Abstract
Biological systems, in general, represent a special type of control system. The physiological processes of homeostasis, which serve to maintain the organism’s internal equilibrium against external influences, are clear forms of biological control system. An example of the homeostasis is the control of the organism thermal state or the thermoregulation. The thermoregulatory control of human skin blood flow, via vasoconstriction and vasodilation, is vital to maintaining normal body temperatures during challenges to thermal homeostasis such as localised cooling. The main objective of this paper is to reverse engineer the localised thermoregulatory cold-induced vasoconstriction/vasodilation (CIVC/CIVD) reactions using a data-based mechanistic approach. Two types of localised cooling were applied to the fingers of 33 healthy participants, namely, continuous and intermittent cooling. Modelling of the thermoregulatory cold-induced vasoconstriction/vasodilation reactions suggested two underlying processes, with one process being 10 times faster. A new term is suggested in this paper, namely, the latent heat of CIVD, which represents the amount of dissipated heat required to trigger the CIVD. Moreover, a new model for the thermoregulatory localised CIVC/CIVD reactions is proposed. The suggested new model states that, with an initial vasodilation state, the initial localised CIVC is triggered based on a certain threshold in the rate of heat dissipation from the skin to the surrounding environment.
Highlights
Biological systems represent a special type of control system
In agreement with previous study [20], the Simplified Refined Instrumental Variable (SRIV) algorithm combined with YIC and RT2 suggested that a second-order discrete-time transfer functions (TF) described the dynamic responses of finger skin temperature to step-decreases in the input (Peltier element’s temperature) most accurately (i.e., RT2 = 0.91 ± 0.04 and YIC = −11.23 ± 2.33) for all 33 test subjects
We suggest a new model for thermoregulatory localised CIVC/cold-induced vasodilation (CIVD) reactions
Summary
Biological systems represent a special type of control system. Control is exercised over the flows of matter and energy to maintain a range of stationarity of their existence [1]. All living organisms are equipped with numerous interconnected control systems, which serve to maintain the organism’s internal equilibrium regardless of outside influences. An example of homeostasis is the control of an organism’s thermal state (thermoregulation system). Heat in biological systems is generated in the course of metabolic conversion and scattered by conduction, convection, radiation and evaporation [4,5,6]
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