An Experimental Study On Evaluation Of The Rabbit’s Myocardial Damage After Crush Injury

Objective：Through making the model of rabbit severe crush injury,we observed the changes ofserum potassium （K⁺）,calcium (Ca²⁺), creatinine （Cr）, blood urea nitrogen （BUN）,myoglobin （MYO）,creatine kinase （CK） et at various times after severe crush injury whilemonitoring the changes of troponin I （cTn-I）,creatine kinase myocardial isoenzyme（CK-MB） and substance atrial natriuretic peptide （Atrial Natriuretic PeptideANP）,endothelin （ET-1） in myocardial and plasma.we also observed myocardial damagechange the various periods by light microscopy and electron microscopy; usingmulti-functional heart ultrasound imaging, especially speckle tracking echocardiography weevaluated the changes of heart function after injury.The aim of this study were to explorethe accuracy and feasibility of the application of ultrasound evaluation of myocardial injuryafter crush injury.Methods：1. Animal model and identification:42rabbits were randomly divided into control and experiment,The experiment weredivided into the immediate group,6h12h,24h,48h and72h group after crush according tothe time point. The self-made crushable equipment using compressed hindquarters about20kg. Removed after6hours of continuous extrusion to make rabbit animal model of crushinjury. Blood was collected approximately4ml from internal jugular vein guiding byB-ultrasound. Detect the concentration of serum BUN,Cr,K⁺,Ca²⁺,CK,MYO. Drawn therabbit thigh after be killed at different time points,observe the pathological changes ofsqueezing the HE staining muscle.2. myocardium secondary injury in crush injury model of rabbitThe establishment of rabbit crush injury model were similar.Then remain as theexperimental control group （n=6） and crush injury （n=36）,after decompression and thendivided into: immediately after decompression group,6h,12h,24h,48h and72h group according to decompression point time. Blood was collected approximately6ml frominternal jugular vein guiding by B-ultrasound.2ml of which were placed in a clean testtube,using the ACS-180automated lighting system to detect of cTnI and CK-MBconcentration. Radioimmunoassay was used to observe the plasma ANP and ET-1concentrations in the remaining4ml. The rabbits were sacrificed after blood wascollected,the chest were cutted when the heart was still beating. Part of the myocardiumwere taked to detect the content of ANP,ET-1in myocardial tissue. Myocardial pathologicalchanges were observed at each time point by using light microscopy and electronmicroscopy.3. Multi-functional composite ultrasonic evaluation of myocardial damage after crushinjuryWith Philips the iE33color Doppler ultrasound（the S5-1probe,2～5MHz,framerates70s-1）,the conventional ultrasonic measurements:measure global left ventricularsystolic function:Left ventricular ejection fraction （LVEF）,Left ventricular circumferenceshortening fraction （LVFS）, Left ventricular wall thickening （△T） and Cardiac output （CO）;global left ventricular diastolic function: Peak flow velocity in early diastolicperiod（PFVE）,and Peak flow velocity in atrial systolic period（PFVA）,PFVE/PFVA PeakFilling Rate（PFR） were all acquisited. Speckle tracking echocardiography measurements:the RS（radial strain）,the CS（circumferential strain）,LS（Longitudinal strain）. the indicator oftorsion: left ventricular peak twist angle（Ptw） were observed.4. Statistical analysis:All variables were continuous quantitative data and represented as x±s.When anormal distribution is assumed,Intra-group variation were compared by LSD-t test usingSPSS software（version17.0）. P<0.05was considered significant.Results：Crush injury of serum K＋、Cr、BUN、CK、MYO increased significantly,peaking about12h waiting,and continuously to the wound24h,72h gradually to normal. On thecontrary,levels of Ca²⁺were significantly decreased （P<0.01）.The muscle pathology aftercrush injury showed edema,hemorrhage,necrosis and other lesions as same as the reports inthe papers of crush injury model and consistent with the clinical manifestations.The levels of serum CK-MB and c-TnI were much higher than that of the control group（P<0.05）,while the cardiac contents of ANP and ET-1decreased remarkable（P<0.05）,while the ANP levels were significantly increased （P <0.01） andET-1level was decreased（P<0.05） in plasma.Myocardial pathological changes:Tissue edema,congestion,inflammatory cell infiltration,mitochondria edema change, the nucleus and other damagewere saw under the light microscope and electron microscopy ultrastructure with timegoing by in12h-24h. After that，the morphologic changes of myocardial tissue injury wereobviously observed, but they were mild and even vanished （72h）. theses indicated crushinjuries could cause myocardial damage.Comparing with the control group, the crush injury，s ventricular systolic functionparameters:（EF,FS,△T,CO） significantly decreased in6h-12h.,while （PFVE, PFVA,PFVE/PFVA, PFR） decreased in12h-24h.Speckle tracking echocardiography: the measurements indicating global cardiaccontraction and twist function index （LS,RS,CS and Ptw） are lower,and statisticallysignificant （P<0.05）from decompression to72h. similarly they were significantly decreased6h-12h（P<0.01）, while the72h after decompression decreased still significantly （P <0.05）.Conclusions：Physically crush injuries can lead to myocardial secondary injury: characteristics ofmyocardial indexes, myocardial pathological microscopic change are suggestive ofmyocardial damage. The degree of myocardial damage after extracting a certain timewindow,gradually increased to peak at12²4h.Conventional heart ultrasound technology allow for a preliminary evaluation aftercrush injury to blood flow dynamics and cardiac function, its evaluation and cardiacmarkers,myocardial histopathology consistent change in time.Speckle tracking echocardiography without the limition of the heart of the overallmovement and the angle, to evaluate myocardial damage after crush injury are scientificaccuracy and reliability comparing with caconventional echocardiography. It suggested itwould have particularly important value on study of crush injury in disaster medicine.