Beyond the classic thermoneutral zone

Abstract

The thermoneutral zone is defined as the range of ambient temperatures where the body can maintain its core temperature solely through regulating dry heat loss, i.e., skin blood flow. A living body can only maintain its core temperature when heat production and heat loss are balanced. That means that heat transport from body core to skin must equal heat transport from skin to the environment. This study focuses on what combinations of core and skin temperature satisfy the biophysical requirements of being in the thermoneutral zone for humans. Moreover, consequences are considered of changes in insulation and adding restrictions such as thermal comfort (i.e. driver for thermal behavior). A biophysical model was developed that calculates heat transport within a body, taking into account metabolic heat production, tissue insulation, and heat distribution by blood flow and equates that to heat loss to the environment, considering skin temperature, ambient temperature and other physical parameters. The biophysical analysis shows that the steady-state ambient temperature range associated with the thermoneutral zone does not guarantee that the body is in thermal balance at basal metabolic rate per se. Instead, depending on the combination of core temperature, mean skin temperature and ambient temperature, the body may require significant increases in heat production or heat loss to maintain stable core temperature. Therefore, the definition of the thermoneutral zone might need to be reformulated. Furthermore, after adding restrictions on skin temperature for thermal comfort, the ambient temperature range associated with thermal comfort is smaller than the thermoneutral zone. This, assuming animals seek thermal comfort, suggests that thermal behavior may be initiated already before the boundaries of the thermoneutral zone are reached.

Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

“…However, it is unlikely that its thermoneutral zone is relevant in determining the vulnerability of a free-living mammal to climate change. The thermoneutral zone is determined in the laboratory as the range of dry-bulb temperatures at which metabolic heat production is lowest, and where a constant body core temperature can be achieved by dry heat loss only (that is, by altering skin blood flow) [74]. That zone is not applicable to an animal that is active, and its derivation ignores the complex suite of climatic factors, other than the dry-bulb temperature, that impact on heat exchange, including solar radiation, wind, and water vapour pressure.…”

Infrared thermography of human face for monitoring thermoregulation performance and estimating personal thermal comfort

“…Temperature homeostasis allows for optimal operations of the internal organs while maintaining heat equilibrium with the environment. The temperatures that are thermally comfortable are a subset of temperatures when the body is in the thermoneutral zone [29]. When there is thermal stress (i.e., heat and cold) caused by external factors (e.g., increased temperature or humidity) or internal factors (e.g., food intake), human body responds and the thermoregulation system adjusts heat dissipation to the external environment by modifying the blood flow via cutaneous arterioles and veins, causing sweating or shivering [30].…”

Neurophysiology of Skin Thermal Sensations

“…From simply looking for shade on a sunny hot day (241), to adding or removing clothing (141), humans constantly adjust their thermal behavior in order to maintain thermal comfort (106,180).…”