<div dir="ltr"><div>Dear colleagues,</div><div><br></div><div>Let me share this info.</div><div><br></div><div>E. Huigen (2000) Noise in biopotential recording using surface electrodes</div><div>
<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><a href="https://www.semanticscholar.org/paper/Noise-in-biopotential-recording-using-surface-Huigen/8fc0837f7af0a36b19799139d9b763969057b985">https://www.semanticscholar.org/paper/Noise-in-biopotential-recording-using-surface-Huigen/8fc0837f7af0a36b19799139d9b763969057b985</a></span>
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<div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><b>%%%%%%%%%%%%%%%%%%%%%</b><br></div></div><div><b><br></b></div><div><b>2.4 Motion artifact</b></div><div>Movement can cause changes in the potentials that are created when an electrode is applied to the skin. Normally, when the patient is relaxed, and high quality electrodes are used, the recording is not distorted by motion artifact. Brinkman (1993) has found no significant correlation between the intentional movement of the arm and the noise signal. The mechanisms that can cause motion artifact are described next.</div><div><br></div><div><b>Liquid junction potential variations by electrode movement</b></div><div>The various phase junctions in the electrode-electrolyte-skin interface all cause junction potentials, sensitive to motion artifact. The skin-electrolyte interface can cause artifacts of <span style="background-color:rgb(244,204,204)">400-600 μV</span> when the electrode is moved parallel to the skin surface <span style="background-color:rgb(207,226,243)">(Smith and Wace, 1995)</span>. When the electrode is moved perpendicular to the skin the potential changes can be up to <span style="background-color:rgb(244,204,204)">900 μV</span>. Firm attachment to the skin can reduce the potential changes. The electrode-electrolyte interface also produces artifacts when mechanically disturbed. Gatzke (1974, as described in Webster, 1984) measured a <span style="background-color:rgb(244,204,204)">15 mV</span> potential change when a pure silver electrode is moved in electrolyte. Coating with silver chloride, thus creating a stable double layer, produces a 10-fold reduction of the artifact. Further reduction (up to negligible value) can be achieved by recessing the electrode-electrolyte interface in a protective cup, in which a sponge soaked in gel is placed (figure 2-2).</div><div><br></div><div><b>Skin potential changes</b></div><div>Earlier, the stratum corneum and the barrier layer have been identified as the major sources of the impedance of the skin. Webster (1984) has also observed a potential difference between the inside and the outside of the barrier layer. Van Wijk van Brievingh (1988) however states that <span style="background-color:rgb(244,204,204)">this skin potential is a liquid junction potential between deeper skin layers and the electrolyte.</span> The skin potential has a typical value of 30 mV at the thorax. Stretching of the skin decreases the skin potential to about 25 mV. This artifact can be reduced to negligible value by abrading the skin. Webster gives 20 strokes with fine sandpaper as an indication. Shackel (1959, as described in Geddes and Baker, 1989) developed a method for shorting the skin potential, called the skin-drilling technique. The epidermis is eroded using a dental burr. The capillaries remain undisturbed, so no blood is drawn. Unfortunately, the epidermis is also the layer that protects the skin from irritation. A mild electrode gel has to be used to prevent</div><div>unwanted effects.</div><div><br></div><div>%%%%%%%%%%%%%%%%%%%%%</div><div><br></div><div>
<div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">Wikipedia 'liquid junction potential'</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><a href="https://en.wikipedia.org/wiki/Liquid_junction_potential">https://en.wikipedia.org/wiki/Liquid_junction_potential</a></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">In Huigen, Peper, Grimbergen (2002) Med. biol. Eng, they described:</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><i>RECORDINGS OF biomedical signals from the body surface often contain a substantial noise component. This noise signal can severely impair the resolution of biomedical recordings as <span style="background-color:rgb(244,204,204)">its magnitude can be as high as 10-60 uVp_p (GONDRAN et aL, 1996). This is in the range of EEG potentials and is at least ten times as high as several types of evoked potentials (e.g. visual evoked potentials or somatosensory evoked potentials).</span></i><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">By the way I could not find Smith and Wave (1995)<i><span> </span>European Journal of Anaesthesiology.<span> </span></i>If you have a copy, please let me know.</div>
<br></div><div>Makoto</div>-- <br><div class="gmail_signature"><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div></div>
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