Medical Electronics Unit 1 New

1 VSA GROUP OF INSTITUTIONS-2013

MEDICAL ELECTRONICS LECTURE NOTES © Ms.V.Ezhilya

VSA SCHOOL OF ENGINEERING

DEPT OF ECE

MEDICAL ELECTRONICS

UNIT – 1: RECORDING & MONITORING INSTRUMENTS

Bio electric signals and Electrodes – Biomedical Recorders – Medical display systems –

monitoring systems.

CLASS – 1

Topic: Medical Electronics Introduction

Medical Electronics:

Def: A branch of electronics in which electronic instruments and equipment are used for

such medical applications as diagnosis, therapy, research, anesthesia control, cardiac

control, and surgery.

Cell & its Structure:

Fig: Structure of Cell

The cell was discovered by Robert Hooke in 1665.

The cell is the basic structural and functional unit of all known living organisms. It is the

smallest unit of life that is classified as a living thing (except virus, which consists only

http://en.wikipedia.org/wiki/Robert_Hooke

http://en.wikipedia.org/wiki/Organism

http://en.wikipedia.org/wiki/Virus



from DNA/RNA covered by protein and lipids), and is often called the building block of

life.

Organisms can be classified as unicellular (consisting of a single cell; including most

bacteria) or multicellular (including plants and animals). Humans contain about 10

trillion (1013) cells.

The different substances that make up the cell are collectively known as PROTOPLASM.

It is composed of

1. Water

2. Electrolyte

3. Protein

4. Lipids

5. Carbohydrates

6. Cytoplasm

7. Ribosome

8. Lysosomes

9. Mitochondria

A cell consists of a plasma membrane, a nucleus and cytoplasm.

Plasma membrane: The cell membrane or plasma membrane is a biological membrane

that separates the interior of all cells from the outside environment. The cell membrane

is selectively permeable to ions and organic molecules and controls the movement of

substances in and out of cells. The basic function of the cell membrane is to protect the

cell from its surroundings. It consists of the lipid bilayer with embedded proteins.

Nucleus: The nucleus is the largest cellular organelle in humans. In mammalian cells,

the average diameter of the nucleus is approximately 6 micrometers (μm), which

occupies about 10% of the total cell volume. The viscous liquid within it is called

nucleoplasm, and is similar in composition to the cytosol found outside the nucleus.[7] It

appears as a dense, roughly spherical organelle.

http://en.wikipedia.org/wiki/Protein

http://en.wikipedia.org/wiki/Lipid

http://en.wikipedia.org/wiki/Unicellular

http://en.wikipedia.org/wiki/Bacteria

http://en.wikipedia.org/wiki/Multicellular

http://en.wikipedia.org/wiki/Plants

http://en.wikipedia.org/wiki/Animals

http://en.wikipedia.org/wiki/Orders_of_magnitude_%28numbers%29#1012

http://en.wikipedia.org/wiki/Biological_membrane

http://en.wikipedia.org/wiki/Cytoplasm

http://en.wikipedia.org/wiki/Extracellular_space

http://en.wikipedia.org/wiki/Semipermeable_membrane

http://en.wikipedia.org/wiki/Lipid_bilayer

http://en.wikipedia.org/wiki/Protein

http://en.wikipedia.org/wiki/Organelle

http://en.wikipedia.org/wiki/Mammal

http://en.wikipedia.org/wiki/Nucleoplasm

http://en.wikipedia.org/wiki/Cytosol

http://en.wikipedia.org/wiki/Cell_nucleus#cite_note-7



Cytoplasm: The cytoplasm is the gel-like substance residing within the cell membrane

holding all the cell's internal sub-structures (called organelles), outside the nucleus. All

the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell

nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the

contents of the cell nucleus are separated from the cytoplasm, and are then called the

nucleoplasm. The cytoplasm is about 70% to 90% water and usually colorless.

