An Illustrative Example -- Riggs' Model of Shivering

These pages shows how a physiological model might be constructed in a step by step manner. The demonstration draws upon Douglas Riggs' model of the regulation of body temperature. The model is documented in his classic text on Control Theory and Physiological Feedback Mechanisms (Riggs 1970, p. 383-400).

Riggs' documentation takes the form of equations, parameter values, feedback loops, electric circuit diagrams and equilibrium conditions. He concentrated on the equilibrium conditions because his purpose was to find the range of homeostatic control. He concluded that the physiological mechanisms (in the model) could control the body's core temperature at 37 degrees C (98.6 degrees F) over a range of ambient temperatures from approximately 5 to 45 degrees C.

At the cold end of the range, control is achieved through shivering.

At the high end, control is achieved through a combination of cutaneous vasodiolation and sweating.

The system dynamics model may be verified by comparison with Riggs' original model. For example, the model may be used to check Riggs' assertions about the range of homeostatic control.

By the end of the demonstration, you will see that we will accomplish more than simply duplicating Riggs' original model. The system dynamics model will show the "time dimension" which is missing from his work. The dynamic variations in body temperatures will appear automatically as the model is simulated on the computer.