Application of Mixed-effect Model in PMI Estimation by Vitreous Humor / 法医学杂志

ABSTRACT

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.