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Anesthesiology Aug 2008Most clinically available thermometers accurately report the temperature of whatever tissue is being measured. The difficulty is that no reliably... (Review)
Review
Most clinically available thermometers accurately report the temperature of whatever tissue is being measured. The difficulty is that no reliably core-temperature-measuring sites are completely noninvasive and easy to use-especially in patients not undergoing general anesthesia. Nonetheless, temperature can be reliably measured in most patients. Body temperature should be measured in patients undergoing general anesthesia exceeding 30 min in duration and in patients undergoing major operations during neuraxial anesthesia. Core body temperature is normally tightly regulated. All general anesthetics produce a profound dose-dependent reduction in the core temperature, triggering cold defenses, including arteriovenous shunt vasoconstriction and shivering. Anesthetic-induced impairment of normal thermoregulatory control, with the resulting core-to-peripheral redistribution of body heat, is the primary cause of hypothermia in most patients. Neuraxial anesthesia also impairs thermoregulatory control, although to a lesser extent than does general anesthesia. Prolonged epidural analgesia is associated with hyperthermia whose cause remains unknown.
Topics: Anesthesia, General; Body Temperature; Body Temperature Regulation; Humans; Hypothermia; Monitoring, Intraoperative; Shivering; Skin Temperature; Sweating
PubMed: 18648241
DOI: 10.1097/ALN.0b013e31817f6d76 -
Annals of the Academy of Medicine,... Apr 2008This review discusses human thermoregulation during exercise and the measurement of body temperature in clinical and exercise settings. The thermoregulatory mechanisms... (Review)
Review
This review discusses human thermoregulation during exercise and the measurement of body temperature in clinical and exercise settings. The thermoregulatory mechanisms play important roles in maintaining physiological homeostasis during rest and physical exercise. Physical exertion poses a challenge to thermoregulation by causing a substantial increase in metabolic heat production. However, within a non-thermolytic range, the thermoregulatory mechanisms are capable of adapting to sustain physiological functions under these conditions. The central nervous system may also rely on hyperthermia to protect the body from "overheating." Hyperthermia may serve as a self-limiting signal that triggers central inhibition of exercise performance when a temperature threshold is achieved. Exposure to sub-lethal heat stress may also confer tolerance against higher doses of heat stress by inducing the production of heat shock proteins, which protect cells against the thermolytic effects of heat. Advances in body temperature measurement also contribute to research in thermoregulation. Current evidence supports the use of oral temperature measurement in the clinical setting, although it may not be as convenient as tympanic temperature measurement using the infrared temperature scanner. Rectal and oesophagus temperatures are widely accepted surrogate measurements of core temperature (Tc), but they cause discomfort and are less likely to be accepted by users. Gastrointestinal temperature measurement using the ingestible temperature sensor provides an acceptable level of accuracy as a surrogate measure of Tc without causing discomfort to the user. This form of Tc measurement also allows Tc to be measured continuously in the field and has gained wider acceptance in the last decade.
Topics: Body Temperature; Body Temperature Regulation; Exercise; Humans; Monitoring, Physiologic
PubMed: 18461221
DOI: No ID Found -
Autonomic Neuroscience : Basic &... Apr 2016Thermoregulation is a vital function of the autonomic nervous system in response to cold and heat stress. Thermoregulatory physiology sustains health by keeping body... (Review)
Review
Thermoregulation is a vital function of the autonomic nervous system in response to cold and heat stress. Thermoregulatory physiology sustains health by keeping body core temperature within a degree or two of 37°C, which enables normal cellular function. Heat production and dissipation are dependent on a coordinated set of autonomic responses. The clinical detection of thermoregulatory impairment provides important diagnostic and localizing information in the evaluation of disorders that impair thermoregulatory pathways, including autonomic neuropathies and ganglionopathies. Failure of neural thermoregulatory mechanisms or exposure to extreme or sustained temperatures that overwhelm the body's thermoregulatory capacity can also result in potentially life-threatening departures from normothermia. Hypothermia, defined as a core temperature of <35.0°C, may present with shivering, respiratory depression, cardiac dysrhythmias, impaired mental function, mydriasis, hypotension, and muscle dysfunction, which can progress to cardiac arrest or coma. Management includes warming measures, hydration, and cardiovascular support. Deaths from hypothermia are twice as frequent as deaths from hyperthermia. Hyperthermia, defined as a core temperature of >40.5°C, may present with sweating, flushing, tachycardia, fatigue, lightheadedness, headache, and paresthesia, progressing to weakness, muscle cramps, oliguria, nausea, agitation, hypotension, syncope, confusion, delirium, seizures, and coma. Mental status changes and core temperature distinguish potentially fatal heat stroke from heat exhaustion. Management requires the immediate reduction of core temperature. Ice water immersion has been shown to be superior to alternative cooling measures. Avoidance of thermal risk and early recognition of cold or heat stress are the cornerstones of preventive therapy.
