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MEDICAL ELECTRONICS
Mr. DEEPAK P.
Associate Professor
ECE Department
SNGCE
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UNIT 1
Introduction to Human
Physiological Systems and
Transducers
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Objective
 At the end of this Unit
 You will learn
 Physiological Systems of human
body
 Bio medical Transducers and
Electrodes
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Introduction to Biomedical
Engineering
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Biomedical Engineering
Biomedical 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
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Biomedical Instruments
Classification of Biomedical Equipments
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1.
Diagnostic equipment
2.
Therapeutic equipment
3.
Clinical equipment
4.
Laboratory equipment
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Man- Instrument System
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Components in Man – Instrument system
Control feedback
Stimulus
Transducer
Transducer
Signal
conditioning
equipment
Display
Transducer
Recording , data
processing and
transmission of data
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Man – Instrument system
Measurement 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
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Sources of Bioelectric potentials
 The 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 potentials
 Certain 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 potentials
 The 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.
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Resting potentials/Polarization
 This resting potential ranging from -60mv to -100 mv.
 Cell in the resting state is called polarized cell.
Cell Membrane
V
-70 mV
Ground
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Depolarization of cell
 When 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
Na+
Na+
Na+
K+
K+
K+
Na+
K+
Na+
K+
K+
Na+
K+
K+
Na+
Na+
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Cell Membrane
Action potentials
Cell Membrane
V
20 mV
Ground
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Re Polarization
 Cell comes from de polarized state in to polarized state is
called Re polarization.
Cell Membrane
V
-70 mV
Ground
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Resting and Action potentials
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Propagation of Action potentials
 When 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
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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.
Input
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System
Output
Physiological Systems in the Human body
Vision
Speech
Appearance
Hearing
Behavior
Taste
Inspired air
Expired air
Body movements
Tactile sensation
Liquid intake
Liquid wastes
Solid wastes
Food intake
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OUTPUTS
INPUTS
Smell
Physiological systems of human body
 There are 11systems in the body:
The Skeletal System
Bones & joints
2. Muscular System
Skeletal muscle
3. Nervous System
Brain, spinal cord & nerves
4. Endocrine System
Hormone-producing cells & glands
5. Cardiovascular System
Blood, heart & blood vessels
6. Respiratory System
Lungs & airways
7. Digestive System
Organs of the gastrointestinal tract
8. Urinary System
Kidneys, bladder and ureters
9. Reproductive System Male & female reproductive organs
10. The Integumentary System
The skin & derived structures
11. Lymphatic & Immune System Lymphatic vessels & fluid
1.
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Physiology of Cardiovascular
system
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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
•
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Study of breathing organs
Cardio Vascular system
Cardio 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
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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
Bicuspid/
Left Atrio-ventricular valve
Right Atrio-ventricular valve
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Heart Layers
Heart wall consists of three layers
Pericardium
1.
•
Myocardium
2.
•
Middle layer, Main muscle of heart, made up of short
cylindrical fibres
Endocardium
3.
•
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Outer most layer, keeps outer surface moist, prevents
friction
Inner layer of heart, Provides smooth lining for blood flow
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Heart Valves
Heart has 4 valves
1.
Tricuspid/Right Atrio-Ventricular valve
•
2.
Bicuspid/ left Atrio-Ventricular valve
•
3.
At right ventricle, It has 3 cusps
Aortic Valve
•
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Between left A and V, Prevents blood flow from left V to A
Pulmonary valve
•
4.
Between Right A and V, Prevents blood flow from right V to A
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Between left ventricle and aorta, It has 3 cusps
Cardio Vascular systems
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Cardio Vascular System
One 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 system
Fluid 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 Circulation
The 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 Circulation
Heart 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 branches
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Cardio Vascular Circulation
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Respiratory system
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Respiratory systems
It 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 systems
At 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 systems
In 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 volume
The volume inspired and expired during each normal breath
Inspiratory reserve volume
Additional volume that can be inspired after a normal
inspiration.
Expiratory reserve volume
Additional volume that can be expired after a normal
expiration.
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Respiratory systems
Residual volume
Amount of air remaining in the lungs after all possible air has
been forced out.
Vital capacity
Tidal volume+ Inspiratory reserve volume+ Expiratory reserve
volume
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Respiratory systems
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Blood purification in the human body
 The 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 body
 When 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 lungs
 The 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
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Muscular System
 The 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 System
 There are three distinct types of muscles: skeletal muscles,
cardiac or heart muscles, and smooth muscles.
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Muscular System
 Smooth 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 System
 Cardiac 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 System
 Muscle 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 System
 These 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
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Nervous systems
 The 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 systems
 It provides regulation of body functions and sensory
perception.
 Functions of Nervous systems
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1.
Control of the body
2.
Integration
3.
Communication
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Nervous systems
 Its 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 systems
 With 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 systems
 This 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 systems
 In 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 systems
 The 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 systems
 Central 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
Cerebrum
Cerebellum
Brain stem
Spinal cord
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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 systems
 The 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 systems
 The 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 systems
 The "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 systems
 Neurons
 Composed of:
 a.
Cell Body
 Part that contains the nucleus
 b.
Dendrite(s)
 Carries a nerve impulse towards the cell body
 c.
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 Neurons
 The three basic types of idealized neurons include;
 Bipolar, (Pseudo)
 Uni polar
 Multi 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 Neurons
 Bipolar – 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
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Sources of Biomedical Signals

