SYLLABUS

• The origin of Bio-potentials

• Biopotential electrodes
• Biological amplifiers
• ElectroCardioGraph (ECG)
• ElectroEncephaloGraph (EEG)
• ElectroMyoGraphy (EMG)
• PhonoCardioGram (PCG)
COMPONENTS OF THE MAN
INSTRUMENT SYSTEM
BIOPOTENTIALS
• Certain part generate own
monitoring signals which
conveys information about the
function they represent.

• These signals are bio electric

potentials.

• They may be due to nerve

conduction, brain activity,
heart beat, muscle activity and
so on.
IONS & CONCENTRATION
• The nerve and muscle cells are encased in a semi
permeable membrane.

• Cells are surrounded by fluids and contains ions.

• The principle ions are Sodium (Na+), Potassium (k+) and

chloride (C-).

• Concentration variations:
Concentration of potassium (K+) ions is 30-50 times higher
inside as compared to outside
Sodium ion (Na+) concentration is 10 times higher outside the
membrane than inside
RESTING POTENTIAL
• Equilibrium is maintained with negative on the inside and positive on the
outside.

• This membrane potential is called the “RESTING POTENTIAL” of the cell and
is maintained until some kind of disturbance upsets the equilibrium.

• Resting potential of the cell is negative and ranges from -60 to -100mV.

• A cell in the resting state is said to be polarized.

ACTION POTENTIAL
• When external energy is applied, the
membrane changes its
characteristics and begins to allow
sodium ions to enter.

• Thereby cell has a slightly positive

potential on the inside due to the
imbalance of potassium ions, this
potential is known as “ACTION
POTENTIAL”

• Action potential of the cell is positive

and is approximately 20mV.

• A cell that has been excited and

displays action potential is said to be
depolarized.
REPOLARIZATION
• By an active process, called “Sodium Pump”, the
ions are transported outside to make the cell to
be polarized.

• This process is called “REPOLARIZATION”.

• The rate of pumping is directly proportional to

the sodium concentration in the cell.
ACTION POTENTIAL WAVEFORM
 DEFINITIONS
• Regardless of the method for stimulation, the action potential is
always the same for any given cell known as “ALL or NOTHING
LAW”

• Some period of time after action potential, cell cannot respond to

any stimulus is called “ABSOLUTE REFRACTORY PERIODS”

• In “RELATIVE REFRACTORY PERIOD” after the period of absolute

refractory period, another action potential can be triggered with a
much stronger stimulation.

• The rate at which an action potential moves down a fiber or

propagates from cell to cell is called the propagation rate otherwise
called as conduction velocity.
WHAT IS AN ELECTRODE?
• The bio electric potential generated in the body are ionic potential,
produced by ionic current flow.

• Efficient measurement requires that it has to be converted into

electronic potential before it is measured by a conventional method.

• Devices that convert ionic potential into electronic potential are

called “ELECTRODES”

• Electrodes are simply electrical terminals or contact points from

which voltages can be obtained at the surface of the body

• Purpose of electrolyte paste or jelly used in such measurements are

for reducing the overall input impedance of the system.
TYPES OF BIO POTENTIAL ELECTRODES
EQUIVALENT CIRCUIT

• This network represent the

impedance of the
electrode.
• Impedance varies with the
effect of polarization, size
and type.
MICROELECTRODES
• Divided into two types (1) Metallic (2) Non-metallic or
Micropipet.

• It must have smaller diameter and during insertion into

cell, there will not be any damage to the cell.

• While measuring, it is located inside the cell and the

reference electrode is situated outside the cell.

• Size of cell is 50microns hence tip of electrode has to be

0.5 to 5microns.
 METALLIC ELECTRODES

• Electrolytically
etching the tip of a
fine tungsten or
stainless steel wire to
a fine point.
(Electropointing)

• Wire is coated with

insulating material.

• Chloriding is done to
reduce impedance.
 MICROPIPET
• Glass micropipet whose tip diameter
is 1 micrometer.

• Filled with electrolyte.

• Thin, flexible metal wire from

chlorided silver, stainless steel or
tungsten is inserted into the stem.

• Friction between wire and stem and

fluid surface tension hold the pipet on
the wire.

