A review of the effects of sedation on thermoregulation : insights for the cardiac catheterisation laboratory

Purpose To examine the effects that the sedative and analgesic medications which are commonly used in the cardiac catheterisation laboratory have on thermoregulation. Design A structured review strategy was used. Methods Medline and CINAHL were searched for published studies and reference lists of retrieved studies were scrutinized for further research. Data were extracted using a standardised extraction tool. Results A total of nine studies examined the effect that sedative and analgesic medications have on thermoregulation. Midazolam has minimal impact on thermoregulation while opioids, dexmedetomidine and propofol markedly decrease vasoconstriction and shivering thresholds. Conclusions Patients who receive sedation in the cardiac catheterisation laboratory may be at risk of hypothermia, due to the use of medications that impair thermoregulation. Further research is required to identify the prevalence of unplanned hypothermia during sedation in the cardiac catheterisation laboratory.

Insights into torpor and behavioural thermoregulation of the endangered Juliana's golden mole

The cryptic, subterranean ways of golden moles (Chrysochloridae) hamper studies of their biology in the field. Ten species appear on the IUCN red list, but the dearth of information available for most inhibits effective conservation planning. New techniques are consequently required to further our understanding and facilitate informed conservation management decisions. We studied the endangered Juliana's golden mole Neamblysomus julianae and aimed to evaluate the feasibility of using implantable temperature sensing transmitters to remotely acquire physiological and behavioural data. We also aimed to assess potential body temperature (T-b) fluctuations in relation to ambient soil temperature (T-a) in order to assess the potential use of torpor. Hourly observations revealed that T-b was remarkably changeable, ranging from 27 to 33 degrees C. In several instances T-b declined during periods of low T-a. Such 'shallow torpor' may result in a daily energy saving of c. 20%. Behavioural thermoregulation was used during periods of high T-a by selecting cooler microclimates, while passive heating was used to raise T-b early morning when T-a was increasing. In contrast to anecdotal reports of nocturnal patterns of activity, our results suggest that activity is flexible, being primarily dependent on T-a. These results exemplify how behavioural patterns and microclimatic conditions can be examined in this and other subterranean mammal species, the results of which can be used in the urgently required conservation planning of endangered Chrysochlorid species.

The sympathetic release test: a test used to assess thermoregulation and autonomic control of blood flow

When a subject is heated, the stimulation of temperature-sensitive nerve endings in the skin, and the raising of the central body temperature, results in the reflex release of sympathetic vasoconstrictor tone in the skin of the extremities, causing a measurable temperature increase at the site of release. In the sympathetic release test, the subject is gently heated by placing the feet and calves in a commercially available foot warming pouch or immersing the feet and calves in warm water and wrapping the subject in blankets. Skin blood flow is estimated from measurements of skin temperature in the fingers. Normally skin temperature of the fingers is 65-75 degrees F in cool conditions (environmental temperature: 59-68 degrees F) and rises to 85-95 degrees F during body heating. Deviations in this pattern may mean that there is abnormal sympathetic vasoconstrictor control of skin blood flow. Abnormal skin blood flow can substantially impair an individual's ability to thermoregulate and has important clinical implications. During whole body heating, the skin temperature from three different skin sites is monitored and oral temperature is monitored as an index of core temperature. Students determine the fingertip temperature at which the reflex release of sympathetic activity occurs and its maximal attainment, which reflects the vasodilating capacity of this cutaneous vascular bed. Students should interpret typical sample data for certain clinical conditions (Raynaud's disease, peripheral vascular disease, and postsympathectomy) and explain why there may be altered skin blood flow in these disorders.

Recent advances in thermoregulation

Thermoregulation is the maintenance of a relatively constant core body temperature. Humans normally maintain a body temperature at 37°C, and maintenance of this relatively high temperature is critical to human survival. This concept is so important that control of thermoregulation is often the principal example cited when teaching physiological homeostasis. A basic understanding of the processes underpinning temperature regulation is necessary for all undergraduate students studying biology and biology-related disciplines, and a thorough understanding is necessary for those students in clinical training. Our aim in this review is to broadly present the thermoregulatory process taking into account current advances in this area. First, we summarize the basic concepts of thermoregulation and subsequently assess the physiological responses to heat and cold stress, including vasodilation and vasoconstriction, sweating, nonshivering thermogenesis, piloerection, shivering, and altered behavior. Current research is presented concerning the body's detection of thermal challenge, peripheral and central thermoregulatory control mechanisms, including brown adipose tissue in adult humans and temperature transduction by the relatively recently discovered transient receptor potential channels. Finally, we present an updated understanding of the neuroanatomic circuitry supporting thermoregulation.

