The post-mortem interval : a study of the body cooling rate and steroid degradation after death
In Part I, the most useful methods for the estimation of the time of death are reviewed, with special emphasis being placed on the post-mortem rate of cooling because this method is commonly used for estimating the interval after death. Theories and models of the post-mortem loss of heat from the human body are summarised and discussed. The Microwave Thermography System, a new device which is applied to this field for the first time, is described and its mode of operation is discussed. Using this device, it is possible to measure temperatures of internal organs of the body by placing the sensory elements on the skin. The reliability of the system and factors affecting the accuracy of temperature measurements made with the device are assessed and discussed. Results of a study of the cooling rate of 117 fatalities are given. All cases were studied under controlled conditions and two groups were collected in which the bodies were monitored either naked or covered with blankets. In each case, the environmental temperature as well as the temperatures at three body sites were continuously monitored over a period beginning shortly after death and ending up to 60 hours post-mortem or more. Rectal and environmental temperatures were measured with thermocouples while the temperature of the brain and liver were measured using microwave probes, therefore by non-invasive and ethically acceptable methods. The data were recorded on tape following Analogue to Digital (AD) conversion using a BBC Microcomputer. These data were processed and temperatures at the moment of death for the three body sites were estimated by extrapolation backwards. Processed data were transferred to a mainframe computer where sophisticated curve-fitting procedures were performed. These indicated that the cooling curves were adequately represented by three-term exponential equations containing six empirically derived parameters. Statistical analysis of the parameters yielded average formulae and the use of these formulae to improve the ease and accuracy of the estimation of the time of death is discussed. Lastly, suggestions for future work are given. In Part II, biochemical methods of estimating the time of death are reviewed and limitations of their use are duscussed. Steroids were selected as potential indicators of the post-morem interval by virtue of their metabolism and degradation after death. Aspects of steroid biochemistry are summarised. Various methods of steroid analysis were assessed using radioassays and thin layer chromatography. Three reversed phase chromatography systems were evaluated for separation and recovery of steroids extracted from blood, tissues and faeces. The use of different numbers of Sep-Pak C18 cartridges for the purification of steroid extracts was examined and steroid recoveries were measured and compared. The results indicated that recoveries were best when 4-6 cartridges were used. Rapid and slow procedures of enzymatic hydrolysis and acidic solvolysis of steroid conjugates were compared. A new and relatively rapid method for analysis of steroid profiles in biological samples was developed. Assessment of this method showed that steroid recoveries were improved compared to existing methods. A pilot study of the post-mortem changes in the steroid profiles of blood, tissues and faeces was carried out using the rat as a suitable and convenient animal model. Liver and adrenal tissues, faeces and blood samples collected from 30 rats either at the moment of death or 24 hours after death were analysed and their steroids were studied qualitatively and quantitatively using selctive ion monitoring GC-MS techniques. Thus chromatographic peaks were identified by comparison of their retention times and mass spectrometric characteristics with those of standards and quantitative analysis was performed. The occurrence of significant steroid changes was difficult to ascertain but some changes in the steroid profiles of the biological samples were shown to have occurred. Lastly, the practicability of this method for the estimation of time of death is discussed.