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Electrode theory- Basic electrode, Electrodes for ECG

Electrode theory- Basic electrode, Electrodes for ECG. Electrode theory Need, types of Bio-potential electrodes. Basic electrode theory Various Electrodes for ECG. ELECTRODE - ELECTROLYTE & ELECTROLYTE-TISSUE INTERFACE. Electric equivalent circuits. :.

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Electrode theory- Basic electrode, Electrodes for ECG

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  1. Electrode theory- Basic electrode, Electrodes for ECG • Electrode theory • Need, types of Bio-potential electrodes. • Basic electrode theory • Various Electrodes for ECG.

  2. ELECTRODE - ELECTROLYTE & ELECTROLYTE-TISSUE INTERFACE

  3. Electric equivalent circuits

  4. :

  5. Electrode theory- Basic electrode, • Need & Types of Bio-potential electrodes • Surface electrodes • Deep seated electrode • Factors to be consider while measurements: • Careful and suitable selection of electrodes for satisfactory record of bioelectric signal. • Comfortable for the patients to wear over long period • They should not produce any moving artefacts • Convenient in practical applications • Good contact with skin (for low contact impedance)

  6. Cont.. • The characteristics of a metalic/nonmetalic surface electrodes depends upon- • Condition at metal-electrolyte interface • Electrolyte –skin interface • Quality of electrolytes • Electrode properties Why electrode jelly is required while measurements of biopotential signals?

  7. Cont.. • Electrode Potentials • All electrode potentials are measured wrt a ref. Electrodes • Ref. Electrodes-Hydrogen electrode (H absorbed on platinum back -Calomel electrode Electrode potentials of few metal electrodes wrt Hydrogen

  8. Cont.. • potential between Electrode s in electrolyte

  9. Electrodes for ECG, EEG, EMG • Electrodes for ECG. • Electrodes for EEG, • Electrodes for EMG, • Biochemical Electrodes

  10. Electrodes for ECG, EEG, EMG Electrodes are used to pickup the biopotentials from the surface of the body of from inside the cells. Basic electrodes are classified as: • Skin surface electrodes • Needle electrodes • Microelectrodes

  11. Body Surface Recording Electrodes Electrode metal Electrolyte • Metal Plate Electrodes (historic) • Suction Electrodes • (historic interest) • Floating Electrodes • Flexible Electrodes

  12. Commonly Used Biopotential Electrodes Metal plate electrodes • Large surface: Ancient, therefore still used, ECG • Metal disk with stainless steel; platinum or gold coated • EMG, EEG • smaller diameters • motion artifacts • Disposable foam-pad: Cheap! (a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c)Disposable foam-pad electrodes, often used with ECG

  13. Commonly Used Biopotential Electrodes • Suction electrodes • No straps or adhesives required • precordial (chest) ECG • can only be used for short periods • Floating electrodes • metal disk is recessed • swimming in the electrolyte gel • not in contact with the skin • reduces motion artifact Suction Electrode

  14. Commonly Used Biopotential Electrodes Metal disk Insulating package Double-sided Adhesive-tape ring Electrolyte gel in recess Reusable (a) (b) External snap Snap coated with Ag-AgCl Gel-coated sponge Disposable Plastic cup Plastic disk Dead cellular material Tack Foam pad Capillary loops Germinating layer (c) Floating Electrodes

  15. Commonly Used Biopotential Electrodes • Flexible electrodes • Body contours are often irregular • Regularly shaped rigid electrodes • may not always work. • Special case : infants • Material : • - Polymer or nylon with silver • - Carbon filled silicon rubber • (Mylar film) (a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode.(c) Cross-sectional view of the thin-film electrode in (b).

  16. Internal Electrodes Needle and wire electrodes for percutaneous measurement of biopotentials (a) Insulated needle electrode. (b) Coaxial needle electrode. (c) Bipolar coaxial electrode. (d) Fine-wire electrode connected to hypodermic needle, before being inserted. (e) Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place.

  17. Fetal ECG Electrodes Electrodes for detecting fetal electrocardiogram during labor, by means of intracutaneous needles (a) Suction electrode. (b) Cross-sectional view of suction electrode in place, showing penetration of probe through epidermis. (c) Helical electrode, which is attached to fetal skin by corkscrew type action.

