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1 In The Name of Allah The Most Beneficent The Most Merciful ECE 4550: Biomedical Instrumentation Lecture: Defibrillators Engr. Ijlal Haider University of Lahore, Lahore 2 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 5 TYPES OF DEFIBRILLATORS Internal defibrillator a) • Electrodes placed directly to the heart • Eg.-Pacemaker External defibrillator b) • Electrodes placed directly on the heart • Eg.-AED DEFIBRILLATOR ELECTRODES Types of Defibrillator electrodes:- a) Spoon shaped electrode • Applied directly to the heart. b) Paddle type electrode • Applied against the chest wall c) Pad type electrode • 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. 12 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 15 16 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 17 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 • Energy delivered in one direction through the patient’s heart a) Biphasic waveform • 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. 28 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 31 •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 32 Thank You!