Possible Questions:

1. Draw the structure of cell. [2]

2. Define protoplasm. [2]

3. Define ICF & ECF. [2]

4. Describe the structure of cell in detail. [8]

Hints:

http://en.wikipedia.org/wiki/Cell_membrane

http://en.wikipedia.org/wiki/Cell_%28biology%29

http://en.wikipedia.org/wiki/Organelle

http://en.wikipedia.org/wiki/Cell_nucleus

http://en.wikipedia.org/wiki/Prokaryote




http://en.wikipedia.org/wiki/Eukaryote


http://en.wikipedia.org/wiki/Nucleoplasm



Resting and Action potential:

Resting Potential:

Dictionary Meaning: The electrical potential of a neuron or other excitable cell relative to

its surroundings when at rest.

Technical Meaning: The potential difference between the two sides of the membrane of a

nerve cell when the cell is not conducting an impulse.

Fig: Resting Potential



Action Potential:

Dictionary Meaning: The change in electrical potential associated with the passage of an

impulse along the membrane of a muscle cell or nerve cell.

Technical Meaning: A momentary change in electrical potential on the surface of a cell,

especially of a nerve or muscle cell, that occurs when it is stimulated, resulting in the

transmission of an electrical impulse.

Characteristics of Resting Potential:

The characteristics of the resting potential are maintained as a constant until some kind

of the disturbances will upset the equilibrium.

It strongly depends on the temperature.

The permeability of different cell types should vary. Hence the corresponding resting

potential also vary.

The range of resting potential is -60 to -100 mV.

The resting potential can be calculated with the Goldman-Hodgkin-Katz voltage equation

using the concentrations of ions as for the equilibrium potential while also including the

relative permeabilities, or conductances, of each ionic species. Under normal

conditions, it is safe to assume that only potassium, sodium (Na+) and chloride (Cl-) ions

play large roles for the resting potential:

VR = (-kT/q)ln{ PK[K+]i+PNa[Na+]i+PCl[Cl-]o / PK[K+]o+PNa[Na+]o+PCl[Cl-]i }

Where the subscript o - outside the cell

the subscript i - inside the cell

VR - resting potential

K - Boltzman constant

T - Absolute temperature in Kelvin

q - Charge of an electron

PK - Permeability of potassium ion

http://en.wikipedia.org/wiki/Goldman_equation

http://en.wikipedia.org/wiki/Semipermeable_membrane

http://en.wikipedia.org/wiki/Electrical_conductance

http://en.wikipedia.org/wiki/Sodium

http://en.wikipedia.org/wiki/Chloride



Absolute & Relative Refractory Period:

Absolute Refractory Period: It is the time duration in which the cell cannot respond to any

new stimulus. Generally it is about 1ms in nerve cells.

Relative Refractory Period: It is one during which another action potential can be

triggered but a higher stimulus is required to reinitiate the action potential and the

subsequent contraction of muscles.

Fig: Absolute and Relative Refractory Period.

All Or Nothing Law:

It states that regardless of the method of excitation of cells or by the intensity of the

stimulus, the action potential is always the same for any given cell.

Possible Questions:

1. Define All or Nothing law. [2m]

2. Define resting & action potential. [2m]



3. What are the characteristics of resting potential? [2m] or [4m] or [8m]

4. State Goldman’s equation of resting potential. [2m]

5. Differentiate absolute & relative refractory period. [2m]

6. Discuss in detail about origin of bioelectric potentials with necessary diagrams. [16]

Books Reffered:

1. Medical Electronics – R.L.Rekha [Pg:No: 1.1 to 1.6]

2. Handbook of biomedical instrumentation – R.S.Khandpur

HINTS:



CLASS – 2

TOPIC: Bioelectric Signals & Electrodes

Definition:

Electrical biosignals ("bio-electrical" signals) are usually taken to be (changes in) electric

currents produced by the sum of electrical potential differences across a specialized tissue,

organ or cell system like the nervous system. Thus, among the best-known bio-electrical

signals are the

Electroencephalogram (EEG)

Magneto encephalogram (MEG)

Galvanic skin response (GSR)

Electrocardiogram (ECG)

Electromyogram (EMG)

Heart Rate Variability (HRV)

1. Electrocardiogram [ECG]:

ECG is the record of electrical activity of the heart.

