The document outlines the syllabus and introductory concepts of medical electronics, focusing on bio-potential recording, bioelectrical phenomena, and the design of biomedical instruments. It highlights the significance of electrodes, transducers, and various types of electrodes used for measuring bioelectric signals in clinical practice. Additionally, it discusses factors influencing the design and functionality of medical devices, emphasizing accuracy, sensitivity, and safety.

1. Medical Electronics
V.Bharathi M.E.,M.B.A.,(PhD)
Asst.Prof Dept of ECE
Kongunadu college of Engg& Tech,Trichy
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2. Syllabus
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3. Unit –I Syllabus
Electro-physiology and Bio-potential
Recording
The origin of Bio-potentials; biopotential electrodes,
biological amplifiers, ECG, EEG, EMG, PCG, lead
systems and recording methods, typical waveforms
and signal characteristics.
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4. Applications of Medical
Electronics
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5. Introduction
 Medical electronics, or more specifically the instrumentation
used in physiological measurement, has changed significantly
over the last few years.
 Developments in electronics technology have offered new
and enhanced applications, especially in the areas of data
recording and analysis and imaging technology.
 These changes have been accompanied by more safety and
liability.
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6. Applications of Medical
Electronics
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7. 29 January 20197

8. 29 January 20198

9. The origin of Bio-potentials
Introduction
 For anyone concerned with the field of bio-medical
instrumentation they should be aware of physical and
chemical factor that are responsible for the origin
 Bioelectric phenomenon is of immense importance to
biomedical engineers because these potentials are routinely
recorded in modern clinical practice
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10. To understand the origin of biopotential
Bioelectric phenomena at the cellular level
 Volume conductor fields of simple bioelectric sources
 Volume conductor fields of complex bioelectric sources
 Volume conductor fields as a necessary link between
cellular activity and gross externally recorded biological
signals as we need to focus on
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11. Cells and their structures
 Basic living unit of the body is the Cell
 To understand the function of organs and their structures of
the body it is essential to know about the basic organization
of the cell and the functions of its component parts
 The entire body contains about 100 trillions Cells .Among
this 25 trillion Cells are red blood cells which transport
oxygen form lungs to the tissues
 Generally all cells have ability to reproduce new cells when
they are destroyed
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12. Cell Structure
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13. A cell consists of a
Plasma membrane
 It is selectively permeable to (various ions such as) Na+, K+
and intracellular anions.
 The fluid inside the plasma membrane called the
intracellular fluid(ICF)
 The fluid outside the plasma membrane is called the
extracellular fluid (ECF)
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14. Nucleus:
 It is the largest single organized cellular component.
 It is a distinct spherical or oval structure located near the
center of the cell. It is covered by a double-layered
membranous structure
Cytoplasm:
 It is a gel-like mass with membrane-bound structures
suspending in it
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15. Bio potential electrodes and
Transducer
 A medical instruments perform a specific function on a
biological system. the function may be the exact
measurement of physiological parameters like blood
pressure ,velocity of blood, action potential of heart muscles,
temperature ,pHValue of the blood
 The biomedical measuring devices should cause minimal
disturbances to the normal physiological function and are to
be used with safety instrumentation
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16. Design of biomedical Instruments
 When we design a medical instrument the following factors
should be considered
1. Accuracy
2. Frequency response
3. Hysteresis
4. Isolation
5. Linearity
6. Sensitivity
7. Signal to noise ratio
8. Simplicity
9. Stability
10. Precision
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17.  Accuracy –It is the closeness with which a instrument
reading approaches the true value of the variable being
measures
 Frequency response – It is the response of the instruments for
various components
 Hysteresis- Output response for the measured value
 Isolation – Electrical safety on the subject where the measurement
is done
 Linearity – Constant output value from the instrument
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18.  Sensitivity-The instrument is how much sensible
 Signal to noise ratio- Ration of input and output
 Simplicity-The components to be simple not complex
 Stability- produces stable output
 Precision- Reproducibility of the measurements
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19. Basic Instrumentation system
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20. Components of Bio medical
Instrument system
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21.  Transducer –Transducer is device capable of converting one
form of energy or signal to electrical signal
 Signal Processor - It an important instrument system which
amplified,modifies,analyzes
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22. Electrodes
 Electrodes are employed to pick up the electrical signals of
the body .
 In the biomedical instrumentation system the pair of
electrodes plays the role of the transducer.
 Since the electrodes are transferring the bio electric event to
the input of the amplifier ,the amplifier should be designed
such that it accommodates the characteristics of electrode
 Medical electrodes comprises of a lead, metal and electrode
conducting paste
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23. Contd…
 Medical electrodes proceed with quantification of internal
ionic currents and results in diagnosis of various ocular,
nervous, cardiac, and muscular disorders.
 The device works through provision of an electrical contact
between apparatus used to monitor activities and patient
 The electrodes used in medical devices can be segmented as
reusable disc, disposable, headbands and saline based
electrodes
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24. Contd…
 In addition, the electrodes can also be classified based on
their applications such as ECG Electrodes, Blood Gas
Electrodes, EEG/EMG/ENG Electrodes, and Defibrillator
Electrodes.
 Moreover, they can also be sub segmented as Fetal Scalp
Electrodes, Electrosurgical Electrodes,TENS Electrodes,
Pacemaker Electrodes, pH Electrodes, Nasopharyngeal
Electrodes, and Ion-selective Electrodes.
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25. Half cell potential or Electrode
potential
 The voltage developed at an electrode interface is designated
as the half cell potential
 When a metal electrode comes into contact with an body
fluid there is a tendency for the electrode to discharge ions
into the solution
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26.  The above figure shows the electrical equivalent circuit of a
surface electrode when it is in contact with the body surface
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27. Measuring Half cell potential
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28. 29 January 201928

