| Background and Objective1.BackgroundThere are about 6 million people died of sudden death each year in the world, cardiac arrest account for 80% of the cardiac death. At present, the survival rate of out-of-hospital cardiac arrest is low in our country, according to incomplete statistics in China, the survival rate of out-of-hospital cardiac arrest is less than 1% in China, even if in the developed countries abroad outside rescue success rate of hospital is only reached 2-11%. CPR is the main rescue means to rescue the CA patients, and chest compressions as the basic and key for it not only can be implemented fast but also operate very simple, easy and effective. Blood perfusion the vital organs can be ensured through the chest compressions, and the regulations of cardiac diastolic and pump function can also be restored. "2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care(ECC)"(2010 AHA Guidelines) emphasize the importance of high quality chest compressions, which points out the frequency and depth of compressions more than 100 times/min and 5 cm respectively, changing the chest compressions sequence from CPR’s A-B-C into C-A-B. It is visible that chest compressions have a very big effect on improving the rescue survival rate. But at the same time, with the further increasing of the depth of chest compressions, its complications are increasingly obvious. The most common is rib cartilage injury, fracture of ribs and sternum. So how to improve the quality of chest compressions and avoid the incidence of chest compressions complications will be our CPR research’s key topic. This requests us have a further understanding about the mechanism of chest compressions, at the same time, a further validation of the effectiveness of the technology of chest compressions. The researches about chest compressions mechanism developed from heart pump mechanism theory to breast pump mechanism theory. In recent years, some scholars put forward the idea of abdominal pump mechanism research. In this researches we will discuss whether there is a resonance effect when compress the chest. In addition, discuss the index of CPR’s effectiveness (depth and frequency of the pressing) conform to our nation or not? Is it the final target? Or is it still needs to study. The research methods of cardiopulmonary resuscitation chest compressions before are always on the human body of clinical research, animal experiment study and simulation model of the human body. But because of the limitation of human medical ethics, the anatomical differences between different species. In addition, the model material and its research methods are very limited, so the research results lack credibility. Is there any other better methods for clinical chest provide a strong basis and guidance pressing it?2. ObjectiveThis research is in the help of imaging technology combining methods of three-dimension finite element biomechanics. Verify the effectiveness of thoracic finite element model by the reconstruction of normal human thoracic three-dimensional finite element model with computer which is through biomechanical experiments for thoracic specimen. We implemented tests on the three-dimensional finite element by chest compressions. By pressing a different position in the analysis of the relationship between chest compressions different compression depth force and displacement; the distribution of stress and strain. Learn pressing clinical best position, the most likely location of the chest injury and prone to damage pressing position, to provide a strong basis for clinical chest and guidance compressions.Materials and Methods1. Choose a fresh cadaver specimen of an adult male. One case of fresh male cadaver specimen was selected and its chest radiography was taken before the experiment to exclude any disease (including fractures, deformity, etc.) that may exist. Scan specimen with chest CT which is German Siemens dual-source CT (model: SOMATOM Definition,2008g). Scan range for complete thoracic:from thoracic 1 to thoracic 12 (including 12 edge of frame), including soft tissue, bone tissue (bone, rib, rib cartilage, vertebrae, clavicle, scapula, homeruns head), the internal organs (heart, lungs, etc.). Scanning resolution is greater than or equal to 512 x 512 x 8 bit. The thick is less than 0.4 mm. The scanning time is 84.79S. All the human thoracic two-dimensional images collected are 1986 layers which are output in DICOM form.2. Import the two-dimensional images collected by CT into Mimics 10.1 (Materialize corporation of Belgium) 3 d reconstruction software by computer (operating system, Windows 7 64bit, memory of 32 G).Then set up the bone threshold range and threshold segmentation to establish the mask (mask). Calculate the three-dimensional entity (Calculate 3D) by using Mimics 10.1 software, after that, reconstruct the mask into 3D model. Extract the anatomical structure such as ribs, cost cartilage and sternum generating thoracic geometric model. Use the reverse engineering software Geomagic Studio 2012 (64 bit) (Geomagic companies in the United States) to process the geometric model and make a patch division, then import its STP format into SolidWorks 2012 x 64 Edition (Dassault company French); Finally imported into ANSYS (format for WBPJ) to make finite element analysis by SolidWorks 2012.And then import the three-dimensional model into ANSYS Workbench 14.5 (ANSYS company, USA) software for meshing. The suffix of output file format is ".lis". After a material distribution, optimization and optimization and intelligent repair In ANSYS on the units of thoracic grid model form the thoracic three-dimensional finite element model.3. Anatomize the same fresh cadaver specimen and take a biomechanical test by chest compressions. Respectively choose chest sternum between 3 and 4,4 and 5,5 and 6 as chest compressions’ loading position. Use the U.S. Material experiment machine (BOSE Electro Force) to load static in 0-300 N respectively, loading it every 50 N increasing step by step. Configure BOSE Electro Force computer to synchronous record the load and displacement. With the same methods, use the established human thoracic