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MEDICAL ELECTRONICS

Mr. DEEPAK P.Associate ProfessorECE Department

SNGCE

1

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UNIT 1

2

Introduction to Human Physiological Systems and

Transducers

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Objective At the end of this UnitYou will learn

Physiological Systems of human body

Bio medical Transducers and Electrodes

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Introduction to Biomedical Engineering

Biomedical EngineeringBiomedical Engineering is the application of engineering principles and design concepts to medicine and biology

The biomedical engineering provides electrical, electronic, electro-optical, and computer engineering support to clinical and biomedical applications.

Biomedical Engineering improves the field of healthcare diagnosis, monitoring and therapy.

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Medical Instruments

Biomedical InstrumentsClassification of Biomedical Equipments

1. Diagnostic equipment

2. Therapeutic equipment

3. Clinical equipment

4. Laboratory equipment

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Man- Instrument System

Components in Man – Instrument system

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Control feedback

Recording , data processing and transmission of data

Signal conditioning equipment

DisplayTransducer

Transducer

Transducer

Stim

ulus

Man – Instrument systemMeasurement in biomedical instrumentation can be divided in to two

1.VIVO•Measurement is made on or within the human body

•Eg . Device inserted in to the blood stream to measure PH of blood

2.VITRO•Measurement is performed outside of the body.

•Eg . Measurement of blood PH from blood samples.

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Bioelectric Potentials

Sources of Bioelectric potentialsThe systems in the human body generate their on

monitoring signals when they carry out their functions.

These signals provide useful information about their function.

Bioelectric potentials are actually ionic voltages produced as a result of electro chemical activity of certain cell.

Transducers are used to convert these ionic potentials in to electrical signals

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Resting and Action potentialsCertain types of cells within the body , such as nerve and

muscle cells are encased in a semi permeable membrane.

This membrane permits some substances to pass through while others are kept out.

Surrounding the cells of the body are the body fluids

These fluids are conductive solutions containing charged atoms known as ions

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Resting potentialsThe principle ions are sodium(Na+) Potassium(K+)

and chloride(C-)

The membrane of excitable cells permit entry of Potassium(K+) and chloride(C-) ions but blocks the entry of sodium(Na+) ions.

So inside the cell is more negative than outside cell

This membrane potentials is called Resting potentials

This potential is measured from inside the cell with respect to body fluids.

So resting potential of a cell is negative. 14 DEEPAK.P

Resting potentials/PolarizationThis resting potential ranging from -60mv to -100 mv.Cell in the resting state is called polarized cell.

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Ground

V

Cell Membrane

-70 mV

Depolarization of cellWhen a cell is exited, the membrane

change its characteristic.

The sodium ions are rushed in to the cell.

At the same time potassium ions try move from inside.

After a equilibrium state is reached, the sodium is moved back to outside

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Depolarization of cell

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Cell MembraneNa+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

K+

K+

K+ K+

K+

K+

K+K+

Action potentials

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Cell Membrane

V

Ground

20 mV

Re PolarizationCell comes from de polarized state in to polarized state is

called Re polarization.

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Ground

V

Cell Membrane

-70 mV

Resting and Action potentials

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Propagation of Action potentialsWhen a cell is exited and generates an action potentials

ionic currents to flow.This process excite neighboring cells or adjacent area of

the same cell

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Physiological Systems in Human body

Physiological systems of human body

In simple terms "Human Physiology" is the study of the body and its functions in each of the different systems in any living body.

