Reduction In Core Temperature Research Articles

Avalanche burial pathophysiology - a unique combination of hypoxia, hypercapnia and hypothermia.

For often unclear reasons, the survival times of critically buried avalanche victims vary widely from minutes to hours. Individuals can survive and sustain organ function if they can breathe under the snow and maintain sufficient delivery of oxygen and efflux of carbon dioxide. We review the physiological responses of humans to critical avalanche burial, a model which shares similarities and differences with apnoea and accidental hypothermia. Within a few minutes of burial, an avalanche victim is exposed to hypoxaemia and hypercapnia, which have important effects on the respiratory and cardiovascular systems and pose a major threat to the central nervous system. As burial time increases, an avalanche victim also develops hypothermia. Despite progressively reduced metabolism, reduced oxygen and increased carbon dioxide tensions may exacerbate the pathophysiological consequences of hypothermia. Hypercapnia seems to be the main cause of cardiovascular instability, which, in turn, is the major reason for reduced cerebral oxygenation despite reductions in cerebral metabolic activity caused by hypothermia. 'Triple H syndrome' refers to the interaction of hypoxia, hypercapnia and hypothermia in a buried avalanche victim. Future studies should investigate how the respiratory gases entrapped in the porous snow structure influence the physiological responses of buried individuals and how haemoconcentration, blood viscosity and cell deformability affect blood flow and oxygen delivery. Attention should also be devoted to identifying strategies to prolong avalanche survival by either mitigating hypoxia and hypercapnia or reducing core temperature so that neuroprotection occurs before the onset of cerebral hypoxia.

The novel chimeric multi-agonist peptide (GEP44) reduces energy intake and body weight in male and female diet-induced obese mice in a glucagon-like peptide-1 receptor-dependent manner.

We recently reported that a novel chimeric peptide (GEP44) targeting both the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2 receptor (Y1R and Y2R) reduced energy intake and body weight (BW) in diet-induced obese (DIO) rats. We hypothesized that GEP44 reduces energy intake and BW primarily through a GLP-1R dependent mechanism. To test this hypothesis, GLP-1R+/+ mice and GLP-1R null (GLP-1R-/-) mice were fed a high fat diet for 4 months to elicit diet-induced obesity prior to undergoing a sequential 3-day vehicle period, 3-day drug treatment (5, 10, 20 or 50 nmol/kg; GEP44 vs the selective GLP-1R agonist, exendin-4) and a 3-day washout. Energy intake, BW, core temperature and activity were measured daily. GEP44 (10, 20 and 50 nmol/kg) reduced BW after 3-day treatment in DIO male GLP-1R+/+ mice by -1.5 ± 0.6, -1.3 ± 0.4 and -1.9 ± 0.4 grams, respectively (P<0.05), with similar effects being observed in female GLP-1R+/+ mice. These effects were absent in male and female DIO GLP-1R-/- mice suggesting that GLP-1R signaling contributes to GEP44-elicited reduction of BW. Further, GEP44 decreased energy intake in both male and female DIO GLP-1R+/+ mice, but GEP44 appeared to produce more consistent effects across multiple doses in males. In GLP-1R-/- mice, the effects of GEP44 on energy intake were only observed in males and not females, suggesting that GEP44 may reduce energy intake, in part, through a GLP-1R independent mechanism in males. In addition, GEP44 reduced core temperature and activity in both male and female GLP-1R+/+ mice suggesting that it may also reduce energy expenditure. Lastly, we show that GEP44 reduced fasting blood glucose in DIO male and female mice through GLP-1R. Together, these findings support the hypothesis that the chimeric peptide, GEP44, reduces energy intake, BW, core temperature, and glucose levels in male and female DIO mice primarily through a GLP-1R dependent mechanism.

The Effects of Post-Exercise Cold Water Immersion on Neuromuscular Control of Knee.

