Rise In Core Body Temperature Research Articles

Comparison of Acute Physiological Responses to Different Passive Heating Modalities

The repeated use of passive heating has gained popularity as a therapeutic approach toward promoting health and wellness. Passive heating elicits a rise in core body temperature and subsequent cardiovascular demand that can result in physiological adaptations beneficial to health. Hot water immersion, traditional sauna, and far-infrared sauna are three common modalities of passive heating; however, current literature lacks a direct comparison between these modalities. The purpose of this study is to characterize and compare the acute thermoregulatory and cardiovascular responses to a single bout of hot water immersion (HWI), traditional sauna (TRAD), and far-infrared sauna (FIR). We hypothesized that HWI will induce more pronounced thermoregulatory and cardiovascular responses when compared to both TRAD and FIR. In a randomized cross-over study design, nineteen healthy adults (9 F; age 24±4 years; body mass index 26.47±5 kg/m2) completed three bouts of acute passive heating: HWI (45 minutes at 40°C), TRAD (3x10 minutes at 80°C, separated by 5 min of thermoneutral rest), and FIR (45 minutes at 45-65°C) separated by at least 1 week. These temperatures and durations were chosen based on previous research and reflect typical use of these modalities. Measurements of arterial pressure, core temperature (Tc), and heart rate (HR) were collected at pre-heating baseline and at 5-min intervals during passive heating. Cardiac output (Q) was measured before, halfway, and at the end of heating using the open-circuit acetylene wash-in method. Mean arterial pressure (MAP) was calculated as 1/3 systolic + 2/3 diastolic and stroke volume (SV) and systemic vascular resistance (SVR) were calculated by Q/HR and MAP/Q. Data were analyzed using one-way ANOVAs to compare the changes from baseline to end of heating and are presented as mean with 95% confidence intervals. The change in Tc from baseline to end of heating was greater in HWI [+1.1°C (1.0, 1.3)] vs TRAD [+0.4°C (0.2, 0.6), p<0.0001], HWI vs FIR [+0.1°C (-0.1,0.2), P <0.0001], and TRAD vs FIR (P=0.0291). The increase in HR was greater in HWI [+39 bpm (35, 43)] vs. FIR [+26 bpm (21, 32), P=0.0017], with no differences in HWI vs. TRAD [+34 bpm (28, 40), P=0.4247] or TRAD vs. FIR (P=0.0793). Cardiac output increased to a greater extent in HWI [+3.9 L (3.3, 4.4)] vs. TRAD [+2.4 L (1.8, 2.9), P=0.0003)] and HWI vs. FIR [+1.7 L (1.2, 2.1), p<0.0001], with no difference between TRAD vs FIR (P=0.1379). MAP decreased in HWI [-14 mmHg (-20, -9)] vs TRAD [-3 mmHg (-8, 1), P=0.0058] and HWI vs FIR [-0.5 mmHg (-5, 4), P=0.0003], with no difference between TRAD vs FIR (P= 0.7506). Conclusion: A single bout of HWI elicits the greatest thermoregulatory challenge and cardiovascular strain compared to both TRAD and FIR. Funded by American Heart Association (19TPA34890033) and NIH (R01HL144128). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Heat stress and adverse pregnancy outcome: Prospective cohort study.

To explore the relationship between occupational heat exposure, physiological heat strain indicators and adverse outcomes in pregnant women. Prospective cohort. Workplaces in Tamil Nadu, India. A cohort of 800 pregnant women engaged in moderate to heavy physical work in 2017-2019 and 2021-2022. Participants were recruited at between 8 and 14 weeks of gestation. Occupational heat exposure and heat strain indicators were captured each trimester. 'Heat exposed' was defined as heat stress exceeding the threshold limit value (TLV) for safe manual work (with maximum wet-bulb globe temperatures of 27.5°C for a heavy workload and 28.0°C for a moderate workload). Physiological heat strain indicators (HSIs) such as core body temperature (CBT) and urine specific gravity (USG) were measured before and after each shift. Heat-related health symptoms were captured using the modified HOTHAPS questionnaire. The main outcome measures included (1) a composite measure of any adverse pregnancy outcome (APO) during pregnancy (including miscarriage, preterm birth, low birthweight, stillbirth, intrauterine growth restriction and birth defects), (2) a composite measure of adverse outcomes at birth (3) and miscarriage. Of the 800 participants, 47.3% had high occupational heat exposure. A rise in CBT was recorded in 17.4% of exposed workers, and 29.6% of workers experienced moderate dehydration (USG ≥ 1.020). Heat-exposed women had a doubled risk of miscarriage (adjusted odds ratio, aOR 2.4; 95% confidence interval, 95% CI 1.0-5.7). High occupational heat exposure was associated with an increased risk of any adverse pregnancy and foetal outcome (aOR 2.3; 95% CI 1.4-3.8) and adverse outcome at birth (aOR 2.0; 95% CI 1.2-3.3). High occupational heat exposure is associated with HSIs and adverse pregnancy outcomes in India.