Level and precision of behavioural thermoregulation in the bearded dragon, Pogona vitticeps : effects of hypoxia and environmental thermal quality /

Most metabolic functions are optimized within a narrow range of body temperatures, which is why thermoregulation is of great importance for the survival and overall fitness of an animal. It has been proposed that lizards will thermoregulate less precisely in low thermal quality environments, where the costs associated with thermoregulation are high; in the case of lizards, whose thermoregulation is mainly behavioural, the primary costs ofthermoregulation are those derived from locomotion. Decreasing thermoregulatory precision in costly situations is a strategy that enhances fitness by allowing lizards to be more flexible to changing environmental conditions. It allows animals to maximize the benefits of maintaining a relatively high body temperature while minimizing energy expenditure. In situations where oxygen concentration is low, the costs of thermoregulation are relatively high (i.e. in relation to the amount of oxygen available for metabolic functions). As a result, it is likely that exposures to hypoxic conditions induce a decrease in the precision of thermoregulation. This study evaluated the effects of hypoxia and low environmental thermal quality, two energetically costly conditions, on the precision and level of thermoregulation in the bearded dragon, Pogona vitticeps, in an electronic temperature-choice shuttle box. Four levels of hypoxia (1O, 7, 5 and 4% 02) were tested. Environmental thermal quality was manipulated by varying the rate of temperature change (oTa) in an electronic temperature-choice shuttle box. Higher oT a's translate into more thermally challenging environments, since under these conditions the animals are forced to move a greater number of times (and hence invest more energy in locomotion) to maintain similar temperatures than at lower oTa's. In addition, lizards were tested in an "extreme temperatures" treatment during which air temperatures of the hot and cold compartments of the shuttle box were maintained at a constant 50 and 15°C respectively. This was considered the most thermally challenging environment. The selected ambient (T a) and internal body temperatures (Tb) of bearded dragons, as well as the thermoregulatory precision (measured by the central 68% ofthe Ta and T b distribution) were evaluated. The thermoregulatory response was similar to both conditions. A significant increase in the size of the Tb range, reflecting a decrease in thermoregulatory precision, and a drop in preferred body temperature of ~2 °C, were observed at both 4% oxygen and at the environment of lowest thermal quality. The present study suggests that in energetically costly situations, such as the ones tested in this study, the bearded dragon reduces energy expenditure by decreasing preferred body temperature and minimizing locomotion, at the expense of precise behavioural thermoregulation. The close similarity of the behavioural thermoregulatory response to two very different stimuli suggests a possible common mechanism and neuronal pathway to the thermoregulatory response.

Characterising Behavioural Thermoregulation in the Bearded Dragon: The Role of TRPM8

Temperature regulation is a necessary part of maintaining life, as most biological processes are influenced by temperature. ThermoTRP channels are considered the primary thermosensors in endotherms, but little is known regarding their function in ectotherms. The goal of this study is to establish TRPM8, a cold sensing channel, as a participant in normal thermoregulation of the bearded dragon (Pogona vitticeps), an ectotherm. Animals were placed inside a ramping temperature shuttle box to assess the common behavioural thermoregulatory strategy of shuttling. Shuttling involves the periodic movement between cold and warm environments to maintain body temperature at moderate levels. The temperatures for cold and warm escapes represent sensory thresholds for inducing the shuttling thermoeffector. Animals were administered with: 1) an injection of the TRM8 antagonist capsazepine, 2) an injection of the TRPM8 agonist menthol, and 3) menthol applied topically. No effect was observed with injected drugs, but topical menthol resulted in a 2-3oC rise in the ambient temperature threshold and 1-2oC rise in skin temperature threshold for escape from the cold compartment. In an additional experiment, gaping behaviour, a warm temperature thermoregulatory strategy, was assessed. No effect was observed in this behaviour when the same dose of menthol was applied topically. These results point to a role for TRPM8 only in thermoregulation as it relates to cold temperature sensation in lizards, since it does not participate in regulating warm temperature behaviours such as gaping.

Modellierung und numerische Simulation der Thermoregulation von Früh- und Neugeborenen

Bei frühgeborenen Säuglingen spielt die Thermoregulation zur Aufrechterhaltung einer überlebenswichtigen Körpertemperatur durch Wärmeproduktion, -abgabe bzw. -aufnahme eine entscheidende Rolle. Der Einsatz moderner Inkubatoren soll die körpereigenen Thermoregulatoren unterstützen, und es ist im Hinblick auf verschiedene medizinische Fragestellungen wünschenswert, diesen Prozess modellieren zu können. Wir stellen ein einfaches Modell auf der Basis von partiellen Differentialgleichungen vor und beschreiben detailliert die numerische Simulation mit Hilfe einer Finite-Volumen-Methode. Dazu wird ein zweidimensionales Modell eines Frühgeborenen trianguliert und das Modell diskretisiert. Zahlreiche numerische Resultate zeigen die Qualität unseres Modells.