Typical bandwidth: 0.5 – 125 Hz

Typical waveform: Rhythmic waveform

Typical amplitude: 1 – 10 mV

Fig: ECG Waveform

http://en.wikipedia.org/wiki/Electric_current



http://en.wikipedia.org/wiki/Electrical_potential

http://en.wikipedia.org/wiki/Nervous_system

http://en.wikipedia.org/wiki/Electroencephalogram

http://en.wikipedia.org/wiki/Magnetoencephalogram

http://en.wikipedia.org/wiki/Galvanic_skin_response

http://en.wikipedia.org/wiki/Electrocardiogram

http://en.wikipedia.org/wiki/Electromyogram

http://en.wikipedia.org/wiki/Heart_rate_variability



Characteristic waves of ECG:

P wave – Atrial depolarization

PQ segment – AV nodal delay

QRS complex – ventricular depolarization (atrial repolarization)

ST segment – ventricular ejection period

T wave – ventricular repolarization

TP segment – ventricular filling period

Clinical significance:

ECG record helps in the diagnosis of various heart arrhythmias such as

tachycardia, bradycardia, heart block etc.

2.ElectroEncephaloGram [ EEG]:

EEG is the record of sum of biopotentials generated by individual neurons or

electrical activities of the brain.

Typical bandwidth: 0.1 – 100 Hz

Typical amplitude: 10 – 100 mV

Typical waveform: Highly random

Fig: EEG Waveform



Subdivided into five bands namely

1. Delta (d): 01 – 4 Hz; found in children; if found in alert adult it is abnormal

2. Theta (q): 4 – 8 Hz; found in children of 2-5 year old; if found in alert adult it is

abnormal

3. Alpha (a): 8 – 13 Hz; found in alert adult with eyes closed (under relaxed

conditions)

4. Beta (b): 13 – 22 Hz; found in alert adult with eyes open (under active

conditions)

5. Gamma (g): >22 Hz.

Clinical Significance:

EEG record helps in the diagnosis of brain asymmetry, epilepsy, mental disorders

etc and in the study of sleep patterns.

PhonoCardioGram [PCG]:

Record of heart sounds – 1st and 2nd heart sounds are heard well but 3rd and 4th

are not. Heart sounds are generally used for diagnosis of valve related diseases. Such

abnormal heart sounds are called murmurs.

1st heart sound: due to closure of AV valves – long, soft & low-pitched sound –

sounds like ‘lubb’ – 0.14-0.2 sec – 30-40 Hz.

2nd heart sound: due to closure of semilunar valves – short, sharp & high-pitched

sound – sounds like ‘dub’ – 0.08-0.1 sec – 50-70 Hz.

3rd heart sound: due to ventricular vibrations resulting from on-rush of blood

immediately after the opening of AV valves – very short – 0.04 sec.

4th heart sound: due to atrial contraction.



Fig: PCG Waveform

ElectroOculoGram [EOG]:

Steady corneal-retinal potential – used to record eye movements in sleep and

dream to evaluate reading ability and visual fatigue – eye movements less than 10 and

greater than 300 is difficult to record because of lack of accuracy and lack of proportion.

Fig: EOG Waveform



Electromyogram [EMG]: EMG is the record of electrical activity of muscles.

Typical bandwidth: 300-3000 Hz

Typical amplitude: 10-100 mV

Fig: EMG Waveform

ELECTRODES:

Electrodes are generally used to pick up the electric signals of the body. There

are various electrodes that are used in instrumentation system. They are

1. Surface electrode

2. Micro electrode

3. Depth electrode

4. Needle electrode

5. Chemical electrode



TYPES OF ELECTRODES:

1. Micro-Electrodes:

They are normally used to measure the potential within a single cell.

The microelectrodes are very small in diameter and so it will not

damage the human cell.

Microelectrodes are classified into Metallic & Non-Metallic.

Metallic Electrode:

The metal microelectrodes are formed by electrolytically etching the tip

of fine tungsten filament into a minute structure.

The final potential within the cell is the difference between the

microelectrode potential and reference potential.

Final potential = EA-ER

Micropipet:

It is used to measure the potential within a single cell, but instead of metal

electrolyte non-metallic material is used.



