Elevated Core Temperature Research Articles

Estimation of heat-related morbidity from weather data: A computational study in three prefectures of Japan over 2013–2018

In recent years, the rates of heat-related morbidity and mortality have begun to increase with the increase in global warming; in this context, it is noteworthy that the number of patients transported by ambulance in heat-related cases in Japan reached 95,137 in 2018. The estimation of heat-related morbidity forms a key factor in proposing and implementing suitable intervention strategies and ambulance availability and arrangements. Heat-related morbidity is known to be fairly correlated to metrics related to ambient conditions, thus necessitating the exploration of new metrics to more accurately estimate morbidity. In this study, we use an integrated computational technique relating to thermodynamics and thermoregulation to estimate daily peak core temperature elevation and daily water loss, which are linked to heat-related illnesses, from weather data of three different prefectures in Japan (Tokyo, Osaka, and Aichi). The correlations of the computed core temperature elevation and water loss as well as conventional ambient conditions are investigated in terms of number of patients suffering from heat-related illnesses transported by ambulance from 2013 to 2018. The estimated water loss per the proposed computation yields better correlation with the number of patients transported by ambulance. In particular, the weight-sum daily water loss for two to three successive days is found to be an important metric for predicting the number of patients transported by ambulance. For the same ambient conditions, morbidity is found to decrease to 0.4 owing to heat adaption at the end of summer (60 days) as compared with that at the end of the rainy season. Thus, the weighted sum of water loss and daily average ambient temperature for successive days can be used as better metrics than conventional weather data for the application of intervention strategies and planning of ambulance arrangements for heat-related morbidity.

Is core temperature the trigger of a menopausal hot flush?

Menopausal hot flushes negatively impact quality of life and may be a biomarker of cardiovascular and metabolic disease risk; therefore understanding the physiology of hot flushes is important. Current thinking is that a small elevation (∼0.03-0.05C) in core temperature surpasses a sweating threshold (that is reduced in the menopause), sweating is activated, and a hot flush ensues. Nevertheless, more recent studies examining thermoregulatory control question whether core temperature per se can explain the trigger for a hot flush. The primary aim of this study was to assess the contribution of increases in core temperature on the occurrence of menopausal hot flushes. For this purpose, 108 hot flushes were objectively assessed in a laboratory setting in 72 symptomatic postmenopausal women (aged 45.8 ± 5.1 years; body mass index 25.9 ± 4.5 kg/m) from five previously reported studies. Women rested, wearing a tube-lined suit (or trousers), which was perfused with 34C water. A subset then underwent mild heat stress (48°C water). Sweat rate, skin blood flow, blood pressure, heart rate, skin, and core temperature were measured continuously throughout. A hot flush was objectively identified during rest (spontaneous hot flush) or mild heating as an abrupt increase in sternal sweat rate. Further, a subset of symptomatic postmenopausal women (n = 22) underwent whole-body passive heating for 60 minutes to identify core temperature thresholds and sensitivities for sweat rate and cutaneous vasodilation, which were compared to a subset of premenopausal women (n = 18). Data were analyzed using t tests and/or general linear modeling, and are presented as mean (95% confidence interval). In the 20 minutes before a spontaneous hot flush, core temperature increased by 0.03 ± 0.12C (P < 0.05), but only 51% of hot flushes were preceded by an increase in core temperature. During mild heating, 76% of hot flushes were preceded by an increase in core temperature. The temperature thresholds for sweating were similar, but the vasodilatory threshold was higher in postmenopausal compared with premenopausal women (37.1 ± 0.2 vs 36.8 ± 0.3°C; P = 0.06). We provide new evidence that menopausal hot flushes are unlikely triggered by an increase in core temperature. These findings provide important information about the physiology of hot flushes that have implications for treatment and management options for menopausal hot flushes.

Calcium Supplementation Alleviates High-Fat Diet-Induced Estrous Cycle Irregularity and Subfertility Associated with Concomitantly Enhanced Thermogenesis of Brown Adipose Tissue and Browning of White Adipose Tissue.

