Medical electronics slide share

Medical Electronics Electro-physiology and Bio-potential Recording

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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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
Bioelectricphenomenaatthecellularlevel
Volumeconductorfieldsofsimplebioelectricsources
Volumeconductorfieldsofcomplexbioelectricsources
Volumeconductorfieldsasanecessarylinkbetween
cellularactivityandgrossexternallyrecordedbiological
signalsasweneedtofocuson
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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 ,pH Value 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.Frequencyresponse
3.Hysteresis
4.Isolation
5.Linearity
6.Sensitivity
7.Signaltonoiseratio
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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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 pasteimproveselectrodecontact when recording
biopotentials.Electrode pasteimproveselectrodecontact
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:
Theseare 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
Microelectrodehavesmallerdiameterandduring
insertionoftheelectrodeintothecell,thereisno
damagetothecell
Whenmicroelectrodeisusedtomeasurethepotential
ofthecell,anotherelectrodecalledreferenceelectrode
isplacedoutsideofthecell
Thesizeofthecellisdeterminedbythesizeofthecell
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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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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.MetalplateElectrode
2.Suctioncupelectrode
3.Adhesivetapeelectrode