| Battle compartment is major unit for combat in modern war. Antiarmor weapons could punch through the shell of the battle cabin and explode. In peace time, modern terrorism attacks and unexpected emergency event usually occured in the relative closed cabin. So explosion in relative enclosure is one of the key features of explosion events in peace or war time. Explosive blast wave frequently lead to intraabdominal organ damage owing to large surface area of abdominal region and many organs in abdominal cavity. In the battlefield, some wounded soldier suffered intraabdominal organ damage without obvious external injury which could further bring about sepsis, and multiorgan dysfunction syndrome(MODS), even threat to life, but it was not taken seriously dut to stronger concealment after closed injury. It is plausible to hypothesise that the bacteria or endotoxin could come from gut tract in patients with sepsis after trauma because ther is no definite source of infection and the intestinal tract is the largest bacteria and endotoxin bank in human body. After trauma, many factors can damage intestinal barrier function and enhance the permeabililty of gut mucosa, the bacteria from the gut lumen transfer to distant organs through variable pathway, and induce SIRS and MODS. So, it was reported that intestinal tract is regared as the central organ following surgical stress reaction and initiator of MODS, gut barrier dysfunction and bacterial transloction paly a vital role in pathogenesis and developing of MODS.In present study, we systemically observed and analyzed morphological and histopathological changes of intraabdominal organs in rats with abdominal closed injury subjected to explosion in relative enclosed space, assessed relationship between degree of abdominal explosive closed injury and physical parameters of blast wave, and then focused on investigating intestinal mucosal lesions and gut bacterial/endotoxin transloction. Main experimental methods and conclusions are as follows:1. We established a valid rat model of abdominal closed blast injury exploded at 10 centimeter distal to instantaneous electric detonator contained 600mg diazodinitrophenol in enclosed space to oberve and analyze the traumatic characteristics at levels of whole-body, organ and tissue. The results showed that the traumatic condition of abdominal closed explosive injury of rats in enclosed spaces is much severe than that in the free-field. The major damaged organs in enclosed space were liver and colon with higher hematocelia, and which in the open air were colon and stomach. Kidney, bladder and spleen were not detected obviously injury with naked eye. There is no difference in injury types between two groups which were subcapsular haemorrhagia, hematoma formation in parenchymatous viscera and subserosal or submucosal bleeding in hollow viscera. Pathohistological findings revealed that injury severity of abdominal viscera in enclosure was more obvious than that in free-field. The pathohsitological changes were mainly congestion, hemorrhage, focal necrosis, higher inflammatory cell infiltration in sold viscera and submucosal bleeding, tissue edema, lower inflammatory cell infiltration in gas-containing organs.2. Rats were subjected to explosion at different distance with various dose levels of diazodinitrophenol in cabin model. Physical parameters of blast wave were measured using pressure transducers. Relationship between degree of abdominal explosive closed injury and physical parameters of blast wave was analyzed. The results demonstrated higher peak pressure, shorter duration and larger explosive impulse in relative enclosure. Elevated multiple trauma, more seious condition and higher mortality rate were discovered with increased diazodinitrophenol dose and minified shorter distance. Half lethal dose of specific impulse of rats in cabin was 73.4KPa·ms. There was a significant positive correlation between degree of abdominal explosive closed injury and specific impulse.3. Malondialdehyde(MDA) content and SOD, GSH-Px activities in serum and intestinal tissue were measured, in addition, apoptosis in gut tissue was detected using TUNEL and plasma D-lactic acid, diamine oxidase levels were assayed. The results indicated that oxidative stress reaction occurred earlier, sustained longer and stronger in rats with abdominal closed explosive injury in enclosed space than that in open space, and serum MDA content, GSH-Px could be one of the diagnostic indicators for oxidative injury of intestinal tissue. Apoptosis and upregulaion of Caspase-3 expression in gut mucosal cell occurred earlier, much severe in rat of compartment than that of open ground. Apoptotic index and positive index of caspase-3 showed a significant positive correlation with the levels of DAO, D-lactic acid, endotoxin, and interleukin-6 which could indirect estimate severity of intestinal mucosa damage and apoptosis. The findings also demonstrated that the degree of intestinal mucosal lesions in rats with abdominal closed blast injury was more severe in enclosed space compared with in free-field. The changes of D-lactic acid and DAO occurred earlier, sustained longer and stronger in rats in enclosed space than that in open space. It was considered that plasma D-lactic acid content could be one of the diagnostic indicators in rats with gut barrier dysfunction.4. Dynamic changes of plasma endotoxin and IL-6, TNF-αlevels were measured. The results showed that enterogenic endotoxemia occurred ealier, elevated significantly and lasted longer in rats of relative enclosure than that of free-field, which indicated that it was getting easier to develop enterogenic endotoxemia in rats of cabin. Detection of plasma endtoxin could assess intestinal endotoxin transloction. Higher IL-6, TNF-αlevels of plasma were found in abdominal blast injury rats in enclosure, which illustrated that rats in cabin were more severe and could be susceptible to to induce SIRS.5. Normal bacteria culture, detection of bacterial DNA were performed to evaluate the bacterial traslocation rate. Enhanced green fluorescent protein labeling Escherichia coli DH5αtracking bacterial translocation confirmed that finding. In addition, early diagnostic indicators were screened by receiver operating characteristic curve analysis. It was observed from the findings that bacterial translocation rate was greater in rats of cabin than that of open ground. The sensitivity of PCR method is higher than that of bacteria culture method. The plasma levels of endotoin, IL-6, DAO, TNF-αwere raised if bacteria from gut lumen translocted to circulatory system or distant organs, which could indirect reflect the bacterial transloction and become one of diagnostic or predicting markers of intestinal bacterial transloction after blast injury.
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