混合效应模型在玻璃体液推断死亡时间中的应用

摘要

目的 通过检测不同温度下家兔尸体玻璃体液内K+、Mg2+浓度随pMI的变化规律,探索应用混合效应模型推断死亡时间(postmortem interval,pMI)的可行性.方法 家兔处死后分别置于5℃、15℃、25℃和35℃温度下保存,在0~120 h内每12 h双眼交替微量提取玻璃体液80~100μL.应用生化免疫分析仪检测玻璃体液中K+、Mg2+的浓度.应用混合效应模型进行分析拟合,建立pMI推断方程.使用放置于10℃、20℃、30℃温度下均经过20、40、65 h的样本检测数据对pMI推断方程进行验证.结果 各温度(y)下家兔玻璃体液中K+、Mg2+浓度[f(x,y)]随pMI(x)延长均呈上升趋势.在5℃~35℃,pMI及温度拟合的K+、Mg2+浓度方程分别为:fK+(x,y)=3.4130+0.3092 x+0.3376 y+0.01083 xy-0.00247 x2(P<0.0001);fMg2+(x,y)=0.7456+0.006432 x+0.0338 y(P<0.0001).经验证,pMI为0~40 h时,K+、Mg2+浓度推断pMI的偏离时间均在10 h以内;pMI为40~65 h时,偏离时间在21 h以内.结论 在5℃~35℃的环境温度区间内,利用混合效应模型拟合的方法可实现利用温度和玻璃体液物质浓度双参数推断pMI,将为解决玻璃体液化学物质在pMI推断中的实际应用提供新方法.%Objective To test the changes of the potassium(K+)and magnesium(Mg2+)concentrations in vitreous humor of rabbits along with postmortem interval(PMI)under different temperatures, and explore the feasibility of PMI estimation using mixed-effect model. Methods After sacrifice, rabbit carcasses were preserved at 5℃, 15℃, 25℃ and 35℃, and 80-100μL of vitreous humor was collected by the double-eye alternating micro-sampling method at every 12 h. The concentrations of K+and Mg2+in vitreous humor were measured by a biochemical-immune analyser. The mixed-effect model was used to perform analy-sis and fitting, and established the equations for PMI estimation. The data detected from the samples that were stoned at 10℃, 20℃ and 30℃ with 20, 40 and 65 h were used to validate the equations of PMI estimation. Results The concentrations of K+and Mg2+[f(x,y)] in vitreous humor of rabbits under different temperature increased along with PMI(x). The relative equations of K+and Mg2+concentration with PMI and temperature under 5℃~35℃ were fK+(x,y)=3.413 0+0.309 2 x+0.337 6 y+0.010 83 xy-0.002 47 x2 (P<0.000 1), and fMg2+(x,y)=0.745 6+0.006 432 x+0.033 8 y(P<0.000 1), respectively. It was proved that the time of deviation for PMI estimation by K+and Mg2+was in 10 h when PMI was between 0 to 40 h, and the time of deviation was in 21 h when PMI was between 40 to 65 h. Conclusion In the ambient temperature range of 5℃-35℃, the mixed-effect model based on temperature and vitreous humor sub-stance concentrations can provide a new method for the practical application of vitreous humor chemi-cals for PMI estimation.