2. Depth Electrode:

Depth electrodes are used to measure the oxygen tension.

These are used to study the electrical activity of neuron of superficial layers

of brain.

In some depth electrode, the supporting element is in the form of capillary

tube, which is used to inject medicine into the brain.

3. Needle Electrode:

Needle electrodes are used to record the peripheral nerve action potential.

The needle electrode will resemble a medicine dropper. There are two

types:

1. Monopolar needle electrode.

2. Bipolar needle electrode.

4. Surface Electrode:

The surface electrodes are used to measure the potential available from the

surface of the skin and used to sense the potential from heart, brain and

nerves.



The smaller area surface electrodes are used to measure EEG,EMG

potentials and the larger area surface electrodes are used to measure ECG

potentials.

Depends on construction, the surface electrodes are classified into

1. Metal plate electrode

2. Suction cup electrode

3. Adhesive tape electrode

4. Multipoint electrode

5. Floating electrode

1. Metal plate electrode:

It is made up of Ag-AgCl (Silver-Silver Chloride). It is used to pick up ECG from

the limb lead positions. It is fixed to the skin surface by means of conductive gel &

rubber belt.

Fig: Metal plate electrode.

2. Metal disc electrode:

It is made up of Ag-AgCl. It is used to pick up EEG from the scalp. It is fixed to the

scalp by means of adhesive tape.



Fig: Metal disc electrode.

3. Metallic suction electrode:

It is made up of Ag-AgCl. It is used to pick up ECG from chest lead positions and

EMG from muscular areas such as calf, thigh etc. It does not require adhesive tapes

or rubber bands. It is fixed to the skin surface by means of air suction.

Fig: Metal suction electrode.

4. Disposable foam-pad electrode:

It is made up of Ag-AgCl. It is used to pick up ECG or EEG for those patients with

contagious skin diseases. It is fixed to the skin surface by means of adhesive tapes

attached to the electrode.

Fig: Disposable foam-pad electrode.

5. Floating electrode:

This type of electrode is used to prevent the motion-artifact from being picked up.



Fig: Floating electrode.

5. Chemical electrodes:

The chemical electrodes are used to measure the pH content and pO2 of

blood. It is also used to determine the oxygen content & CO2 content in

blood.

Various types of chemical electrodes are

1. Hydrogen electrode.

2. Practical reference electrode.

3. pH electrode.

4. pO2 electrode.

5. pCO2 electrode.

Possible Questions:

1. Define the process of depolarization & repolarization.[2m]

2. What is the specific usage of signal average? [2m]

3. What is ERP? [2m]

4. Write down the Nernst equation. [2m]

5. What is a PCG? [2m]

6. Write a detail note on electrodes. [16m]

Books Reffered:

1. Medical Electronics –

R.L.Rekha [Pg:No: 1.18

to 1.]

2. Handbook of

biomedical

instrumentation –

R.S.Khandpur



CLASS – 3

TOPIC: Bio Amplifiers

BASIC COMPONENTS OF BIOMEDICAL SYSTEM:

Fig: Basic Components Of Bio-medical System

SYSTEM: The measurements are made on the subject. i.e.: Human being.

STIMULUS: The response to external stimulus is necessary in many biomedical

instrument systems.

TRANSDUCER: It is used to convert biosignals to electrical signal.

SIGNAL CONDITIONING EQUIPMENT: The electrical output from the transducer is

amplified and modified by using this block.

MEASUREMENT (or) DISPLAY (or) RECORDING UNIT: The output can be displayed

using CRT display (or) DSO.

CONTROL FEEDBACK: The output of control feedback block is connected with stimulus

block the input applied to the subject.



BIO-AMPLIFIER:

DEF: A Bioamplifier is a device used to gather and increase the signal integrity of

human neurophysiologic electrical activity for output to various sources.

BASIC REQUIREMENT FOR BIOLOGICAL AMPLIFIERS:

Bio-Amplifiers must have high input impedance.

It must have isolation and protection circuits.

Voltage gain of bio-amplifiers should be more than 100db.

Constant gain should be maintained throughout the required bandwidth.

