Research On Combined Impedance Compensation Strategy For Automated External Defibrillators

China has the highest death toll from cardiac arrest in the world,and ventricular fibrillation is the most important cause of cardiac arrest.Early electrical defibrillation is the only effective treatment for ventricular fibrillation.Electrical defibrillation refers to the process in which the defibrillator generates enough defibrillation energy through the heart to restore spontaneous circulation of cardiac cells.Transthoracic impedance is one of the key factors affecting the success of defibrillation.The transthoracic impedance will directly affect the amount of defibrillation energy reaching the heart.The impedance compensation technology is one of the key technologies of automatic external defibrillator,which adjusts defibrillation parameters according to the patient’s transthoracic impedance.The impedance compensation strategy used in the mainstream automated external defibrillators for sale can be divided into two categories according to the design principle: energy-based impedance compensation strategy and current-based impedance compensation strategy,the former is designed to maintain the same defibrillation energy under different impedances,and the latter is designed to maintain a relatively constant first phase defibrillation current under different impedances.Among them,the energy-based impedance compensation strategy fluctuates greatly in the distribution of defibrillation current under different transthoracic impedances,especially at low impedance levels,which will produce a large defibrillation current and bring additional damage to the myocardium,while the current-based impedance compensation strategy has relatively unstable defibrillation energy,especially at high impedance levels,it is difficult to produce sufficient defibrillation energy.Therefore,this study design a combined impedance compensation strategy,based on the energy-based impedance compensation strategy and based on the current-based impedance compensation strategy to improve,and developed a set of automated external defibrillator on combined impedance compensation strategy implementation,the last of the defibrillator defibrillation performance and impedance compensation performance test.The test results show that the combined impedance compensation strategy has better impedance compensation effect.First,this paper expounds the basic principles of cardiac arrest and electrical defibrillation,and introduces the development status of automated external defibrillators and impedance compensation technologies.Taking the typical impedance compensation strategy of the automated external defibrillator used in clinical practice as an example,the design principle,implementation method,advantages and disadvantages of the energy-based impedance compensation strategy and the current-based impedance compensation strategy are compared and analyzed.A combined impedance compensation strategy aimed at optimizing defibrillation energy distribution,defibrillation current distribution,and impedance compensation accuracy is proposed,and a hardware and software implementation scheme is designed.Secondly,this paper designs and implements the ecglyctic detection circuit,high voltage charging circuit,discharge circuit,transthoracic impedance detection circuit,impedance compensation circuit,main control circuit and other hardware circuits and control software of each circuit of the automatic external defibrillator.In order to realize the combined impedance compensation strategy,a variable resistance circuit,an adaptive algorithm for defibrillation voltage and defibrillation pulse width,and a finer compensation resistance strategy are designed.Then,the performance tests of the integrated defibrillator system such as charge and discharge control,high voltage detection,transthoracic impedance detection and other functional modules were tested using equipment such as defibrillator analyzers and impedance simulators.Finally,taking the developed automated external defibrillator as the experimental machine,and using two automatic external defibrillators based on the energy impedance compensation strategy and the current impedance compensation strategy as the control machines,the impedance compensation optimization effect of the prototype is compared and tested in this paper.The performance test results of the automated external defibrillator show that the relative error of the system’s high voltage detection is <2.5%,and the relative error of the thoracic impedance detection is < 3%.The test results of the impedance compensation effect of the automaton external defibrillator show that the combined impedance compensation strategy can implement the impedance compensation function according to the change of transthoracic impedance.The combined impedance compensation strategy developed in this paper can implement impedance compensation according to the change of transthoracic impedance,and there is a steadier distribution of defibrillation energy and defibrillation current: compared with the energy-based impedance compensation strategy,this strategy can significantly reduce the peak current(25 Ω: 27.8 A vs 54.7 A;50 Ω: 20.7 A vs 32.3 A)and average current(25 Ω: 24.8 A vs37.5 A)of defibrillation at low impedance,and compared with the current impedance compensation strategy,it can significantly reduce the defibrillation energy(150 Ω: 8.6%vs 1.7%,175 Ω: 15.6% vs 4.9%,200 Ω: 21.9% vs 8.5%)at high impedance.Impedance compensation is more precise and the current passing during defibrillation is steadier.