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Bio- Potential Electrodes
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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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 .
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Bio Potential Electrodes
 Bio-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 Electrodes
 Propagation 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
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Body
Electrolytes
Metal Electrode
Equivalent circuit for bio-potential electrode
Vha=Electrode potential developed across interface
C=Charges at the Interface at the skin metal interface
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Equivalent circuit for bio-potential with two
electrode
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Bio Potential Electrodes
 Bio-potential electrodes transduce ionic conduction to
electronic conduction so that bio-potential signals can be
obtained
 They 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
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Bio Potential Electrodes
1.
Micro Electrodes--- Bio electric potential near or within a
single cell
 Metal Type—Tip must be tungsten or stainless steel
 Micro 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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Microelectrodes
 Used 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 electrodes
 These 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 ELECTRODES
 Historically, 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 electrodes
 Conductive paste reduces effect of electrode slippage
and resulting motion artifact
Needle electrodes
 Unipolar 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
Transducers
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Transducers
 A 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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Transducers
 Transducer can be classified in to two
 Active Transducer
 Known principles is used to convert variables in to electrical
signal
 Passive Transducer
 It involves control of an excitation voltage or modulation of
a carrier signal
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Principles used in Active Transducers
 It 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 Transducers
 Utilize 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 Transducers
 Using Resistive element
Ordinary Potentiometer
a. Linear
b. Rotary
2. Strain gage
a. Un bonded
b. Bonded
c. Semiconductor strain gage
 Using Inductive element
1. Variable reluctance Transducer
 LVDT
• Using Capacitive element
1.
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Transducers for Biomedical field
 Force transducer
 Photoelectric displacement transducer
 Pressure Transducers
 Flow transducers
 Transducers with digital O/P
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Transducers for Biomedical field
1.
2.
3.
4.
5.
6.
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Resistive transducers - Muscle force and Stress (Strain guge),
Spirometry (Potentiont) , humidity, (Gamstrers), Respiration
(Thermistor)
Inductive Transducers - Flow measurements, muscle
movement (LVDT)
Capacitive Transducers - Heart sound measurement, Pulse
pick up
Photoelectric Transducers - Pulse transducers, Blood
pressure, oxygen Analyses
Piezoelectric Transducers - Pulse pickup, ultrasonic blood
flowmeter
Chemcial Transducer - Ag-Agfallas (Electrodes, PH electrode
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pH Electrode
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pH Electrode
 This 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 Electrode
 When 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 Electrode
 The 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 Electrode

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Agcl Electrode
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Ag-Agcl Electrode

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Ag-Agcl Electrode
 A 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
 The 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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