Drift free amplifiers can acts as good bio-amplifiers.

CMRR of bio-amplifiers should be more than 80db.

TYPES OF BIO-AMPLIFIERS:

1. Differential amplifier.

2. Operational amplifier.

3. Instrumentation amplifier.

4. Chopper amplifier.

5. Isolation amplifier.

1. Differential amplifier:

Fig: Single ended amplifier.

http://en.wikipedia.org/wiki/Neurophysiology



Fig: Differential amplifier

Fig: Input and Output Waveforms of differential amplifier.

2. OPERATIONAL AMPLIFIER:

Fig: Operational amplifier

If the input is applied to inverting input terminal (-), then the output can be

obtained with 1800 phase shift. This is known as “INVERSION OF THE SIGNAL”.



Ideal Op-Amp Properties:

1. Infinite input impedance

2. Zero output impedance

3. Infinite open loop voltage gain

4. Zero noise level

5. Infinite frequency response.

Configurations of Op-Amp:

1. Inverting amplifier:

Fig: Inverting amplifier

AV=Vo/Vin= -Rf/Rin

2. Non-Inverting amplifier:

Fig: Non-Inverting amplifier



AV=Vo/Vin= 1+(Rf/R1)

3. Instrumentation amplifier:

Fig: Instrumentation amplifier

Advantages:

1. High gain

2. Extremely high input impedance

3. CMRR is good.

4. CHOPPER AMPLIFIERS:

Analog signal is sampled in this amplifier circuit. Hence this circuit is known

as chopper amplifier.

Chopper amplifiers are classified into mechanical and non-mechanical

choppers.



Advantages:

1. Stable gain

2. Provides low noise operation.

5. ISOLATION AMPLIFIER:

Fig: Symbol of isolation amplifier

Fig: Isolation amplifier

Advantages:

1. Isolation amplifiers withstand high voltage.

2. It amplifies the signals while passing only low leakage current to prevent

shock.



Books Reffered:



POSSIBLE QUESTIONS:

1. What are the ideal op-amp characteristics? [2m]

2. Define chopper amplifier. [2m]

3. Explain the various types of amplifiers with a neat diagram. [16 m]

HINTS:



CLASS – 4

TOPIC: ELECTROCARDIOGRAPHY

DEF:

ECG shows the electrical activity of the heart muscles. The recorded ECG

waveform is known as electrocardiograph & the instrument is termed as

electrocardiogram. It gives the valuable information about the cardiac disorders.

Cross Section Of Heart:

Fig: Cross section of heart

Heart is divided into four chambers. The 4 chambers are

1. Left atrium

2. Right atrium



3. Left ventricle

4. Right ventricle

TRICUSPID VALVE [Right Atrio Ventricular Valve]: It is located in between the

right atrium and right ventricle. It is located in between the right atrium and right

ventricle. It prevents backward blood flow from right ventricle to right atrium.

BICUSPID VALVE [Left Atrio Ventricular Valve]: It is located in between left

atrium and left ventricle. It prevents backward blood from left ventricle to left

atrium.

PULMONARY VALVE: It is located at the right ventricle. It has half moon shaped

cusps. It does not allow blood to come back to the right ventricle.

AORTIC VALVE: It is located between left ventricle and aorta. It does not allow

the blood to come back to the left ventricle.

Heart consists of 3 layers namely,

1. Peri cardium

2. Endo cardium

3. Myo cardium

Pericardium: It is the outer layer of heart. It keeps the outer surface and prevents

the heart from friction.

Endocardium: It is the inner layer of the heart. It provides smooth path for blood

flow.

Myocardium: It is the middle layer of the heart. It acts as the main muscle of the

heart and it is made up of short cylindrical fibers.



ECG LEAD SYSTEMS:

Types of ECG lead systems are

(i) Limb lead systems and (ii) Chest lead systems

(i) Limb lead systems:

(a) Bipolar limb lead systems

(b) Unipolar or augmented limb lead systems.

(a)Bipolar limb lead systems:

Potential between any two limb leads is measured with RL grounded.

(i)Lead I: Potential between LA & RA with RL grounded.



