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Thermal Physiology and Thermoregulation
Published in James Stewart Campbell, M. Nathaniel Mead, Human Medical Thermography, 2023
James Stewart Campbell, M. Nathaniel Mead
As cooled venous blood returns from the extremities, adjacent arteries warm it by conduction. The slightly warmed blood enters the thorax to be carried toward the right atrium of the heart by the great veins. These veins are located adjacent to deposits of Brown Adipose Tissue (BAT). This heat-producing fat is stimulated by cold conditions to help re-warm the returning blood to maintain body temperature. Metabolic heat production in all the active body organs, especially the liver, also heats the returning blood.
Temperature Regulation
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
There is some evidence that humans can acclimatize to cold environments, and most homeothermic animals increase non-shivering thermogenesis in response to repeated exposure to cold temperatures. Studies in adult humans who spent at least 6 months in Antarctica showed that the core temperature increased when exposed to cold, suggesting an increased metabolic response to cold by increased non-shivering thermogenesis. As there is no increase in brown fat mass, the enhanced non-shivering thermogenesis is likely to involve the liver and skeletal muscles, with an increased sensitivity to the calorigenic effects of norepinephrine in humans following cold acclimatization. Eskimos and the Alakaluf Indians at the southern tip of South America do not shiver in ambient temperatures of 2°C–5°C and have a BMR that is 30%–40% higher than other populations. Cold environments increase appetite, and increased food intake increases metabolic heat production.
Neuroendocrine Regulations
Published in Miroslav Holub, Immunology of Nude Mice, 2020
Metabolic heat production is increased by stimulation of the adrenergic systems and by thyroid hyperfunction.58,59 The thyroid of the nude homozygote is all but hyperfunctional (see Section I), but thyroxine (T4) production is obviously sufficient. Nonshivering thermogenesis during all kinds of cold adaptation of the nude mouse is based on catecholamine-mediated metabolic changes in the brown adipose tissue depots.
Increased air temperature decreases high-speed, but not total distance, in international field hockey
Published in Temperature, 2022
Carl A James, Ashley G.B. Willmott, Aishwar Dhawan, Craig Stewart, Oliver R Gibson
Increased air temperature, particularly >25°C, appears detrimental to running performance in elite middle- and long-distance endurance events [1]. The magnitude of performance decrement is proportional to both the event duration and the temperature difference versus purported optimal conditions for endurance performance of ~10–15°C [2]. Increased atmospheric water vapor (i.e. humidity) and exposure to solar radiation (i.e. direct sunlight) also concurrently exacerbate the decrement [3,4]. Therefore, it is the interplay between high internal metabolic heat production (i.e. exercise intensity), clothing, and the environment, that determines heat storage and increases in body temperature, leading to performance impairment. Increased body temperature does not directly impact performance, with elite endurance athletes demonstrating resistance to core temperatures >40°C [5], and team-sport athletes eliciting core temperatures of 39–40°C [6–8]. However, the combination of cardiovascular strain [9] and elevated skin temperature that occur when air temperature increases impairs performance via multiple mechanisms [10], including behavioral modifications of exercise intensity [11,12].
Influences of ovarian hormones on physiological responses to cold in women
Published in Temperature, 2022
Andrew M. Greenfield, Nisha Charkoudian, Billie K. Alba
Little is known about cold-induced proton leak in human skeletal muscle. Future research is certainly warranted given that humans possess substantially greater muscle mass than BAT mass (42% vs <1% of total body mass) and skeletal muscle contributes significantly more to whole-body thermogenesis than BAT (~40% vs ~1%) [86,99,100]. Moreover, the primary mechanisms from which metabolic heat production occur require further elucidation. While UCP3 activity seems to be modulated by ROS to some degree [95], cold exposure, whether acute or chronic, does not seem to elevate UCP3 levels, leaving some uncertainty to its ultimate influence in a cold-adaptive response [88,97]. Relevant to the current review, muscle-derived NST remains uninvestigated in women. Therefore, future research should aim to include women and evaluate the effect of female sex hormones on the skeletal muscle NST response to cold exposure, particularly with regard to menstrual cycle influences in NST recruitment.
Numerical analysis of local non-equilibrium heat transfer in layered spherical tissue during magnetic hyperthermia
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
In magnetic hyperthermia, the power dissipation of particles is one of main factors to determine the temperature within tumor. For a suitable control of temperature distribution in tissues, Salloum et al. (Salloum et al., 2008) experimentally studied the distribution of the magnetic particles and discovered that the concentration of magnetic particles is in Gaussian distribution along the radial direction as magnetic fluid is injected into the tissue structure. Zhang (Zhang, 2009) further indicated that the blood temperature undergoes a transient process before onset of equilibrium and proposed a model to account the transient effect of blood temperature. Thus, the present work would use the generalized dual-phase lag model of bioheat transfer to investigate the non-equilibrium heat transfer in layered spherical tissue with the transient blood temperature and Gaussian distribution source. Bioheat transfer modeling depend also on the physics considered (Andreozzi et al., 2019b). The metabolic heat generation and blood perfusion rates are important characteristics of living tissues. In accordance with Refs. (Gautheric, 1980; Hu et al., 2004), the metabolic heat generation and blood perfusion rates are different between tumor and normal (tissues) tissue. Maenosono and Saita (Maenosono and Saita, 2006) regarded their same values for tumor and normal tissue. Andrä et al. (Andrä et al., 1999) predicted the temperature distribution in breast with neglecting the effects of blood perfusion and metabolism. This paper is aimed at evaluation of the model in its initial and non-modified forms.