• Other end is mounted to rigid support

and free end is resting on the cell.
SURFACE ELECTRODES
SKIN SURFACE ELECTRODE
(a)Metal-plate electrode
used for application to
limbs.

(b) Metal-disk electrode

applied with surgical
tape.

(c) Disposable foam-pad

electrodes, often used
with
electrocardiograph
monitoring apparatus.
SUCTION PUMP ELECTRODE
• A paste is introduced into
the cup.

• The electrodes are then

suctioned into place.

• Ten of these can be with

the clinical
electrocardiograph – limb
and pericardial (chest)
electrodes
FLOATING METAL ELECTRODE
(a)Floating metal
electrode with top-
hat structure.

(a) Cross-sectional
view of the
electrode in (a).

(a) Cross-sectional
view of a
disposable Floating
electrode
WHAT IS BIOLOGICAL AMPLIFIERS?
• Biological signal amplifiers
are amplifiers designed to
convert the weak voltage
signal generated by various
biological processes (nerve
activity in EEGs, heart
muscle activity in EKGs,
etc.) into a strong signal. 

• Almost every biological

signal amplifier is built
from an integrated circuit
instrumentation amplifier.
REQUIREMENTS OF BIO AMPLIFIERS

• Voltage gain of amplifier must be more than

100dB.

• Gain and frequency must be uniform throughout

the bandwidth.

• The input impedance must be large and the

output impedance must be small.

• The CMRR value must be greater than 80 dB

SIGNAL AMPLIFICATION SYSTEM
BLOCK DESCRIPTION
• The biological signal is too weak and its amplitude is very low
and hence to improve its quality the signal must be amplified.
This preliminary amplification is performed by preamplifier.

• In order to avoid the high frequency components (noise) we

need this high pass filter.

• In order to maintain complete safety of the patient the input

impedance of the patient must be high. The input impedance
can be improved by using this isolation amplifier.

• In order to avoid the low frequency components(noise and

artifacts) the low pass filter is used.
TYPES OF BIO AMPLIFIERS USED
• Operational amplifier • Instrumentation amplifier

• Differential amplifier
ISOLATION AMPLIFIER
• These amplifiers are used to increase
the input impedance of the
monitoring system in order to isolate
the patient from the biomedical
instrument

• In a bio potential amplifier, the main

purpose of the isolation is the
protection of the patient by
eliminating the hazard of electric
shock resulting from the interaction
among patient, amplifier, and other
electric devices in the patient’s
environment, specifically
defibrillators and electrosurgical
equipment. It also adds to the
prevention of line frequency
interferences.
CHOPPER AMPLIFIER
BIO POTENTIAL RECORDERS

• Lead system

• Recording methods

• Waveforms

• Signal characteristics
ELECTROCARDIOGRAPHY (ECG)
Measures the electrical activity of the heart muscles.

Recorded waveform is known as Electrocardiograph.

The instrument used is called as Electrocardiogram.

Gives the info about the cardiac disorders.

Electrocardiogram reflects the rhythemic electrical

depolarization and repolarization of myocardium.
HEART STRUCTURE & WORKING
CIRCULATION OF BLOOD

• 3 layers – peri cardium, endo cardium & myo cardium.

• PULMONARY CIRCULATION – pumps the

blood(impure) to the lungs for purification.

• SYSTEMIC CIRCULATION – pumps the pure blood

to all other parts.
TWO NODES

• SA node(Sinoatrial node): initiates heart activity

by generating electrical impulses.

• AV node(Atrioventricular node): electrical

control system that co-ordinates heart beat rate.
ECG LEAD SYSTEM
 2 categories;
• Limb lead systems.
• Chest lead systems.

Limb lead systems is classified in to 2 types;

• Bipolar limb lead systems.

 Recorded by using 2 electrodes & final
output is taken as the difference of
potential b/w these 2 electrodes.
LIMB LEAD SYSTEM
• Bipolar limb lead systems.

