The Forensic Research Of Estimation Of The Postmortem Interval By The Level Of Chemical Components In Human Vitreous Humor At Different Time After Death

Background:The estimation of postmortem interval (PMI) is one of the important issues to be solved for the examination of dead body in the medical jurisprudence. PMI is great value to determine the nature of the case and to clarify the process of crime in the forensic medicine.There are many ways to estimate the PMI.The ways refer to multidisciplinary fields. The current methods of estimating the PMI mainly include postmortem phenomena, contents of in intestines and stomach, DNA degradation, enzyme chemistry and histology, entomology.Human vitreous humor is under the protection of the orbital and isolated from the outside.The Corruption,contamination and other factors exercise influence over human vitreous.The humor vitreous can be acquired easily and be detected simply.The results of the test is relatively reliable.The postmortem change of chemical components of human vitreous varies more slowly than of blood and cerebrospinal fluid. It is more stable and more irregular. According to reports in the literature, most of experimental research still remains at the stage of trials on animals. As the human and animal species diversity, many of the findings are of little value in the forensic practice. We can detect more chemical components of human vitreous which are undiscovered and are closely related to PMI by advanced equipment and effective ways. Objective:To estimate the PMI with multi-index and set up their separate regression equation and calculate the prediction intervals of PMI is to analyze comprehensively and try to decrease the error. Thus we could make human vitreous humor be widely used in forensic medicine practices and estimate the PMI correctly.Methods:1. HITACHI.7060 auto-biochemistry instrument made in Japanese was used to analyze all the collected samples.2. The checking sampling of human vitreous humor in different time after death: the vitreous humor was taken from the death from 0.3 to 109 hours.3. Statistical analysis was performed using the SPSS program package (SPSS, version 13.0). The collected data were test by Gaussian distribution (Q-Q plots) first, then analyzed the linear correlation between the PMI and one of the chemical compositions in vitreous humor separately and all together.Results:1. The relationship between the contents of these chemical components (includes the sodium, chlorine, urea, creatinine, potassium, calcium, magnesium, phosphorus) and PMI is certain.2. The content of potassium appeares best linear relation with PMI. The equation of PMI is PMI=0.702+0.186K⁺(r=0.512; R²=0.262, regulate R²=0.259). The prediction interval of PMI is (PMI - 1.96×3.60, PMI+1.96×3.60). The content of phosphorus ascends with the time since death and has remarkable relevance to PMI. The equation of PMI is PMI=1.617 + 0.681P (r =0.544; R²=0.296, regulate R²=0.293). The prediction interval of PMI is (PMI-1.96x0.85, PMI+1.96×0.85).3. The gradual regression equation of PMI is PMI=5.292+0.142K⁺-0.022Na⁺+0.670P-1.007Mg²⁺ (r=0.633; R²=0.4000, regulate R²=0.388). The prediction interval of PMI is (PMI-1.96×1.31, PMI+1.96×1.31).Conclusions:1. The concentration of sodium and chloridion are inversely related to PMI.The concentration of urea, creatinine, potassium, calcium, magnesium, phosphorus are on the contrary. There is a significantly linear relation between the concentration of phosphorus and potassium and PMI.2. The gradual regression equation was obtained for the concentration phosphorus of, calcium, potassium and sodium.It can improve the fit of the equation, reflects the linear relation between the chemical components of human vitreous humor and PMI. We can estimate PMI more accurately.3. The chemical components of human vitreous have no differences between left and right eyes in this study.