Study On The Relationship Between Electrical Conductivity Change And Postmortem Interval At Ambient Temperature

[BACKGROUND]The postmortem interval(PMI)or the time since death(TSD)inference has always been a hot and difficult issue in forensic research.The accuracy of inferring PMI plays an important role in providing case clues,dividing the scope of investigation,screening suspects and other homicide cases,as well as civil disputes such as insurance claims and medical disputes.Forensic scientists at home and abroad have made a series of new progress in the study of the temporal changes of various indicators after death by applying the mature techniques and methods of molecular biology,physical chemistry,spectroscopy,metabolomics,microbiology and many other disciplines.However,PMI inference is interfered by individual differences,temperature,humidity,animal and insect damage and other internal and external factors.What is more,many studies are limited to the laboratory level due to limited conditions or cumbersome operation.it remains to be further studied to find a simple and accurate method for PMI inference.Electrical conductivity(EC)initially as evaluation index of the shelf life of meat in food science,has been transformed into a study of forensic PMI estimation.Studies have shown that corpse decomposition degree scores are well correlated with accumulated degree-days(ADD),and the established quantitative models have potential for PMI inference.Previous studies showed that EC and PMI have a good correlation under constant temperature conditions.The determination of EC is fast and convenient,which met the actual requirements of forensic workers to quickly infer PMI at the crime scene.This study focused on the relationship between EC changes and TSD in muscle tissue at outdoor ambient temperature,recorded the changes of outdoor environmental temperature,and analyzed the relationship between EC and TSD.Meanwhile,the change law of EC under indoor constant temperature conditions was used as a control with the former experiment.This research preliminaryly explore the feasibility of using the EC and ADD to estimate TSD.At the same time,the cadaver tissues of death cases were further collected for EC determination,and the influence of ambient temperature on EC changes in human tissues was analyzed.the feasibility of EC inferring PMI in actual work.The feasibility of using EC to estimate PMI in actual work was explored.[OBJECTIVES]1.The EC values of pig hind leg muscles at different times of day and night were measured under outdoor environment in Luoyang autumn,and compared with the changes of EC under indoor constant temperature conditions.The changes of EC values with TSD under the two environmental conditions were analyzed and compared.The effect of ambient temperature on EC changes was preliminaryly discussed.2.The EC of muscle tissue at different time intervals in the outdoor environment were measured,and the environmental temperature changes during the experiment were recorded.Using the EC and ADD for PMI estimation was preliminarily discussed.3.The EC values of liver,spleen,kidney,lung,pancreas and skeletal muscle were determined in the death case.This paper preliminarily explores the factors that influence EC changes,and discuss the applicability of EC in practical work.[METHODS]1.The muscles of 5 pigs that were immediately slaughtered,which divided into two parts and randomly divided into two groups.The two groups were placed in an outdoor environment(temperature range 12~22?)in the fall and an indoor constant temperature environment of 18?(simulated winter indoor heating environment),respectively.The ambient temperature change during the experiment was recorded every 1 h with a temperature recorder.5g muscles were obtained at 8 o'clock and 20 o'clock(every 12h)during 10 days.The tissues were homogenized with 50ml deionized water and continuously stirred with scissors.The liquids were filtered to obtain a extraction liquid having a mass concentration of 0.1 g/ml after 30 minutes,and the EC value of the extraction liquid was measured by a conductivity meter.The relationships between EC and TSD were carefully analyzed under two environmental modes.2.The informations about death case were record in detail,such as gender,age,PMI,ambient temperature,cause of death.Liver,spleen,kidney,lung,pancreas,muscle of cadaver were extracted,and there extraction liquids were prepared with deionized water by cutting and grinding.Then,the EC value of each tissue extractions liquid were determined.According to the recorded outdoor ambient temperature,the average temperature within the experimental interval of 12 hours was calculated to obtain ADD,and the variation law of EC and ADD was discussed.[RESULTS]1.The change laws between EC and TSD were similar in the two environmental conditions and the correlations between EC and TSD were significant.The quadratic regression equation were y(outdoor)=0.039x~2-1.68x+1479.12(R~2=0.97,P=0.004)and y(indoor)=0.025x~2+0.84x+1349.49(R~2=0.98,P=0.002).2.In Luoyang autumn outdoor environment,the temperature fluctuation during the experimental period is in the range of 5.7~28.2?,the average daytime temperature is18.4?,and the average nighttime temperature is 11.9?.EC increased significantly at daytime but increased little at night in the ambient temperature.Especially,there was a obvious platform phenomena when the ambient temperature was below 13?,showing a striking difference to the constant temperature which present a sustaining rise of EC.3.The EC of muscle tissue gradually increases with the accumulation of ADD at outdoor temperature,and the correlation between EC and ADD is significant.Its quadratic regression equation was y=0.027x~2-2.92x+1590.54(R~2=0.96,P<0.05).4.Ambient temperature has a greater influence on the determination of cadaver EC values.The EC of cadaver tissue gradually increases with the increase of TSD.[CONCLUSIONS]1.The correlation between EC and TSD in muscle tissue were significant under outdoor temperature and indoor constant temperature,suggesting that EC measurement of muscle has a certain application value for estimation of long TSD in actual cases.2.Under the ambient temperature in autumn,the EC value increases significantly during the day,and EC value grow slowly at night with low temperature.The difference between day and night should be taken into account when using EC for the specific analysis in forensic cases.3.EC can be used as a good indicator to assess the degree of corpse muscle decomposition.The early changes of muscle EC are not obvious.The relationship between EC and ADD is used to estimate that late TSD has certain application value in actual cases,but it still needs actual cases to verify its accuracy.4.The individual factors of the corpse(such as the cause of death)are not taken into account for analyzing.The determination of EC was influenced by ambient temperature and the cause of death in actual death cases.This study preliminarily explores the change laws of EC in cadaver tissue.