Obesity has been demonstrated as a disruptor of female fertility. Our previous study showed the antiobesity effects of calcium on HFD-fed male mice. However, the role of calcium in alleviating reproductive dysfunction of HFD-fed female mice remains unclear. Here, we found that HFD led to estrus cycle irregularity (longer cycle duration and shorter estrus period) and subfertility (longer conception time, lower fertility index, and less implantations) in mice. However, the HFD-induced reproductive abnormality was alleviated by calcium supplementation. Additionally, calcium supplementation enhanced activation/thermogenesis of BAT and browning of WAT in HFD-fed mice. Consequently, the abnormality of energy metabolism and glucose homeostasis induced by HFD were improved by calcium supplementation, with elevated metabolic rates and core temperature. In conclusion, these data showed that calcium supplementation alleviated HFD-induced estrous cycle irregularity and subfertility associated with concomitantly enhanced BAT thermogenesis and WAT browning, suggesting the potential application of calcium in improving obesity-related reproductive disorders.

Different thermoregulatory responses of people from tropical and temperate zones: A computational study

Long-term heat acclimation in the tropics is a well-known positive response to cope with heat stress. A computational model of thermoregulatory responses from the population in the tropics has not yet been developed. This is partially because only a limited number of comparisons between the thermoregulation of people from different regions have been reported.Our group developed an integrated computational code of thermodynamics and thermoregulatory responses (blood flow and sweating rate) with anatomical human models. We explored parameters in the conventional formula of the thermoregulatory response model to consider the population from the tropics.A comparison of the computed core and local temperatures with those measured in previous studies suggests that the difference in thermoregulatory characteristics between populations from the tropical and temperate zones is mainly characterized by the difference in the countercurrent coefficient of blood, in addition to sweating rate. The estimated core temperature elevation in male adults from a tropical zone is 60% of the temperature of adults from temperate zones for low relative humidity. However, the difference becomes marginal for relatively high humidity, including the case for walking in an urban area of Tokyo, summer 2017, because the effect of the evaporative heat loss becomes marginal.The difference in thermoregulatory responses of people from tropical and temperate zones can be modeled by the core-to-limbs heat transfer and the sweating rate. The computational model developed here is useful to discuss the differences between heat-related illness and thermal comfort of the population in the tropical and temperate zones.

PENINGKATAN HIGH-SENSITIVE CARDIAC TROPONIN (HS-CTN) SETELAH LATIHAN INTENSITAS TINGGI YANG INTENSIF

ABSTRACTThe role of exercise as a strategy for prevention, management and therapy in cardiovascular disease has been well described, but in some studies, it has been suggested that there is an increase in biomarkers in cardiac damage or cardiac troponin (cTn) after intensive, high-intensity exercise in healthy individuals. Several studies have shown significant increases in cardiac troponins after different types of exercise. The latest meta-analysis, showing that high-sensitivity cardiac troponin (hs-cTn) increases in about 83% of individuals after long and intensive exercise. The current pathophysiology of hs-cTn is not well understood. Several hypotheses have been proposed, such as transmembrane leakage from cytoplasmic free cTnT and cTnI or decreased troponin clearance from plasma, both caused by overloading of free radicals, myocardial stretching, elevated core temperature, or alteration of pH. Further research is needed with a full prospective study to evaluate the underlying pathophysiology of enhancing high sentivity cardiac troponin (hs-cTn) is an effective strategy for preventing or limiting cardiac injury and sport exercise safe for heart.Keywords: cardiac Troponin (cTn), high sensitivity cardiac troponin (hs-cTn), high intensity intensive exercise

Thermal Behavior Differs between Males and Females during Exercise and Recovery.