three-dimensional finite element model to simulate the above chest compressions biomechanical testing. Then compare the two groups of experimental data to verify the validity of the finite element model by its trend chart.4. The thoracic model of the simulated human body is fixed and located in the supine position. The press point of it was set to over the center of the chest whose diameter is 5 cm. By constraining the boundaries and setting the conditions above to restore an effective human thoracic finite element model which is used to simulate the ways of vertical chest compressions in clinical. Analysis the load conditions of chest sternum between 3 and 4,4and5,5 and 6 when the chest compressions points’depth was 3-7 cm in ANSYS Workbench software 14.5. Analyze the stress and strain distribution of each part when pressing. And the frame damage in the process of loading.Resultl.The three-dimensional finite element model was successfully build including vertebral column, rib, sternum and other structures of human thorax with 175015 nodes and 92348 elements.2.Comparing biomechanical tests on the same samples of fresh adult male and the model of finite element in respective chest compressions showed that the curve trend are basically same between the two group. It can be seen that the constructed human thoracic finite element model is effective3. The analyses results on the thorax finite element model imitating human chest compression:①.sternal rib (A pinch point) between 3 and 4,4 and 5 pressure point (B) between the ribs,5 and 6 ribs between pressure point (C) three different human thorax compressions points, as the displacement increases gradually (3 to 7 centimeters) required loading force, stress and strain are increasing gradually, as the same displacement three pressing point required loading force, stress and strain distribution are A>B>C. ②.Each pressure point is distributed regularly by stress and strain. The strain distribution of chest compressions are occurred in the costal cartilage, the sternum and costal cartilage junction is obvious, and the most obvious in the fifth costal cartilage. Stress distribution of three pressing points occurred in the thoracic ribs, and back at the junction of thoracic spine and rib with obvious. Among them, the Maximum stress of point B and C existed in the fifth posterior rib and thoracic junctions. The Maximum stress of point A existed in the first rib and thoracic junction. ③.Imitating continuous chest compressions in the loading process, three pressing point of thoracic injury occurred at the junction of the earliest in the fifth costal cartilage and the sternum, respectively, the loading force of 196 N(point A), 146N(point B),118N(point C), obvious that human thorax between 5 and 6, on the point when the thorax compressions are most likely to cause costal cartilage damage, even fracture. However, A and B two pressure points when at the same displacement required the loading force A> B, so it can be inferred that the best external thorax compression point are between the fourth and fifth rid, and it is consistent with the clinical practice.Conclusions1. In this study, with the help of CT imaging technology, a normal male adult human thorax finite element model was successful constructed by the computer. We verified the authenticity and accuracy of model through the corpse specimen experimental and confirmed it further. It is indicated that this model is effective.2. Analyze the finite element model established by the method of simulated clinical thorax compressions. When compress the thorax, with the increasing of displacement, the loading force, stress and strain distribution are increased. And it does not change because of the difference in pressing position. If the displacement is the same when the press position from top to bottom, the loading force, session and strain distribution gradually become smaller. But from chest compressions sustained loading experiment, most likely to damage and even the position of the fracture occurred in the fifth costal cartilage and sternal junction induce thoracic compressions of different pressing position, here the sternum, fifth the 6 intercostal space to press the point most likely to cause damage, so the biomechanical point of view, the sternum in fourth,5 intercostal is the best pressing position. From the view of stress and strain distribution, chest compressions both uniform distribution, different press strain were located in the costal cartilage, and in the fifth costal cartilage and sternal border maximum, this also implies that the rib cartilage injury position may be related to strain. The sternum in fourth,5 and fifth,6 intercostal pressing point with fifth posterior rib stress is maximum; and the third,4 intercostal pressing point with first posterior rib stress is maximum, here to deviate from the position of the heart cardiac compression, direct effect and the first two, so the sternum fourth,5 intercostal press position ideal.3. One weakness of this study is that the complexion of the human chest bone structure, and model data processing amount is large, time-consuming or other factors, construction just thoracic bony structure of three-dimensional finite element model of the human thorax, failed to establish a complete chest finite element model including soft tissue, visceral, and at the same time, due to the lack of internal organs, but also lead to resonance effect exists whether this experiment failed to investigate the chest compressions. In order to facilitate the analysis of finite element model, the experiment in the assignment of thoracic model material properties is still too simple, objective may cause analysis result has the certain difference. The inadequacies exist in finite element model are common. Furthermore the number of single modeling, failed to carry out the research of related control. Therefore, more accurate chest organization structure information was needed to construct human thoracic three-dimensional finite element model and to provide biomechanical basis for human thoracic chest compressions. |
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