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MODULE 1
Human Physiology Systems and Transducers
Problems encountered in measuring living systems - Cardio-vascular–Respiratory- nervous and
muscular systems of the body.
Electrode theory-Bioelectric potential - Resting and action potential - Generation and propagation
Bioelectric potentials associated with physiology systems (ECG, EEG and EMG).
Electrodes Theory - Surface electrode - Needle electrode -Microelectrode
Transducers for the measurement of Pressure, temperature and respiration rate.

DEVELOPMENT OF BIOMEDICAL INSTRUMENTATION

 The field of medical instrumentation is not new

 Many instruments were developed in the 19th century like electrocardiograph

 After that, a number of electronic equipments such as amplifiers and recorders became available

 Many technicians and engineers started to experiment with and modify the the existing equipments
for medical use but the results were disappointing because the physiological parameters were not
measured in the same way as physical parameters

 During the next decade many instrument manufacturers entered the field of medical instrumentation,
but development costs were high and the medical professionals and hospital staffs were suspicious
of the new equipments and were uncooperative

 During this period, some progressive companies decided that rather than modifying existing
hardware, they would design instrumentation specifically for medical use

 Although many of the components used were same, the philosophy was changed; equipment
analysis and design were directly applied to the medical problems

 A large measure of help was provided by the US government particularly by NASA(National

Aeronautics and Space Administration).

 The mercury, Gemini and Apollo programs needed accurate physiological monitoring for the
astronauts

 The aerospace medicine programs were expanded considerably

 Some of the concepts and features of patient monitoring systems presently used in hospitals evolved
from the base of astronaut monitoring

 The use of biotelemetry also finds some basis in NASA programs

 In 1960s, the major engineering technical societies formed „Engineering in Medicine and Biology‟
subgroups and new societies were organised.

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 Along with the medical research programs at the universities, a need developed for courses and
curricula in biomedical engineering

 Today, almost every major university has some type of biomedical engineering program

PHYSIOLOGICAL SYSTEMS OF THE BODY

 Physiology: is the science that deals with the normal function of the organs of the body.
 Human body contains various systems such as electrical, mechanical, hydraulic, pneumatic,
chemical and thermal etc.
 Systems communicate internally with each other and with external environment.
 With this, enable to perform useful tasks, sustain life and reproduce itself.
CARDIO VASCULAR SYSTEM
 Cardio means “heart” and Vascular means “vessels”.
 System made up of “heart”, “vessels and “blood”.

Function:
 It helps in the transportation of oxygen, carbon dioxide, numerous chemical compounds and
the blood cells.

STRUCTURE OF HEART
 Heart is divided into two parts right and left- each part has two chambers called atrium and
ventricle.
 Heart has four valves:
1. Tricuspid valve or Right Ventricle valve:
 It is on the right side of the heart, between the right atrium and the right ventricle.
 The function is to prevent back flow of blood from right ventricle to right atrium.
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2. Bicuspid Valve / Mitral Valve / Left Ventricle Valve:

 This valve is situated between the left atrium and the left ventricle.
 It permits blood to flow one way only, from the left atrium into the left ventricle.
3. Pulmonary Valve:
 A semilunar valve between the right ventricle and pulmonary artery .
 It prevents the blood from flowing back into the right ventricle.
4. Aortic Valve:
 The aortic valve is between the left ventricle and the aorta.
 It is also a semilunar valve
 Heart wall consist of three layers:
1. Pericardium:
 The membrane enclosing the heart.
 Consists of an outer fibrous layer and an inner double layer of serous membrane.
2. Myocardium:
 The middle muscular layer of the heart wall.
3. Endocardium:
 It is the innermost layer that lines the chambers of the heart.
 3 types of blood vessels:
1. Arteries:
 Carry blood away from the heart
 Arteries carry oxygen-rich blood
 The largest artery in the body is the Aorta having thick walls that are both strong and
flexible.
2. Veins:
 Carry impure blood towards the heart
3. Capillaries:
 They are the smallest blood vessels in your body.
 As blood flows through the capillaries, oxygen and dissolved nutrients diffuse through
the capillary walls into the body cells.
 Functions of Blood
 Carries oxygen from lungs to all body cells and removes carbon dioxide from the cells
 Carries waste products of cell activity to the kidneys to be removed from the body
 Transports nutrients from the digestive system to body cells