This study tested the hypothesis that females rely on thermal behavior to a greater extent during and after exercise, relative to males. In a 24°C ± 1°C; (45% ± 10% RH) environment, 10 males (M) and 10 females (F) (22 ± 2 yr) cycled for 60 min (metabolic heat production: M, 117 ± 18 W·m; F, 129 ± 21 W·m), followed by 60-min recovery. Mean skin and core temperatures, skin blood flow and local sweat rates were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom-made device. Neck device temperature provided an index of thermal behavior and mean body temperature provided an index of the stimulus for thermal behavior. Data were analyzed for total area under the curve for exercise and recovery time points. To further isolate the effect of exercise on thermal behavior during recovery, data were also analyzed the minute mean body temperature returned to preexercise levels within a subject. There were no sex differences in metabolic heat production (P = 0.71) or body temperatures (P ≥ 0.10) during exercise. Area under the curve for neck device temperature during exercise was greater for F (-98.4°C·min ± 33.6°C·min vs -64.5°C·min ± 47.8°C·min, P = 0.04), but did not differ during recovery (F, 86.8°C·min ± 37.8°C·min; M, 65.6°C·min ± 35.9°C·min; P = 0.11). In M, mean skin (P = 0.90), core (P = 0.70) and neck device (P = 0.99) temperatures had recovered by the time that mean body temperature had returned to preexercise levels. However, in F, neck device temperature (P = 0.04) was reduced while core temperature remained elevated (P < 0.01). Females use thermal behavior during exercise to a greater extent than M. During recovery, thermal behavior may compensate for elevated core temperatures in F despite mean body temperatures returning to preexercise levels.

Heating-induced contraction in airways smooth muscle: A possible causative factor of exercise-induced bronchoconstriction

Asthmatic patients often suffer from bronchoconstriction or asthma following breathing hot air or exposure to exercise due to raises the core body temperature. However, the direct effect of heating airways has not been studied yet. The aim of this study is to investigate the effect of heating on tracheal and bronchiolar smooth muscles. Isolated ovine tracheal strips and bronchiolar segments preparations were suspended in organ baths containing Krebs’ solution for isometric tension recording. Tissues responses were examined during decreasing and elevating baths temperature (20 °C, 40 °C–45 °C and 50 °C). Cooling or heating induced rapid and reproducible contractions proportional with decreasing or increasing temperature respectively in tracheal and bronchiolar preparations. On reset to 37 °C the tone returned rapidly to basal level. Changing the bath’s temperature from 37 °C to 20 °C or to 40 °C and 45 °C for tracheal strips or to 45 °C and 50 °C for bronchiolar segments induced contractions in both preparations. Changing the temperature below or above the normal body temperature (37 °C), leads to airways contractions. Heating induced contractions in tracheal and bronchiolar smooth muscle proportional to the heating temperature. Therefore, breathing hot air or elevation of body core temperature due to exercise can be considered possible causative factor of heating- or exercise-induced bronchoconstriction.

Risk of heat illness in men and women: A systematic review and meta-analysis

BackgroundHeat illness (HI) is a growing global concern; its incidence has risen dramatically across the world in recent years. The individual factors whereby elevated core temperature produces HI are not well-understood. Given known physiological differences between men and women pertaining to temperature regulation, we hypothesized that women would be at increased risk of HI than men. ObjectivesWe aimed to determine the relative risk of HI in women compared with men through an exhaustive literature review and meta-analysis. MethodsWe search PubMed and Ovid Medline databases from inception to Apr 2017. Search terms included all permutations of sex and heat illness (including heatstroke and exertional heat illness) with no language restrictions. We included adult or adolescent human data reporting comparable male and female HI rates. One reviewer identified and screened titles and abstracts. Two independent reviewers applied eligibility criteria. Disagreements were resolved with a third reviewer. ResultsOf 5888 articles identified by searches, 36 were included in the systematic review and 22 in the meta-analysis. The mean (standard deviation) quality score was 3.31(1.25)/5. Overall the rate among women was consistently lower than men across the lifespan. The male: female pooled IRR was 2.28 (p < 0.001, 95% CI: 1.66–3.16). There was modest heterogeneity (between-studies variance (τ2) = 0.02). The rates did not differ significantly when corrected for severity or occupation. DiscussionThe rate of HI was significantly increased in men compared with women. Risk for HI might be conferred by psychological and behavioral factors rather than physiological ones. Further research is required to delineate which groups are at greatest risk, leading to the development of mitigation strategies against HI. OtherNo funding was received. The authors acknowledge the support of the UK Women in Ground Close Combat Review. The Study was registered with PROSPREO CRD42017064739