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SystemInput Output

Physiological Systems in the Human body

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Behavior

Liquid wastes

Solid wastes

Body movements

Expired air

Appearance

Speech

Food intake

Liquid intake

Vision

Smell

Taste

Hearing

Inspired air

Tactile sensation

INPU

TS

OU

TPU

TS

Physiological systems of human bodyThere are 11systems in the body: 1. The Skeletal System Bones & joints2. Muscular System Skeletal muscle3. Nervous System Brain, spinal cord & nerves4. Endocrine System Hormone-producing cells & glands5. Cardiovascular System Blood, heart & blood vessels6. Respiratory System Lungs & airways7. Digestive System Organs of the gastrointestinal tract8. Urinary System Kidneys, bladder and ureters9. Reproductive System Male & female reproductive organs10.The Integumentary System The skin & derived structures11.Lymphatic & Immune System Lymphatic vessels & fluid

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Physiology of Cardiovascular system

Physiology•Physiology can be classified in to

1.Cell Physiology

• Study of cells

2.Patho Physiology

• Pathological Functions

3.Circulatory Physiology

• Study of blood circulation

4.Respiratory Physiology

• Study of breathing organs

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Cardio Vascular systemCardio vascular system can be viewed as closed hydraulic system with 4 chamber pump.

Cardio Vascular system is mainly used for transportation of oxygen, Carbon dioxide, numerous chemical compounds and the blood cells.

•Pump-----Heart

•Flexible tubes---Blood vessels

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Cardio Vascular system•In some part of the system diameter of the arteries are changed to control pressure.

•Pump(heart) is a isolated two stage synchronized chamber

1.The first stage is to collect blood from the system and pump it in to 2nd stage.

2.The second stage then pump these blood to the system

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Heart & Valves

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Bicuspid/Left Atrio-ventricular valve

Heart LayersHeart wall consists of three layers

1.Pericardium• Outer most layer, keeps outer surface moist, prevents

friction

2.Myocardium• Middle layer, Main muscle of heart, made up of short

cylindrical fibres

3.Endocardium• Inner layer of heart, Provides smooth lining for blood flow

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Heart ValvesHeart has 4 valves

1.Tricuspid/Right Atrio-Ventricular valve• Between Right A and V, Prevents blood flow from right V to A

2.Bicuspid/ left Atrio-Ventricular valve• Between left A and V, Prevents blood flow from left V to A

3.Pulmonary valve• At right ventricle, It has 3 cusps

4.Aortic Valve• Between left ventricle and aorta, It has 3 cusps

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Cardio Vascular systems

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Cardio Vascular SystemOne of the two stage pump(Right side) collect fluid from the system and pump it through oxygenation system(Lungs).

Other side pump receives blood from oxygenation system(Lungs) and pump blood to main hydraulic system.

Blood act as communication and supply network for all parts of the body

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Cardio Vascular systemFluid contains fuel suppliers and waste particles are transported to destination.

Fluid contain mechanism for rejecting foreign elements and mechanism for repairing small system puncture.

Sensors are provided to detect the changes in the need of suppliers, the build of waste material and out-of- tolerance pressure in the system known as chemoreceptors, Pco2 sensors and baroreceptors respectively.

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Cardio Vascular CirculationThe blood is carried out to the various parts of the body through blood vessels.

There are three types of blood vessels

1)Arteries--- Thick, Carries oxygenated blood

2)Veins--- Thin, De-oxygenated blood

3)Capillaries---Smallest, Last level of blood vessels, 800000 km of capillaries

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Cardio Vascular CirculationHeart pumps blood through the pulmonary circulation to the lungs and through the systemic circulation to the other parts of the body.

1)Pulmonary circulation

2)Systemic circulation

In pulmonary circulation, venous blood(de-oxygenated) flows from right ventricle through pulmonary artery to lungs .

The arterial( oxygenated) blood flows to left atrium through pulmonary veins. In systemic circulation blood flows from left auricle to left ventricle and it is pumped to aorta and its branches37 DEEPAK.P

Cardio Vascular Circulation

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Respiratory system

Respiratory systemsIt is the Pneumatic system.

A system that work with air pressure.An air pump(diaphragm) which alternatively create negative and positive pressures in a sealed chamber(Thoracic cavity).Thoracic cavity sucked air in to and forced out to two elastic bags(Lungs).The lungs are connected to the external environment through a pass way (nasal cavities, pharynx, larynx, trachea, bronchi and bronchioles)

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Respiratory systems

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Respiratory systemsAt one point , this passage is common with the tube that carries liquid and solids to stomach.

