The Study On Relationship Between Vitreous Humor And Pmi In Rats Under Different Altitude

Objective To study the changes of K⁺,P³⁺,Na⁺,Ca²⁺,Mg²⁺,Cl^-,Glu and Hx concentrations in rats vitreous humor after death under high altitude hypoxia,and to explore the influence of altitude factors,on the related biochemical indexes of vitreous humor after death in order to provide reference for the study of vitreous humor inferred death time in high altitude areas.Methods 70 SD rats were randomly divided into two groups（2260m and 5000 m altitude）,with 35 rats in each group.Rats were sacrificed by cardiac air embolization.At a temperature of 15±1 and a humidity of 37±1%,vitreous humor ℃was extracted at 0,3,6,9,12,18,and 24 hours after death.The concentrations of K⁺,P³⁺,Na⁺,Cl^-,Ca²⁺,Mg²⁺ and Glu in vitreous humor collected at different times after the death were measured with a automatic biochemical analyzer,and the concentrations of Hx was determined by high performance liquid chromatography.According to the relationship between concentrations and time,drawing the change curves,correlation analysis,linear regression analysis and multiple linear regression analysis were performed to derive the regression equation,validated.Results The concentrations of vitreous humor at the same time after death were different under different altitudes.Correlation analysis showed that the concentrations of K⁺,P³⁺ and Mg²⁺ were positively correlated with PMI while the concentrations of Na⁺ were negatively correlated with PMI at two altitudes.Besides,Cl^-concentrations were negatively correlated with PMI at 2260 m altitude.By linear regression analysis,the goodness of fit of K⁺ is 0.941 at the altitude of 2260 m.By linear regression analysis,the goodness of fit of K⁺ is 0.941 at the altitude of 2260 m,which indicates that the linear regression equation has a good fit.At the altitude of 5000 m,the goodness of fit of K⁺,P³⁺ and Mg²⁺ are 0.943,0.960 and 0.928,indicating that their linear regression equations have good fit.Multiple linear regression analysis found that after increasing the altitude parameter variable,or adding the other impact parameters,the accuracy of the inferred PMI of the obtained equation was relatively improved.K⁺,Na⁺ and Mg²⁺ concentrations mixed regression equation: f（x,y）=-48.90²⁺3.112X1-4.166X²⁺21.017X4+0.0039 Y,goodness of fit is 0.854;Na⁺,Cl^-concentration regression equation: f（x,y）= 103.846-2.434X3-0.308X5-0.0052 Y,and the goodness of fit is 0.772.Na⁺ and Cl^-concentrations mixed regression equation: f（x,y）=103.846-2.434X3-0.308X5-0.0052 Y,goodness of fit is 0.772.After the internal validated,the goodness of fit value could not simply represented the accuracy of the inferred PMI of the regression equation.The multiple linear regression equations were more reliable.Conclusion Altitude has influence on the concentration of various substances in vitreous humor of rats after death.In high altitude areas,the influence of altitude factors should be considered when inferring PMI from vitreous humor.Mixing the altitude parameters,the multiple linear regression equation had a high accuracy in inferring PMI.