Label-free quantitative proteomics of rat hypothalamus under fever induced by LPS and PGE2

Fever is a brain-mediated increase in body temperature mainly during inflammatory or infectious challenges. Although there is considerable data regarding the inflammation pathways involved in fever, metabolic alterations necessary to orchestrate the complex inflammatory response are not totally understood. We performed proteomic analysis of rat hypothalamus using label-free LC–MS/MS in a model of fever induced by lipopolysaccharide (LPS) or prostaglandin E2 (PGE2). In total, 7021 proteins were identified. As far as we know, this is the largest rat hypothalamus proteome dataset available to date. Pathway analysis showed proteins from both stimuli associated with inflammatory and metabolic pathways. Concerning metabolic pathways, rats exposed to LPS or PGE2 presented lower relative abundance of proteins involved in glycolysis, pentose phosphate pathway and tricarboxylic acid cycle. Mitochondrial function may also be altered by both stimuli because significant downregulation of several proteins was found, mainly in complexes I and IV. LPS was able to induce downregulation of important proteins in the enzymatic antioxidant system, thereby contributing to oxidative stress. The results offered comprehensive information about fever responses and helped to reveal new insights into proteins potentially involved in inflammatory signaling and metabolic changes in the hypothalamus during systemic LPS and central PGE2 administration. SignificanceThe evolutionary persistence of fever, despite the elevated cost for maintenance of this response, suggests that elevation in core temperature may represent an interesting strategy for survival. Fever response is achieved through the integrated behavioral, physiological, immunological and biochemical processes that determine the balance between heat generation and elimination. The development of such complex response arouses interest in studying how the cell metabolism responds or even contributes to promote fever. Our results offered comprehensive information about fever responses, including metabolic and inflammatory pathways, providing new insights into candidate proteins potentially involved in inflammatory signaling and metabolic changes in the hypothalamus during fever induced by systemic LPS and central PGE2 perturbation.

Hot water immersion elevates interleukin-6 in persons with cervical spinal cord injury

Core temperature elevations can impact positively on immunity, potentially due to increases of catecholamines acting on immune cells’ adrenergic receptors. The dysfunctional sympathetic nervous system in individuals with cervical spinal cord injury (CSCI) impairs adrenergic responses and may contribute to depressed immunity and the occurrence of low-grade systemic inflammation related disorders. However, some immune markers improve following exercise in CSCI, even though the positive effects are often blunted. Non-exercise induced body temperature manipulations have yet to be investigated in CSCI. Seven male participants with a motor complete CSCI and 8 male able-bodied controls were immersed for 60 min in water set at a temperature 2 C above the individuals’ resting oesophageal temperature. Blood was collected before, during, and every hour up to 4 h after immersion and analyzed for interleukin-6 (IL-6). Hot water immersion increased IL-6 in both groups ( P < 0.001). IL-6 plasma concentrations were higher in CSCI, but it was not significant. Possibly, the reduced active muscle mass in CSCI does not allow for sufficient core temperature elevations during exercise to increase these cytokines. Together with the lower catecholamine levels usually found in CSCI, this may explain the blunted exercise response on some aspects of immunity. This seems especially concerning as higher average levels of IL-6 support the indication of chronic low-grade systemic inflammation in CSCI. This is the first study to show an acute cytokine response induced by hot water immersion in CSCI. Passive elevation of core temperature may help to improve the cytokine profile in CSCI.

