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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
Heat is a measure of the average kinetic energy of a substance per degree of freedom of its constituent molecules. Temperature is the physical state of a substance which determines whether or not the substance is in thermal equilibrium with its surroundings; heat energy is transferred from a region of higher temperature to a region of lower temperature. Mammals maintain a constant body temperature, and enzyme systems of the body function optimally within a narrow range between 35°C and 41°C. Above 45°C, enzymes become denatured. A convenient expression of the relationship between rate of a reaction and temperature is Q10 value. This is the ratio of the velocity of a reaction at T + 10°C to its velocity at T°C. The enzyme reactions in the body increase 2- to 2.5-fold for each 10°C rise in temperature (i.e., Q10 = 2–2.5). The specific heat of water is 4.2 kJ/kg/°C (1 kcal/kg/°C), whereas the specific heat of body tissue is about 85% that of water, that is, 3.6 kJ/kg/°C. Body temperature is regulated by a balance between heat loss and heat production. Heat is lost from the body via radiation, convection, evaporation and conduction from the skin, as well as evaporation from the respiratory tract and via urination and defaecation. Radiation, or emitting electromagnetic energy, contributes to about 40%–50% of the heat loss of the body. About 15% of heat loss is through conduction and convection, and 30% is via evaporation (latent heat of vaporization of water = 2.4 MJ/kg or 580 cal/g at 37°C). Heat loss via respiration is approximately 5%.
The Anatomy and Physiology of Normal Thermoregulation
Published in Benedict Isaac, Serge Kernbaum, Michael Burke, Unexplained Fever, 2019
Heat regulation is achieved by a dynamic balance between heat production and heat loss. There are several mechanisms of heat loss: Radiation and conduction from skinAdjusting temperature and humidity of inspired airSweatingBy urine and feces
Heat, cold and electrical trauma
Published in Jason Payne-James, Richard Jones, Simpson's Forensic Medicine, 2019
Jason Payne-James, Richard Jones
Hypothermia occurs when a person's normal body core temperature of around 37°C (98.6°F) drops below 35°C (95°F). Core temperature is best measured by an oesophageal probe. If core temperature cannot be measured, the degree should be estimated using clinical signs. Treatment is to protect from further heat loss, minimise afterdrop – the continued fall of deep body temperatures during rewarming – and prevent cardiovascular collapse during rescue and resuscitation. It is usually caused by being in a cold environment, and can be triggered by a combination of factors, including prolonged exposure to cold (such as staying outdoors in cold conditions or in a poorly heated room for a long time), inadequate clothing, rain, wind, sweat, low BMI, inactivity or being in cold water.
COVID-19 and thermoregulation-related problems: Practical recommendations
Published in Temperature, 2021
Hein Daanen, Stephan Bose-O’Reilly, Matt Brearley, D. Andreas Flouris, Nicola M. Gerrett, Maud Huynen, Hunter M. Jones, Jason Kai Wei Lee, Nathan Morris, Ian Norton, Lars Nybo, Elspeth Oppermann, Joy Shumake-Guillemot, Peter Van den Hazel
Heat acclimatization is a powerful method to increase wet and dry heat loss: at similar work rates, heat-acclimatized individuals have lower heart rates, lower body core temperatures, and increased sweat rates [17]. Since the reliability of heat wave warnings increases with decreasing number of days prior to the heat wave, attempts have been made to construct short-term heat acclimation programs to adjust people to the expected heat. Although a program of 5 days may lead to adaptations in thermoregulation [18–20], it is recommended to use more days to have more effective adaptations [21]. It is recommended to give extra attention to heat acclimation adaptions in females since they are more vulnerable in the heat than men [22]. Studies including elderly females in heat acclimation are scarce but there is some evidence showing that sweat rates and cooling overall seem to fall in line with the latter recommendation [23,24].
Heat-related issues and practical applications for Paralympic athletes at Tokyo 2020
Published in Temperature, 2020
Katy E. Griggs, Ben T. Stephenson, Michael J. Price, Victoria L. Goosey-Tolfrey
The aforementioned sections have demonstrated how thermoregulation and sporting performance of Paralympic athletes with various impairments may be compromised when competing in the heat. In summary, in relation to heat exchange, both convective and evaporative heat loss and metabolic heat production will be affected as a result of the Paralympic athlete’s disability, highlighted in Figure 3. The metabolic heat production of Paralympic athletes is likely to be altered because of their impairment, for instance being lower in athletes with an SCI, while greater in athletes with CP and athletes with an amputation, compared to the AB. In relation to heat loss, convective and evaporative heat loss are likely to be impaired due to a smaller body surface area of active muscle mass, reductions in vasomotor and sweating control and alterations in pacing strategy. Thus, the disability groups mentioned in the sections above are likely to store a greater amount of heat leading to an increase in thermal strain, as a result of a reduction in convective and evaporative heat loss and, for some groups, also an increase in metabolic heat production (Figure 3).
Towards establishing evidence-based guidelines on maximum indoor temperatures during hot weather in temperate continental climates
Published in Temperature, 2019
Glen P. Kenny, Andreas D. Flouris, Abderrahmane Yagouti, Sean R. Notley
The relationship between weather (e.g., outdoor ambient temperature) and human health typically exhibits a U- or J-shaped curve wherein the heat-related morbidity and mortality rises exponentially when temperatures exceed a threshold value [101,115]. The assessment of the thermal environment on temperature-attributable mortality has served as a valuable tool to assess the acute health effects of heat exposure over time [20,102,115–121]. The consistency of this heat-mortality relationship has spawned heat management strategies to protect health, which have included heat warning systems for entire metropolitan areas or regions [28,43–49,122]. However, there are a number of factors such as geographical location and climate type, seasonal influences (i.e., time of year when the heat wave occurs such as early in the summer versus late in the summer) and others (Figure 2) that have been shown to affect human health during heat waves and, therefore, the temperature-attributable mortality [20,99,102,115–121,123–127]. Humidity is an equally important factor in defining when climatic conditions become fatal. The threshold at which temperature becomes deadly decreases with increasing relative humidity [1]. This is because air saturated with water vapour prevents sweat evaporation, which is our primary heat loss mechanism [128]. Consequently, as the body dissipates less heat, a greater amount of heat is stored in the body leading to potentially dangerous increases in body core temperature paralleled by a progressive state of dehydration and therefore elevated level of cardiovascular strain [129].