time since death and body cooling: revaluation of the henssge nomogram

La temperatura cadaverica ed il suo decremento rappresentano, insieme a rigidità e lividure ipostatiche la famosa triade dei dati tanatocronologici. Tali variabili assumono un ruolo fondamentale per la stima dell'epoca della morte. A partire dalla fine del diciannovesimo secolo si sono susseguite numerose ricerche scientifiche che hanno condotto al rilievo della misurazione della temperatura cadaverica rettale dopo quella ascellare, auricolare o semplicemente cutanea. Si ottenevano in tal modo dei risultati da inserire in specifiche equazioni atte a valutare l'effettiva coincidenza fra epoca della morte e valore presunto. L'equazione ad oggi universalmente più riconosciuta è stata elaborata da Henssge che, tiene conto di temperatura cadaverica e ambientale, entità degli indumenti, ventilazione. Scopo del presente studio è valutare l'efficacia del metodo applicandolo su una casisitica di decessi a intervallo post mortem noto. Sono stati raccolti 46 casi (12 donne, 34 uomini) con decesso a seguito di sinistro stradale ed un intervallo post mortem fra le 2 e le 44 ore. Le misurazioni sono state eseguite fra il gennaio 2008 ed il dicembre 2010 con un censimento di 15 casi nelle stagioni fredde e 31 nelle stagioni calde. La temperatura era misurata inserendo entro l'ampolla rettale la sonda di un termometro digitale HD2107.2 [Delta Ohm, Boxes Selvazzano (PD)] per un estensione di 8 cm. Al fine di verificare la precisione della tecnica in ogni occasione si manteneva inserita la sonda eseguendo sei misurazioni. Si misurava anche la temperatura ambientale. I dati ottenuti, unitamente ad entità degli indumenti e stima del peso (al fine di ricreare la situazione verificantesi in corso di sopralluogo) venivano utilizzati per il nomogramma di Henssge fermo restando il ricorso ad eventuali fattori di correzione. Il confronto fra dati reali e calcolati di PMI ha permesso di rilevare una percentuale del 17% di netta coincidenza fra I due valori (con uno scarto di 30 minuti), il 52% dei casi nei quali il PMI reale rientrava pur sempre nel range offerto da Henssge ed infine un 31% di assoluta incompatibilità. Vista l'influenza esercitata da condizioni ambientali e peso del cadavere si è anche tentato di standardizzare sia la temperatura ambientale (a 20°C e 25°C) sia il peso (a 90,80,70 e 60 Kg). Tale metodica ha permesso di apprezzare come l'accuratezza del metodo rimanesse accettabile solo laddove la differenza di peso fra standard e reale fosse entro i 10 Kg. Nella seconda fase dello studio abbiamo suddiviso il campione in due gruppi ciascuno con 23 casi: il primo in cui è stata fatta una sola misurazione, il secondo in cui le misurazioni sono state almeno due per cadavere. Confrontando tali due gruppi è emerso come al trascorrere del tempo l'accuratezza del metodo venisse meno. Nei casi reali di utilizzo del nomgramma infine, si è comunque dimostrato come il raffreddamento cadaverico per la datazione del decesso non possa essere utilizzato senza tener conto di altre variabili tanatocronologiche (come rigidità ed ipostasi).

Temperature up corpses along with rigor mortis and the hypostasis, are the classic triad of so-called thanatochronological data. As it is well known, these variables have a key role, for the reconstruction of the time of death. As regards the temperature, by the end of the nineteenth century was introduced to measure rectal, flanked by other venues such as detecting external acoustic meatus, trachea, etc. axillary cavity. The data thus obtained are usually evaluated with different equations for calculating post-death interval (PMI) and then the time of death. Today, the equation most used is that proposed by Henssge, which takes account of temperature and body weight, ambient temperature, clothing worn, ventilation. Paradoxically, few experimental tests of the accuracy of the estimates obtained using this method is available in the literature. The purpose of this study was the assessment of the reliability of this method, in terms of accuracy of the estimate, applied to a series of traumatic deaths with known PMI. The present study included 46 cases (12 females and 34 males) of death from traffic accident with PMI ranging from 2 to 44 hours. The measurements were performed between January 2008 and December 2010, with 15 cases collected during the cold season (Autumn-Winter) and 31 in the warm season (Spring-Summer). The temperature was measured by inserting the probe metal corpse of the digital thermometer HD2107.2 [Delta Ohm, Boxes Selvazzano (PD)] in the rectal ampulla at a depth of 8 cm. In order to verify the precision of the technique, the measurement was repeated 6 times in the space of 6 minutes keeping the probe inserted in the rectum. The ambient temperature was also measured with same instrument. The data obtained were recorded along with variables such as clothing, sex, age. In order to reproduce the typical situation of a judicial spot where the body can not be weighted, the weight was assessed on the basis of stature and muscle distribution. Using the Henssge nomogram the after-death interval was calculated then compared with the real one. The actual influence on the estimation of PMI exerted by the various correction factors (clothing, weather conditions, etc.) proposed by the author was also tested. In all cases, the relative standard deviation of the temperature values in the 6 repeated measurements was < 0.05% confirming the precision of the technique. Comparing the PMI data calculated by the equation of Henssge with the real PMIs, in 17% of cases the two PMIs coincided with a tolerance of 0.5 hours, in 52% of cases the real PMI fell within the range calculated by Henssge’s equation, whereas in 31% of cases the real PMI was outside the range calculated. Taking into consideration the difficulty in the real cases of assessing the ambient temperature, subject to changes over time, and the uncertainties about the influence of the different situations where the body can be found (in air, on soil, immersed in water), we attempted to evaluate the change of body temperature independently of environment temperature, using for all the cases temperature "standard" values (20°C and 25°C, respectively). However, this approach increased the inaccuracy of the results. Another relevant factor for the calculation of PMI is represented by the body weight, being the speed of cooling directly depending on the fat percentage and distribution. However, at it is well known, is often impossible to measure the body weight at the crime scene. On this basis, we attempted to calculate the PMI using for all the cases different standard weight values (90, 80, 70, 60 Kg). By using this approach the accuracy of the PMI estimate was acceptable only if the difference between the real weight and the standard value was < 10 kg. In the last step we analized the difference between 2 groups: in the first (23 corpses) we made only one determination; in the second (23 corpses) it were at least two determinations on the corpses. The comparison between the two groups highlighted the importance of repeated measurements to demonstrate the performance of the cooling. The data obtained until now shows that the accuracy of the estimates varied in relation to time elapsed since death, with a progressive deterioration with the increase of PMI intervals. In the present study, although performed on a limited number of cases, the exact match (± 0.5 hours) between real PMIs and calculated according Henssge has been restricted to a few cases (17%). On the other hand, taking into account the confidence intervals proposed by Henssge, a "assessment within range" was observed in 70%. Be noted, however, the wide margin of error allowed (between ± 2.8 and ± 7 hours). The method is more accurate when applied within ten hours after death, when the percentage reaches 33% exact correlation.