Sex Differences in Thermal Behavior During Exercise Recovery

PurposeFemales (F) more rapidly withdraw heat loss thermoeffectors post‐exercise compared to males (M), prolonging elevations in core temperature (Tcore). Thermal behavior may compensate for this response, but it is not known if thermal behavior differs between M and F. We tested the hypothesis that thermal behavior remains engaged post‐exercise for a longer time in F than M.MethodsIn a 24°C (43% RH) environment, 17 adults (9 F, 22 ± 2 y) cycled for 60 min, followed by 60 min seated recovery. Mean skin temperature (Tskin, 10 site), Tcore (intestinal) and mean skin wetness (wskin, 4 site) were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom made fluid filled device. Neck device temperature (Tdevice) provided an index of thermal behavior. A linear regression was performed with Tskin, Tcore, and wskin as independent variables and Tdevice as the dependent variable. Standardized beta coefficients were used to determine the relative contribution of each variable to Tdevice.ResultsMetabolic heat production did not differ between sexes during exercise (M: 133 ± 5, F: 123 ± 8 W/m2, P=0.40). Tskin (P=0.80), Tcore (P=0.97), wskin (P=0.76), and Tdevice (P=0.13) did not differ between sexes during exercise or recovery. During exercise, Tskin increased in F (Pre‐Exercise (PreEx): 29.6 ± 0.7°C; End‐Exercise (EndEx): 30.4 ± 0.6°C, P≤0.02), and decreased in recovery (End‐Recovery (EndRec): 29.7 ± 0.6°C, P≤0.01). Tskin did not change throughout in M (PreEx: 29.5 ± 0.6; EndEx: 30.0 ± 0.8, EndRec: 29.5 ± 0.7°C, P≥0.42). Tcore increased in F (PreEx: 37.3 ± 0.3, EndEx: 38.1 ± 0.2°C, P&lt;0.01) and M (PreEx: 37.0 ± 0.3; EndEx: 37.5 ± 0.3°C, P&lt;0.01) during exercise, remaining elevated until 40 min recovery (F: 37.5 ± 0.2, P=0.20; M: 37.3 ± 0.4°C, P=0.08). wskin increased in F (PreEx: 0.21 ± 0.06; EndEx: 0.25 ± 0.03 a.u., P=0.01) and M (PreEx: 0.17 ± 0.06; EndEx: 0.22 ± 0.05 a.u., P=0.03) during exercise, remaining elevated during recovery (F ‐ EndRec: 0.27 ± 0.04, P&lt;0.01, M ‐ EndRec: 0.21 ± 0.05 a.u., P≤0.03). Tdevice decreased in F (Pre: 27.4 ± 0.9; EndEx: 6.1 ± 6.1°C, P≤0.01) and M (Pre: 27.3 ± 1.5; EndEx: 11.8 ± 10.5°C, P≤0.01) during exercise, returning to PreEx 20 min into recovery (F: 20.1 ± 8.0, P≥0.09; M: 19.1 ± 9.2°C, P≥0.06). During exercise, Tcore (51 ± 25%) contributed to Tdevice more than Tskin in M (13 ± 8%, P=0.05), but neither were different to wskin (36 ± 25%, P≥0.37). In F, Tcore (31 ± 26%), Tskin (35 ± 31%) and wskin (34 ± 24%) contributed equally to Tdevice (P≥0.98). During recovery, Tcore (55 ± 21%) contributed more than Tskin (17 ± 13%, P=0.02) in F, but neither were different to wskin (28 ± 20%, P≥0.15). In M, Tcore (37 ± 35%), Tskin (27 ± 23%) and wskin (36 ± 22%) contributed equally to Tdevice (P≥0.84).ConclusionsThermal behavior during and post‐exercise does not differ between M and F. However, Tcore contributes more to thermal behavior during exercise in M and post‐exercise in F. These findings may be related to temporal differences in Tskin during and following exercise.Support or Funding InformationSupported by lululemon athletica inc.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pre‐race Inflammatory Cytokines Are Not Consistent Predictive Biomarkers of the Magnitude of Post‐race Core Temperature Elevations at the Falmouth Road Race