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PUMPING OF BLOOD

• Oxygen poor blood is pumped into right atrium from different parts of body
• Blood from upper body returns through the superior venacava
• Blood from lower body returns through the inferior venacava
• When the blood filled right atrium contracts ,the tricuspid valve opens and the blood is
pumped into the right ventricle of the heart
• When the right ventricle is full, the tricuspid valve closes and prevents the back flow of blood
into atrium
• When right ventricle contracts blood is pumped through the pulmonary valve into the
pulmonary artery into the lungs
• Pulmonary valve closes and prevents the blood from back flow into the ventricle
• Oxygen rich blood returns to the left atrium of the heart from the lungs
• When left atrium contracts, mitral valve opens
• Blood is pumped into the left ventricle
• This happens at the same time when the right atrium pumps blood into the right ventricle.
• When left ventricle becomes full and mitral valve closes
• When left ventricle contracts, oxygenated blood is pumped through aortic valve into the aorta to
reach all parts of the body
• This happens at the same time when the right ventricle pumps the blood into pulmonary artery at
the other side of the heart
• This cycle repeats

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PHYSIOLOGY OF RESPIRATORY SYSTEM

 The human respiratory system is a series of organs responsible for taking in oxygen and
expelling carbon dioxide.
 The main organ is Lungs
LUNGS
 The primary organ of the respiratory system is lungs . The lungs are situated in the thoracic
cavity.
 Red blood cells collect the oxygen from the lungs and carry it to the parts of the body where it
is needed.
 During the process, the red blood cells collect the carbon dioxide and transport it back to the
lungs, which leaves the body when we exhale.
 The lungs are spongy in texture.
 Right lung has three lobes and left lung only has two.
 The right lung is a little larger than the left lung.
 The right lung weighs about 625 gms. It is about 50 gms heavier than left lung.
 The exhaling rate is faster in kids than in adults.
 It is healthier to breathe through the nose than mouth, because nose hairs and mucus clean
the air.

PHARYNX:
 Wide muscular tube situated behind the nose, mouth and larynx.
 It is a part of the upper respiratory passages where infections are common.
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LARYNX
 The larynx is the organ that produces of voice.
 It is also an air passage.
TRACHEA:
 It is called the wind pipe,
 It is a cartilaginous tube that connects the pharynx and larynx to the lungs, allowing
the passage of air.
BRONCHUS
 It is a passage of airway in the respiratory tract that conducts air into the lungs.
ALVEOLI
 These are many tiny air sacs of the lungs which allow for rapid gaseous exchange.

ANATOMY OF NERVOUS SYSTEM

 The nervous system is a complex network of nerves and cells
 The nerves carry messages from the brain and spinal cord to various parts of the body and vice
versa.
 Nervous system coordinates the functions of various organs
Functions of nervous system:
Gathers information from both inside and
Sensory Function outside the body
Transmits information to the processing
areas of the brain and spine
Processes the information in the brain and
Integration Function spine
Sends information to the muscles, glands,
Motor Function and organs so they can respond appropriately

 Basic Cells of the Nervous System: Neuron

 Neuron transmits electrical signals called nerve impulses in response to any stimuli
 Parts of neuron: Cell body, Axon, Dendrites
 Cell body: Consists of nucleus
 Axons: Conduct electrical impulses away from the cell body
 Dendrites: Tiny branches on cell body
 Dendrites conduct impulses towards the cell body

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The nervous system can be divided into two major regions

1. Central nervous system
2. Peripheral nervous systems

1.Central nervous system(CNS)

 Largest part of the nervous system

 Two major parts: Brain and Spinal cord
 Brain is protected by skull and Spinal cord is protected by the spinal cavity
 CNS is protected by a three layered protective coating called meninges
 Brain has three parts: Cerebrum, Cerebellum, Brain Stem
Cerebrum: It is the largest part of the brain
 Cerebrum consists of left and right cerebral hemispheres
 Right cerebral hemisphere controls the left side activities of body and left cerebral hemisphere
controls the right side activities of body
Cerebellum: Coordinates all the muscular movements
 It also enables a person to maintain balance
 It is located just above the brain stem and towards the back of the brain
Brain stem (Medulla Oblongata)
 It connects the spinal cord to the center of the brain
 It regulates the work performed by the heart.
 Regulates heart rate, breathing, sleep cycles and emotions.
 Spinal cord
 Downward continuation of medulla oblongata
 It conducts impulses to and from the brain to the various organs
2. Peripheral Nervous System(PNS)

 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:
1. The somatic nervous system

2. Autonomic Nervous systems

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1. The somatic nervous system

 The somatic system is 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.

2. Autonomic Nervous systems

 The autonomic system is the part of the peripheral nervous system responsible for regulating involuntary
(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.

