| Cardiac arrest is a medical emergency with absent or inadequate contraction ofthe left ventricle of the heart that immediately causes bodywide circulatory failure. Atleast 225,000 people die in the United States every year from out-of-hospital suddencardiac arrest (CA) before they reach a hospital, and an estimated 370,000 to 750,000patients per year have a cardiac arrest and undergo cardiopulmonary resuscitation(CPR) during hospitalization. The overall incidence of cardiac arrest in China isestimated about 6,000,000 per year.There are two different types of cardiac arrest: dysrhythmic cardiac arrest thatmost victims demonstrate ventricular fibrillation (VF) and asphyxial or respiratorycardiac arrest such as drowning, drug overdose or traumatic injuries, that bout5%～15% victims have VF. The primary cardiac arrest is emphasize on earlierdefibrillation and immediate CPR, while the best results for the resuscitation ofsecondary cardiac arrest is obtained by a combination of effective chest compressionsand ventilations.Three major restraints are likely to account for currently poor outcomes, namely1) delays in starting cardiopulmonary resuscitation, including chest compression andexternal ventilation, 2) ineffective and interrupted chest compressions, and 3) limited access to, or delayed implementation of electrical defibrillation.An important advance has been the capability for automated prompting of thelay rescuer through basic life support (BLS) maneuvers by newer versions ofautomated external defibrillators (AEDs). Current versions of AEDs have a sensitivityof 94% and a specificity approaching 100% for identifying shockable rhythms. Afterintroduction and expanded use of current versions of AEDs, multicenter trials haveindicated that the number of survivors may double or triple.In most out-of-hospital situations, however, the patient is past the initial phaseof (Ventricular Tachycardia, VT) and is in the rhythm of VF, which is treated withdefibrillation. If no CPR is given, the electrical activity of the heart disappearsgradually and the final rhythm before death is termed asystole, which is a (nearly) flatline in the ECG tracing and is not treated with defibrillation. CPR and drugadministration may increase circulation of blood and oxygen to the ischemicmyocardium and might result in a conversion from asystole to VF, which then can bedefibrillated. During asystole and VF, the heart does not contract and these rhythmsare therefore pulseless. If no mechanical activity corresponds to an existing electricalactivity of the myocardium, the resulting rhythm is called "electromechanicaldissociation" (EMD) or "pulseless electrical activity" (PEA). This rhythm oftenappears in the transition from VF to asystole and is treated with medications and CPR,but does not respond to defibrillation attempts.Presently, resuscitation is guided by a standardized protocol (the internationalguidelines) which includes cardiac rhythm, respiration and pulse detection fordecision support. But currently used AEDs can only perform automated rhythmanalysis. The respiration and pulse detection are depending on the rescuers. For theautomation of CPR, some key problems still need to be solved:(1)Rhythm classification during uninterrupted chest compression. Current AEDs require repetitive analyses of ECG rhythms prior to prompting the delivery of anelectrical shock. Reliable analyses can only be achieved when both chest compressionand ventilation are discontinued for an interval of 12 seconds or more in addition tothe time that may be required for charging the capacitor of the defibrillator anddelivering a shock. With these interruptions, the lifesaving benefits of chestcompression are therefore seriously compromised. Interruption of chest compressionsis also documented as a major factor accounting for poor outcomes in victims ofcardiac arrest. Significantly better outcomes have therefore been reported if effectivechest compression precedes electrical defibrillation and especially if interruptionsmandated by a "hands off" interval are avoided.(2)Monitoring the effectiveness of chest compression. The likelihood of returnof spontaneous circulation (ROSC) after more than 5 minutes of untreated VF isimproved when chest compressions precede the first defibrillation attempt. Therecognized role of chest compression is to restore the flow of oxygenated blood tovital organs, and thereby minimize ischemic injury, especially in the brain and in theheart. The quality of chest compressions relates to compression depth, compressionrate and the completeness of the recoil of the chest. Since chest compressions areusually performed without feedback and relatively small changes in the depth ofcompression profoundly alter hemodynamic effectiveness and outcomes, there is anincreasingly recognized need for such quality controls.