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Bioelectrodes for ecg- Raghav Mishra
- 1. Name- Raghav Mishra Registration No.- 10919210005 SRM University 03-12-2020 1
- 2. Purpose of a bioelectrode A bioelectrode is a conductor that is designed to serve as an interface between biological structures and electronic systems. Its function is to either sense and measure (passive) the electrical activity within the biological structure or stimulate (active) it by inducing external electrical potential. Depending upon the purpose, the same electrode may perform either the passive or active function 03-12-2020 2
- 3. Principal The size of bioelectrodes generally ranges from microscopic intracellular research electrodes (microelectrodes) to large (8–12 cm) defibrillation paddles. Electrocardiography is the process of recording the electrical activity of the heart over a period of time using metallic electrodes placed on a patient’s body. The electrical activity generated by the heart within the body is conducted to the surface of the body through the body tissues, reaches the electrodes through the skin electrode transition, and is then conducted by direct wire connection to the input circuit of the recording machine. 03-12-2020 3
- 4. Contact Impendence The impedance at the electrode–skin junction comes in the overall circuitry of the recording machine and, therefore, has significant effect on the final record. Skin electrode impedance is known as the contact impedance. So we need to minimize this contact impendence. Electrolytic gels are used to minimize this 03-12-2020 4
- 5. The most commonly used electrodes in patient monitoring and routine recording of ECG are surface electrodes. The surface electrodes are available both as reusable and disposable electrodes. Important Characteristic: These electrodes should not polarize. To overcome this polarization problem Silver/Silver Chloride are used to make the electrodes. Another problem to overcame: half-cell potential. 03-12-2020 5 Types of ECG Electrodes
- 6. Reusable ECG Electrodes Properties 1. Can be used for several years 2. Can be used multiple times 3. Made of German silver 4. Takes about 5-10 minutes for recording ECG 5. Requires up to 10 electrodes 03-12-2020 6
- 7. 1. Plate Electrode 03-12-2020 7 • Used for routinely recording ECG. • They can be rectangular or circular. • They are used on the limbs only and are placed on all the four limbs. • A conductive gel is required for them to work properly by reducing the contact impendence. • They show a contact impendence of 2-5 kΩ when measured at 10 Hz. • Also called limb electrodes. • Usually they have a size of 3 x 5 cm • These are preferred for use during surgery.
- 8. 2. Clamp Electrodes •They are the modern version of the limb plate electrode. •They have a continent spring clip mechanism. •They have a dimension of 3cm x 8cm which provide 24 cm2 area to maximize the contact. •They also require electrode gel. 03-12-2020 8
- 9. 3. Welsh Electrode Also known as the cup electrode. Used for recording ECG from various position on the chest. Commonly used to record the unipolar chest leads. Consists of a hollow, metallic, cylindrical electrode that makes contact with the skin at its base. It has a high contact impedance. Can be used anywhere on the chest even on hairy subjects. The cup electrode has been popular for its practicality, being easily attachable to fleshy parts of the body. 03-12-2020 9
- 10. Disposable ECG Electrodes Designed to overcome the problems during prolonged application. They are flexible and more comfortable to wear. They have integrated gel They have Ag-/AgCl-plated plastic eyelets, and the leads are connected to the electrodes via snap fastener studs. high-absorbency buffer layer with isotonic electrolyte. 03-12-2020 10
- 12. Reference Bioelectrodes: ECG Electrodes Book Author(s): Raghbir Singh Khandpur First published: 13 December 2019 https://doi.org/10.1002/9781119288190.ch33 03-12-2020 12
Editor's Notes
- Various biological structures generate electrical currents that give rise to potential differences. These potentials can be measured using bioelectrodes that can give an insight in the functioning of the biological structure. Electrocardiograph (ECG) electrodes are one type of bioelectrodes that are used to pick up electrical potentials generated by the pumping action of the heart from the surface of the skin.
- ECG electrodes are available in different shapes and sizes and are made up of different materials depending upon the different clinical applications such as routine ECG recording, ambulatory ECG, intensive care units (ICUs), etc. Electrodes make a transfer from the ionic conduction in the tissue to the electronic conduction, which is necessary for making measurements. Therefore, a bioelectrode is generally considered as a transducer that converts ionic current into electronic current or vice versa.
- When the surface electrode pick up the potential difference from the tissue surface placed over it without damaging. and is of a value much greater than the electrical impedance of the body tissue as measured beneath the skin. The outer horny layer (Stratum corneum) of the skin is responsible for the bulk of the skin contact impedance and, therefore, a careful skin preparation is essential in order to obtain best results when using ECG electrodes This gel contains Ca+ ions which increases the conductivity
- This means that the electrode potential must not vary considerably even when current is passed through them. By properly preparing and selecting the electrodes, pairs have been produced with potential differences between them of only fractions of a millivolt. In addition, there is an uneven distribution of cations and anions at the electrodes, which gives rise to a small voltage called half-cell potential associated with the current. The difference between the half-cell potential and the zero potential is known as the DC offset, which is an undesirable characteristic
- German Silver: which is an alloy of zinc, copper, and nickel
- An elastic rubber strap is used to hold the electrode in position Limb electrodes are generally preferred for use during surgery because the patient’s- limbs are relatively immobile. Moreover, chest electrodes cannot be used as they would interfere with the surgery.
- have a convenient spring clip mechanism, which dispenses wit the need for the rubber strap.
- It has a high contact impedance as only the rim of the electrode is in contact with the skin A single electrode can, if necessary, be used to take a measurement at a given location and then moved to another site. However, the weight and bulk of the electrode generally rules out its use on upright, ambulatory, or clothed subjects. They are, therefore, now being gradually replaced with disposal electrodes, as they are liable to infection due to inadequate cleaning procedures
- Electrodes, which are employed in stress testing or long-term monitoring, present additional problems because of the severe stresses, perspiration, and major body movement encountered in such studies. This necessitates both design considerations and application techniques of electrodes to prevent random noise on the baseline and baseline wandering on the ECG record. They are very handy because of integrated gel and adhere very well to the contours of the skin. The main design feature of these electrodes, which helps in reducing the possibility of artefacts, drift, and baseline wandering is the provision of a high-absorbency buffer layer with isotonic electrolyte.
- In construction, the electrode has a small retaining ring or plastic cup that is held in place by means of a surrounding disk of adhesive foam as shown in Figure 33.4. The plastic cup holds the gel-impregnated sponge in place and stops the gel from spreading beyond the defined boundary during storage or use on the patient. The plastic eyelet has a diameter of 0.5–1.5 cm and is electroplated with silver up to a thickness of 10 mm. The rigid retaining ring is, however, uncomfortable as it does not allow the electrode to conform optimally to body contours. The rigid ring is now removed in many modern disposable electrodes and replaced with a recess formed by a hole in the adhesive foam layer. The backing label serves to hold the snap and eyelet in place as well as to present the company’s logo. The main design feature of these electrodes, which helps in reducing the possibility of artefacts, drift, and baseline wandering is the provision of a high-absorbency buffer layer with isotonic electrolyte. This layer absorbs the effects of movement of the electrode in relationship to the skin and attempts to maintain the polarization associated with the half-cell potential constant.