双眼交替微量取样检测兔玻璃体液钾镁离子浓度推测死亡时间

目的研究死后眼玻璃体液钾镁离子浓度变化及其与死亡时间的关系。方法取健康家兔处死,死后不同时间于双眼玻璃体液交替微量取样,采用全自动生化分析仪检测样本中K+]、Mg2+],对所得数据进行统计学处理。结果死后12~120h,家兔玻璃体液中K+]由11.01mmol/L上升至32.97mmol/L,Mg2+]1.12mmol/L上升至2.22mmol/L,两种离子浓度与PMI进行回归分析自变量为K+]的二次多项式回归方程为y=0.1756x2-3.3188x+29.804(R2=0.9868);自变量为Mg2+]的二次多项式回归方程为y=-46.916x2+248.01x-213.81(R2=0.9340);自变量为K+]和Mg2+]的二次多项式回归方程为y=-17.55-4.82K+]+0.20K+]2+75.77Mg2+]-19.47Mg2+](R2=0.9881)。用K+]的方程推测PMI,当K+]<26.0mmol/L(PMI<60h)时,平均偏离时间为2.7~9.4h,当K+]>28mmol/L(PMI>72h)时,平均偏离时间>15h;用Mg2+]的方程推测PMI,平均偏离时间几乎均在10h以上;用二元方程推测PMI,平均偏离时间较前两者小。结论死后眼玻璃体液K+]、Mg2+]随时间延长而升高,且浓度变化与时间呈强相关性。但从实际运用角度考虑,R2<0.98,或平均预测偏离时间过大的回归方程,不宜用于PMI推测;应用多指标建立多元回归方程是提高推测PMI准确性的可行方法。

Concentration of K+ and Mg2+ in vitreous humor taken by alternative micro-sampling method from both eyes of rabbits for the estimation of postmortem interval

Objective Study the relationship between changes of the concentration of K~+] and Mg~(2+)] in the vitreous humor of rabbits and the postmortem interval. Methods Vitreous humor from two eyes of healthy rabbits is taken by alternative micro-sampling method at different postmortem intervals (PMI), and the K~+] and Mg~(2+)] in it is measured by automatic biochemistry analyzer. Results During 12 h to 120 h since death, K+] in the vitreous humor rises from 11.01 mmol/L to 32.97 mmol/L and Mg2+] rises from 1.12 mmol/L to 2.22 mmol/L. Having K+] as the independent variable, the quadratic polynomial regression equation is y=0.1756x2-3.3188x+29.804 (R2=0.9868)(Equation 1); having Mg2+] as the independent variable, the quadratic polynomial regression equation is y=-46.916x2+248.01x-213.81 (R2=0.9340)(Equation 2); and having both of K+] and Mg2+] as the independent variables, the quadratic polynomial regression equation is y=-17.55-4.82 K+] +0.20 K+] 2+75.77 Mg2+] -19.47 Mg2+] 2(R2=0.9881)(Equation 3)。 If we estimate PMI by Equation 1, when K+]<26.0mmol/L (PMI<60h), the average deviations are about 2.7~9.4h, and whenK+]>28mmol/L (PMI>72h), the average deviations are over 15 hours. The average deviations of Equation 2 are almost all above 10 hours. The average deviations of Equation 3 are the lowest of the three.Conclusion The K~+] and Mg~(2+)] in the vitreous humor rises while the PMI extends. There are correlations between the concentration of K~+ and Mg~(2+) in the vitreous humor and the PMI. For the estimation of PMI, we suggest that the equation with R2 lower than 0.98, or with high average deviations should not be used. It seems that multiple regression equation could increase the accuracy of PMI estimation.