29. Polarization
 If there is a current between the electrode and
electrolyte, the observed half cell potential is often
altered due to polarization
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30. Purpose of electrode paste
 The dry outer skin of the body is highly non conductive and
will not establish a good electrical contact with an electrode
 Electrode paste improves electrode contact when recording
biopotentials. Electrode paste improves electrode contact
when recording biopotentials
 The skin should be washed and rubbed briskly to remove the
outer cells .that area should be coated with an electrically
conducting cream that is called electrode paste.
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31.  Generally the conductivity of the skin is directly proportional
to the moisture of the skin
 Example the ECG electrode contact impedance on dry skin is
about 100 Kilohms means after applying electrode paste it is
reduced to 10 Kilohms
 Alcohol, electrode paste ,saline solution has negligible
impedance around 1000Hz
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32. Electrode material
 The electrode ,electrode paste and body fluids can produce a
battery like action causing ions to accumulate on the
electrodes, such polarization of the electrode will affect the
signal transfer
 Polarization- If there is a current between the electrode
and electrolyte, the observed half cell potential is often
altered due to polarization.
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33. Nernst Equation
 When two aqueous ionic solutions of different concentration
are separated by an ion-selective semi-permeable membrane,
an electric potential exists across the membrane.
 The Nernst equation for half cell potential is
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34. Polarizable and Non-Polarizable
Electrodes
Polarizable Electrodes:
These are electrodes in which no actual charge crosses
the electrode-electrolyte interface when a current is applied.
The current across the interface is a displacement current
and the electrode behaves like a capacitor.
Example :Ag/AgCl Electrode
Non -Polarizable Electrodes:
These are electrodes where current passes freely
across the electrode-electrolyte interface, requiring no
energy to make the transition
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Use for recording
Use for stimulation

35. Types of Electrodes
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There are three types of electrodes
 Micro Electrode: these are used to measure the bio
electric potential near or with in a single cell.These are
called intracellular electrodes
 Depth and needle Electrodes:These are used to measure
the bio electric potential of the highly localized extra cellular
regions in brain or group of muscles
 Surface electrodes:These are used to measure the
potential available from the surface of the skin and are usede
to sense the potential form heart, brain and nerves

36. Micro Electrodes
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37. Micro Electrodes
 Micro electrode have smaller diameter and during
insertion of the electrode into the cell ,there is no
damage to the cell
 When micro electrode is used to measure the potential
of the cell ,another electrode called reference electrode
is placed outside of the cell
 The size of the cell is determined by the size of the cell
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38. Metal electrode
 Metal micro electrode are formed by electrolytically
etching the tip of a fine tungsten or stainless steel wire
to a fine point, this technique is known as
Elecrtopointing
 Micro electrode are coated with insulating material
 The figure shows the position of the electrode and its
equivalent circuit
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39. Position of Electrode
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40. Equivalent circuit
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41. Non metallic or Micropipettes
 The nonmetallic micropipette consists of a glass micropipette
whose tip diameter is 1 Micrometer. the micropipette is
filled with electrolyte solution
 A thin wire from silver, tungsten is inserted to the stem of
the micropipette
 Other end of the metal wire is mounted to the rigid support
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42. 29 January 201942

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44. 29 January 201944

45. Depth and needle Electrode
 Depth and needle electrode is used to study the electrical
activity of neurons in superficial layers of the brain.Normaly
each electrode consists of bundle of teflon insulated
platinum(90%) and iridium(10%)
 The end of the wire is rounded for ease of insertion into the
brain
 Each individual wire is acts as electrode.Therefore the depth
of the electrode impedance is smaller than the
Microelectrode
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46.  In some depth electrode the supporting steel wire is in the
form of capillary tube which is used to inject medicine in
brain
 It is also used to measure oxygen tension
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47. Surface Electrode
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 Generally larger area surface electrodes are used to sense
ECG potentials ad smaller area surface electrodes are used to
sense EEG & EMG potentials
1. Metal plate Electrode
2. Suction cup electrode
3. Adhesive tape electrode