To date, most studies examined the effects of cold water immersion (CWI) on neuromuscular control following exercise solely on measuring proprioception, no study explores changes in the brain and muscles. The aim of this study was to investigate the effects of CWI following exercise on knee neuromuscular control capacity, and physiological and perceptual responses. In a crossover control design, fifteen participants performed an exhaustion exercise. Subsequently, they underwent a 10 min recovery intervention, either in the form of passively seated rest (CON) or CWI at 15 °C. The knee proprioception, oxygenated cerebral hemoglobin concentrations (Δ[HbO]), and muscle activation during the proprioception test, physiological and perceptual responses were measured. CWI did not have a significant effect on proprioception at the post-intervention but attenuated the reductions in Δ[HbO] in the primary sensory cortex and posterior parietal cortex (p < 0.05). The root mean square of vastus medialis was higher in the CWI compared to the CON. CWI effectively reduced core temperature and mean skin temperature and improved the rating of perceived exertion and thermal sensation. These results indicated that 10 min of CWI at 15 °C post-exercise had no negative effect on the neuromuscular control of the knee joint but could improve subjective perception and decrease body temperature.

Effects of skin and mild core cooling on cognitive function in cold air in men.

This study tested the effects of skin and core cooling on cognitive function in 0°C cold air. Ten males completed a randomized, repeated measures study consisting of four environmental conditions: (i) 30 min of exposure to 22°C thermoneutral air (TN), (ii) 15 min to 0°C cold air which cooled skin temperature to ~27°C (CS), (iii) 0°C cold air exposure causing mild core cooling of ∆-0.3°C from baseline (C-0.3°C) and (iv) 0°C cold air exposure causing mild core cooling of ∆-0.8°C from baseline (C-0.8°C). Cognitive function (reaction time [ms] and errors made [#]) were tested using a simple reaction test, a two-six item working memory capacity task, and vertical flanker task to assess executive function. There were no condition effects (all p > 0.05) for number of errors made on any task. There were no significant differences in reaction time relative to TN for the vertical flanker and item working memory capacity task. However, simple reaction time was slower in C-0.3°C (297 ± 33 ms) and C-0.8°C (296 ± 41 ms) compared to CS (267 ± 26 ms) but not TN (274 ± 38). Despite small changes in simple reaction time (~30 ms), executive function and working memory was maintained in 0°C cold air with up to ∆-0.8°C reduction in core temperature.

Brief ambient cooling preserves autophagy in peripheral blood mononuclear cells from older adults during 9 hours of heat exposure.

Heat waves can cause dangerous elevations in body temperature that can compromise cellular function and increase the risk of heat stroke and major cardiovascular events. Visiting a cooling center or other air-conditioned location is commonly recommended by health agencies to protect heat-vulnerable older persons but the associated cellular effects remain underexplored. We evaluated cellular stress responses in peripheral blood mononuclear cells (PBMC) from 19 older adults (71 [SD 2] years; 9 females) before and after a 9-hour heat exposure (40.3°C and 9.3% relative humidity [RH]), with exposure to a cool room (~23°C) for hours 5 and 6 (cooling group). Responses were compared to 17 older adults (72 [4] years; 7 females) who remained in the heat for the entire 9 hours (control group). Changes in proteins associated with autophagy, apoptotic signaling, acute inflammation, and the heat shock response (HSR) were assessed via Western blot. While both groups experienced similar elevations in physiological strain prior to the cooling center intervention, brief cooling resulted in stark albeit transient reductions in core temperature and heart rate. At the end-exposure, autophagy proteins LC3-II and p62 were elevated 1.9-fold [95% CI: 1.2, 2.8] and 2.3-fold [1.4, 3.8], respectively, in the control group relative to cooling group. This was paired with a 2.8-fold [1.6, 4.7] greater rise in apoptotic protein cleaved-caspase-3 in the control group compared to the cooling group. Our findings indicate that 2-hours of ambient cooling midway through a 9-hour simulated heat wave may preserve autophagy and mitigate heat-induced cellular stress in older adults.

Metabolic Manipulation and Therapeutic Hypothermia.

