Research On Physiological Signal Acquisition System Of Automated External Defibrillator

Sudden Cardiac Death (SCD) is the most serious symptoms of arrhythmia, which accounts for about50%to the cause of the cardiovascular disease death. While fatal arrhythmia as Ventricular Fibrillation (VF) is the main factor lead to Sudden Cardiac Arrest (SCA), when SCA failed to rescue, it will lead to a real SCD, even more, once SCD occurred, the patient will die in a short period. So, clearing up the VF is the key to rescue the SCD patients’ life. Now, early defibrillation is widely recognized as the most effective method to treat VF. The appearance of Automated External Defibrillator (AED) makes early defibrillation possible, and greatly improved the survival rate of SCA patients outside of the hospital.The main work of this paper is the study about physiological signal acquisition system of AED. With the extraction, collection and calculation of ECG and chest impedance signal from VF patients, AED analyze arrhythmia automatically, and can quick tell if there a defibrillated rhythm, then it through voice prompt and frequency display to remind the operator to carry out shock defibrillation. The research of AED physiological signal acquisition system see AED as the research background, and the collection and analysis of physiological signal is the research object, Main work as:Firstly, introduces the AED defibrillation principle, ECG generation principle and chest impedance measurement principle, based on these principles, it given the overall design scheme of AED. According to the overall structure design, system with sub-module gives ECG acquisition module circuit design, chest impedance measurement module and high voltage charging module circuit design.The orignial ECG from human body surface through filter, amplification and some other pretreatment, then put it into the processor for AD sampling, the sampled ECG data will through the sample entropy algorithm for VF detecting, according to the value of sample entropy algorithm to judge if the a VF, once VF happened,then start the high voltage charging circuit.Before the high voltage charging module, it must finish the measurement of chest impedance, by the controlling and programming of AD9854to produce a sine signal with desired frequency and amplitude. This sine signal through VCCS conversion circuit can directly see as the excitation of chest impedance measurement system, under current excitation, using the voltage electrodes to detect its voltage signal, then enlarge and extract the detected voltage signal.Write the AD driver for ECG, and PWM driver for high voltage charging control circuit.After PCB drawn and system debug, it proves that the design of the system is simple and feasible, and can be in progress of module integration and new function research.