Department of Forensic Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Laboratory of Wildlife Medicine, Nippon Veterinary and Life Science University, 1-7-1 Kyonan-cho, Musashino-shi, Tokyo 180-8602, Japan.
Department of Forensic Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Education and Research Center of Legal Medicine, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba-shi, Chiba 260-8670, Japan.
Forensic Sci Int. 2021 Oct;327:110983. doi: 10.1016/j.forsciint.2021.110983. Epub 2021 Aug 25.
In forensic medicine, the diatom test is used to diagnose drowning. Drowning and postmortem immersion can be distinguished by calculating the ratio of diatom concentration in the lungs and drowning water (L/W ratio). However, this claim was based on the unproven hypothesis that diatoms may be concentrated in the lungs due to respiratory movements. This study was conducted to examine whether the L/W ratio increased with experimental water injection.
A total of two experiments was performed using 22 non-drowned cat carcasses found on dry land. First, for the experimental postmortem immersion, we soaked seven whole-body cat carcasses in pond water for an hour. Second, the pond water was experimentally injected one or ten times into each harvested lung from seven and eight cats, respectively. In the diatom test, two diatom species (Aulacoseira ambigua and Discostella asterocostata) that were dominantly observed in pond water as well as other diatom species were counted separately. The L/W ratios of each cat were calculated. Univariate linear regression analysis was performed to demonstrate the association among L/W ratios and the three categories of the experiments. The L/W ratios of the two experiments were compared with those of drowning or postmortem immersion cases of humans or cats.
It was revealed that the clear L/W ratio differences between the three groups (experimental postmortem immersion<0.02, 1-injection < 0.2, 10-injection > 0.9 for all diatom counting) were with statistically significant as proven by the univariate regression analyses. In actual cases of cats and humans, L/W ratios were>0.4 for drowning and<0.04 for postmortem immersion.
The L/W ratio increased with multiple experimental water injections into the lungs, thereby verifying the validity of the diatom concentration test to diagnose drowning. The diatom test can be used to distinguish between drowning and postmortem immersion in humans and cats by calculating the L/W ratio.
在法医学中，硅藻检验被用于诊断溺死。通过计算肺部和溺死水中硅藻浓度的比值（L/W 比值）可以区分溺死和死后入水。然而，这一说法基于一个未经证实的假设，即硅藻可能由于呼吸运动而集中在肺部。本研究旨在检验向肺部注入实验用水是否会增加 L/W 比值。
共进行了两项实验，使用了在干燥地面上发现的 22 具非溺死猫尸体。首先，对于实验性死后入水，我们将 7 具整体猫尸体浸泡在池塘水中 1 小时。其次，分别向 7 只和 8 只猫的每只收获肺中实验性注入 1 次或 10 次池塘水。在硅藻检验中，我们分别对在池塘水中占主导地位的两种硅藻物种（Aulacoseira ambigua 和 Discostella asterocostata）以及其他硅藻物种进行了计数。计算每只猫的 L/W 比值。采用单变量线性回归分析来证明 L/W 比值与三个实验类别之间的关联。将两个实验的 L/W 比值与人类或猫的溺死或死后入水病例进行了比较。
通过单变量回归分析证明，三个组之间的 L/W 比值差异明显（实验性死后入水<0.02，1 次注射<0.2，10 次注射>0.9，所有硅藻计数）。在猫和人类的实际病例中，L/W 比值>0.4 表示溺死，<0.04 表示死后入水。
向肺部多次注入实验用水会增加 L/W 比值，从而验证了通过计算 L/W 比值诊断溺死的硅藻浓度检验的有效性。通过计算 L/W 比值，可以区分人类和猫的溺死和死后入水。
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