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

System
Muscular System
 The muscular system is an organ system, involved majorly in the movement of the body.
 There are nearly 700 muscles that are connected to the bones of the skeletal system, which
roughly half make up the human‟s body weight.
 Every muscle is a different organ made of blood vessels, skeletal muscle tissue, nerves, and
tendons. Muscle tissues are found in the heart, blood vessels, and digestive system

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There are three kinds of muscle tissues, namely cardiac, visceral and skeletal.

Cardiac Muscle
 This muscle is present only in the Heart and responsible for supplying blood all over the body.
 It is also an involuntary muscle since it cannot be controlled.
 When the brain signals adapt the rate of contraction, the cardiac muscle triggers by itself to
contract.
 The natural pace of the heart is composed of cardiac muscle tissue and triggers other cardiac
muscle cells to shrink.
 The cardiac muscle cells are straight which reveals that they seem to have dark and light stripes
when seen under a microscope.
 The protein fibres arrangement within the cells is responsible for these dark and light stripes.

Visceral Muscle
 These muscles are found in the organs like intestines, blood vessels, and stomach.
 It is the weakest of all muscle tissues and causes contraction of organs to pass substances through
the organ.
 It is said to be an involuntary muscle because it cannot be controlled directly by the conscious
mind, but controlled by the unconscious part of the brain.
 It is also known as a smooth muscle since it has a uniform and a smooth appearance when
observed under the microscope.

Skeletal Muscle
 It is the voluntary muscle tissue that can be controlled in conscious condition.
 All physical actions that a human performs (e.g. walking, writing) needs skeletal muscle.
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 The skeletal muscle is responsible for moving the body parts that are connected to the bone.
 Skeletal muscles from many ancestor cells combine themselves together to produce a straight,
long fibre.
 These skeletal muscles are strong just like cardiac muscles. The name is derived from the known
fact that these are connected to the skeleton in one region at least.
PROBLEMS ENCOUNTERED IN BIOMEDICAL MEASUREMENTS
1. Inaccessibility of variables to measurement: One of the greatest problems is the difficulty in
gaining access to the variable being measured.
2. Variability of the data: measurements taken under a fixed set of conditions at one time will not
be the same as similar measurements made under the same conditions at another time.
3. Lack of knowledge about interrelationship: The foregoing variability in measured values could
be better explained if more were known and understood about the interrelation within the body.
4. Interaction among physiological systems: Because of the large number of feedback loops
involved in the major physiological systems, a severe degree of interaction exists both within a
given system and among the major systems. The result is that stimulation of one part of a given
system generally affects all other parts of that system in some way .
5. Effect of the transducer on the measurement: All kind of measurement is affected in some
way by the presence of the measuring transducer. If the used transducer is a faulty one, then the
entire measurements will give wrong data.
6. Artifacts: In medicine and biology, random noise generated within the measuring instrument,
electrical interference, cross talk, and all other unwanted variations in the signal are considered
artifacts.
7. Energy limitations: Many physiological measurement techniques require that a certain amount
of energy be applied to the living system in order to obtain a measurement. In most cases, this
energy level is so low that its effect is insignificant. However, in dealing with living cells, care
must continually be taken to avoid the possibility of energy concentrations that might damage
cells or affect the measurements.
8. Safety considerations: The methods employed in measuring variables in a living human subject
must in no way endanger the life or normal functioning of the subject

SOURCES OF BIOELECTRIC POTENTIALS

 The body system generates signals while carrying out various functions.
 These signals are bioelectric potentials associated with nerve conduction, brain activity,
heartbeat, muscle activity etc.

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 Bioelectric potentials are actually ionic voltages produced as a result of electrochemical

activity in certain special types of cells.
 Transducers are used to convert these ionic potentials in to electrical signals
RESTING POTENTIAL (POLARISATION)
 Special type of cells, like nerve and muscle cells, in the body are encased in semipermeable
membrane
 This semipermeable membrane permits some substance to pass through it while others are kept
out.
 The cells are surrounded by body fluids
 These fluids contain charged particles called ions
 The principle ions are sodium (Na+) Potassium (K+) and chloride (Cl-).
 The membrane of cells permits 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 potential is called Resting potentials.

 The membrane potential is generally measured from inside the cell with respect to body fluids.

 So, the resting potential is –ve, ranging from -60 mV to -100 mV.

 Cell in the resting state is called polarised cell.

ACTION POTENTIAL (DEPOLARISATION)

 When a section of a cell membrane is excited by some form of externally applied energy,the
cell membrane changes its characteristics and begins to allow some of sodium ions to enter.
 At the same time, potassium ions, in higher concentration inside the cell during resting
state, try to leave the cell, but are unable to move as fast as sodium ions.
 The result is that the cell always attains small +ve potential on the inside known as action
potential, which is nearly +20 mV.

