Research On The Method Of Transthoracic Impedance For The Monitoring Of Quality Of Cardiopulmonary Resuscitation

Cardiac arrest（CA）,which also be called sudden cardiac death (CSD)，is a medicalemergency with absent or inadequate contraction of the left ventricle of the heart thatimmediately causes body wide circulatory failure. More than80%cardiac arrests haveoccurred out of the hospital, which also is called out-of-hospital cardiac arrest (OHCA).According to statistics, an estimated330,000victims in USA,350,000in Europe and544,000in China experience OHCA each year.Cardiopulmonary resuscitation (CPR), which has been a focus research in the field ofmedicine all over the world, is the only effective methods to rescue the patients whoexperience CA. CPR consist of chest compression, ventilation and electrical shock and soon. The2010guidelines, therefore, emphasized the importance of performing optimal chestcompression.The quality of chest compressions including adequate depth, frequency and full chestrecoil between compressions. Adequate depth, in particular, is the key to keeping certaincoronary perfusion pressure (CPP). CPP has been proved to be the most direct indicator toforecast the return of spontaneous circulation (ROSC). However, studies have shown thatmany patients experience CA have not get effective chest compression during CPR, mainlyshowing the lack of compression depth, low frequency and inadequate blood flow to thecirculatory system. A large quantity of investigations has confirmed that immediate andeffective CPR initiated by layperson can dramatically improve survival rate of OHCAvictims. It is report that the overall success rate of CPR is lower than10%.The current method for monitoring the quality of chest CPR includes CPP,compression depth and frequency during CPR. CPP is a highly predictive indicator of thelikelihood of ROSC, yet it is an invasive measurement and its application is restricted. Compression depth and frequency can be obtained by placing acceleration sensors ordisplacement sensors above the chest of patients, but this method require additional sensorsand devices. Although transthoracic impedance (TTI) has been widely applied during CPR,the research that TTI for monitoring the quality of chest compressions and giving real-timedisplay has not been reported. And then, the relationship between TTI changes, CPP andcompression depth has not been established. Thus, it is a significant research topic that howto make use of the TTI signal to evaluate the quality of CPR and give a real-time feedback.According to the above problems, in this thesis, the following two aspects of contentswere studied:1. Building an animal experimental model and studying the relationship between TTIchanges, CPP and compression depth. In this porcine model, CA (6minutes VF) anddifferent quality of CPR model were established. Contrast study was carried out betweenhigh quality and low quality groups. Optimal depth of manual compression in high qualitygroup was defined as a decrease of25%(50mm) in anterior posterior diameter of the chest,while suboptimal compression was defined as70%of the optimal depth (35mm). Allanimals had ROSC after optimal compressions; this contrasted with suboptimalcompressions, after which only2of the animals had ROSC (100%vs.28.57%, p=0.021).The correlation coefficient was0.89between TTI amplitude and compression depth (p <0.001),0.83between TTI amplitude and CPP (p <0.001).2. Monitoring the quality of CPR via TTI signal and giving a real-time feedback. Toaccurately get the indexes, such as TTI changes, compression frequency, compression/ventilation ratio, chest compression fraction etc, we have designed a detection algorithmbased on TTI signal, which is mainly consist of three parts:(1) detecting the peaks andtroughs of the TTI signals through the extremum search method, and then removing falsedetection.(2) Dividing the detected signal into ventilation waves and compression wavesthrough feature extraction and automatic classification.(3)Calculating the parameters suchas TTI changes, compression frequency, compression/ventilation ratio, compressionfraction to evaluate the quality of CPR and giving a real-time feedback to the rescuer.In thesis, through the establishment of CPR model, we have studied and confirmed thatthere are significant positive correlation between the TTI changes, CPP and thecompression depth. And it has shown important meaning for guiding CPR by using TTI signals for evaluating and monitoring the quality of CPR. Because the TTI signal can beobtained from the defibrillation electrodes, there are no additional electronic devices areneeded. Therefore, the method which based on TTI for monitoring the quality of CPR andgiving a real-time feedback has a broad application prospect during CPR.