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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 3  |  Issue : 3  |  Page : 111-114

Determining the electrical conductivity of rat cadaveric liver, spleen, and kidney to estimate early postmortem interval


Department of Forensic Medicine, Forensic Medicine School, Henan University of Science and Technology, Luoyang, Henan, China

Date of Web Publication29-Sep-2017

Correspondence Address:
Yaonan Mo
Forensic Medicine School, Henan University of Science and Technology, Luoyang, Henan
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jfsm.jfsm_23_17

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  Abstract 

Previous research has found that electrical conductivity (EC), an important index to predict meat freshness and shelf life, is very promising for estimating the late postmortem interval (PMI). However, whether it has potential use in the early PMI has not been fully studied yet. To test this possibility in the present study, EC of three internal organs of rat liver, spleen, and kidney were determined within 24 postmortem hours, and then, EC changes at different PMIs were carefully analyzed. The overall results showed that EC of liver and spleen increased significantly with PMI while EC of kidney had minor changes during the same period. Specifically, significant linear positive correlations between EC of liver and spleen and PMI were found and the coefficients of their regression functions were R2 = 0.98 and R2 = 0.95, respectively. It can be concluded that determination of EC in certain internal organs such as liver and spleen may be a potential tool in the early PMI estimation. However, more researches on its influencing factors are needed to facilitate its final use in practice.

Keywords: Early postmortem interval, electrical conductivity, forensic science, kidney, liver, spleen


How to cite this article:
Zheng Z, Zhai X, Xia Z, Mo Y. Determining the electrical conductivity of rat cadaveric liver, spleen, and kidney to estimate early postmortem interval. J Forensic Sci Med 2017;3:111-4

How to cite this URL:
Zheng Z, Zhai X, Xia Z, Mo Y. Determining the electrical conductivity of rat cadaveric liver, spleen, and kidney to estimate early postmortem interval. J Forensic Sci Med [serial online] 2017 [cited 2017 Oct 23];3:111-4. Available from: http://www.jfsmonline.com/text.asp?2017/3/3/111/215808


  Introduction Top


Estimation of the postmortem interval (PMI) is very crucial in criminal investigations. Accurate PMI estimation, however, is hard to achieve due to the complexity of its influential factors.[1],[2] Currently, the method most widely used in the postmortem period is algor mortis (or cooling of the body). This approach proves objective and effective in practice, but it also has numerous influential factors (e.g., clothing, airflow and obesity) as well as limitations of its use in extreme high- or low-temperature conditions. Therefore, it is imperative that more methods be developed to meet these diverse demands and complexity in terms of the early PMI estimation.

In food science, meat freshness and shelf life are major focuses that have been investigated for almost centuries and the parameters, such as electrical conductivity (EC), total volatile basic nitrogen, and aerobic plate count, are considered the most effective to predict them.[3],[4],[5] Since EC determination is rather simple, rapid, accurate, and economic; it was introduced by Xia et al. to forensic science to study cadaveric decomposition rate and PMI.[6],[7],[8] They found that muscle EC could be as a promising method for late PMI estimation. Hence, we hypothesis EC of the internal organs may increase during early PMI for intestines bacteria are active and resulted in decomposing in the very early period. To test this hypothesis that EC also has potential use in early PMI estimation, EC of three selective internal organs were measured, and their correlations with early PMI were carefully studied.


  Materials and Methods Top


Rats division and disposition

Forty-five male Sprague-Dawley rats with weights ranging from 250 to 300 g were provided by Henan University of Science and Technology in Luoyang (China). All the rats were sacrificed by cervical vertebra dislocation and divided into nine groups and stored in confined environment at 25°C.

Sample preparation and detection

Liver, spleen, and kidney of rats were extracted and accurately weighed (Discovery, America) at PMIs of 0, 3, 6, 9, 12, 15, 18, 21, and 24 h. The EC of organs was measured using the method described by Xia et al. with a little change.[7] About 5 g of liver, both kidneys, and the whole spleen were put into mortars separately and cut up by scissors. Then, the organs were homogenized with deionized water at the ratio of 1 g: 10 ml and keep cutting. Dynamic EC monitoring of the extracted organ fluid was performed to ensure the conductive substances in the organs were fully extracted. The mixture was filtered until the EC keep constant. The EC was measured using a EC meter (Mettler Toledo FE30, Shanghai, China). The temperature compensation coefficient was set to α = 2%/°C.

Statistical analysis

The data of EC were evaluated using the SPSS13.0 (IBM, America) and the curves were drawn using OriginPro 8 (OriginLab, America). The mean and standard deviation values were calculated as descriptive statistics. We also drew the curves of three organs changes with PMIs separately and the comparison curves of EC for different organs.