A special valving arrangement interrupts the respiratory system whenever solid or liquid passes through the common region.

The passage divides to carry air in to each bag.

In each bag , it is sub divided many times to carry air in to and out of each of many tiny air spaces (pulmonary alveoli).

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Respiratory systemsIn case of nasal blockage , air input can be taken from mouth.

Oxygen is taken from the air and transferred in to blood.

Cabondioxide is transferred from blood to air.

The system has a number of fixed volumes and capacities.

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Respiratory systems

Tidal volumeThe volume inspired and expired during each normal breath

Inspiratory reserve volumeAdditional volume that can be inspired after a normal inspiration.

Expiratory reserve volumeAdditional volume that can be expired after a normal expiration.

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Respiratory systemsResidual volumeAmount of air remaining in the lungs after all possible air has been forced out.

Vital capacityTidal volume+ Inspiratory reserve volume+ Expiratory reserve volume

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Respiratory systems

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Blood purification in the human bodyThe overall functioning of our body heavily depends on the

proper functioning of our blood.

We take toxins into our body daily and these toxins disrupts the functions of our internal organs.

Regular detoxification of our blood is important

Detoxifying the blood and body helps to remove harmful toxins from our body and improve the functioning of our vital organs such as the kidney and liver

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Blood purification in the human bodyWhen our body has too much toxins,

our vital organs start to get damage and under-perform and we start to develop symptoms of allergies, low immunity, headaches, fatigue and several other health related problems.

The lungs help remove carbon dioxide, the kidneys remove water-soluble waste and the liver removes fat soluble wastes and many other impurities from the blood.

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Blood purification by lungsThe un oxygenated (unpurified) blood comes

into right atrium of heart by superior and inferior vena-cava which then passes to right ventricle, then to lungs by pulmonary artery.

In lungs this blood gets oxygenated (purified) which then goes into left chamber of heart from which blood is passed to aorta and then circulated to whole body

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Blood purification by lungs

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Blood purification by lungs

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Muscular System

Muscular SystemThe muscular system is the biological system of humans that produces movement.

It permits movement of the body, maintains posture, and circulates blood throughout the body.

The muscular system is controlled through the nervous system.

Muscles provide strength, balance, Posture, movement and heat for the body to keep warm.

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Muscular System• More than 50% of body weight is muscle.

• Muscle is made up of proteins and water

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Muscular SystemThere are three distinct types of muscles: skeletal muscles,

cardiac or heart muscles, and smooth muscles.

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Muscular SystemSmooth muscle or "involuntary muscle" consists of spindle

shaped muscle cells found within the walls of stomach, intestines, bronchi, uterus, ureters, bladder, and blood vessels.

Smooth muscle cells contain only one nucleus.

Cardiac muscle is also an "involuntary muscle" but it is striated in structure and appearance.

Like smooth muscle, cardiac muscle cells contain only one nucleus.

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Muscular SystemCardiac muscle is found only within the heart.

Skeletal muscle or "voluntary muscle" is anchored by tendons to the bone and is used to effect skeletal movement such as locomotion.

Skeletal muscle cells are multinucleated with the nuclei peripherally located.

Skeletal muscle is called 'striated' because of the longitudinally striped appearance under light microscopy.

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Muscular SystemMuscle is composed of muscle cells (sometimes known as

"muscle fibers").

Within the cells are myofibrils; myofibrils contain sarcomeres which are composed of actin and myosin.

Individual muscle cells are lined with endomysium.

Muscle cells are bound together by perimysium into bundles called fascicles.

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Muscular SystemThese bundles are then grouped together to form muscle, and

is lined by epimysium.

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Muscular System

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Muscular System

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Nervous systems

Nervous systemsThe task of controlling various functions of body and

coordinating them in to a integrated living organism(human body) is the function of Nervous system

It is the most complex system in the human body

It is the communication network in the human body.

It composed of Brain, Sensors, high speed communication links ,spinal cord.

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Nervous systemsIt provides regulation of body functions and sensory

perception.

