Determination of lime-dependent skin temperature decrease rates in the case of abrupt changes of environmental temperature

The present study deals with the development of a method fur determining ti me-dependent temperature decrease rates and its application to postmortem s urface cooling. The study concentrates on evaluating shin cooling behavior since data on skin cooling in the forensic literature are scarce. Furthermo re, all heat transfer mechanisms strongly depend on the temperature gradien t between body surface and environment. One of the main problems in modelli ng postmortem cooling processes is the dependence on the environmental temp erature. All models for postmortem rectal cooling essentially presuppose a constant environmental temperature. In medico-legal practice, the temperatu re of the surrounding of a corpse mostly varies; therefore, an approach for extending the models to variable environmental temperatures is desirable. It consists: in 'localizing' them to infinitesimal small intervals of time. An extended model differential equation is obtained and solved explicitly. The approach developed is applied to the single-exponential Newtonian mode l of surface cooling producing the following differential equation: T-S'(t) = -lambda(t)(T-S(t)-T-E(t)) (with T-S(t) the surface/skin temperature, T-E(t) the environmental tempera ture, lambda(t) the temperature decrease rate and T-S'(t) the actual change of shin temperature or first-order derivative of T-S). The differential eq uation directly provides an estimator: lambda(t) = -T-S'(t)/T-S(t) - T-E(t) for the time-dependent temperature decrease rare. The estimator is applied to two skin cooling experiments with different types of abrupt changes of e nvironmental temperature, peak-like and step-like; the values of the time-d ependent temperature decrease r rate function were calculated. By reinserti ng them, the measured surface temperature curve could be accurately reconst ructed, indicating that the extended model is well suited for describing su rface cooling in the case of abrupt changes of environmental temperature. ( C) 2000 Elsevier Science Ireland Ltd. All rights reserved.