Used to overcome ventricular fibrillation may be due to coronary occlusion, shock, or abnormalities in blood chemistry

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Arthur Carr
5 years ago
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Used to overcome ventricular fibrillation may be due to coronary occlusion, shock, or abnormalities in blood chemistry Main problem: heart muscle fibers are continuously stimulated

2 Used to overcome ventricular fibrillation may be due to coronary occlusion, shock, or abnormalities in blood chemistry Main problem: heart muscle fibers are continuously stimulated by adjacent muscles no synchronization succession of events Results in steep fall in cardiac output Defibrillator high energy shock causes all muscle fibers to contract simultaneously

3 Energy storage capacitor charged at slow rate (few seconds) Discharged in few milliseconds Charging Ac Mains and rectifier (or) Battery and DC to DC converter Some shaping of discharge current is needed Simplest discharge through patient s R exponential decay typical of RC circuit Truncated Ratio of duration of shock to RC is small Pulse is rectangular shape Truncated Ratio of duration of shock to RC is larger current appears trapezoidal

4 Variable Autotransformer Vacuum type high voltage change-over switch Current limiting, 100 mh, R = 20W 4000 V, 20mS Oil-filled 16 mf

5 Patient pure resistance W for 80cm 2 electrode area RLC circuit underdamped, damping factor <1 Pulse duration: 5 ms or 2.5 ms Damped sinusoidal waveforms (DSW) Used in over 90% of devices C = 30-50mF R = 40-70W Overdamped Energy = 360 J for 50 W patient Lown Waveform 335 J to 405 J

6 Monophasic Escalating high levels of energy delivered in one direction Output Biphasic Delivers energy in both directions More preferred A defibrillator provides a 5 ms pulse of 20 A to a 50 W load. Thus the energy delivered is E = Pt = I 2 Rt = (20 A) 2 (50 W)(0.005 s) = 100 J. Watt-seconds or Joules as a measure of electrical energy stored in a capacitor Range: J

7 External: Metal discs about 3-5 cm in diameter attached to highly insulated handles Circular, concave shaped with sharp rims and insulated-back side Should be able to deliver large currents Contain safety switches Capacitor is discharged only when electrode makes good firm contact with patient s skin Internal: Large spoon shaped electrodes (a) A spoon-shaped internal electrode that is applied directly to the heart. (b) A paddle-type electrode that is applied against the anterior chest wall.

8 Some electrodes are provided with spring contacts. Burns can be prevented Pre-gelled and self-adhesive electrodes are used now-a-days Provides better conformity to body shape Chest wall impedance Size of electrode, paddles, energy of discharge, no. and time-interval of previous shocks and interface material used between paddle electrode and chest wall

9 Mainly used when there is atrial fibrillation, ventricular tachycardia, and other arrhythmias Synchronization is required to avoid ventricular fibrillation The period ~20 to 30 ms after QRS peak is most preferred least risk of ventricular fibrillation Called Cardio-version Shock-wave during vulnerable T-wave is avoided Synchronizer consists of ECG amplifier that detects QRS complex and uses this to trigger a time delay circuit After the time delay defibrillator capacitor is discharged across the chest through the electrodes Generates a marker pulse on ECG monitors to show when the counter shock occured

10 Output of defibrillating circuit is kept isolated or floating Total energy is always contained between the two electrodes There is no loss of energy to grounds high efficiency is maintained No direct path to ground electrical safety Portable Defibrillators operate on batteries Have DC to Dc converter to step-up the voltage required to charge capacitor Patient impedance is very critical for defibrillator effectiveness Knowledge of peak current, patient impedance changes, actual delivered energy is very important for operator to choose right parameters Can be determined if stored energy and defibrillator circuit parameters (C, L, R) are known

11 Operator selects desired energy to be delivered to 50 W load Microprocessor determines corresponding value of stored energy internal resistance and patient impedance are taken for setting this value Storage capacitor voltage (V) is determined using: E stored = 0.5 CV 2 Discharge current passes through a current-sensing transformer It also provides ground isolation for patient circuit Provides voltage that is peak-detected and recorded by µp Peak discharge current, Stored energy Patient impedance Poor paddle contact alarm when patient impedance > 100W

Also called Advisory External Defibrillators (AED) Accurately analyses ECG and makes

specificity comparable to paramedics Then delivers automatic or recommended high energy

Four key indicators Heart rate, conduction (width of R wave), stability and amplitudes

12 Also called Advisory External Defibrillators (AED) Accurately analyses ECG and makes reliable shock decisions Detects ventricular fibrillation with sensitivity and specificity comparable to paramedics Then delivers automatic or recommended high energy defibrillating shock Requirement Self adhesive electrodes More accurate, fast and safer Four key indicators Heart rate, conduction (width of R wave), stability and amplitudes Automatic self-test features are included: - internal discharge and recalibration Maintenance free

IMPULSE 6000D/7000DP DEFIBRILLATOR/TRANSCUTANEOUS PACER ANALYZER. 25 reasons to differentiate Impulse 6000D/7000DP from all others

IMPULSE 6000D/7000DP DEFIBRILLATOR/TRANSCUTANEOUS PACER ANALYZER INTRODUCTION 25 reasons to differentiate Impulse 6000D/7000DP from all others Function 1. Compatible with full range of defibrillation technologies