DEPARMENT OF ELECTRONICS ENGINEERING

SUBJECT:-ANALOG SYSTEM DESIGN

ELECTROCARDIOGRAM (ECG) PREPARED BY:-

Himanshu.v.Gawande-55GUIDED BY:- BRANCH- ELECTRONICS PROF. T.G.DEOTALE 5th semester SEC-A

CONTENTS• INTRODUCTION• CHARACTERISTICS• ECG CIRCUIT DIAGRAM• WORKING OF ECG • AMPLIFIERS IN ECG• FILTERING

INTRODUCTION• WHAT IS ECG? A technique of recording bioelectric currents generated by the heart. It records any problems with the heart’s rhythm, and the conduction of the

heart beat through the heart which may be affected by underlying heart disease.

• WHY IS ECG USED?To check how well medicines are working and whether they are causing side effects that affect the heart.-To check the health of the heart when other diseases or conditions are present such as high B.P., high cholestrol, diabetes, etc..-To assess if the patient has had a heart attack or evidence of a previous heart attack.-To observe the effects of medicines used for coronary heart disease.-To see if there are too few minerals in the blood.-To diagnose poor blood flow to the heart, heart attack and abnormalities of the heart.

CHARACTERISTICS• The ECG signal consists of low amplitude voltages in the presence of

high amplitude offsets and noise.• The large offsets present in the system are due to halfcell potential

developed at the electrodes

• Ag/AgCl(Silver-silverchloride) is the common electrode used in ECG

systems and has a maximum offset voltage of +/- 300 mV.• -The actual desired signal is +/- 0.5 mV superimposed on the

electrode offset.• In addition, the system also picks up the 50/60 Hz noise from the

power lines which forms the common mode signal.

• The amplitude of the power line noise may be very high . So, it has to

be filtered.

PRINCIPLE OF ECG• The ECG device detects and amplifies the tiny electrical changes on

the skin that are caused when the heart muscle depolarizes during each heartbeat.

• It can give information regarding the rhythm of the heart (whether or not the electrical impulse consistently arises from the part of the heart where it should and at what rate), whether that impulse is conducted normally throughout the heart,

• It can also give information regarding the balance of salts (electrolytes) in the blood (e.g. hyperkalaemia) or even reveal problems with sodium channels within the heart muscle cells .

• It is one of the key tests performed when a heart attack (myocardial infarction or MI) is suspected; the ECG can identify if the heart muscle has been damaged in specific areas, though not all areas of the heart are covered.

ECG CIRCUIT DIAGRAM

WORKING OF ECG• ECG machines use electrodes to convert the ionic signals from the

body into electrical signals to be displayed and used for data analysis. However, due to the size of the signals and outside noise, ECG requires amplification and filtering to produce high quality signals.

• An ECG’s job is to amplify the small signal measured from the heart as well as to filter outside and internal noise. The amplification is mainly implemented through a differential amplifier whereas filtering is completed through common and differential mode filtering.

•

AMPLIFIERS IN ECG• ECG signals vary from the microvolt to the millivolt range. Due to this

small range, the signals measured need to be amplified in order to be better interpreted.

• Typical biopotential amplifiers have high input impedance and are designed for safety first. This is due to the fact that the signal amplified is being drawn from a living organism so precautions must be taken in order to prevent macro and micro shock.

• Isolation and protection circuitry are used to limit current through electrodes to safe levels.

• The output impedance of the amplifier should be very low to drive any external load with minimal distortion. Again, due to the small size of the signal, the gain should be large.

•The amplifiers should have a high common mode rejection ratio to eliminate large offset signals. Finally, most biopotential amplifiers are differential.

•Differential amplifiers are used to make sure that noise are not amplified thus yielding . Thus combinations of differential amplifiers are used to

construct what is called an instrumentation amplifier.

Basic Instrumentation Amplifier

FILTERINGECGs are subject to many different kinds of noise internally and externally.

These artifacts can be filtered digitally

as well as through analog practices.

For example, the analog band stop filter

shown in figure can be used to

modulate 60 Hz noise from power lines

based on what resistor,

capacitor, and inductor values

are chosen.

Different types of noises are:-•Baseline wander(low frequency noise)• Power line interference(50Hz or 60 Hz noise• Muscle noise

Second order band stop filter

ECG artifacts

• An ECG can show damage to the heart.

• How fast your heart is beating and the beating in normal rhythm .ECG helps to Show the effects of drugs or devices used to control the heart.

• An ECG can show the size and position of your heart chambers.

LIMITATIONS• A good ECG reading does not preclude having the underlying heart

disease and other symptoms, such as chest pain, must be taken into account and further evaluation may be required.

• Not all heart problems will show up on an ECG. A prime example is vulnerable plaque (a form of atheroma). which is a major cause of heart attacks.

• False positives and false negatives are common among clinical tests. A doctor has to weight all the evidence prior to making a diagnosis.

APPLICATIONS

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