Daily Brief Heat Therapy Reduces Seizures in A350V IQSEC2 Mice and Is Associated with Correction of AMPA Receptor-Mediated Synaptic Dysfunction.

Purposeful induction of fever for healing, including the treatment of epilepsy, was used over 2000 years ago by Hippocrates. More recently, fever has been demonstrated to rescue behavioral abnormalities in children with autism. However, the mechanism of fever benefit has remained elusive due in large part to the lack of appropriate human disease models recapitulating the fever effect. Pathological mutations in the IQSEC2 gene are frequently seen in children presenting with intellectual disability, autism and epilepsy. We recently described a murine A350V IQSEC2 disease model, which recapitulates important aspects of the human A350V IQSEC2 disease phenotype and the favorable response to a prolonged and sustained rise in body core temperature in a child with the mutation. Our goal has been to use this system to understand the mechanism of fever benefit and then develop drugs that can mimic this effect and reduce IQSEC2-associated morbidity. In this study, we first demonstrate a reduction in seizures in the mouse model following brief periods of heat therapy, similar to what was observed in a child with the mutation. We then show that brief heat therapy is associated with the correction of synaptic dysfunction in neuronal cultures of A350V mice, likely mediated by Arf6-GTP.

SK-Channel Activation Alters Peripheral Metabolic Pathways in Mice, but Not Lipopolysaccharide-Induced Fever or Inflammation.

PurposePreviously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.MethodsMice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.ResultsCyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.ConclusionOverall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.

The impact of elevated body core temperature on critical power as determined by a 3-min all-out test.

Critical power (CP) delineates the heavy and severe exercise intensity domains, and sustained work rates above CP result in an inexorable progression of oxygen uptake to a maximal value and, subsequently, the limit of exercise tolerance. The finite work capacity above CP, W', is defined by the curvature constant of the power-duration relationship. Heavy or severe exercise in a hot environment generates additional challenges related to the rise in body core temperature (Tc) that may impact CP and W'. The purpose of this study was to determine the effect of elevated Tc on CP and W'. CP and W' were estimated by end-test power (EP; mean of final 30 s) and work above end-test power (WEP), respectively, from 3-min "all-out" tests performed on a cycle ergometer. Volunteers (n = 8, 4 female) performed the 3-min tests during a familiarization visit and two experimental visits (thermoneutral vs. hot, randomized crossover design). Before experimental 3-min tests, the subjects were immersed in water (thermoneutral: 36°C for 30 min; hot: 40.5°C until Tc was ≥38.5°C). Mean Tc was significantly greater in the hot condition than in the thermoneutral condition (38.5 ± 0.0°C vs. 37.4 ± 0.2°C; means ± SD, P < 0.01). All 3-min tests were performed in an environmental chamber [thermoneutral: 18°C, 45% relative humidity (RH); hot: 38 °C, 40% RH]. EP was similar between thermoneutral (239 ± 57 W) and hot (234 ± 66 W; P = 0.55) conditions. WEP was similar between thermoneutral (10.9 ± 3.0 kJ) and hot conditions (9.3 ± 3.6; P = 0.19). These results suggest that elevated Tc has no significant impact on EP or WEP.NEW & NOTEWORTHY The parameters of the power-duration relationship (critical power and W') estimated by a 3-min all-out test were not altered by elevated body core temperature as compared with a thermoneutral condition.

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies.

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.

Occupational heat stress and heavy workload induce 'productivity losses’- Epidemiological evidence from a large cross-sectional study in Indian occupational settings.

