2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
458
PROCESS- AND/OR CONTROLLER-ADAPTATIONS DETERMINE
THE PHYSIOLOGICAL EFFECTS OF COLD ACCLIMATION
Jürgen Werner
Center of Biomedical Methods, Ruhr-University, Bochum, Germany
Contact person: juergen.werner@ruhr-uni-bochum.de
INTRODUCTION
At first sight, experimental results on physiological effects of cold adaptation published in the
literature seem confusing and apparently incompatible with one another. Mean body
temperature is reported to decrease, to stay constant or even to increase. The same is true for
skin blood flow. Metabolic heat production is said to decrease or increase. This contribution
will explain that such a variety of results may be deduced from a common system concept
underlying different adaptational phenomena.
METHODS
For a functional clarification, it is indispensable to differentiate where and how the adaptive
processes take place in the body. Generally, morphological and functional adaptations are
distinguished, meaning that the first alter the anatomical properties and the second the
physiological properties. This enables a correct interpretation of many, but not of all
phenomena, because the essence is not whether anatomical or physiological facts are
involved, but whether these are changing the (passive) heat transfer process or the (active)
controller system in the closed control loop (cf. Fig.1A).
Figure1. A: Closed-loop system “Process” and “Controller”. B: Open-loop characteristics of
process and con-troller in common coordinate system. Closed-loop operation for intersections
of characteristics. Abbr. see text.
For clarification, a core/shell treatment (“model”) of the thermoregulatory system is used,
with mean body temperature Tb as the controlled variable, metabolic heat production M as
actuating signal and ambient temperature Ta as disturbance to the system. Adaptation, as a
higher control level, is introduced into the system. Due to persistent stressors (disturbances),
either the (heat transfer) process or the controller properties (parameters) are adjusted (or
both). This differentiation is substantial, because these two ways of adaptation have very
different physiological effects. It is convenient to call the one “process adaptation” and the
other “controller adaptation”.