Functions of Nervous systems

1. Control of the body

2. Integration

3. Communication

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Nervous systemsIts center is a self adapting processor(Brain).

Self adapting means --- If a certain section is damaged, other sections can adapt take over the function of damaged sections

This processor has memory, computational power, decision making capability.

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Nervous systemsWith the use of this processor , human can take decisions,

solve complex problems, create art, poetry and music, feel emotions and integrate input information from all parts of the body and produce output signals of meaningful information.

Central computer has millions of communication lines( afferent and efferent nerves) that bring sensory information and transfer control information from brain.

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Nervous systems

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Nervous systemsThis lines are not single lines but complicated networks.

Information signal are normally coded by means of electro

chemical pulses that travel along the nerves.

The output control signals are channeled to specific motor

devices(motor units of muscles)

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Nervous systemsIn addition to brain , a large number of simple decision making

g devices(Spinal reflexes) are present to control directly

certain motor devices from certain sensory inputs.

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Divisions of Nervous systemsThe human nervous system can be divided into three main parts: 1. Central nervous system (CNS)

*is composed of brain and spinal cord...*

2. Peripheral nervous system (PNS)*is composed of all body nerves that lie outside of your

central nervous system...*

3. Autonomic nervous system (ANS) *Controls the involuntary actions of your body

organs...*

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1. Central Nervous systemsCentral Nervous System (CNS)Structures of the CNS: [1]  Brain[2]  Spinal cord

The CNS coordinates and interprets information to determine the best response 

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Anatomy of the Central Nervous systems

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Spinal cord

CerebellumBrain stem

Cerebrum

2. Peripheral Nervous systems

The primary role of the PNS is to connect the CNS to the

organs, limbs and skin.The nerves that make up the peripheral nervous system are

actually the axons or bundles of axons from neuron cells.

The peripheral nervous system is divided into two parts:The somatic nervous system The autonomic nervous system

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Somatic Nervous systemsThe somatic system is the part of the peripheral nervous

system responsible for carrying sensory and motor

information to and from the central nervous system.This system contains two major types of neurons:

Sensory neurons (or afferent neurons) that carry information

from the nerves to the central nervous system.Motor neurons (or efferent neurons) that carry information from

the brain and spinal cord to muscle fibers throughout the body.

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3. Autonomic Nervous systemsThe autonomic system is the part of the peripheral nervous

system responsible for regulating involuntary (reflex/Un

intentional)body functions, such as blood flow, heartbeat,

digestion and breathing.

This system is further divided into two branches:

The sympathetic system regulates the flight-or-fight responses.

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Autonomic Nervous systemsThe "fight or flight response" is our body's primitive,

automatic, inborn response that prepares the body to "fight" or "flee" from perceived attack, harm or threat to our survival.

Parasympathetic system helps maintain normal body functions and conserves physical resources

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Anatomy of the Nervous systems

Basic unit of nervous system is the neuron.

Neurons are the basic building blocks of the nervous system.

Neuron is a single cell with a cell body.

It is sometimes called soma

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Anatomy of the Nervous systems

Neuron cells are the information-processing units of the brain

responsible for receiving and transmitting information.

One or more I/P fibers branches are called dendrites

Long transmitting fiber is called axon

Each part of the neuron plays a role in the communication of

information throughout the body.

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Anatomy of the Nervous systems

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Anatomy of the Nervous systemsNeurons Composed of: a.     Cell Body

Part that contains the nucleusb.      Dendrite(s)

Carries a nerve impulse towards the cell bodyc.       Axon(s)

Carries a nerve impulse away from the cell body (and towards the dendrite of the next neuron)

Axons are also called nerve fibers.

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Types of NeuronsThe three basic types of idealized neurons include;

Bipolar, (Pseudo) Uni polarMulti polar neurons,

Typically these neurons are found in different places around the body:

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Types of Neurons

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Types of NeuronsBipolar – Specialized sensory neurons for the transmission of

special senses.

As such, they are part of the sensory pathways for smell, sight, taste and hearing functions.

