Measurement, 31(1):13-33.
Page last modified 19Jan2015