Testing the 2nd Model

The results of a "cold step" test with a 5 degree drop in ambient temperature is shown in Figure 9. The temperature drop occurs in the 12th hour of the simulation. The test shows that skin temperature would decline over the next two or three hours. The model exhibits a slight decline in the core temperature in the 12th hour, but the decline is not discernable in Figure 9. Nevertheless, this small decline trigers the shivering. Shivering increasing to around 45 kcal/hour. The increase is caused by the first of the two multipliative factor (the shivering initiation multiplier from cooler core).

Figure 9. Simulated cold step test with the second model.

This cold step test confirms that the body would be able to maintain homeostatic control in the face of a five degree drop in ambient temperature. This result was expected from Rigg's description of the span of control. The test reveals that shivering would increase over a two to three hour period before reaching a steady state. If the body were permanently exposed to the 5 degree challenge, it would call upon 18% of the "standard amount of shivering." This test indicates that the shivering is triggered by the multiplicative factor involving small changes in core temperature. This response agrees with Riggs use of the term "core modulated shivering."

At this point, you are probably wondering if the dynamic response in Figure 9 matches Rigg's description of shivering. For example, you might be curious if Rigg's calculations show that the body requires 2-3 hours to attain the new equilibrium. You should know that the transient response can not be confirmed or contradicted by Rigg's calculations. Riggs' analysis allowed him to derive staeady state conditions, but it says nothing about the transient response. To confirm or reject the transient response in Figure 9, one might turn to Milsum (1966, p. 77) for examples of physiological responses to "cold step" tests.

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