Hypothermia has multiple physiological effects, including decreasing metabolic rate and oxygen consumption (VO2). There are few human data about the magnitude of change in VO2 with decreases in core temperature. We aimed to quantify to magnitude of reduction in resting VO2 as we reduced core temperature in lightly sedated healthy individuals. After informed consent and physical screening, we cooled participants by rapidly infusing 20 mL/kg of cold (4°C) saline intravenously and placing surface cooling pads on the torso. We attempted to suppress shivering using a 1 mcg/kg intravenous bolus of dexmedetomidine followed by titrated infusion at 1.0 to 1.5 μg/(kg·h). We measured resting metabolic rate VO2 through indirect calorimetry at baseline (37°C) and at 36°C, 35°C, 34°C, and 33°C. Nine participants had mean age 30 (standard deviation 10) years and 7 (78%) were male. Baseline VO2 was 3.36 mL/(kg·min) (interquartile range 2.98-3.76) mL/(kg·min). VO2 was associated with core temperature and declined with each degree decrease in core temperature, unless shivering occurred. Over the entire range from 37°C to 33°C, median VO2 declined 0.7 mL/(kg·min) (20.8%) in the absence of shivering. The largest average decrease in VO2 per degree Celsius was by 0.46 mL/(kg·min) (13.7%) and occurred between 37°C and 36°C in the absence of shivering. After a participant developed shivering, core body temperature did not decrease further, and VO2 increased. In lightly sedated humans, metabolic rate decreases around 5.2% for each 1°C decrease in core temperature from 37°C to 33°C. Because the largest decrease in metabolic rate occurs between 37°C and 36°C, subclinical shivering or other homeostatic reflexes may be present at lower temperatures.

Efficacy of Cooling Centers for Mitigating Physiological Strain in Older Adults during Daylong Heat Exposure: A Laboratory-Based Heat Wave Simulation.

Health agencies, including the U.S. Centers for Disease Control and Prevention and the World Health Organization, recommend that heat-vulnerable older adults without home air-conditioning should visit cooling centers or other air-conditioned locations (e.g., a shopping mall) during heat waves. However, experimental evidence supporting the effectiveness of brief air-conditioning is lacking. We evaluated whether brief exposure to an air-conditioned environment, as experienced in a cooling center, was effective for limiting physiological strain in older adults during a daylong laboratory-based heat wave simulation. Forty adults 64-79 years of age underwent a 9-h simulated heat wave (heat index: 37°C) with (cooling group, ) or without (control group, ) a cooling intervention consisting of 2-h rest in an air-conditioned room (, hours 5-6). Core and skin temperatures, whole-body heat exchange and storage, cardiovascular function, and circulating markers of acute inflammation were assessed. Core temperature was 0.8°C (95% CI: 0.6, 0.9) lower in the cooling group compared with the control group at the end of the cooling intervention (; hour 6), and it remained 0.3°C (95% CI: 0.2, 0.4) lower an hour after returning to the heat (; hour 7). Despite this, core temperatures in each group were statistically equivalent at hours 8 and 9, within (). Cooling also acutely reduced demand on the heart and improved indices of cardiovascular autonomic function (); however, these outcomes were not different between groups at the end of exposure (). Brief air-conditioning exposure during a simulated heat wave caused a robust but transient reduction in core temperature and cardiovascular strain. These findings provide important experimental support for national and international guidance that cooling centers are effective for limiting physiological strain during heat waves. However, they also show that the physiological impacts of brief cooling are temporary, a factor that has not been considered in guidance issued by health agencies. https://doi.org/10.1289/EHP11651.

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest.

Physical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min-1), and forty-two datasets reported reducing core temperature (-0.002 to -0.070 °C min-1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of -0.004 °C min-1 (-0.032 to +0.013 °C min-1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.

Physiological And Thermoregulatory Responses Of Body Cooling During Cycling In A Hot Environment