The most common example are the bipolar neurons found in the retina

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Types of Neurons(Pseudo) Unipolar

Many types of primary sensory neurons are Unipolar.

Multi polar – Multi polar neurons constitute the majority of neurons in the brain and include motor neurons and interneuron's.

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Sources of Biomedical Signals

Sources of Biomedical Signals

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Bio- Potential Electrodes

Measurement of Bioelectric potentials

To measure bioelectric potentials , a transducer is required.

Electrical signals produced by various body activities are

used in monitoring / diagnosis

In order to measure and record potentials and, hence, currents

in the body, it is necessary to provide some interface

between the body and the electronic measuring apparatus.

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Bio Potential ElectrodesBio-potential electrodes carry out this interface function.A transducer consists of two electrodes, which measure ionic

potential difference between two points.

The designation of the Bio potential waveform ends with

“Gram”.

The name of the instrument bio potential normally ends

with “Graph”

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Bio Potential ElectrodesPropagation of action potential through different body tissues

produces final waveform recorded by electrodes

Electrical activity is explained by differences in ion concentrations within the body (sodium, Na+; cloride, Cl–; potassium, K+)

A potential difference (voltage) occurs between 2 points with different ionic concentrations

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Electrodes Theory

Equivalent circuit for bio-potential electrode

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Bod

y El

ectro

lyte

s

Vha=Electrode potential developed across interface

C=Charges at the Interface at the skin metal interface

Met

al E

lect

rode

Equivalent circuit for bio-potential with two electrode

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Bio Potential ElectrodesBio-potential electrodes transduce ionic conduction to

electronic conduction so that bio-potential signals can be

obtainedThey generally consist of metal contacts packaged so that they

can be easily attached to the skin or other body tissues

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Classification of Electrodes

Bio Potential Electrodes1. Micro Electrodes--- Bio electric potential near or within a

single cellMetal Type—Tip must be tungsten or stainless steelMicro pipette---It is a glass micropipet with size of 1

micron, It is filled with electrolyte

2. Skin surface electrode —Measure ECG,EEG,EMG

3. Needle electrode ---Penetrate the skin to record EEG

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MicroelectrodesUsed to measure bio-potential signals at

the cellular level

Due to small dimensions (mm), impedance levels are high

So amplifier needs very high input impedance

Microelectrodes

METAL MICROELECTRODES

MICROPIPETTE ELECTRODES

Surface electrodesThese are placed in contact with the skin of

the subject

Early stages immersion electrodes were used.

A bucket of saline water is used

An improvement of immersion electrode is the plate electrode.

Another old type electrode is suction type

Immersion electrodes

Surface electrodes

METAL-PLATE ELECTRODESHistorically, one of the most frequently used forms of

bio-potential sensing electrodes is the metal-plate electrode.

In its simplest form, it consists of a metallic conductor in contact with the skin.

An electrolyte soaked pad or gel is used to establish and maintain the contact.

METAL-PLATE ELECTRODES

Floating electrodesConductive paste reduces effect of

electrode slippage and resulting motion artifact

Needle electrodesUnipolar electrode---Single wire inside a

needle

Bipolar electrode---Two wires inside a needle

Mostly used for contacting with internal body tissues

(a) Insulated needle electrode .(b) Coaxial needle electrode .(c) Bipolar coaxial electrode .(d) Fine -wire electrode connected to

hypodermic needle, before being inserted .(e) Coiled fine -wire electrode in place

Needle electrodes

Implantable electrodes

ELECTRODE ARRAYS

ELECTRODE ARRAYS

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Transducers

TransducersA transducer is necessary to convert one variable in to another

form

Used to measure physiological variables

Variable is a quantity that vary with time.

The term active and passive has different meaning when they are applied to Transducers

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TransducersTransducer can be classified in to twoActive Transducer

Known principles is used to convert variables in to electrical signal

Passive TransducerIt involves control of an excitation voltage or modulation

of a carrier signal

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Principles used in Active TransducersIt can convert electrical signal in to physical variables and

also in reverse direction.

