Effect of pressure and padding on motion artifact of textile electrodes

Abstract

BackgroundWith the aging population and rising healthcare costs, wearable monitoring is gaining importance. The motion artifact affecting dry electrodes is one of the main challenges preventing the widespread use of wearable monitoring systems. In this paper we investigate the motion artifact and ways of making a textile electrode more resilient against motion artifact. Our aim is to study the effects of the pressure exerted onto the electrode, and the effects of inserting padding between the applied pressure and the electrode.MethodWe measure real time electrode-skin interface impedance, ECG from two channels, the motion artifact related surface potential, and exerted pressure during controlled motion by a measurement setup designed to estimate the relation of motion artifact to the signals. We use different foam padding materials with various mechanical properties and apply electrode pressures between 5 and 25 mmHg to understand their effect. A QRS and noise detection algorithm based on a modified Pan-Tompkins QRS detection algorithm estimates the electrode behaviour in respect to the motion artifact from two channels; one dominated by the motion artifact and one containing both the motion artifact and the ECG. This procedure enables us to quantify a given setup’s susceptibility to the motion artifact.ResultsPressure is found to strongly affect signal quality as is the use of padding. In general, the paddings reduce the motion artifact. However the shape and frequency components of the motion artifact vary for different paddings, and their material and physical properties. Electrode impedance at 100 kHz correlates in some cases with the motion artifact but it is not a good predictor of the motion artifact.ConclusionFrom the results of this study, guidelines for improving electrode design regarding padding and pressure can be formulated as paddings are a necessary part of the system for reducing the motion artifact, and further, their effect maximises between 15 mmHg and 20 mmHg of exerted pressure. In addition, we present new methods for evaluating electrode sensitivity to motion, utilizing the detection of noise peaks that fall into the same frequency band as R-peaks.

Textile Concentric Ring Electrodes: Influence of Position and Electrode Size on Cardiac Activity Monitoring

“…The most commonly used electrode for ECG monitoring is a gel-type silver/silver chloride (Ag/AgCl) electrode. However, as some pathologies require extended monitoring during the patient's normal activities, interest in mobile and long-term monitoring has grown for diagnosis, screening, risk assessment, prevention, and rehabilitation [2]. Wet electrodes are limited in their long-term use because they can irritate the skin.…”

Design and Evaluation of Novel Textile Wearable Systems for the Surveillance of Vital Signals

“…The motion artefact interference may be caused by eventual pulling from the cables, but the main source is due to the change of potential across the epidermis during skin deformation by stretching and/or induced by applied pressure [36]. Electrical equivalent models of the electrode-skin interface of gel and textile electrodes have been proposed [31,32,[35][36][37]. The gel electrode model includes the contribution of an electrolyte half-cell potential and the epidermis potential.…”

“…The amount of pressure applied on the electrode-skin contact surface also affects the electrode's performance. High pressure lowers the impedance contact and restricts the motion by friction of the electrodes [30,31,36]. Figure 11 shows ECG signals obtained from two Holter exams realized in a hospital environment with an internal patient; in one exam, the patient was wearing the cardio surveillance t-shirt system, while the other used gel electrodes taped to the thorax.…”

“…Several studies in the field describe the importance of moisture in the textile electrodes. It considerably improves the electrode-skin interface, consequently lowering the noise amplitude of the signals to values similar to those of gel electrodes [17,31,38]. Dry electrodes with larger surface tend to exhibit lower noise amplitude and lower contact impedance [38,39].…”

Smartware electrodes for ECG measurements : Design, evaluation and signal processing

“…Normal electrodes use adhesive collars or suction cups to stabilize this interface, but for textile electrodes the fit and placement of the sensor are parameters to optimize. Comert et al [25] have investigated how different paddings and pressures applied to the electrode improve the detectability of R-waves in a ECG recorded with textile electrodes. The outcome of the study indicated that by padding the electrode, it stabilizes the electrode-skin contact and improves the R-wave detectability.…”