Rapid cooling techniques are essential for populations that are active in the heat. In attempt to reduce overheating, the vasomotor reflex increases blood flow to the skin for radiative heat loss, causing peripheral vasodilation. Cooling of the extremities can be a strategy to reduce core temperature (Tc) due to their large surface area and the increased blood flow during elevations of Tc. PURPOSE: To examine the effects of four hand-cooling methods on physiological strain following two interval blocks of cycling in the heat. METHODS: Twelve participants [mean ± SD; age, 24 ± 4 years; maximal oxygen consumption; 44.5 ± 6.4 ml/kg/min; body mass, 75.7 ± 8.2 kg; height, 177.3 ± 8.4 cm] performed two 40-min blocks of cycling at 6 Watts per kilogram of body mass (W/kg) to 15 W/kg in the heat (36 °C, 30 °C relative humidity). Metabolic heat production (Hprod) was used to prescribe this exercise intensity. Each 40-min exercise block was followed by 20-min of cooling. Participants completed four trials on four separate days that included four different cooling modalities during the rest block: 1) hand mist-fan cooling (FAN), 2) forearm ice-water immersion (IMM), 3) forearm ice-towel cooling (TOW), and 4) passive cooling (PAS). Heart rate (HR) and rectal temperature (Tc) were measured throughout each trial. Repeated measures analysis of variance (ANOVA) tests were used to identify differences between experimental groups. Statistical significance was set at p ≤ 0.05. RESULTS: There were no differences between the three cooling modalities compared to passive cooling for Tc and HR. There were no significant differences between HR and Tc at any time points from block 1 and 2 of exercise. CONCLUSION: The cooling modalities FAN, IMM, and TOW provided no additional cooling benefits on Tc and HR compared to PAS. Populations that are exposed to environmental heat-stress should consider alternative cooling strategies or mixed methods cooling modalities that will improve heat loss and attenuate Tc.

Supplementation with artificial sweetener and capsaicin alters metabolic flexibility and performance in heat-stressed and feed-restricted pigs.

Substantial economic losses in animal agriculture result from animals experiencing heat stress (HS). Pigs are especially susceptible to HS, resulting in reductions in growth, altered body composition, and compromised substrate metabolism. In this study, an artificial high-intensity sweetener and capsaicin (CAPS-SUC; Pancosma, Switzerland) were supplemented in combination to mitigate the adverse effects of HS on pig performance. Forty cross-bred barrows (16.2 ± 6 kg) were assigned to one of five treatments: thermal neutral controls (TN) (22 ± 1.2 °C; 38%-73% relative humidity) with ad libitum feed, HS conditions with ad libitum feed with (HS+) or without (HS-) supplementation, and pair-fed to HS with (PF+) or without supplementation (PF-). Pigs in heat-stressed treatments were exposed to a cyclical environmental temperature of 12 h at 35 ± 1.2 °C with 27%-45% relative humidity and 12 h at 30 ± 1.1 °C with 24%-35% relative humidity for 21 d. Supplementation (0.1 g/kg feed) began 7 d before and persisted through the duration of environmental or dietary treatments (HS/PF), which lasted for 21 d. Rectal temperatures and respiration rates (RR; breaths/minute) were recorded thrice daily, and feed intake (FI) was recorded daily. Before the start and at the termination of environmental treatments (HS/PF), a muscle biopsy of the longissimus dorsi was taken for metabolic analyses. Blood samples were collected weekly, and animals were weighed every 3 d during treatment. Core temperature (TN 39.2 ± 0.02 °C, HS- 39.6 ± 0.02 °C, and HS+ 39.6 ± 0.02 °C, P < 0.001) and RR (P < 0.001) were increased in both HS- and HS+ groups, but no difference was detected between HS- and HS+. PF- pigs exhibited reduced core temperature (39.1 ± 0.02 °C, P < 0.001), which was restored in PF+ pigs (39.3 ± 0.02 °C) to match TN. Weight gain and feed efficiency were reduced in PF- pigs (P < 0.05) but not in the PF+ or the HS- or HS+ groups. Metabolic flexibility was decreased in the HS- group (-48.4%, P < 0.05) but maintained in the HS+ group. CAPS-SUC did not influence core temperature or weight gain in HS pigs but did restore core temperature, weight gain, and feed efficiency in supplemented PF pigs. In addition, supplementation restored metabolic flexibility during HS and improved weight gain and feed efficiency during PF, highlighting CAPS-SUC's therapeutic metabolic effects.

Evaluation of Amino Acid Infusion preventive effect on Hypothermia during Spinal Anesthesia for Hip Arthroplasty.

