2007, Piran, Slovenia

Modelling
RESULTS
From this kind of analysis, it is evident that, as to the (passive) heat transfer process, the
parameters heat transfer coefficient skin/environment α and heat transfer index core/shell k
may be suited to modification by process adaptation. The parameter α may e.g. be altered by
a fat or a fur layer, the parameter k by vasomotor action.
As to the (active) metabolic controller, the parameters, threshold T0 and gain g, may be used
for controller adaptation. Theoretically also the weighting parameter c for core and skin
temperature may be a candidate for adaptational modification.
Steady-states in the closed control-loop are determined by intersections of the open-loop
process- and controller-characteristics M=f(Tb), cf. Fig.1B.
The most commonly demonstrated effect of autonomic cold acclimation is a change in the
controller threshold T0, meaning that the body temperature, at which metabolic heat
production M is activated above its basic level, is shifted downwards. As a consequence of
this controller adaptation, the whole controller characteristic is shifted to the left.
How does the closed control loop react to such an adaptational threshold shift ?
It is obvious that the only possible post-adaptive state is given by the intersection of the
unaltered process characteristic with the altered controller characteristic, because this is the
only state which is compatible with the properties of both subsystems. This will necessarily
mean a lowering of body temperature by Tb, because of a metabolic rate lowered by M.
This concept explains experimental results both on Europeans in the climatic chamber and on
Aborigines in the natural environment.
Exclusive autonomic process adaptation, in the form of a better insulation (either in form of a
fat or fur layer, morphological adaptation, and/or of further vasoconstriction, physiological
adaptation), is represented by a right and downward shift of the positive sloping process
characteristic. A post-adaptive steady-state can now only be achieved, if the controller system
reduces metabolism M, as dictated by the point of intersection between the unchanged
characteristic of the controller and the changed process characteristic. Thus, the new state is
inevitably characterised by a rise of body temperature by Tb, in spite of a decrease of
metabolic rate by M.
If both process and controller adaptations are simultaneously present, there may not be any
change of body temperature at all, as e.g. demonstrated in animal experiments. Both
alterations together are described by a shift of the characteristics both of the process and the
controller. The post-adaptive state is now depicted by the intersection of both shifted
characteristics. Whether this delivers a decrease, an increase or no change of mean body
temperature, depends on the proportion of process and controller adaptation.
DISCUSSION
So in summary, a class of very different observations may be explained by variations in the
contributions of the process and controller adaptation.
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