A model is developed for the regulation of temperature in man. The thermal properties of the body are presented in circuit form and simplified to eliminate all features not essential to an understanding of control. In this modeling, perspiration is treated as a source which can pump heat against a temperature gradient while lung heat loss appears as a high-frequency alteration in effective heat production. To this simplified thermal circuit are appended the principal mechanisms which are available to the nervous system for controlling body heat balance-increased metabolism as in shivering, increased heat loss by perspiration, and alteration of thermal conductance through changes in blood flow-and a block diagram of the resulting control system is given. The description of these mechanisms follows that of Benzinger and co-workers Benzinger & Benzinger, Pratt & Kitzinger, 1961. To formulate the problem on a feedback control basis, an error signal representing deviations of hypothalamic temperature from a reference value or set point of 37°C is defined. The reference temperature may have no precise natural coorelate and its choice seems arbitrary. Since man normally spends most of his time neither shivering or perspiring, particular emphasis is palced upon an analysis of the vascular mechanism by which fine control is achieved. A non-linear differential equation governing the system under this mode of control is presented and solved for transient disturbances in mtabolic heat production and environmental temperature. The analysis indicates a quantity-dependent on level of metabolism and degree of control over peripheral blood flow-which is a measure of the strength or effectiveness of vascular control. Both response time and steady-state error are reduced by this factor, which is estimated to have a numerical value of about 10. From this analysis it is clear that regardless of how additional assumptions might complicated a description of the system, the data on vascular control reported by Benzinger 1959 lead to a model of human temperature regulation exhibiting powerful multiplicative control over heat flow out of the body.
ASJC Scopus subject areas
- Statistics and Probability
- Modeling and Simulation
- Biochemistry, Genetics and Molecular Biology(all)
- Immunology and Microbiology(all)
- Agricultural and Biological Sciences(all)
- Applied Mathematics