Hypothermia increases bleeding during surgery, risk of ischemic heart disease and postoperative wound infection. Intravenous amino acid increases cell synthesis and produces heat. Our goal was evaluating of the effect of amino acid on intraoperative hypothermia under spinal anesthesia. This is a randomized, double-blinded clinical trial that 36 adults undergoing Hip Arthroplasty were randomly assigned into two groups of 18 each. One group received Amino Acids solution (Aminoven 10%) 500ml (240ml/h) throughout spinal anesthesia, and control group received saline solution. We measured core body temperature, MAP and HR each 10 minutes, and also postoperative shivering, blood loss, operation time, postoperative BUN and Cr were compared in two groups. Throughout surgery, the reduction in core temperature was more in the control group than the amino acids group (statistically not clinically). The decrease in core temperature was significantly larger in the controls (0.96°C ± 0.7°C) than in the amino acid patients (0.94°C ± 0.4°C), (P value= 0.02). Postoperative shivering was 73% in the controls regarding 11% in the amino acids patients. Overall, there were no significant statistical differences between other variables that we measured in two groups of patients. Amino acids infusion during spinal anesthesia exerted a thermogenic effect. Our findings showed hypothermia was less in the aminoacid group, and also postoperative shivering was more in the control group.

A coupled CFD-thermoregulation model for air ventilation clothing

The present work explains a coupled CFD-thermoregulation model developed for the air ventilation clothing to predicts its performance. The coupled model predicts heat transfer coefficients for various torso segments of the human body using a 3D CFD model and then uses these heat transfer coefficients as input parameters to the JOS-3 thermoregulation model to determine physiological responses such as skin and core temperatures, by numerically simulating heat exchange within the body and that between the body and the environment. Based on local boundary conditions which represent both ambient conditions and individual characteristics, the coupled model can be used to analyze local and overall thermal comfort. The coupled model can analyze the performance of air ventilation clothing without conducting human trials or manikin experiments, which saves time, effort, and resources. Human trials are conducted, and the developed coupled model is validated with experimental data under different scenarios. It is observed that the developed coupled model can provide reliable value and trend of the human physiological responses in terms of mean skin, mean torso and core temperatures. Further, the developed and validated coupled model is used to analyze performance of the air ventilation clothing under different climatic conditions and activity levels under three different clothing setting [control with fan OFF (CON), low air flow rate (LV) and high air flow rate (HV)]. Maximum reductions in the mean torso, mean skin, and core temperatures, in case of HV is found to be 3.4 °C, 1.3 °C, and 0.3 °C, respectively, as compared to the CON case in all set of climate conditions and activity level studied in present work. At a moderate activity level (3.2 MET), the air ventilation clothing with HV can reduce core temperature by 0.2 °C in temperate (27 °C, 50%), hot-dry (36 °C, 30%), and hot-humid (38 °C, 45%) climate conditions. Further, it is observed that in case of an intermittent working situation (environmental condition: 45 °C, 10% RH), overall working duration can be increased by 18 min in case of HV as compared to the CON case.

Can Finnish Sauna Bathing Induce Heat Acclimation in Adults with Stable Coronary Artery Disease?

IntroductionExtreme heat is associated with a greater risk of mortality that particularly affects older adults with cardiovascular disease (CVD). Regular heat exposure induces an adaptation of thermoregulatory mechanisms (acclimation) that may alleviate thermal and/or cardiac strain during subsequent heat exposure. However, limited research has examined practical heat acclimation protocols that could be recommended to vulnerable populations, such as adults with CVD. The objective of this study was to test the hypothesis that 8 weeks of Finnish sauna bathing reduces core temperature and heart rate and increases sweating during heat exposure.Method14 participants (11 men/3 women, 63 ± 5 years, 28.7 ± 3.8 kg/m2) with stable coronary artery disease participated in an 8‐week Finnish sauna intervention (4 sessions/week, 20 to 30 min/session, at ~80°C, 20% humidity). Core temperature (ingestible telemetric pill), heart rate (Polar watch), and sweat rate (change in nude body weight) were measured during the first and last sauna sessions.ResultsResting core temperature prior to the first sauna session was 37.4 ± 0.4°C, compared to 37.1 ± 0.3°C prior to the last session (p= 0.04). Core temperature at the end of sauna bathing did not differ between the first (37.77 ±0.34°C) and the last (37.59 ± 0.31°C, p=0.20) sessions. Heart rate at the end of sauna bathing was greater during the last (90 ± 17 bpm) compared to first (85 ± 16 bpm, p=0.13) sessions. Sweat rate was greater during the last sauna session (first session: 8.6 ± 5.9 mL/min vs. last session: 5.1 ± 3.0 mL/min, p&lt;0.01).ConclusionEight weeks of Finnish sauna bathing reduces resting core temperature and increases sweat rate during heat exposure in adults with stable coronary artery disease. However, these adaptations did not translate into reduced thermal and cardiac strain during heat exposure.