• Recorded by using 2
electrodes & final output
is taken as the difference
of potential b/w these 2
electrodes.
LEAD I
LEAD 2
LEAD 3
EINTHOVEN TRIANGLE

• Leads I, II, III

together form a
triangle known as
EINTHOVEN
TRIANGLE
UNIPOLAR OR AUGMENTED UNIPOLAR LEAD SYSTEMS:
Recorded by using 1 electrode & 1 augmented electrodes ( 2
electrodes are connected together).
• 3 types;
1)aVR (Augmented Voltage Right Arm).
2)aVL (Augmented Voltage Left Arm).
3)aVF (Augmented Voltage Foot).
LEAD aVR
LEAD aVL
LEAD aVF
CHEST LEAD SYSTEM
• Chest electrodes are placed at 6 different places on the
chest and connected to the positive terminal of the
amplifier.
• RA, LA, LL are connected with resistors and common
point is taken and connected with negative terminal of
the amplifier.
• RL is used as reference point (i.e) GROUND.
ECG RECORDING METHOD
• Defibrillator protection circuit:
• Feed back network:
 Employs buffer amplifier & over
voltage protection circuits.
 Consists of R-C circuit & it
• Lead selector: Provides damping to the pen
 For selecting the type of lead motor.
systems. • Auxiliary Amplifier:
• Calibration circuit:  Connected b/w the lead selection
 for calibrating the signal after lead logic and RL of the patient.
selection is changed.  Output of auxiliary amplifier is
• Pre amplifier: connected with right leg. So, this
 Differential amplifier with high output drives to zero common
gain and high CMRR is used. voltage. So noise get reduced.
• Power amplifier: • Output display unit:
 Used to drive the output unit.  CRO or paper chart recorder is
 Pen motor is used in output unit & used as output unit.
it needs sufficient electrical power  Paper speed = 25 mm/sec in US
for recording. manufacturing.
 Paper speed = 50 mm/sec in
European manufacturing.
ECG WAVEFORM & CHARACTERISTICS

WAVE FUNCTION

P - WAVE Atrial Depolarization

PQ - WAVE AV Nodal Delay

QRS Ventricular Depolarization (Atrial

COMPLEX repolarization)

ST - Ventricular Ejection Period

SEGMENT
T -WAVE Ventricular Repolarization

TP- Ventricular Filling Period

SEGMENT
ECG SIGNAL ANALYSIS
• (a) Normal ECG curve

• (b) First degree AV block

• (c) Bundle block

• (d) Myocardial infarction

• (e) Coronary insufficiency

• (f) Ventricular fibrillation

• (g) Death signal

ELECTROENCEPHALOGRAPHY (EEG)
• Study the electrical • Brain consists of 4 parts, namely
activity of the • Cerebrum.
brain. • Cerebellum.
• Medulla Oblongata.
• Biological name of • Spinal cord..
brain  • Cerebrum consists of 2
ENCEPHALON. hemispheres,
• Frontal lobe.
• Here, electrodes • Parietal lobe
are placed on the • Temporal lobe.
scalp.
• Occipital lobe.
HUMAN BRAIN
ACTION POTENTIALS OF THE BRAIN
• IPSP – Inhibitory Post Synaptic Potential.

• EPSP – Excitatory Post Synaptic Potential.

• Evoked potential – potential developed due to

external stimuli like light, sound etc.
EEG LEAD SYSTEM
• 10 – 20 electrode system is normally used.

• In this system, distance b/w 2 electrodes is 10%

and 20% of the distance b/w specified points on
the scalp.

• The distance b/w the Nasion-Inion over the

head is divided into 5 points.

• Frontal pole (FP), Frontal(F), Central(C),

Parietal(P), Occipital(O).
EEG LEAD SYSTEM
EEG RECORDING METHOD
• Diff.Amplifier  reduces •o/p of filter  display recorder
noise & used as pre- unit.
amplifier. It has
CMMR(>80 dB) & i/p •Recorder unit – pen recorder with
impedance >10 mega ohm. 8 pens are used. 1 pen is dedicated
• o/p of diff. amp  Signal for each channel. Normal paper
processing unit  speed in recorder is 30mm/sec.
memory further
processing  output unit. •Extra Facilities :
• o/p of the diff. amp are •Potential from sensory parts
connected with the filter are also recorded.
bank circuit (i.e) LPF, •Time delay between stimulus
HPF, BPF. and the response from the brain
• They are used to select diff can also be measured.
types of brain waves
without noise.
EEG WAVEFORM
EEG WAVEFORM
ELECTROMYOGRAPHY (EMG)
• Recording the electrical
activity of the muscles.