Exercise in stressful environmental conditions induces multiple independent signaling pathways that result in inflammatory cytokine release. Immune responses that cause and are driven by the systemic release of inflammatory and pyrogenic cytokines contribute to endotoxemia, sepsis, and other immunity‐related exertional heatstroke (EHS) pathophysiology. Our preliminary data from the Falmouth Road Race (FRR, 11.3 km, Falmouth, MA), a race, known to have high incidence (15–20 annually) of EHS, suggest that at least one particular pro‐inflammatory pathway stimulated by circulating lipopolysaccharide (LPS) is robustly upregulated post‐race. In this study, we aimed to test the hypothesis that competing in a high intensity running road race in a hot and humid environment will result in increased cytokine levels that may serve as biochemically downstream predictive measures of an EHS susceptibility marker, core temperature. We recruited 32 (2015), 33 (2016), and 32 (2017) subjects (43±12 years, 174.2±8.6 cm, 72.3±12.6 kg, 17.0±5.1% body fat, 43.49±8.01 mL·kg−1·min−1 VO2max) participating in the FRR. We measured environmental and physiological variables, and acquired venous blood pre (PRE) and immediately post (POST) race. We quantified six different cytokines (IL‐6, IL‐8, IL‐10, IL‐1β, TNF‐α, and IL‐12p70) in anti‐coagulant treated blood plasma (pg·ml−1). ANOVA with Bonferroni post hoc tests and Pearson correlations were calculated to determine statistically significant (p&lt;0.05) differences in cytokine concentration and correlations between cytokine concentrations and POST gastrointestinal temperature (Tgi). POST (vs. PRE) Tgi was elevated significantly each year and for the pooled 3‐year data (mean±SD °C, PRE: 36.97±0.48, POST: 39.55±0.79, p&lt;0.00001). Pooled (3‐year) IL‐6 (mean±SD, PRE: 29.25±17.45), IL‐10 (PRE: 18.54±11.95), and IL‐8 (PRE: 53.99±22.56) were increased at POST (IL‐6: 51.41±44.56, IL‐10: 29.55±22.02, IL‐8: 64.99±28.21). POST (vs. PRE) cytokine responses were consistent within each year (p&lt;0.05) and with pooled, 3‐year data (p&lt;0.0001). Although analysis of individual years suggested that PRE markers such as TNF‐α (p&lt;0.019) and IL‐12p70 (p&lt;0.0066) positively correlated with elevated post race gastrointestinal temperatures, analysis of the pooled 3‐year data revealed that PRE cytokine values are not significantly correlated with POST Tgi. Overall, we observed that resting cytokine levels did not identify any chronic inflammation present in subjects who experienced markedly high POST Tgi or exertional heat illness. Ongoing work will elucidate whether post race cytokine values, relative change in individual cytokine responses, or other mechanisms of inflammatory signaling correlate to exertional heat illness incidence and/or abnormally elevated core temperature.Support or Funding InformationFalmouth Road Race, McNair Scholars Program (UConn), CICATS, KSIThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Potential Role of Structural Variants of Circulating Lipopolysaccharide in Exercise‐Induced Heat Illness

Previous investigations at the Falmouth Road Race (FRR; Falmouth, MA) indicated that combined exercise, heat, and dehydration stress increased gastrointestinal tract permeability. This subsequently exposed the circulatory system to components of the microbiome usually found only in the gut. Lipopolysaccharide (LPS), a component of Gram‐negative bacterial membranes, is one such element released into circulation, especially post‐exercise. LPS in circulation activates host immune cell signaling cascades that can lead to inflammatory responses (e.g. cell pyroptosis, exertional heat stroke, and sepsis) and upregulated proinflammtory gene expression (e.g. TNF‐α and IL‐1β). While subjects of the 2015 FRR (N=30) had elevated core temperature post race compared to pre (pre 36.87°C vs. post 39.87°C, p&lt;0.05), there is unexplained variation in the relationship among the level of circulating LPS (2.90EU/ml pre vs. 3.48EU/ml post, p&lt;0.05; Hycult Biotech, ELISA), core temperature, and subsequent heat stroke presentation. Since some strains of bacteria induce a strong immune response while others do not, it is of interest to determine if structural variations in LPS contribute to varying immune system activation during exercise‐heat stress. Diet influences the composition of the microbiome and different microbiome species have varying LPS structures. Because of this, even short‐term alterations in macronutrient consumption can alter the composition and gene expression of the microbiome. Ongoing research will utilize extraction of LPS from pre‐race and post‐race plasma and HPLC/MS to characterize structural variations in LPS in individuals of the 2015, 2016, and 2017 FRR.Support or Funding InformationNew investigator start‐up, McNair Scholar Program, FRRThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Thermal behavior remains engaged following exercise despite autonomic thermoeffector withdrawal