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 When a cell is excited and displays an action potential, it is said to be “depolarized” and the
process of changing resting state to action potential, is called as depolarization

A typical action potential waveform.

PROPAGATION OF ACTION POTENTIAL
 If a cell is excited and generates an action potential, an ionic current flows.
 Such process excites the neighbouring cells.
 In case of a nerve cell with a long fibre, the action potential is generated in a very small segment
of fibre‟s length but is propagated in both directions from original point of excitation.
 The rate at which an action potential moves down a fibre or is propagated from cell to cell is
called the propagation rate
 In nerve fiber the propagation rate is also called the nerve conduction rate, or conduction
velocity. Velocity range in nerves is from 20 to 140 meters per second. In heart muscle, the rate is
slower, average 0.2 to 0.4 m/sec.

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BIOELECTRIC POTENTIALS
 To measure a bioelectric potential, we need a transducer for converting ionic potentials into
electric potentials.
 The waveforms obtained in bioelectric potential measurements, generally ends in the suffix
“gram”.
 For example, electrocardiogram is the waveform resulting from the heart‟s electrical activity.
 The waveform is measured by an instrument called electrocardiograph.
Examples of bioelectric potentials are:

1. The Electrocardiogram(ECG)

 The bio-potentials generated by the muscles of the heart result in the electrocardiogram
(ECG).German word EKG. The Electrical activity of the heart is recorded by electrocardiogram
(ECG).

 P wave corresponds to Atrial depolarization of SA node

 Atrial repolarization record is masked by the larger QRS complex
 QRS complex corresponds to ventricular depolarization
 T wave corresponds to ventricular repolarization
2. The Electroencephalogram (EEG)
 The recorded representation of bioelectric potential by the neuronal activity of the brain is called the
electroencephalogram.
 The waveform varies greatly with the location of the measuring electrodes on the surface of the scalp

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2. Electromyogram [EMG]:
 The bioelectric potentials associated with muscle activity constitute the electromyogram.
 Can be measure on the surface of the body or by penetrating the skin using needle electrodes.

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Nernst Relation
 It can be shown that an electric potential E will exist between the solutions on either side of the
membrane, based upon the relative activity of the permeable ions in each of these solutions. This
relationship is known as the Nernst equation.
 The relationship between the ionic concentration (activity) and the electrode potential is given by
the Nernst equation:
 When no electric current flows between an electrode and the solution of its ions or across an ion
permeable membrane, the potential observed should be the half-cell potential or the Nernst
potential, respectively. If, however, there is a current, these potentials can be altered

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ELECTRODE TYPES
A wide variety of electrodes can be used to measure bioelectric potentials, The three basic types are:

1. SKIN SURFACE ELECTRODES

Placed on the surface of the skin to obtain bioelectric potentials from the surface. The types are:
1. Metal-plate electrodes
2. Suction electrodes
3. Floating electrodes

1. METAL PLATE ELECTRODES

b) Metal-disk electrode
 The metal disk has a lead wire soldered to the back surface.

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3. SUCTION ELECTRODES
 A modification of the metal plate electrode
 These electrodes don’t require any adhesives for holding it in place.
 These are well suited for attachment to flat surfaces of the body and to regions where the
underlying tissue is soft

3. FLOATING ELECTRODES

 It does not make direct contact with the skin.

 The electrical contact is established through the electrolyte paste filled in the cavity

3. NEEDLE ELECTRODES

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TRANSDUCERS FOR BIOMEDICAL APPLICATIONS

 The device that performs the conversion of one form of energy into another is called a transducer.
 There are two types of transducers.

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3.Piezoelectric type transducer:

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 Silicon photoelectric cells are used as pulse sensors and they are also used to determine
sodium and potassium ion concentration in human body.
4. Thermoelectric transducer:

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2. Thermistor type transducer:

 Based on principle that the resistance of material changes due to change in temperature.
 The resistivity of a material changes due to the change in mobility of charge carriers.
 If the resistance of the thermistor decreases with increase in temperature, they are called
negative temperature coefficient thermistors.
 If the resistance increases with increase in temperature then they are known as positive
temperature coefficient thermistors.
 Thermistors used for biomedical instrumentation are all small in size.

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Linear Variable Differential Transformer (LVDT)

Advantages:
 Output is more accurate
 High efficiency
 Simple construction
 Light weight

Sarath kumar S. Asst. Prof. SNIT ADOOR