Digital cardiac defibrillator tester

Abstract

The cardiac defibrillator is the most commonly used instrument in hospital, ambulance and industry for resuscitation after electrocution or cardiac arrest. Defibrillation involves the application of a short pulse of electric current (4–10ms) through the chest of the patient; it has been demonstrated that the required energy is a function of the patient's weight. A knowledge of the performance of a defibrillator is essential; front panel meters, although calibrated in joules, read capacitor voltage only, and a loss of capacitance is not easily detected in use. We have had personal experience of this loss on several occasions. Commercial defibrillator testers employ analogue circuitry and are no more reliable in calibration than defibrillators themselves. This paper discusses the design of a microprocessor-based defibrillator analyser which has a performance far superior to existing testers. It gives an absolute digital readout of the energy delivered into a standard 50 Ω load, the peak defibrillating voltage, and the rise time of the defibrillator output wave. Facilities are also provided for storage of the defibrillator output waveform, so that the profile can be examined on an oscilloscope.