1. Magnetic Induction

2. Piezoelectric effect

3. Thermoelectric effect

4. Photoelectric effect

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Passive TransducersUtilize the principles of controlling a DC excitation or an AC

carrier signal.

It consists of a passive circuit element which changes it value as a function of physical variables to be measured.

It cannot convert electrical signal in to physical variables

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Principles used in Passive TransducersUsing Resistive element

1. Ordinary Potentiometera. Linearb. Rotary

2. Strain gagea. Un bondedb. Bondedc. Semiconductor strain gage

Using Inductive element1. Variable reluctance Transducer

LVDT• Using Capacitive element

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Transducers for Biomedical field1. Force transducer

2. Photoelectric displacement transducer

3. Pressure Transducers

4. Flow transducers

5. Transducers with digital O/P

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Transducers for Biomedical field1. Resistive transducers - Muscle force and Stress (Strain guge),

Spirometry (Potentiont) , humidity, (Gamstrers), Respiration (Thermistor)

2. Inductive Transducers - Flow measurements, muscle movement (LVDT)

3. Capacitive Transducers - Heart sound measurement, Pulse pick up

4. Photoelectric Transducers - Pulse transducers, Blood pressure, oxygen Analyses

5. Piezoelectric Transducers - Pulse pickup, ultrasonic blood flowmeter

6. Chemcial Transducer - Ag-Agfallas (Electrodes, PH electrode

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Ag-Agcl Electrode

Reference ElectrodeThe usual method of measuring the ion concentration by

combination of two electrode.

1. Active Electrode

2. Reference Electrode

• Commonly used reference electrode is Hydrogen Electrode.• It contains a piece of platinum wire partially immersed in

a solution containing hydrogen ions.

• This electrode is not stable.

• Two stable electrodes are

1. Silver- Silver chloride Electrode

2. Calomel Electrode

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Ag-Agcl ElectrodeA silver chloride electrode is a type of reference electrode,

commonly used in electrochemical measurements.

The silver/silver chloride reference electrode is a widely used reference electrode because it is simple, inexpensive, very stable and non-toxic.

Typical laboratory electrodes use a silver wire that is coated with a thin layer of silver chloride either by electroplating or by dipping the wire in molten silver chloride.

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Ag-Agcl Electrode

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Ag-Agcl ElectrodeThe electrode functions as a redox electrode and the reaction is

between the silver metal (Ag) and its salt — silver chloride (AgCl, also called silver(I) chloride).

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pH Electrode

pH Meter

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pH ElectrodeThis is a device for measuring the concentration of hydrogen

ions and hence the degree of acidity of a solution.pH is defined as the negative logarithm of the hydrogen ion

concentration.pH=7 means a concentration of 1x10-7 moles per litre. The most essential component of a pH electrode is a special,

sensitive glass membrane which permits the passage of

hydrogen ions, but no other ionic species.

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pH ElectrodeThe relationship between the ionic concentration (activity) and

the electrode potential is given by the Nernst equation:E = E0 + (2.303RT/ nF) x Log(A)Where  E = the total potential (in mV) developed between the sensing and reference electrodes. E0 = is a constant which is characteristic of the particular ISE/reference pair. (It is the sum of all the liquid junction potentials in the electrochemical cell, see later) 2.303 = the conversion factor from natural to base10 logarithm. R = the Gas Constant (8.314 joules/degree/mole). T = the Absolute Temperature. n = the charge on the ion (with sign). F = the Faraday Constant (96,500 coulombs). Log(A) = the logarithm of the activity of the measured ion.

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pH ElectrodeWhen the electrode is immersed in a test solution containing

hydrogen ions the external ions diffuse through the

membrane until an equilibrium is reached between the

external and internal concentrations.Thus there is a build up of charge on the inside of the

membrane which is proportional to the number of hydrogen

ions in the external solution.The potential difference developed across the membrane is in

fact directly proportional to the Logarithm of the ionic concentration in the external solution.

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pH Reference Electrode

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pH Electrode

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Glass pH Electrode

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