A presentation on Biomedical Instruments

1. Presentation On
Biomedical Instruments

2. Topics to be discussed today:-
 Electro-encephalography (EEG)
 Applications of EEG
 Electrocardiography (ECG)
 Applications of ECG
 Electromyography (EMG)
 Applications of EMG

3. Introduction to ECG
An electrocardiogram is a test that measures the electrical
activity of the heartbeat. With each beat, an electrical
impulse travels through the heart. This wave causes the
muscle to squeeze and pump blood from the heart. A normal
heartbeat on ECG will show the timing of the top and lower
chambers.

4. Block Diagram of ECG

5. Explanation
 Defibrillator Protection Circuit:-
The one end of the electrode leads are connected along RA,
LA, chest and LL of the patient. The other end of electrode
passes through defibrillator protection circuit. The protection
circuit has buffer amplifier and over-load voltage protection
circuit.
 Lead Selection Logic:-
This block helps to select the type of electrode lead system.
We can choose either bipolar or augmented electrode system.
 Calibration Circuit:-
Calibration is a process that helps to eliminate errors in the
system. Here, any changes in the lead selection circuit results
in artifacts in the ECG output. Therefore, the calibration unit
helps the technician to correct the error in ECG output.

6.  Pre Amplifier:-
An instrumentation amplifier and a differential amplifier with
high gain and high CMRR is used as pre amplifier.
 Power Amplifier:-
The output unit is driven with power amplifier. After the signal is
amplified using pre-amplifier it goes to the power amplifier. The
output unit is attached with a pen motor. A high electrical power
is required to initiate recording with pen recorder. Hence, a
high power gain amplifiers are used as power amplifier.
 Feedback Network:-
Feedback network is used to provide damping to the pen
motor.
 Output Display Unit:-
Either a CRO or a pen chart recorder acts as the output
device.

7. ECG Waveform

8. Applications of ECG
 It indicates the rate and rhythm or pattern of contraction of
heart.
 It gives a clue about the condition of heart muscle and is
used to diagnose heart disorders.
 It can also reveal irregularities in heart’s rhythm known as
‘arrhythmia’.
 An ECG also helps to determine the location and amount of
injury caused by heart attack and later helps to assess the
extent of recovery.

9. Introduction to EEG
 An electroencephalogram (EEG) is a
test that detects electrical activity in
your brain using small, metal discs
(electrodes) attached to your scalp.
Your brain cells communicate via
electrical impulses and are active all
the time, even when you're asleep.
This activity shows up as wavy lines
on an EEG recording.
 An EEG is one of the main diagnostic
tests for epilepsy. An EEG can also
play a role in diagnosing other brain
disorders. It can also diagnose brain
tumor and brain damage.

10. Block Diagram of EEG

11. Explanation
 Montage selector:-
Montages are patterns of connections between the electrodes
and the recording channels. The montage selection switch is
used for selecting a particular channel. Different channels
convey different information. Montages are always symmetrical
and hence in the 10-20 electrode placement system the
electrodes are also placed symmetrically.
 Pre-amplifier:-
The function of pre-amplifiers in the EEG measuring system is
that the EEG signals are having amplitude levels in microvolt
range it is compulsory that they are to be amplified before
further processing. It is to ensure that the information from the
EEG electrodes is not affected by any external noise.

12.  Filters :-
The muscle artifacts (noise) are a major problem regarding the
EEG waveform. These noises can make the representation
dishonest. So we have to filter out these noise contents. This
function is done by a bank of filters in the EEG machine
systems, which are selected according to the need.
 Analog and Digital Converters :-
For the detailed analysis of the EEG waveform, we use
computers and oscilloscopes. As the computers only accept
digital data we have to convert the analog EEG information in
to digital form. The function of ADC is to convert the analog
EEG signal to digital form.
 Writing Recorder and Paper Drive:-
The writing part of an EEG machine is usually consists of an
ink type direct writing recorder. The recorder will be a chart
paper which is driven by a synchronous motor.

13. EEG Waveform

14. Applications of EEG
 An EEG is mainly used when there is a need to diagnose and
manage epilepsy.
 It can be used to investigate other conditions such as
encephalitis,dementia,head injuries,brain tumors,hemorrhage.
 An EEG can identify areas of the brain that are not working
properly.
 EEGs are also used to determine the level of brain function in
people who are in coma.

15. Introduction to EMG
Electromyography (EMG) is a diagnostic procedure that
evaluates the health condition of muscles and the nerve cells
that control them. These nerve cells are known as motor
neurons. They transmit electrical signals that cause muscles to
contract and relax. An EMG translates these signals into
graphs or numbers, helping doctors to make a diagnosis.

16. Block Diagram of EMG

17. Explanation
 EMG Electrodes:-
The electrode used for EMG recording can be of surface type
or needle type depending on the area from which the EMG is
to be obtained and the type of measurement. If we need to
have EMGs from many individual muscle cells rather than from
the surface as a group, needle electrodes are the best choice.
 Bioelectric Amplifier:-
The bioelectric amplifiers are used to amplify the bioelectric
signals obtained from EMG electrodes.
 Oscilloscope:-
The measured EMG can be connected to the oscilloscope to
visualize the EMG. The abnormalities in the working of nerves
and muscle cells can be identified by analyzing the EMG
waveform.

18.  Audio Frequency (AF):-
Under normal condition the sound does not undergo large
variations. But abnormal and spontaneous activity may be
distinguished by the sudden change in sound and this can be
analyzed by the doctor with the help of an AF amplifier.
 EMG Recorder:-
The readings in EMG cannot be recorded in a low speed chart
paper recorders because of its extreme low frequencies. So it
is less useful. So, normally we use the photographic recording
of EMG. For this a light sensitive paper is moved over the
recording CRT.

19. EMG Waveforms

20. Applications of EMG
 EMG is used as a diagnostics tool for identifying neuromuscular
diseases, or as a research tool for studying kinesiology.
 EMG signals are also used as a control signal for prosthetic devices
such as prosthetic hands, arms and lower limbs.
 Needle EMG may aid with the diagnosis of nerve compression or
injury.

21. Thank You