(ii) Lead II: Potential between RA & LL with LA tied to RL & RL grounded.

(iii) Lead III: Potential between LA & LL with RA tied to RL & RL grounded.



EINTHOVAN TRIANGLE:

An imaginary equilateral triangle having the heart at its center and formed by

lines that represent the three standard limb leads of the electrocardiogram.

Fig: Einthovan’s Triangle

(b) Unipolar or augmented limb lead systems:

Potential at a particular limb lead with other two limb leads augmented. This

increases the amplitude of the ECG signal without changing its waveform.

(i)Lead aVR: Potential at RA with LA & LL augmented & RL grounded.



(ii)Lead aVL: Potential at LA with RA & LL augmented & RL grounded.

(iii)Lead aVF: Potential at LL with RA & LA augmented & RL grounded.



(ii) Chest leads systems:

Potential at one of six chest leads with RA, LA & LL augmented and RL grounded.

CHEST LEAD POSITIONS:



V1 – Fourth intercostals space at right sternal margin

V2 – Fourth intercostals space at left sternal margin

V3 – midway between V2 and V4

V4 – Fifth intercostals space at mid-clavicular line

V5 – Same level as V4 on anterior auxiliary line

V6 – Same level as V4 on mid auxiliary line

ECG WAVEFORM:

ECG RECORDING METHOD:

Electrode system: Metal plate electrodes made of Ag/AgCl are placed at desired

limb positions. Good contact between electrodes & skin is ensured with the help

of gel and belts.

Lead fault detect: The function of this block is to detect the improper connection of

the electrodes on to the skin by continually measuring the contact resistance and

to warn the operator of this via either an audible tone or a visual indication.

Amplifier protection circuitry: The function of this block is to protect the remaining

part of the circuit from large electrical discharges resulting from defibrillation

process.

Lead selector: The function of this block is to select a desired lead system from 12

possible lead systems. This can be carried out either manually by an operator or

automatically by microprocessor or microcontroller or microcomputer.



Fig: ECG recording system

Preamplifier: The function of this block is to eliminate noise such as other

biopotentials and various electromagnetic interferences resulting from nearby

communication links etc. Generally a differential amplifier with high input

impedance and CMRR is used for this purpose.

Calibration signal: The function of this block is to calibrate the display or the

recorder for predetermined amplitude. A sine wave of 1 mV is generally used for

this purpose.

Baseline restoration: The function of this block is to restore any baseline shift

resulting from the low operating frequency of the amplifier.

Right leg driven system: The function of this block is to provide a reference point on

the patient generally at ground potential.

Isolation circuitry: The function of this block is to provide electrical isolation

between the high power section that is generally driven by 230 V 50 Hz ac mains

and the low power patient section that is generally driven by a low power

battery. This is required to protect the patient from any electrical hazards

resulting from leakage currents.

Driver amplifier: The function of this block is to amplify the ECG signal sufficiently to

level required for the display or the recorder.



ADC & memory: The ECG signal can be digitized and stored for future analysis.

Microcomputer: A microcomputer along with a user-friendly software package

developed on a high-level language such as VC++ can be used

(i) to control the entire process of acquiring the ECG and

(ii) to analyze it automatically for various parameters such as heart rate, PR

interval, QRS interval etc using sophisticated digital signal processing techniques.

Recorder-printer/display: A heat sensitive paper can be used to get a hard copy of

the ECG signal obtained or a CRO can be used to display the ECG signal

obtained for visual analysis.

POSSIBLE QUESTIONS:

1. Define the terms systole & diastole in heart activity.[2m]

2. Define cardiac output. [2m]

3. Define Einthovan’s triangle. [2m]

4. Draw ECG Waveform. [2m]

5. Name the four valves of heart and define it. [2m]

6. Write a short notes on ECG lead system and its types. [8m]

7. Describe in detail about ECG recording system with neat block diagram. [16m]

Books Reffered:



HINTS:



CLASS – 5

TOPIC: ELECTROENCEPHALOGRAPHY [EEG]

DEF:

Electroencephalography is the study of electrical activity of the brain. In EEG

measurement, electrical activity of brain is measured from electrodes which are placed

on scalp.

