Dry Electrodes:
The Need
Overview | The Need | The Solution
Classic Electrodes
Classic and current ECG electrodes rely on the presence of an electrolytic solution/gel to conduct the bio-electrical signal of an ECG from the surface of the skin to and through the electrode. Success and failure of these gel based electrodes is largely dependent on the hydration level of the electrode. A dried out electrode will yield a signal
dominated by artifact.
Further, gel based electrodes are impaired by the high electrical impedance of the outermost layer of the skin known as the Stratum Corneum (SC). To overcome this high impedance, aggressive skin preparation techniques such as abrasion with emery paper are standard clinical practice when using gel based electrodes.
Continuous Application / Shelf Life
The gel electrodes have several limitations, particularly for the long duration, continuous applications. Primarily, the level of hydration of the electrolyte gel is continuously variable. It can range from dried out to hyponatremic (from exposure to water, such as from a shower). This electrolyte variability will yield a corresponding range of signal quality. As a result, storage time and conditions must be carefully monitored, particularly for unsealed packages.
Attention must also be paid to the duration of time, and the type of activities performed while the electrode is being worn. Standard gel based electrodes may also cause discomfort when the saline gel is placed in contact with the irritated skin. The irritation results either deliberately (from skin abrasion) or inadvertently as a result of the presence of the electrode on the skin.
Skin Irritation with Current Electrodes
Placing a salt based electrode (solution)on the skin by definition is the cliché, ‘adding salt to a wound'. In ambulatory ECG applications where the monitoring periods can extend to as much as 4 contiguous weeks, the frequent replacement of the electrodes (typically every 48 hours) can increase the irritation and decrease patient compliance.
Pilot studies have shown Orbital Research has successfully demonstrated the ability of their electrodes to be worn in excess of five days. Over that five day period, the ECG signal remained clean and the electrode was non-irritating. |