(3)Automated respiration and pulse detection. In the past 20 years, the incidenceof VF or VT during cardiac arrest has declined remarkably to less than 50%. Yet, theincidence of PEA and overall cardiac arrest remained unchanged. The decrease in theincidence of VF was accounted for by increases in the incidence of asystole. So it isnecessary for a person who is not a medical professional, to evaluate the condition ofa weak patient who has signs of cardiopulmonary arrest, especially when the patient is partly or completely unconscious. One of the first steps of a rescuer is to determineif there is sufficient breathing and adequate blood circulation. Unfortunately,evaluation of there two parameters for out-of-hospital patients is difficult. Foridentification of blood circulation by detecting a pulse, a common method is to placea hand on a region of the body (e. g. carotid artery) and feel for small fluctuations. Forevaluation of breathing, a common method is to place the rescuer’s face near themouth to feel or hear the flow of air or movement of the chest. Although detection ofpulse and breathing is not difficult in normal people, such identification is difficult inweak patients, such as a patient in shock, where there is low flow of blood and of air.The inability to detect pulse and respiration at this time increases the probability of anincorrect diagnosis between cardiac arrest, breathing arrhythmia (irregular heartbeat),or asphyxia.For the automation of CPR, we extended ECG characteristic analysis of themyocardium status of the victims for monitoring the effectiveness of chestcompression and thus to optimizing the time for defibrillation. For the automatedrespiration and pulse detection, we expanded the conventional precordial AEDsensing and defibrillation electrodes for transthoracic impedance measurement. Thealgorithms developed for automated CPR including:1) Detecting a potential shockable rhythm during uninterrupted chestcompression. Wavelet based transformation and shape based morphology consistencydetection were utilized for rhythm classification. Morphological consistencies ofwaveform representing QRS components were analyzed to differentiate betweendisorganized and organized rhythms. For organized rhythms, the heart rate was thenestimated for further classification between shockable VT and non-shockable sinnsrhythms (SR). When disorganized rhythms were identified, the amplitude spectrumarea (AMSA) was computed in the frequency domain to then distinguish between shockable VF and non-shockable asystole.2) Monitoring the effectiveness of chest compression and optimizing timing ofdefibrillation. Earlier investigations based on ECG recordings of VF obtained fromhuman victims of cardiac arrest focused on the amplitude of VF wavelets as apredictor of the likelihood of successful defibrillation. Subsequently, frequencyanalysis of VF wavelets and, specifically, median frequency was proposed as a moreprecise value which correlated with CPP in canine and porcine models and in humanvictims. The measurement was subsequently refined by us by combing amplitude andfrequency. This method of measurement evolved into the amplitude spectrum area(AMSA) which was defined by the area under the curve of amplitude and frequencyhas since been incorporated into commercially available AEDs. We were thereforeattracted to the possibility that AMSA derived from the conventional two precordialelectrodes, used for both sensing and defibrillation in conjunction with AEDs wouldserve as a monitor of effectiveness of chest compressions.3) Automated respiration and pulse pressure detection. An algorithm used forrespiration and pulse pressure detection with the use of ECG and transthoracicimpedance signal that collected by the conventional electroacrdiographic sensing anddefibrillation electrodes applied for AEDs was proposed. By applying an adaptivefiltering method with the reference of heart rate derived from ECGs, the breathimpedance signal and cardiac impedance signal that represents the mechanical heartbeat are separately derived. The tidal volume and pulse pressure are then can beestimated from the breath impedance signal and cardiac impedance signal.These algorithms are optimized and validated on human and animal data whichwere collected at the Weil Institute of Critical Care Medicine (Rancho Mirage, CA,U.S.A). The rhythm classification algorithm during chest compression yielded asensitivity of 93%, a specificity of 89% for detecting a shockable rhythm with dataset collected from out-of-hospital cardiac arrest victims by AEDs. In an animalexperiment of arrhythmia cardiac arrest model, the effectiveness of chestcompressions was reflected in the AMSA value as it previously was in CPP.Accordingly, the more routinely available electrocardiographic AMSA value mayserve to monitor the effectiveness of chest compression during CPR. In an animalexperiment of asphyxial cardiac arrest model, the change in the measured cardiacimpedance was linearly correlated with the pulse pressure (R~2=0.95). Likewise, themagnitude of the measured respiratory impedance signal was quantitatively related tothe tidal volume (R~2=0.91).The research fulfilled the potential life saving advantages by differentiatebetween asphyxial cardiac arrest and dysrhythmic arrest and prompting accordinglywith respiration and pulse detection, and avoid the adverse effects of unsuccessfulelectrical shocks by rhythm analysis during uninterrupted chest compression andmonitoring the effectiveness of CPR. |
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