  18. Insulated leads Contacts Ag/AgCl electrodes Ag/AgCl electrodes Contacts Base (b) Base Insulated leads (a) Tines Exposed tip Base (c) Electrode Arrays Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array, (b) Two-dimensional array, and (c) Three-dimensional array

  19. Microelectrodes Why Measure potential difference across cell membrane Requirements • Small enough to be placed into cell • Strong enough to penetrate cell membrane • Typical tip diameter: 0.05 – 10 microns Types • Solid metal -> Tungsten microelectrodes • Supported metal (metal contained within/outside glass needle) • Glass micropipette -> with Ag-AgCl electrode metal Intracellular Extracellular

  20. Metal Microelectrodes C Microns! R Extracellular recording – typically in brain where you are interested in recording the firing of neurons (spikes). Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier!

  21. Metal Supported Microelectrodes (a) Metal inside glass (b) Glass inside metal

  22. Ag-AgCl wire+3M KCl has very low junction potential and hence very accurate for dc measurements (e.g. action potential) Glass Micropipette heat pull A glass micropipet electrode filled with an electrolytic solution (a) Section of fine-bore glass capillary. (b) Capillary narrowed through heating and stretching. (c) Final structure of glass-pipet microelectrode. Fill with intracellular fluid or 3M KCl Intracellular recording – typically for recording from cells, such as cardiac myocyte Need high impedance amplifier…negative capacitance amplifier!

  23. Electrical Properties of Microelectrodes Metal Microelectrode Metal microelectrode with tip placed within cell Equivalent circuits Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier!

  24. Electrical Properties of Glass Intracellular Microelectrodes Glass Micropipette Microelectrode

  25. Electrodes for ECG, EEG, EMG • Various Electrodes used for the measurement or recording of ECG signal. • Immersion electodes(not used now) • Limb electrodes • Suction cup electrodes • Floating electrodes • Spray –on electrodes • Pregelled disposable electrode • Pasteless (dry) electrodes • Air –jet ECG electrodes

  26. ECG Electrodes ECG plate electrode. The electrode is usually Fastened to the arm or leg with a perforated Rubber strap which keeps it in position during ECG recording Light weight floating Electrode with press Stud for long term monitoring

  27. ECG Electrodes

  28. ECG Electrodes Disposable pre-gelled ECG Electrode. A porous tape overlaying placed over the electrode resists perspiration and Ensures positive placement Under stress conditions Air –Jet ECG Electrodes

  29. ECG Electrodes Suction cup electrode (Unipolar chest ECG Electrode.) Floating type skin surface ECG Electrodes 29

  30. Electrodes for ECG, EEG, EMG • Various Electrodes used for the measurement or recording of EEG signal. • Scalp surface electrodes (chlorided silver discs) • Ear-clip electrodes (reference electrode) • Small needle electrodes • Silver ball or pellet electrodes(exposed cortex, high resistance) • Pad electrode(silver ball is belled out at the end and padded with a sponge) • Chlorided silver wire in plastic cup electrodes

  31. EEG Electrodes EEG Electrode which can Be applied to the surface Of the skin by an adhesive tape. Ear-clip Electrodes & EEG scalp surface Electrodes

  32. EEG Electrodes

  33. Electrodes for ECG, EEG, EMG • Various Electrodes used for the measurement or recording of EMG signal. • Needle electrodes • Monopolar • Bipolar • Concentric core needle • Multi-element needle electrodes • Biochemical Electrodes • Reference electrode • pH electrodes • Blood Gas electrode

  34. EMG Electrodes

  35. Micro Electrodes

  36. Metal micro-electrodes

  37. Biochemical Electrodes • Biochemical Electrodes • Reference electrode • pH electrodes • Blood Gas electrode • pO2 Electrode • pCO2 Electrode

  38. L7, L8: Nernst eq. & Skin contact impedance • Nernst equation • Skin contact impedance • Skin contact impedance measurement • Motion artifacts

  39. Nernst Equation: Dept. of Electronics and Telecommunication Engineering

  40. SKIN CONTACT IMPEDANCE MEASUREMENT: Dept. of Electronics and Telecommunication Engineering

  41. : Dept. of Electronics and Telecommunication Engineering

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