## 1 Introduction  
Biological systems represent a special type of control system. In all of these, control is exercised over the flows of matter and energy to maintain a range of stationarity of their existence [1]. Hence, all living organisms are equipped with numerous interconnected control systems, which serve to maintain the organism's internal equilibrium regardless of outside influences. This condition is known as _homeostasis_. In the 19 th century, Claude [PERSON] discovered the \"amazing constancy\" of the internal environment of the organism [2], and in 1927, [PERSON] named it the _homeostasis_[3]. 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]. The hands and feet form powerful thermoregulatory regulators in the body, serving as heat radiators (exchanger) and evaporators in hot environments and as thermal insulators in the cold [7]. [PERSON] et al. [8] estimated that each hand and foot can dissipate 150-220 W\(\cdot\)m\({}^{-2}\) through radiation and convection at rest in an ambient temperature of 27 \({}^{\circ}\)C, with even greater heat dissipation through sweating. Additionally, the extremities can serve as thermal sensor acting in feedback and feedforward fashion to the thermoregulation system of the body [7]. Arteriovenous anastomoses (AVAs) are direct connections between small arteries and small veins (Figure 1), with no capillary section between them. Since there is no capillary transportation, the only transport function they could possibly have is the transport of heat from the body core to surface areas containing AVAs [9]. [PERSON] and [PERSON] [10] investigated the role of AVA in thermoregulation. They found a relation between the number of AVAs in a body part and the change in local skin temperature due to local cold [11]. When the extremities of the hand and feet are exposed locally to a cold environment, their AVAs respond with sympathetically mediated vasoconstriction, which is termed cold-induced vasoconstriction (CIVC). CIVC reduces the blood flow to the peripheries in favour of a central pooling of blood in the torso and deep body core [7; 12; 13]. Due to this vasoconstriction and the high surface area-to-volume ratio, the skin temperature of the extremities tends and exponentially decreases to a level approaching that of the ambient environment. After a brief period of lowered skin blood flow and temperature, due to the CIVC, a temporary increase in blood flow and rewarding occurs. During these episodes, skin temperature can rise by as much as 10 \({}^{\circ}\)C, and this fall and rise can occur repeatedly in a cyclic fashion [7]. This pattern of periodic warming was first reported by [PERSON] [14], who labelled it the \"hunting response\", due to its apparent oscillatory pattern. This response is also termed the cold-induced vasodilation (CIVD) phenomenon [15]. There is a definite variation in the occurrence, magnitude, and duration of the CIVD [16]. It was found that the CIVD occurs in about 5 to 10 min after the exposure of the hand to cold [15; 17], and is initiated by the dilation of the AVAs [7; 13; 15; 18]. Because of the elevated extremity blood flow and temperature, CIVD has generally been presumed to provide a protective function by maintaining local tissue integrity and minimizing the risk of cold injuries. However, the mechanisms underlying CIVD are unclear, yet understanding the nature of CIVD is of important occupational and clinical relevance [7]. Additionally, the review studies of [PERSON] et al. [7; 19] have shown that it is not easy to compare different research findings due to the inconsistent methodologies in the experimental protocols, and most of the studies on CIVD are largely descriptive, lacking sufficient quantification of CIVD responses.