Differential effects of thyroid hormone manipulation and ß adrenoceptor agonist administration on uncoupling protein mRNA abundance in adipose tissue and thermoregulation in neonatal pigs

We have shown that there is significant disparity in the expression of uncoupling proteins (UCP) 2 and 3 between modern-commercial and ancient-Meishan porcine genotypes, commercial pigs also have higher plasma triiodothyronine (T(3)) in on the first day of life. T(3) and the sympathetic nervous system are both known to regulate UCPs in rodents and humans; their role in regulating these proteins in the pig is unknown. This study examined whether thyroid hormone manipulation or administration of a selective beta3 adrenoceptor agonist (ZD) influenced plasma hormones, colonic temperature and UCP expression in adipose tissue of two breeds of pig. To mimic the differences observed in thyroid hormone status, piglets from Meishan and commercial litters were randomly assigned to control (1 ml/kg water), T(3) (10 mg/kg) (Meishan only), methimazole (a commonly used antithyroid drug) (50 mg/kg) (commercial only) or ZD (10 mg/kg) oral administration for the first 4 days of postnatal life. Adipose tissue UCP2/3 mRNA abundance was measured on day 4 using PCR. T(3) administration raised plasma T(3) concentrations and increased colonic temperature on day 4. UCP3 mRNA abundance was higher in Meishan, than commercial piglets (p = 0.042) and was downregulated following T(3) administration (p = 0.014). Irrespective of genotype, ZD increased UCP2 mRNA abundance (Meishan p = 0.05, commercial p = 0.03). Expression of neither UCP2 nor 3 was related to colonic temperature, regardless of treatment. In conclusion, we have demonstrated a dissociation between thyroid hormones and the sympathetic nervous system in the regulation of UCPs in porcine adipose tissue. We have also suggested that expression of adipose tissue UCP2 and 3 are not related to body temperature in piglets.

A method of evaluating the accuracy of human body thermoregulation models

Human Body Thermoregulation Models have been widely used in the field of human physiology or thermal comfort studies. However there are few studies on the evaluation method for these models. This paper summarises the existing evaluation methods and critically analyses the flaws. Based on that, a method for the evaluating the accuracy of the Human Body Thermoregulation models is proposed. The new evaluation method contributes to the development of Human Body Thermoregulation models and validates their accuracy both statistically and empirically. The accuracy of different models can be compared by the new method. Furthermore, the new method is not only suitable for the evaluation of Human Body Thermoregulation Models, but also can be theoretically applied to the evaluation of the accuracy of the population-based models in other research fields.

Thermoregulation in young athletes exercising in hot environments.

Children are less efficient thermoregulators than are adults. During exercise, sweat evaporation is the most important physiological means of cooling the body. The sweat response in children, however, is less efficient than in adults, so children dissipate less heat though evaporative sweating and more through convection (the loss of heat through the skin) plus radiation. Children and adolescents with high levels of body fat and heavy builds are more susceptible to heat stress because they dissipate body heat less efficiently. Maintaining adequate hydration is crucial for preventing heat stress, Although water is often described as the best choice of fluid, studies on voluntary drinking habits and flavor preferences in children and adolescents suggest that greater consumption occurs when sports drinks are offered instead of water. Although a child's sweat contains less sodium and chloride than an adult's does, there appears to be no evidence that a child's performance improves when given beverages more diluted than those currently recommended for adults, More information is necessary to identify the optimal electrolyte and carbohydrate content of sports drinks for young athletes.

Effect of glycerol-induced hyperhydration on thermoregulation and metabolism during exercise in the heat

This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H₂O.kg^-1 body weight (bw) (GLY) or 20 ml H₂O.kg^-1bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98 % of lactate threshold in dry heat (35 degrees C, 30 % RH), with ingestion of CHO-electrolyte beverage (6 % CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 ± 97 vs. 1503 ± 146 ml· 120 min^-1; p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 ± 1.5 vs. 13.7 ± 3.0 ml.100 g tissue·min^-1; p < .05) and rectal  temperature lower (38.7 ± 0.1 vs. 39.1 ± 0.1 ° C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5'-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5 % greater in GLY (252 ± 10 vs. 240 ± 9 kJ; p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.

The influence of cover on nesting Red-capped Plovers: a trade-off between thermoregulation and predation risk?

 Some ground-nesting birds adopt a mixed strategy of nesting in the open, or under cover (e.g. vegetation). This may represent a trade-off between thermally favourable nest sites (covered) and those that enable the early detection and avoidance of predators (open). This study examined whether such a trade-off exists for Redcapped Plover Charadrius ruficapillus, whose eggs are preyed upon principally by Little Raven Corvus mellori. For real and artificial nests, nest temperatures under cover (real, 25.9 ± 0.1°C; false, 16.2 ± 0.5°C) were cooler than those in the open (real, 26.8 ± 0.1°C; false, 17.4 ± 0.9°C). Covered nests had more visual obstructions than open nests (covered, 65.5% ± 11.4%; open, 7.4% ± 2.8%) and a standardised measure of incubator escape distance, initiated by experimental human approaches, indicated incubators fled open nests at longer distances than for covered nests. Nests under cover showed a slightly (non-significant) higher probability of surviving one day (Daily Survival Rate [DSR] = 0.978) than those in the open (DSR = 0.950). For false nests containing model eggs, covered nests exhibited better survival to 10 days compared with open nests (20.4% vs. 4.7%). Thus, covered nests are associated with enhanced thermal environments and egg survival, but predators can approach the incubator more closely. Overall, the proposed trade-off between thermal and predation risks associated with nest sites appears to exist and explains the ongoing occurrence of nests in open and covered locations.