Topics: Animals; Body Temperature; Body Temperature Regulation; Cold Temperature; Fever; Hot Temperature; Humans; Hypothermia
PubMed: 26794588
DOI: 10.1016/j.autneu.2016.01.001 -
Neuron Apr 2018The regulation of body temperature is one of the most critical functions of the nervous system. Here we review our current understanding of thermoregulation in mammals.... (Review)
Review
The regulation of body temperature is one of the most critical functions of the nervous system. Here we review our current understanding of thermoregulation in mammals. We outline the molecules and cells that measure body temperature in the periphery, the neural pathways that communicate this information to the brain, and the central circuits that coordinate the homeostatic response. We also discuss some of the key unresolved issues in this field, including the following: the role of temperature sensing in the brain, the molecular identity of the warm sensor, the central representation of the labeled line for cold, and the neural substrates of thermoregulatory behavior. We suggest that approaches for molecularly defined circuit analysis will provide new insight into these topics in the near future.
Topics: Animals; Body Temperature; Body Temperature Regulation; Brain; Homeostasis; Humans; Neural Pathways; Thermosensing
PubMed: 29621489
DOI: 10.1016/j.neuron.2018.02.022 -
Anaesthesiology Intensive Therapy 2017Fever is a common symptom in the Intensive Care Unit. At least half of febrile episodes are caused by infection. Excluding infectious etiology and other non-infectious... (Review)
Review
Fever is a common symptom in the Intensive Care Unit. At least half of febrile episodes are caused by infection. Excluding infectious etiology and other non-infectious causes of fever, especially in patients with central nervous system (CNS) disorders, attention should be paid to disturbances of thermoregulatory centre. In particular, subarachnoid haemorrhage, cerebral trauma, along with ischaemic or haemorrhagic stroke are strongly associated with the development of central fever. Proper, speedy diagnosis of the cause of fever makes it possible to implement preventive measures against the harmful effects of hyperthermia on the CNS and to avoid the consequences of inappropriate treatment. The aim of this review is to present the current treatment options for the management of central fever and to analyze recent recommendations for the treatment of hyperthermia, including the use of hypothermia. The recommendations of American and European associations are inconsistent, mainly due to the lack of randomized clinical trials confirming the effectiveness of such treatment. The diagnosis of central fever is still made by the exclusion of other causes. The authors of the review intended to present the characteristic features of central fever, differentiating this state from infectious fever and also analyze the presence of central fever in particular neurological diseases. It seems particularly important to establish diagnostic criteria for central fever or to find diagnostic markers. It is also necessary to conduct further randomized clinical trials evaluating the indications for treatment of hyperthermia.
Topics: Body Temperature Regulation; Central Nervous System Diseases; Fever; Humans; Infections; Intensive Care Units
PubMed: 28803441
DOI: 10.5603/AIT.2017.0042 -
Neuron Feb 2023Precise monitoring of internal temperature is vital for thermal homeostasis in mammals. For decades, warm-sensitive neurons (WSNs) within the preoptic area (POA) were...
Precise monitoring of internal temperature is vital for thermal homeostasis in mammals. For decades, warm-sensitive neurons (WSNs) within the preoptic area (POA) were thought to sense internal warmth, using this information as feedback to regulate body temperature (T). However, the cellular and molecular mechanisms by which WSNs measure temperature remain largely undefined. Via a pilot genetic screen, we found that silencing the TRPC4 channel in mice substantially attenuated hypothermia induced by light-mediated heating of the POA. Loss-of-function studies of TRPC4 confirmed its role in warm sensing in GABAergic WSNs, causing additional defects in basal temperature setting, warm defense, and fever responses. Furthermore, TRPC4 antagonists and agonists bidirectionally regulated T. Thus, our data indicate that TRPC4 is essential for sensing internal warmth and that TRPC4-expressing GABAergic WSNs function as a novel cellular sensor for preventing T from exceeding set-point temperatures. TRPC4 may represent a potential therapeutic target for managing T.
Topics: Mice; Animals; Body Temperature; Body Temperature Regulation; Hypothalamus; Preoptic Area; GABAergic Neurons; Mammals
PubMed: 36476978
DOI: 10.1016/j.neuron.2022.11.008 -
Biological Reviews of the Cambridge... Feb 2016Advances in biologging techniques over the past 20 years have allowed for the remote and continuous measurement of body temperatures in free-living mammals. While... (Review)
Review
Advances in biologging techniques over the past 20 years have allowed for the remote and continuous measurement of body temperatures in free-living mammals. While there is an abundance of literature on heterothermy in small mammals, fewer studies have investigated the daily variability of body core temperature in larger mammals. Here we review measures of heterothermy and the factors that influence heterothermy in large mammals in their natural habitats, focussing on large mammalian herbivores. The mean 24 h body core temperatures for 17 species of large mammalian herbivores (>10 kg) decreased by ∼1.3°C for each 10-fold increase in body mass, a relationship that remained significant following phylogenetic correction. The degree of heterothermy, as measured by the 24 h amplitude of body core temperature rhythm, was independent of body mass and appeared to be driven primarily by energy and water limitations. When faced with the competing demands of osmoregulation, energy acquisition and water or energy use for thermoregulation, large mammalian herbivores appear to relax the precision of thermoregulation thereby conserving body water and energy. Such relaxation may entail a cost in that an animal moves closer to its thermal limits for performance. Maintaining homeostasis requires trade-offs between regulated systems, and homeothermy apparently is not accorded the highest priority; large mammals are able to maintain optimal homeothermy only if they are well nourished, hydrated, and not compromised energetically. We propose that the amplitude of the 24 h rhythm of body core temperature provides a useful index of any compromise experienced by a free-living large mammal and may predict the performance and fitness of an animal.
