Human thermoregulation: separating thermal and nonthermal effects on heat loss

Abstract

Human thermoregulatory control during heat stress has been studied at rest, during exercise and more recently during exercise recovery. Heat balance in the body is maintained by changes in the rate of heat loss via adjustments in skin blood flow and sweating. Independent of thermal control, the actions of nonthermal factors have important consequences in the control of heat loss responses during and following exercise. While the effect of these nonthermal factors is largely considered to be an inhibitory or excitatory stimulus which displaces the set-point about which temperature is regulated, their effects on human thermoregulatory control are far reaching. Many factors can affect the relative contribution of thermal and nonthermal influences to heat balance including exercise intensity, hemodynamic status, and the level of hyperthermia imposed. This review will characterize the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on sweating and skin blood flow in humans. Further, recent calorimetric evidence for the understanding of thermal and nonthermal contributions to human heat balance will also be discussed.

Time required to stabilize thermographic images at rest

“…The central body regions (i.e., the abdomen and chest) exhibited higher temperatures than the peripheral regions (i.e., the hand, forearm, upper arm, thigh and leg). In the resting position, the body shifts blood flow to central regions, where vital organs such as the heart and lungs are located [1]. This behavior of the human thermoregulatory system can result in higher T SK values in the central region.…”

“…A cold environment causes vasoconstriction of the skin to preserve the internal heat of vital organs [1]. Under extreme heat conditions, the opposite occurs; vasodilatation facilitates heat loss, and the T SK is elevated [7].…”

“…In humans, core body temperature (CT) is maintained nearly constant by physiological mechanisms that maintain a balance between the internal heat and heat released to the environment [1]. These adjustments are essential to maintaining an inner temperature of approximately 37°C, thus preserving vital metabolic functions.…”

Brain stem representation of thermal and psychogenic sweating in humans

“…HUMAN ECCRINE SWEAT GLANDS respond to both thermal and nonthermal drives (26,27), and their secretions serve a wide range of secondary functions, such as facilitating tactile and thermal sensitivity, increasing contact friction (grip), and reducing the risk of tissue damage (55). The main nonthermal drive to sweating in resting individuals is mental stress or arousal, referred to here as psychogenic sweating (32).…”

Wärmeanwendungen unter Berücksichtigung der Wärmeregulation - Teil 2

“…Die wesentliche und initiale Wärmeabwehr der Haut ist ihre direkte Kühlung durch eine Erhöhung der lokalen Durchblutung [29]. Ihre Beeinträchtigung erhöht das Risiko thermischer Schädigung massiv [30].…”