The distributed temperature abatement by the phase changing materials for battery in electric tools and its influence on aging

Battery thermal management system is of great importance, and there are numerous methods at present. Due to spatial efficiency, phase-change materials are particularly welcomed in applying electric tools where extremely high current (10–15 C) and temperature (40 °C) are typical. However, the C-rate and environmental temperature in many studies are not large enough to meet this need. In this study, Samsung 18,650 20R NCM batteries with wrapping storage materials are taken as the research object. This study explores the temperature distribution from the battery core to the surface at high environmental temperature (40 °C) and large discharging current (15 C). The proposed model and its predicted temperature results are validated with experimental data. The results indicate that the full-discharged battery's surface temperature decreases by 18.60 °C compared with the naked battery (103.78 °C) when 2 mm PCMs are applied (85.17 °C). In contrast, the core temperature reduction is much lower, only from 139.70 °C to 133.29 °C, causing the radical temperature difference to rise from 35.92 °C to 48.12 °C. The significant temperature difference and high internal temperature are that the heat generation rate exceeds the rate of heat conductivity at high temperatures and large currents. The study further evaluates the effects of internal high temperature on the battery lifetime at electric tools' working conditions. The single discharge capacity of batteries with 2 mm PCMs is approximately 80–100 % more than that of the naked batteries, while the capacity of the former fades 90–250 % faster than the latter.

The Effect of Aging on Body Temperature: A Systematic Review and Meta- Analysis.

Since age is the major risk factor for chronic diseases and mortality, it seems mistaken that older adults have lower basal temperature than young individuals. Many confounding factors could hinder the achievement of a consensus, such as the different sites of measurement, control of basal conditions, health conditions, age difference compared, sex, and others. The aim was to meta-analyze previous studies in order to find a consensus regarding the effects of aging on body temperature in humans, considering different types of temperature assessments, age difference and sex. A systematic search was performed in PubMed and 16 studies comparing basal temperature between older and young adults were meta-analyzed. Older adults have significantly lower body temperature than young adults (-0.17 °C (-0.30; -0.03), p=0.04). Considering the different sites of measure, while core temperature tended to be lower in older adults (-0.13 °C (-0.27; 0.01), p=0.07), and skin temperature was not different (-0.21 °C (-0.5; 0.08), p=0.15). The aging effects were more prominent in men when assessed by oral temperature and when compared between higher age difference. Indeed, there is a small reduction in overall temperature with aging, drove by the reduction in core temperature rather than skin temperature. The confirmation of these findings by this meta-analysis, now provide the base for the development of strategies to face the impairment in thermoregulation and metabolic efficiency with aging.

WaFFLe

Managing thermal imbalance in contemporary chip multi-processors (CMPs) is crucial in assuring functional correctness of modern mobile as well as server systems. Localized regions with high activity, e.g., register files, ALUs, FPUs, and so on, experience higher temperatures than the average across the chip and are commonly referred to as hotspots. Hotspots affect functional correctness of the underlying circuitry and a noticeable increase in leakage power, which in turn generates heat in a self-reinforced cycle. Techniques that reduce the severity of or completely eliminate hotspots can maintain functional correctness along with improving performance of CMPs. Conventional dynamic thermal management targets the cores to reduce hotspots but often ignores caches, which are known for their high leakage power consumption. This article presents WaFFLe , an approach that targets the leakage power of the last-level cache (LLC) and hotspots occurring at the cores. WaFFLe turns off LLC-ways to reduce leakage power and to generate on-chip thermal buffers. In addition, fine-grained DVFS is applied during long LLC miss induced stalls to reduce core temperature. Our results show that WaFFLe reduces peak and average temperature of a 16-core based homogeneous tiled CMP with up to 8.4 ֯ C and 6.2 ֯ C, respectively, with an average performance degradation of only 2.5 %. We also show that WaFFLe outperforms a state-of-the-art cache-based technique and a greedy DVFS policy.

