Transcript In The Name of Allah The Most Beneficent The

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In The Name of Allah
The Most Beneficent The Most Merciful
ECE 4550:
Biomedical
Instrumentation
Lecture:
Defibrillators
Engr. Ijlal Haider
University of Lahore, Lahore
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NEED FOR A DEFIBRILLATOR
Ventricular fibrillation is a serious cardiac
emergency
resulting from asynchronous contraction of the
heart
muscles.
Due to ventricular fibrillation, there is an irregular o
rapid heart rhythm.
Fig. Ventricular fibrillation
Fig. Normal heart beat
NEED FOR A DEFIBRILLATOR
Ventricular fibrillation can be converted into a more
efficient rhythm by applying a high energy shock to the
heart.
This sudden surge across the heart causes all musc
to contract simultaneously.
Possibly , the fibres may then respond to normal
physiological pacemaking pulses.
The instrument for administering the shock is called
DEFIBRILLATOR.
TYPES OF DEFIBRILLATORS
Internal
External
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TYPES OF DEFIBRILLATORS
Internal defibrillator
a)
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Electrodes placed directly to the heart
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Eg.-Pacemaker
External defibrillator
b)
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Electrodes placed directly on the heart
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Eg.-AED
DEFIBRILLATOR ELECTRODES
 Types of Defibrillator electrodes:-
a) Spoon shaped electrode
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Applied directly to the heart.
b) Paddle type electrode
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Applied against the chest wall
c) Pad type electrode
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Applied directly on chest wall
DEFIBRILLATOR ELECTRODES
DEFIBRILLATOR ELECTRODES
Fig.- Pad electrode
DEFIBRILLATOR ELECTRODES
Electrodes have insulated handles
Designed to prevent the spread of jell from
electrodes to handles for the safety and ease
of operator
PRINCIPLE OF DEFIBRILLATION
Energy storage capacitor is charged at relatively sl
from AC line.
Energy stored in capacitor is then delivered at a rel
rapid rate to chest of the patient.
Simple arrangement involve the discharge of capa
energy through the patient’s own resistance.
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PRINCIPLE OF DEFIBRILLATION
PRINCIPLE OF DEFIBRILLATION
The discharge resistance which the patient represe
purely ohmic resistance of 50 to 100Ω approximate
a typical electrode size of 80cm2.
This particular waveform Fig 13.9(b) is called ‘ Lown
waveform.
The pulse width of this waveform is generally 5-10 m
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Peak current of 50 A
Time 5 sec
Resistance 50 ohm
Power delivered = 320 J
To overcome losses across capacitor and inducto
25% additional energy required
Energy to be stored is 400 J
Capacitor of 16 micro farad
Voltage required is 7000V
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For Internal electrodes only 50 J is needed
Classes of discharge waveform
Monophasic pulse or waveform
Bi-phasic pulse or wavefor
Classes of discharge waveform
There are two general classes of waveforms:
a) mono-phasic waveform
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Energy delivered in one direction through the
patient’s heart
a) Biphasic waveform
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Energy delivered in both direction throuth the
patient’s heart
Classes of discharge waveform
Fig:- Generation of bi-phasic waveform
Classes of discharge waveform
The biphasic waveform is preferred over monophas
waveform to defibrillate .why?????
• A monophasic type, give a high-energy shock,
up to 360 to 400 joules due to which increased ca
injury and in burns the chest around the shock pa
• A biphasic type, give two sequential lower-energ
of 120 - 200 joules, with each shock moving in an
opposite polarity between the pads.
Classes of discharge waveform
Dual Peak Waveform
10 msec
Truncated Waveform
Time can be adjusted
AUTOMATIC EXTERNAL DEFIBRILLATOR
AUTOMATIC EXTERNAL DEFIBRILLATOR
 AED is a portable electronic device that automatic
diagnoses the ventricular fibrillation in a patient.
Automatic refers to the ability to autonomously ana
the patient's condition.
 AED is a type of external defibrillation process.
 AEDs require self-adhesive electrodes instead of
hand
held paddles.
The AED uses voice prompts, lights and text messag
tell the rescuer what steps have to take next.
ELECTRODE PLACEMENT OF AED
Anterior electrode pad
Apex electrode pad
Fig. anterior –apex scheme of electrode placement
WORKING OF AED
 turned on or opened AED.
 AED will instruct the user to:-
• Connect the electrodes (pads) to the patient
• Avoid touching the patient to avoid false
readings by the unit.
• The AED examine the electrical output from t
heart and determine the patient is in a shock
rhythm or not.
WORKING OF AED
•when device determined that shock is
warranted, it
will charge its internal capacitor in
preparation to
delivercharged,
the shock.
•When
the device instructs the user to en
one is touching the victim and then to press a red
to deliver the shock.
Many AED units have an 'event memory' which store
ECG of the patient along with details of the time the
was activated and the number and strength of any
delivered.
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Courtesy Texas Instruments
Testing Defibrillators
A dummy load is connected across the
defibrillator electrodes
Discharge is observed
50 ohm resistance is taken as human
resistance connected in series with a
low value resistor. Neon light is connected
with low value resistor and lights when
defibrillator is discharged
Testing Defibrillators
Some defibrillators have built-in test
system
If they do not have, it can be designed
and mounted on the trolley
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•Current requirements normally range up to 20 A.
•Voltage ranges from 1000V to 6000V
•Time of discharge is kept from 5 to 10 msec
•Current is dependent on the body (chest) resistance
•For reference visit:
•http://www.resuscitationcentral.com/defibrillation/biphas
ic-waveform/
•And various other resources on internet
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Thank You!