Topics: Adaptation, Physiological; Animals; Body Size; Body Temperature Regulation; Herbivory; Mammals
PubMed: 25522232
DOI: 10.1111/brv.12166 -
Philosophical Transactions of the Royal... Jul 2017The importance of colour for temperature regulation in animals remains controversial. Colour can affect an animal's temperature because all else being equal, dark... (Review)
Review
The importance of colour for temperature regulation in animals remains controversial. Colour can affect an animal's temperature because all else being equal, dark surfaces absorb more solar energy than do light surfaces, and that energy is converted into heat. However, in reality, the relationship between colour and thermoregulation is complex and varied because it depends on environmental conditions and the physical properties, behaviour and physiology of the animal. Furthermore, the thermal effects of colour depend as much on absorptance of near-infrared ((NIR), 700-2500 nm) as visible (300-700 nm) wavelengths of direct sunlight; yet the NIR is very rarely considered or measured. The few available data on NIR reflectance in animals indicate that the visible reflectance is often a poor predictor of NIR reflectance. Adaptive variation in animal coloration (visible reflectance) reflects a compromise between multiple competing functions such as camouflage, signalling and thermoregulation. By contrast, adaptive variation in NIR reflectance should primarily reflect thermoregulatory requirements because animal visual systems are generally insensitive to NIR wavelengths. Here, we assess evidence and identify key research questions regarding the thermoregulatory function of animal coloration, and specifically consider evidence for adaptive variation in NIR reflectance.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.
Topics: Animal Communication; Animals; Body Temperature Regulation; Color; Invertebrates; Light; Pigmentation; Vertebrates
PubMed: 28533462
DOI: 10.1098/rstb.2016.0345 -
Physiological Reports Sep 2023The cardiovascular system is primarily controlled by the autonomic nervous system, and any changes in sympathetic or parasympathetic activity also have an impact on... (Review)
Review
The cardiovascular system is primarily controlled by the autonomic nervous system, and any changes in sympathetic or parasympathetic activity also have an impact on myocardial activity. Heart rate variability (HRV) is a readily available metric used to assess heart rate control by the autonomic nervous system. HRV can provide information about neural (parasympathetic, sympathetic, reflex) and humoral (hormones, thermoregulation) control of myocardial activity. Because there are no relevant reference values for HRV parameters in rats in the scientific literature, all experimental results are only interpreted on the basis of changes from currently measured control or baseline HRV values, which are, however, significantly different in individual studies. Considering the significant variability of published HRV data, the present study focused primarily on comparing control or baseline HRV values under different conditions in in vivo experiments involving rats. The aim of the study was therefore to assess whether there are differences in the starting values before the experiment itself.
Topics: Male; Animals; Rats; Heart Rate; Autonomic Nervous System; Body Temperature Regulation; Myocardium; Reference Values
PubMed: 37735345
DOI: 10.14814/phy2.15827 -
Anesthesiology Jan 2013Although suppression of thermoregulatory mechanisms by anesthetics is generally assumed, the extent to which thermoregulation is active during general anesthesia is not...
Although suppression of thermoregulatory mechanisms by anesthetics is generally assumed, the extent to which thermoregulation is active during general anesthesia is not known. The only thermoregulatory responses available to anesthetized, hypothermic patients are vasoconstriction and nonshivering thermogenesis. To test anesthetic effects on thermoregulation, the authors measured skin-surface temperature gradients (forearm temperature - fingertip temperature) as an index of cutaneous vasoconstriction in unpremedicated patients anesthetized with 1% halothane and paralyzed with vecuronium during elective, donor nephrectomy. Patients were randomly assigned to undergo maximal warming (warm room, humidified respiratory gases, and warm intravenous fluids; n = 5) or standard temperature management (no special warming measures; n = 5). Skin-surface temperature gradients of 4°C or more were prospectively defined as significant vasoconstriction. Normothermic patients (average minimum esophageal temperature = 36.4° ± 0.3°C [SD]) did not demonstrate significant vasoconstriction. However, each hypothermic patient displayed significant vasoconstriction at esophageal temperatures ranging from 34.0 to 34.8°C (average temperature = 34.4° ± 0.2°C). These data indicate that active thermoregulation occurs during halothane anesthesia, but that it does not occur until core temperature is approximately 2.5°C lower than normal. In two additional hypothermic patients, increased skin-temperature gradients correlated with decreased perfusion as measured by a laser Doppler technique. Measuring skin-surface temperature gradients is a simple, noninvasive, and quantitative method of determining the thermoregulatory threshold during anesthesia.
Topics: Anesthesia, Inhalation; Body Temperature Regulation; Halothane; Humans
PubMed: 23221865
DOI: 10.1097/ALN.0b013e3182784df3