Classical methods for the determination of PMI

Traditionally, time of death was defined by an irreversible termination of circulation caused by a cessation of cardiac function. This definition had to be modified in intensive care medicine where circulation and respiration were maintained artificially. The resulting working definition uses brain death as the moment that characterizes individual death (Kurthen et al., 1989 ; Capron, 2001). Nevertheless, cessation of cardiac function still represents the time of death in the vast majority of forensic cases and thus the transition of the body into the so-called supravital state (Madea and Henssge, 1991). Supravital reactions are, by definition, phenomena that can be observed in the time between irreversible loss of function of the organ systems and the actual death of the cells in a particular organ. Since the resistance of various tissues to oxygen deficiency differs greatly, these phenomena in different tissues can cover a time span from a few minutes to some hours following the irreversible loss of brain function.

In the early PMI (Figure 14.1), i.e. during the first 3 days postmortem, estimation of the PMI in forensic medicine is mostly based on the evaluation of supravital signs (e.g. livor mortis, rigor mortis) and the decrease of body temperature after death (Mallach and Mittmeyer, 1971; Krompecher and Fryc, 1979). The medico-legal significance of livor and rigor mortis is limited by non-standardized and subjective examination techniques (Schleyer, 1975) and various ante- and postmortem factors (Forster et al., 1974; Krompecher et al., 1983; Fechner et al., 1984). The decrease of body temperature after death - alone or in combination with non-temperature-based indicators (Henssge et al., 2000b) -

___ entomology morphology (including putrefaction) decreasing body temperature additional supravital signs L rigor mortis ! livor mortis r _

time postmortem [d]

Figure 14.1 Overview of the periods in which the classical forensic methods can be used for estimation of the postmortem interval (PMI). It illustrates that reliable parameters such as decreasing body temperature and rigor and livor mortis are available no longer than the first few days. After that short period, rather subjective and non-standardized methods need to be consulted is a reliable and thoroughly investigated phenomenon (Marshall and Hoare, 1962; Shapiro, 1965; Marty, 1995; Henssge et al., 2000a). Considering the weight of the body and environmental factors, the body core temperature permits a retro-calculation of a time span within which death occurred. However, body temperature approaches ambient temperature approximately 30 hours after death and thereafter is no longer of value for assessing time of death. A survey at the Institute of Forensic Medicine at the University of Bern revealed that 16% of 559 bodies were not found before two or more days after death. This corresponds to a significant number of cases where an objective method for determination of the PMI is missing. In that later postmortem phase, an estimation of the PMI has to rely on the evaluation of putrefaction signs of the body (Schneider and Riese, 1980), fragmentary criminological information from witnesses or, in certain cases, entomological studies of insects colonizing the body (Figure 14.1).

Putrefaction signs can be observed starting at 2-3 days postmortem, however, while the general sequence of their appearance has been described frequently (Berg, 1975), a review of the forensic literature showed that no systematic description of morphological changes during decomposition of the body giving precise time frames for each sign had been established. This finding was additionally documented by an internal survey including nine experienced forensic pathologists. It was found that even common changes being observed in the majority of cases led to an uncertainty of up to 5 days for PMIs of the same time range. Thus, it is generally accepted that morphological signs cannot be used as reliable and objective indicators of the PMI (Schneider and Riese, 1980), particularly since they are strongly dependent on external (e.g., temperature, humidity) and internal factors (e.g., antemortem treatment and diseases) (Mann et al., 1990). Forensic entomology uses the fact that insects colonize bodies during the process of decomposition in various waves (Smith, 1986), depending on the stage of decomposition of the corpse. While this method allows for an estimation of the PMI in certain cases (Benecke, 1996), it is extremely time-consuming and demanding. In addition, insect populations vary with geographical region, season and environment (Campobasso et al., 2001; Grassberger and Reiter, 2001), making standardization almost impossible.

The disintegration of the chemical, physical and morphological organization starting immediately after death is known as 'autolysis' and results from the action of endogenous enzymes and the cessation of oxygen-dependent biochemical processes. The failure of the body to maintain homeostasis leads to a breakdown of the internal equilibrium as well as to the degradation of proteins, carbohydrates and fats. This results in an increase of breakdown products. Chemical analyses for the purpose of a PMI estimation based on concentration changes have been performed on body fluids such as blood and blood serum (Coe, 1974), cerebrospinal fluid (Endo et al., 1990), vitreous humor of the eyes (Coe, 1989), synovial fluid (Madea et al., 2001) and skeletal muscle (Mayer and Neufeld, 1980; Mittmeyer, 1980). Some projects concentrated on specific groups of metabolites, e.g. the decomposition of fats (Lindlar, 1969; Doring, 1975) or proteins (Bonte et al., 1976; Bonte, 1978). Collection of body fluids can be very difficult depending on the PMI and the state in which the individual body is found (Henssge and Madea, 1988). While this could be less problematic in brain tissue due to the protection by the skull, only a few studies were published (Diessner and Lahl, 1969; Daldrup, 1983, 1984) that analysed brain tissue chemically for an estimation of the PMI. On the other hand, examinations of the brain would be particularly interesting because inter-individual differences in tissue composition are very small compared to other tissues of the body (e.g. skeletal muscle or liver).

To date, none of the chemical methods have become generally accepted, nor are they routinely applied for PMI estimation. One reason for this disappointing outcome may be the fact that most of these methods attempted to characterize PMI by a few or even just one specific parameter. It seems that chemical methods based on multiple metabolite concentrations lead to more successful PMI estimations while methods based on a single metabolite failed to be used regularly in the past.

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