  Results Top


Descriptive analysis

The descriptive statistics of the measured EC values in liver, spleen, and kidney at different PMIs are presented in [Table 1].
Table 1: Electrical conductivity changes with postmortem interval for three organs

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The relationship between electrical conductivity and postmortem interval for different organs

The curves of EC changes with PMIs for three organs were drawn separately [Figure 1],[Figure 2],[Figure 3]. The results showed that the EC of liver and spleen increased dramatically within 24 h, whereas the EC of kidney changed slightly in the same period. We had established the regression equation of EC and PMI. The regression equations of liver and spleen were y = 16.4x + 1056.2 (R2 = 0.98) and y = 15.6x + 1354.6 (R2 = 0.95).
Figure 1: Relationship between electrical conductivity and postmortem interval for liver

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Figure 2: Relationship between electrical conductivity and postmortem interval for spleen

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Figure 3: Relationship between electrical conductivity and postmortem interval for kidney

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Comparison of electrical conductivity changes with postmortem interval for three organs

Comparison curves of EC and PMI for three organs are drawn in [Figure 4]. From the figure, we can see the initial EC (0 h) of the spleen and kidney were similar (around 1300 μs/cm), but greater than that of the liver (1000 μs/cm). Despite the obvious difference of initial EC between liver and spleen, their total increases were equivalent (around 400 μs/cm within 24 h). However, the EC of kidney ranged from 1290 μs/cm to 1460 μs/cm which changed little during the same period.
Figure 4: Comparison of electrical conductivity changes with postmortem interval for three organs

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  Discussion Top


PMI estimation is crucial but complicated in forensic casework. Although algor mortis has been extensively used to estimate early PMI in practice, there is still demand for more methods to meet the diversity and complexity in actual conditions.

In food science, meat freshness and shelf life are major focuses that have been studied for centuries. Since determination of EC is rather rapid, accurate, and economical, it has been widely used to evaluate the freshness of meat productions.[9],[10],[11],[12] Food science researches indicate that EC of meat will increase as its storage time extends for the reason that large amounts of conductive substances could accumulate during the molecule degradation process caused by enzymes and micro-organisms. Consequently, the higher degree of meat spoilage is, the larger the EC value will turn.[13],[14],[15],[16] In addition, such law was extensively reported in researches on different kinds of meat such as pork, beef, poultry, fish, and shrimps implying that it may also apply to human tissue and might be useful for early PMI estimation.

In this study, EC of liver, spleen, and kidney were determined at different times, and their correlations with PMI were analyzed. Male rats were selected and environment was controlled at a constant temperature to reduce the discrepancies caused by variations of genders and temperatures. Liver, spleen, and kidney were chosen since they were relatively close to intestinal bacteria which may lead to the significant change of EC in these organs in the very early period.[9] The deionized water was utilized to avoid bringing in conductive substances that may exist in plain distilled water. To improve the accuracy of EC determination, the temperature compensation coefficient was set to a fixed value (α = 2%/°C) which was validated in our previous research.[7]

The results showed the EC of these organs correlated with early PMI, though to various extend. Overall, as the PMI increased, the EC of liver and the spleen increased within 24 h while the EC of kidney showed minor changes throughout the same period, indicating EC of the kidney was probably less useful for early PMI estimation. Specifically, during the first 3 h, the changes of EC were not significant for the liver, but rapid for the spleen. Both liver and spleen EC increased dramatically during 6–24 h while there was a little increase for kidney in this period. On the whole, the initial EC of spleen and kidney were similar and larger than the counterpart of the liver. Despite the obvious difference of initial EC between liver and spleen, the total increases for both organs were equivalent, 400 μs/cm within 24 h approximately, suggesting their total amount of conductive substances produced in this whole period were almost equal.

Previously, Xia et al. first researched on the EC changes in the postmortem muscle at different PMIs which suggested that EC of muscle was only significant in the late PMI estimation, but its use in early PMI estimation was rather scarce.[7] However, a meat science research by Yang and Zhang on the relationship between EC and the freshness of fresh pork (muscle) indicated that EC increased as the meat spoilage developed, which could be explained by the immediate exposure of food meat to environmental microbes.[17] Finally, our results showed that EC in only two of three tested organs increased with early PMI; although, they were all adjacent to the intestine. Among the two organs, EC of spleen increased rapidly during the first 6 h, especially, which meant the overall autolysis of spleen was probably earlier than liver. The possible reason for the slow EC increase in kidney was that the kidney capsule thicker than that of liver and spleen may act as a better protector during the bacterial invasion into the organ. In addition to this reason, variations may also attribute to the differences of structures and compositions among various organs. Developing more practical methods that can apply to early PMI estimation are imperative at present. Fortunately, our research found that determination of EC in certain internal organs may be a potential alternative method in estimation of PMI in the future forensic practice. However, the EC of organs may present different change rules under the influence of various environmental factors, and the PMI estimation is rather complicated in forensic practice.[18] Therefore, a model employing multiple parameters (including algor, EC, and pH,[19] etc.) and influential factors (temperature, moisture and cause of death, etc.) will be our major focus in the future researches.


  Conclusion Top


Accurate early PMI estimation calls for more methods in forensic practice and determination of EC in certain organs might be a potential alternative tool. Hence, more researches are needed to measure the EC in human organs under different ambient temperatures in future studies.

Acknowledgment

This study was supported by the Basic and Frontier Study of Technology Project of Henan Province (Grant No. 112300410082), the Doctor Foundation and the Youngs' Foundation of Henan University of Science and Technology (Grant No. 09001309, 2013ZCX024 and 2011QN52), Key Laboratory of Forensic Medicine Identification in Luoyang (No. 11550002).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1]



 

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