Characteristics of mechanical asphyxia: A retrospective epidemiological study in two developed cities in China

Background: Mechanical asphyxia (MA) is multi-classified. Some epidemiological characteristics are shared and the others different among different MA types. Aims and Objectives: To reveal the characteristics of different types of MA and provide reference data for forensic identification of MA. Materials and Methods: We analyzed 913 cases to reveal the epidemiological characteristics of MA in Dongguan and Guangzhou, China. Results: Seven types of MA were identified and strangulation accounted for up to 89.2%. Those aged 20-29 were the most susceptible to all types, except for traumatic and positional asphyxia. Suicide accounted for 96.6% of hanging cases, and accident was the main manner of death in cases of choking, traumatic, and positional asphyxia. Homicide was the most common in cases of ligature strangulation (LS), manual strangulation (MS), smothering, and asphyxia concomitant with lethal mechanical injury. The homicide rate in LS was positively correlated with the rate of female victims (P<0.001, OR=21.14). In MS, the ratio of female : male was 101 : 15 in homicide. Compared to native residents, migrant workers were more likely to suffer from LS and MS. Rope was used in 50.8% of hanging cases, while LS tools were evenly distributed. Ligature marks were mostly found above the thyroid cartilage in both hanging and LS cases. The U shaped marks were shown in 51.01% of hanging cases but absent in LS cases. In LS, ligature marks completely encircling the neck, discontinuous marks, as well as ≥two marks, were more (P<0.001) than in hanging. In LS and MS cases, abrasion and subcutaneous hemorrhages on the neck were more frequent than in hanging cases (P=0.004 and P<0.001), but the difference in frequency of blister marks was opposite (P<0.001). Conclusion: In summary, this study revealed the epidemiological characteristics of the MA cases in Guangzhou and Dongguan cities. The characteristics of death scene and autopsy findings are important in differentiation of different types of MA, especially between suicide and homicide.