We tested the hypothesis that thermal behavior during the exercise recovery compensates for elevated core temperatures despite autonomic thermoeffector withdrawal. In a thermoneutral environment, 6 females and 6 males (22 ± 1 y) cycled for 60 min (225 ± 46 W metabolic heat production), followed by 60 min passive recovery. Mean skin and core temperatures, skin blood flow, and local sweat rate were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom-made neck device. Neck device temperature provided an index of thermal behavior. Mean body temperature, calculated as the average of mean skin and core temperatures, provided an index of the stimulus for thermal behavior. To isolate the independent effect of exercise on thermal behavior during recovery, data were analyzed post-exercise the exact minute mean body temperature recovered to pre-exercise levels within a subject. Mean body temperature returned to pre-exercise levels 28 ± 20 min into recovery (Pre: 33.5 ± 0.2, Post: 33.5 ± 0.2 °C, P = 0.20), at which point, mean skin temperature had recovered (Pre: 29.6 ± 0.4, Post: 29.5 ± 0.5 °C, P = 0.20) and core temperature (Pre: 37.3 ± 0.2, Post: 37.5 ± 0.3 °C, P = 0.01) remained elevated. Post-exercise, skin blood flow (Pre: 59 ± 78, Post: 26 ± 25 PU, P = 0.10) and local sweat rate (Pre: 0.05 ± 0.25, Post: 0.13 ± 0.14 mg/cm2 min−1, P = 0.09) returned to pre-exercise levels, while neck device temperature was depressed (Pre: 27.4 ± 1.1, Post: 21.6 ± 7.4 °C, P = 0.03). These findings suggest that thermal behavior compensates for autonomic thermoeffector withdrawal in the presence of elevated core temperatures post-exercise.

Elevated core temperature: not only useful in the context of exercise to combat chronic low-grade inflammation?

Elevated core temperature: not only useful in the context of exercise to combat chronic low-grade inflammation?

Relationship of External Field Strength With Local and Whole-Body Averaged Specific Absorption Rates in Anatomical Human Models

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines and the IEEE C95.1 standard are currently under revision. In the guidelines/standard, the dominant effect for electromagnetic field exposures at frequencies above 100 kHz is the thermal effect. The whole-body-and 10g-averaged specific absorption rates (SARs), which are surrogates for core and local temperature elevations, respectively, are set as metrics for exposure evaluation. The external field strengths or incident power density, corresponding to the limit for SARs, are also used as metrics for practical compliance purposes. Although the limits for the SARs are identical amongst the guidelines/standard, the limits for the external field strengths differ by a factor of 7.4–12.9 in an intermediate frequency range (100 kHz–100 MHz). Due to the fact that the standard/guidelines were published before the computation with anatomical human models was available, it is worth revisiting the relationship between the SARs and external field strengths by computations using the human models. Intercomparison using different numerical codes was also performed to verify the results. For the main finding, as expected, the 10g-averaged SAR was a less restrictive factor for whole-body exposure over the frequencies considered in this paper. It was also found that the relationship between SARs and external field strength was satisfied, but was more conservative in the ICNIRP guidelines, whereas there were slight discrepancies below 30 MHz in the IEEE standard. The computational results would be useful for revising the permissible external field strength based on scientific results.

Heat stroke and heat exhaustion: An update

Heat-related illnesses are part of a continuum comprising heat cramps, heat exhaustion, heat syncope and heat stroke, and are associated with significant morbidity and mortality, especially in a tropical country like India. Heat stroke, which is the most severe, is caused by failure of thermoregulation with elevation of core temperature to 40°C (104°F) or more, associated with central nervous system dysfunction. The two important principles in management of heat stroke are lowering of core temperature immediately to 38.9°C and supporting organ systems injured by heat, hypotension, inflammation and coagulopathy. It is important to initiate cooling as fast as possible and keep the individual adequately hydrated to prevent complications.

Population-based case-control study of the association between weather-related extreme heat events and neural tube defects.

