A system-analytical approach to the process of fever

Abstract

Pyrogen-induced fever is a strictly dynamic process without steady-states before reaching again the normal temperature level. Therefore former models of central control of metabolic heat production (Stitt, 1980; Simon, 1981; Werner, 1981) do not enable an adequate computation of the dynamics of fever, as the equations are formulated on the basis of steady-state relations. The purpose of this study is to derive from experimental results a simple model describing the febrile process.

Female rabbits were exposed to air-temperatures < 20°C in a climatic chamber. After the animals had reached their thermal equilibrium, bacterial pyrogen was injected intravenously.

The dependence of metabolic heat production on the rate of change of core temperature dT_C/dt in the course of the experiment is a quasilinear one, independently of the type of experiment. This is a property of the passive system due to instationary heat flow. The properties of the closed control-loop imply a strictly proportional controller. A pure change of controller-gain in fever is excluded, as this would not evoke changes of core temperature observed in the experiment. Fever is primarily due to a parallel shift of the controller characteristic via the pyrogen. The set of equations enables the determination of the central controller gains and of the fever-signal controlling directly metabolic heat production.

(Supported by the Deutsche Forschungsgemeinschaft, SFB 114)