• Study of neuromuscular
function also possible.

• Muscular contractions are

caused by the depolarization
of muscle fibers.

• Recording of peripheral
nerve’s action potential is
called as electroneurography.
EMG LEAD SYSTEM
• TYPES OF ELCTRODES USED

• SURFACE ELECTRODES :
▫ Usually used.
▫ But, Not possible to measure deeper potential.

NEEDLE ELECTRODES:
 Inserted into tissue to measure the electrical activity of
the muscle.
EMG RECORDING METHOD
• EMG given to the
amplifier having high
gain & high bandwidth.

• Amplifier Frequency
range – 10 Hz to 10 KHz.

• Amplifier CMRR = 80- •Nerve conduction time &

100 db & i/p impedance nerve velocity are measured
is 10 Mega ohm. by stimulating the nerves.

•CV measurement is used to

indicate the location and
type of nerve lesion.
• usually l2 < l1 and t2 < t1.
• C.V - = l1 - l2 / t1 - t2 .
• Normally C.V = 50 m/s.
• If C.V < 40 m/s, there is some disorder.
PHONOCARDIOGRAM (PCG)
• Graphical record of heart sound.
• Device  Phonocardiograph
• operation: pickup heart sounds, filter out the heart sounds
& finally display them.
• 2 events – heart sounds & murmurs.
• The technique of listening sounds produced by organs and
vessels is called “Auscultation”
•4 types - namely,

•valve closure sound.

•Ventricular filling period.
•Valve opening sound.
•Extra cardiac sound
ORIGIN OF HEART SOUNDS
NAME FREQUENCY DURATION ASCULATOR REASON FOR
Y AREA PRODUDTION
1ST 30-50 Hz 0.1 – 0.12 S Apex of Mid Closure of mitral &
pericardium tricuspid valves

2nd Up to 250 Hz 0.08 – 0.14 S Aortic and Vibration setup by

pulmonary closure of semi
area lunar valves.

3rd 10-100 Hz 0.04 – 0.08 Apex and left When ventricle

S lateral relaxed, it occurs.
position after
lifting the
legs
4th 10-50 Hz 0.03-0.06 S Not audible Accelerated blood
in any area flow into
ventricles.
PCG RECORDING METHOD
RELATIONSHIP BETWEEN BP, HEART
SOUND AND ECG WAVEFORM
PCG WAVEFORM
POLYSOMNOGRAPHY
• Polysomnography (PSG), a type of sleep
study, is a multi-parametric test used in the
study of sleep and as a diagnostic tool in sleep
medicine. The test result is called a
polysomnogram.
ULTRA SOUND SCANNER
• Used to scan the heart, kidney, fetus etc..
• Ultrasound is sound waves with frequencies
which are higher than those audible to humans
(>20,000Hz). Ultrasonic images also known as
sonograms are made by sending pulses of
ultrasound into tissue using a probe. The sound
echoes off the tissue; with different tissues
reflecting varying degrees of sound. These echoes
are recorded and displayed as an image to the
operator.
X RAY C ARM
• A mobile image intensifier generally consists of two
units, the X-ray generator and image system on a
portable imaging system (C-arm) and the workstation
unit used to store and manipulate the images. The
imaging system unit can perform a variety of
movements that allow for use in a variety of surgical
procedures such as cardiology, orthopedics and
urology. This unit provides the appropriate structure
to mount an image intensifier and an X-ray tube with
a beam limiting device positioned directly opposite
from and aligned centrally to each other.
NEW TECH

• Development of an ambulatory universal

bio potential recording device
• The proposed research focuses on the development of an ambulatory
universal 2-electrode biopotential recording device for recording
electrocardiogram (ECG), electromyogram (EMG) and electroocculogram
(EOG). The designed device will help the health caregivers to quickly
acquire the signals in a computer and digitally record the biopotential
signals for analysis at a later stage. The digitally recorded signals can be
easily sent by email or SMS to a doctor for his comments and medical
advice. Hence, this proposed device is expected to help in easy medical
check-up of the persons residing in the remote areas and villages. Since the
device is compact and can be used for recording signals for longer periods,
it may also be used for long-term investigation of the patients.