1155-P: Neurocircuits Controlling Adaptive Thermogenesis Rely on Skin Detection of External Temperatures through Calcitonin Gene-Related Peptide Expressing Spinal Neurons

Heat-sensory neurons arising from the dorsal root ganglia (DRG) play a pivotal role in the detection of cutaneous temperature and transmission of external signals to the brain, ensuring the maintenance of thermoregulation. However, whether these thermoreceptor neurons contribute to adaptive thermogenesis has remained elusive. We show that genetic ablation of heat sensing Calcitonin Gene-Related Peptide α (CGRPα) neurons promotes resistance to weight gain upon high fat diet (HFD) feeding and increases energy expenditure in mice. Mechanistically, we find that loss of CGRPα-expressing sensory neurons is associated with reduced lipid deposition in adipose tissue, enhanced expression of fatty-acid oxidation genes, higher ex-vivo lipolysis in primary white adipocytes and enhanced mitochondrial respiration from iBAT. Remarkably, mice lacking CGRPα sensory neurons manifest increased tail cutaneous vasoconstriction at room temperature. This exacerbated cold perception was not associated with reduced core temperature, suggesting that heat production and heat conservation mechanisms are engaged. Specific denervation of CGRPα neurons in intrascapular BAT did not contribute to the increased metabolic rate observed upon global sensory denervation. Taken together, these findings highlight an important role for cutaneous thermoreceptors in regulating energy metabolism, by triggering counter-regulatory responses involving energy dissipation processes including lipid fuel utilization and cutaneous vasodilation. Disclosure C. Riera: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-15-INI-12 to C.R.)

Temperature Regulation during Cold Water Immersion is Modified by Normobaric Hypoxia

Purpose Indigenous diving populations and recreational breath-hold divers often develop hypoxia while diving in cold water. Hypoxia may delay the onset and reduce magnitude of shivering during cold exposure. It is unclear if these hypoxia-induced alterations in the control of shivering reduce total energy expenditure, a function of both shivering and non-shivering thermogenesis, and/or modify the ability to maintain core temperature during cold water immersion. Therefore, this study tested the hypothesis that normobaric hypoxia decreases total energy expenditure and results in a greater decrease in core temperature during one hour of head out cold water immersion. Methods In a randomized crossover design, 6 healthy adults (27 ± 2 y, 1 woman) completed one hour of head out cold (22°C) water immersion breathing either normobaric normoxia (FiO2 = 0.21) or normobaric hypoxia (FiO2 = 0.13). Data were collected for 10 minutes prior to water immersion (baseline) and during water immersion. Energy expenditure was estimated from oxygen consumption (V̇O2) and respiratory exchange ratio (RER) measured via indirect calorimetry. Arterial oxyhemoglobin saturation (SpO2) was estimated using pulse oximetry on the forehead. Rectal temperature was used to estimate core temperature. Brown adipose tissue activation was estimated by measuring bilateral supraclavicular skin temperature. In a subset of subjects (n = 2) skin temperature was measured bilaterally on the back over the trapezius muscle, to confirm the unique profile of changes in supraclavicular skin temperature. Data during cold water immersion were compared relative to the last two-minutes of baseline and integrated throughout water immersion (60 minutes). Data are presented as mean ± SD. Results During water immersion, SpO2 was lower in hypoxia (90 ± 3%) compared to normoxia (98 ± 2%, P < 0.01). Baseline rectal temperature was not different between hypoxia (37.3 ± 0.2°C) and normoxia (37.4 ± 0.2°C, P = 0.52). At the end of water immersion, rectal temperature in hypoxia (36.6 ± 0.4°C) was lower than in normoxia (36.9 ± 0.3°C, P < 0.01). No differences in the total increase above baseline during water immersion were observed in V̇O2 (Hypoxia: 28.3 ± 7.2L; Normoxia: 29.5 ± 6.8 L, P = 0.74) or energy expenditure (Hypoxia: 191 ± 69 KJ·min; Normoxia: 143 ± 81 KJ·min, P = 0.32) between trials. Supraclavicular skin temperature increased with water immersion (P < 0.01), while back skin temperature decreased (P = 0.02). No differences were observed in the total increase from baseline in supraclavicular skin temperature (Hypoxia: 66.6 ± 30.3°C·min; Normoxia: 66.1 ± 35.3°C·min, P = 0.54) or total decrease from baseline in back skin temperature (Hypoxia: -42.3 ± 30.8°C·min; Normoxia: -56.6 ± 7.9 °C·min, P = 0.14). Conclusions These preliminary findings support that, compared to normoxia, normobaric hypoxia promotes a greater reduction in core temperature during one hour of head out cold water immersion. The mechanism(s) underlying this observation remains unclear as no differences in energy expenditure and brown adipose tissue activation were observed, but alterations in cutaneous blood flow cannot be excluded.