ACTION POTENTIAL OF THE BRAIN:

Inhibitory Post Synaptic Potential:

If the transmitter substance is inhibitory, then the membrane potential of

the receptor neuron increases in a negative direction. So that it is less

likely to discharge. This induced potential change is called as Inhibitory

Post Synaptic Potential.

Excitatory Post Synaptic Potential:

If the transmitter substance is excitatory, then the receptor membrane

potential will increase in a positive direction. So that it is more likely to

discharge and produces a spike potential. This induced potential

change is called as Excitatory Post Synaptic Potential.

EVOKED POTENTIAL:

These are the potentials developed in the brain as the responses to external

stimuli like sound, light etc.

PLACEMENT OF ELECTRODES IN EEG MEASUREMENT:

The distance between the Nasion and Inion over the head is divided into 5 points:

1. Frontal Pole (FP): 10% of Nasion & Inion distance above Nasion.

2. Frontal (F): 20% of Nasion & Inion distance from FP.

3. Central (C): 20% of Nasion & Inion distance from F.



4. Parietal (P): 20% of Nasion & Inion distance from C (Central Point).

5. Occipital (O): 10% of Nasion & Inion distance from Inion.

Fig: Anterior – Posterior Measurement

Fig: Lateral Measurement.



EEG RECORDING SETUP:

Fig: Block diagram of EEG

Electrode system: Metal disc electrodes made of Ag/AgCl are placed at scalp

positions. Good contact between electrodes & skin is ensured with the help of gel

and adhesive tapes.

Channel selector: The function of this block is to select a desired combination of

19 possible electrodes. This can be carried out either manually by an operator or

automatically by microprocessor or microcontroller or microcomputer.

Preamplifier: The function of this block is to eliminate noise such as other

biopotentials and various electromagnetic interferences resulting from nearby

communication links etc. Generally a differential amplifier with high input

impedance and CMRR is used for this purpose. A minimum gain of 1000 is

required as typical amplitude range of EEG is from 1 to few microvolts.



Calibration signal: The function of this block is to calibrate the display or the

recorder for predetermined amplitude. A sine wave of 1 mV is generally used for

this purpose.

Isolation circuitry: The function of this block is to provide electrical isolation

between the high power section that is generally driven by 230 V 50 Hz ac mains

and the low power patient section that is generally driven by a low power battery.

This is required to protect the patient from any electrical hazards resulting from

leakage currents.

Driver amplifier: The function of this block is to amplify the EEG signal

sufficiently to level required for the display or the recorder.

ADC & memory: The EEG signal can be digitized and stored for future analysis.

Microcomputer: A microcomputer along with a user-friendly software package

developed on a high-level language such as VC++ can be used

(i) to control the entire process of acquiring the EEG and

(ii) to analyze it automatically for various parameters using sophisticated

digital signal processing techniques.

Recorder-printer/display: A heat sensitive paper can be used to get a hard copy

of the EEG signal obtained or a CRO can be used to display the EEG signal

obtained for visual analysis.

POSSIBLE QUESTIONS:

1. Define EEG.[2m]

2. What is meant by Evoked potential? [2m]

3. Draw EEG lead placement for anterior – posterior measurement. [2m]

4. Write a detail note on EEG recording setup with neat sketch. [16m]



CLASS – 6

TOPIC: EMG, EOG, ERG & PCG

ELECTROMYOGRAPH:

Def: Electromyograph is an instrument used for recording the electrical activity of

the muscles to determine whether the muscle is contracting or not.

Surface and needle electrodes are generally used for EMG.

EMG RECORDING SYSTEM:

Fig: EMG Recording system

APPLICATIONS:

1. Electrophysiology testing

2. Clinical neurophysiology

3. Neurology

4. Psychiatry



ELECTROOCULOGRAM [EOG]:

DEF: EOG is the recording of the biopotentials generated by the movement of

eyes. Surface electrodes are used to measure EOG.