Elevated body core temperature has been shown to have teratogenic effects in animal studies. Our study evaluated the association between weather-related extreme heat events (EHEs) in the summer season and neural tube defects (NTDs), and further investigated whether pregnant women with a high pregestational body mass index (BMI) have a greater risk of having a child with NTDs associated with exposure to EHE than women with a normal BMI. We conducted a population-based case-control study among mothers of infants with NTDs and mothers of infants without major birth defects, who participated in the National Birth Defects Prevention Study and had at least 1 day of the third or fourth week postconception during summer months. EHEs were defined using the 95th and the 90th percentiles of the daily maximum universal apparent temperature. Adjusted odds ratios and 95% confidence intervals were calculated using unconditional logistic regression models with Firth's penalized likelihood method while controlling for other known risk factors. Overall, we did not observe a significant association between EHEs and NTDs. At the climate region level, consistently elevated but not statistically significant estimates were observed for at least 2 consecutive days with daily universal apparent maximum temperature above the 95th percentile of the UATmax distribution for the season, year, and weather monitoring station in New York (Northeast), North Carolina and Georgia (Southeast), and Iowa (Upper Midwest). No effect modification by BMI was observed. EHEs occurring during the relevant developmental window of embryogenesis do not appear to appreciably affect the risk of NTDs. Future studies should refine exposure assessment, and more completely account for maternal activities that may modify the effects of weather exposure. Birth Defects Research 109:1482-1493, 2017.© 2017 Wiley Periodicals, Inc.

Thermal response to firefighting activities in residential structure fires: impact of job assignment and suppression tactic

Firefighters’ thermal burden is generally attributed to high heat loads from the fire and metabolic heat generation, which may vary between job assignments and suppression tactic employed. Utilising a full-sized residential structure, firefighters were deployed in six job assignments utilising two attack tactics (1. Water applied from the interior, or 2. Exterior water application before transitioning to the interior). Environmental temperatures decreased after water application, but more rapidly with transitional attack. Local ambient temperatures for inside operation firefighters were higher than other positions (average ~10–30 °C). Rapid elevations in skin temperature were found for all job assignments other than outside command. Neck skin temperatures for inside attack firefighters were ~0.5 °C lower when the transitional tactic was employed. Significantly higher core temperatures were measured for the outside ventilation and overhaul positions than the inside positions (~0.6–0.9 °C). Firefighters working at all fireground positions must be monitored and relieved based on intensity and duration.Practitioner Summary: Testing was done to characterise the thermal burden experienced by firefighters in different job assignments who responded to controlled residential fires (with typical furnishings) using two tactics. Ambient, skin and core temperatures varied based on job assignment and tactic employed, with rapid elevations in core temperature in many roles.

Should Workers Avoid Consumption of Chilled Fluids in a Hot and Humid Climate?

Despite provision of drinking water as the most common method of occupational heat stress prevention, there remains confusion in hydration messaging to workers. During work site interactions in a hot and humid climate, workers commonly report being informed to consume tepid fluids to accelerate rehydration. When questioned on the evidence supporting such advice, workers typically cite that fluid absorption is delayed by ingestion of chilled beverages. Presumably, delayed absorption would be a product of fluid delivery from the gut to the intestines, otherwise known as gastric emptying. Regulation of gastric emptying is multifactorial, with gastric volume and beverage energy density the primary factors. If gastric emptying is temperature dependent, the impact of cooling is modest in both magnitude and duration (≤ 5 minutes) due to the warming of fluids upon ingestion, particularly where workers have elevated core temperature. Given that chilled beverages are most preferred by workers, and result in greater consumption than warm fluids during and following physical activity, the resultant increased consumption of chilled fluids would promote gastric emptying through superior gastric volume. Hence, advising workers to avoid cool/cold fluids during rehydration appears to be a misinterpretation of the research. More appropriate messaging to workers would include the thermal benefits of cool/cold fluid consumption in hot and humid conditions, thereby promoting autonomy to trial chilled beverages and determine personal preference. In doing so, temperature-based palatability would be maximized and increase the likelihood of workers maintaining or restoring hydration status during and after their work shift.