Sensory neurons expressing calcitonin gene-related peptide α regulate adaptive thermogenesis and diet-induced obesity

ObjectivesHeat-sensory neurons from the dorsal root ganglia (DRG) play a pivotal role in detecting the cutaneous temperature and transmission of external signals to the brain, ensuring the maintenance of thermoregulation. However, whether these thermoreceptor neurons contribute to adaptive thermogenesis remains elusive. It is also unknown whether these neurons play a role in obesity and energy metabolism. MethodsWe used genetic ablation of heat-sensing neurons expressing calcitonin gene-related peptide α (CGRPα) to assess whole-body energy expenditure, weight gain, glucose tolerance, and insulin sensitivity in normal chow and high-fat diet-fed mice. Exvivo lipolysis and transcriptional characterization were combined with adipose tissue-clearing methods to visualize and probe the role of sensory nerves in adipose tissue. Adaptive thermogenesis was explored using infrared imaging of intrascapular brown adipose tissue (iBAT), tail, and core temperature upon various stimuli including diet, external temperature, and the cooling agent icilin. ResultsIn this report, we show that genetic ablation of heat-sensing CGRPα neurons promotes resistance to weight gain upon high-fat diet (HFD) feeding and increases energy expenditure in mice. Mechanistically, we found that loss of CGRPα-expressing sensory neurons was associated with reduced lipid deposition in adipose tissue, enhanced expression of fatty acid oxidation genes, higher exvivo lipolysis in primary white adipocytes, and increased mitochondrial respiration from iBAT. Remarkably, mice lacking CGRPα sensory neurons manifested increased tail cutaneous vasoconstriction at room temperature. This exacerbated cold perception was not associated with reduced core temperature, suggesting that heat production and heat conservation mechanisms were engaged. Specific denervation of CGRPα neurons in intrascapular BAT did not contribute to the increased metabolic rate observed upon global sensory denervation. ConclusionsTaken together, these findings highlight an important role of cutaneous thermoreceptors in regulating energy metabolism by triggering counter-regulatory responses involving energy dissipation processes including lipid fuel utilization and cutaneous vasodilation.

Impact of a 10,000-m Cold-Water Swim on Norwegian Naval Special Forces Recruits.

Special Operation Forces (SOF) operate regularly in extreme environmental conditions that may affect tactical and physical performance. The main aims of the present study were to elucidate the impact of a long cold-water swim on SOF recruits' dexterity, performance, and reaction time. Eleven recruits from Norwegian Naval Special Operation Command (NORNAVSOC) that were participating in a 10,000-m open water swim with a dry suit in 5°C cold water volunteered to participate in this study. The exercise was part of their training. Grip strength, lower body power, and dexterity were measured before, immediately after, and 24 hours after the swim. In addition, core and skin temperatures were measured continuously during the swim and until 45 minutes after the swim. After the swim, moderate to large reductions in core temperature, lower body power, and reaction time were observed. Moreover, very large to extremely large reductions in skin temperature, grip strength, and dexterity were also observed. These results demonstrate that exposure to a 10,000-m swim in 5°C water using standard equipment led to a significant drop in the recruits' temperature and performance. These findings could have a meaningful impact on the planning of training, operations, and gear used for SOF.