EOG ELECTRODES:

Fig: EOG Electrodes

Fig: EOG Measurement system

APPLICATIONS:

1. It is used to analyze the state of semicircular canals.

2. Diagnoses of the neurologic disorders are possible.

3. The level of anesthesia can be indicated by the characteristics of eye movement.



ELECTRORETINOGRAPH [ERG]:

DEF: Electro Retinography is the method of recording and interpreting the

electrical activity of the eye. The process of recording the change in potential when light

falls on the eye is known as electroretinography.

ERG RECORDING SYSTEM:

ERG WAVEFORM:

Fig: Electroretinogram

a – Due to Early Receptor Potential generated by light.

b – Due to Late Receptor Potential.

c- Obtained at the offset of the light stimulus.

d- Due to the off response of ERP and LRP.



PHONOCARDIOGRAM:

DEF: The device which is used to measure heart sound is known as

Phonocardiogram. These heart sounds are due to the vibrations set up in the blood

inside the heart by the sudden closure of valves.

AUSCULTATION:

The technique of listening sound produced by organs and vessels of the body is

known as Auscultation.

CLASSIFICATION OF HEART SOUND:

1. Valve closure sound

2. Ventricular filling sound

3. Valve opening sound

4. Extra cardiac sound.

PCG RECORDING SYSTEM:

Fig: PCG Recording System

Types Of Microphones Used in PCG:

1. Air-Coupled Microphone

2. Contact Microphone



PCG WAVEFORM:

Relationship between blood pressure & heart sound & ECG Waveform

POSSIBLE QUESTIONS:

1. Define Auscultation.[2m]

2. Name the microphones used in PCG. [2m]

3. Differentiate ERG and EOG. [2m]

4. Give EMG signal characteristics. [2m]

5. How is the pulse rate is measured? [2m]

6. What is the advantage of instrumentation amplifier over differential amplifier? [2m]

7. What are the frequency range of ECG, EEG and EMG waves? [2m]

8. Compare the signal characteristics of ECG and PCG. [2m]

9. How the PCG signals are generated? Explain the measurement of PCG. [8m]

10. Draw the 12 lead system used in ECG. [8m]

HINTS:



CLASS – 7

TOPIC: MONITORING SYSTEMS

MONITORING SYSTEM:

DEF: A quantitative assessment of the important physiological variables of the

patients during critical periods of their biological functions.

Types Of Monitoring System:

1. Cardiac Monitor

2. Bedside patient monitoring system

3. Central monitors.

MEASUREMENT OF HEART RATE:

Heart rate is derived by the amplification of the ECG signal and by measuring

either the average or instantaneous time intervals between two successive R peaks.

Techniques used to calculate heart rate include:

1. Average calculation – Oldest and most popular technique. An average rate is

calculated by counting the number of pulses in a given time.

2. Beat-to-beat calculation – This is done by measuring the time in seconds,

between two consecutive pulses and converting this time into beats/min.,

using the formula beats/min = 60/T.

3. Combination of beat-to-beat calculation with averaging: This is based on a four

or six beats average.

MEASUREMENT OF PULSE RATE:

The pulse pressure and waveform are indicators for blood pressure and flow.

Instruments used to detect the arterial pulse and pulse pressure waveforms in the

extremities are called Plethysmographs.



The method used for the detection of pulse changes due to blood flow are:

1. Electrical impedance changes

2. Strain Gauge or microphone

3. Optical changes

The most commonly used method to measure pulsatile blood volume changes is by the

photoelectric method. Two methods are common:

1. Reflectance method

2. Transmittance method.

BLOOD PRESSURE MEASUREMENT:

Blood pressure is the most often measured and the most intensively studied

parameter in medical practice. The most frequently monitored pressures, which have

clinical usefulness in medium and long term patient monitoring, are arterial and venous

pressure.

The two basic method for measuring blood pressure are

1. Direct

2. Indirect.

Books Reffered:


2. Handbook of biomedical instrumentation – R.S.Khandpur [Pg:No:186]

POSSIBLE QUESTIONS:

1. How partial pressure of blood can be measured and explain the measurement techniques.[6m]

2. Why conducting gel is applied during biosignal recording?[8m]

3. Describe in detail about basic component of biomedical system.[16m]

Documents

Medical Electronics Unit 1 New