Background: Climate change is expected to exacerbate heat stress at the workplace in tropical settings. The health impacts of heat stress have been well documented in India and elsewhere. But Productivity Losses (PL) due to heat stress among workers has received less attention in Indian work settings and therefore vital to study the current status of heat impacts on the worker's health and productivity, so that appropriate control intervention can be implemented to avert present and future economic losses. Methods: We used a mixed-method approach to assess the perceived PL among~2892 workers from 25 occupational sectors in India. We conducted seasonal WBGT exposures, measured standard heat-strain indicators and captured self-reported productivity losses through questionnaires and observations.Results: WBGT heat exposures exceeded the Threshold Limit Values for moderate/heavy work for 74% workers (29.1°C±3.1°C). 16.1% of workers reported PL that was significantly associated with WBGT exposures (OR: 1.3; 95% CI: 1.03-1.66; p=0.0001), and heavy workload (OR: 1.5; 95% CI: 1.28 - 1.94; p=0.0001). Quantified heat-strain indicators such as a rise in Core Body Temperature, Sweat Rates, and Urine Specific Gravity were significantly associated with WBGT exposures. Though there was no significant difference in PL between informal and formal sectors, outdoor workers with exposures above TLV had 1.5 times higher risk of PL compared to indoor workers (95% CI: 1.27-2.00; p=0.0001). The impact of the season was significant on the PL with summer having 1.8 times higher PL compared to the cooler season (95% CI: 1.44-2.40; p=0.0001). Conclusions: Productivity losses due to workplace heat stress are evidenced in the study and are expected to increase in the rising temperature scenario. Intervention, adaptation and prevention strategies with a focus on workers’ and a concerted effort must be made to promote workers' adaptive capacity and inform policy decisions in the imminent hotter world.

Epidemiological evidence from south Indian working population—the heat exposures and health linkage

Changing climate and rising temperatures are predicted to affect millions of workers due to heat stress risks, especially in tropical settings. We used a cross-sectional study design to profile the heat exposures of ~1500 workers from eight-industrial sectors using a QuesTemp wet bulb globe temperature (WBGT) monitor, quantified the heat-strain indicators viz., rise in Core Body Temperature (CBT), Sweat Rate (SwR), and Urine Specific Gravity (USG) by standard methods and evaluated the health impacts of heat stress using a structured questionnaire. Heat exposures (Avg.WBGT: 28.4 ± 2.6 °C) exceeded the Threshold Limit Value (TLV) for 70% of workers and was significantly associated with the rise in CBT >1 °C in 11.3% and elevated USG >1.020 in 10.5% of the workers. The heat-exposed workers had 2.3 times higher odds of reporting adverse health outcomes (84%) compared to the unexposed workers (95% CI: 1.74-3.19; p value ≤ 0.0001). Mild reduction in kidney function observed in 49% of salt -pan workers, and a high prevalence of kidney stones (33%) among the 91 steelworkers subjected to kidney ultrasound had a significant association with chronic high WBGT exposure above the TLV (p value < 0.034). Further, in-depth assessments are warranted to develop strategies for interventions and protective labor policies to avert adverse occupational health and productivity consequences for millions of workers globally, especially in the rising temperature scenario.

Postoperative fever in patients undergoing elective surgeries-etiology, investigations, management: a longitudinal study

Background: Fever is rise in core body temperature above normal diurnal variations. Surgical procedures often disturb normal physiological process and one such manifestation is rise in body temperature. Present study was conducted to study the etiology of post-operative fever, correlation of etiology of fever with post-operative day of onset of fever and to study the investigations of postoperative fever.Methods: This study was conducted over a period of 24 months from 1st November 2017 to 31st October 2019 at Department of Surgery at a tertiary care hospital. A total of 339 patients were enrolled. Data analysis done using descriptive statistics and continuous variables were analyzed using Chi square test.Results: Out of 339 patients of post-operative fever, 207 patients (61%) were in age group of &gt;20-50 years. Mean age was 44.56 years. Male to female ratio was 1.4:1. Maximum incidence of fever were seen after spinal anesthesia. It was observed that the incidence increases as the operative time increases. Incidence were more during months of summer. Around 88.49% developed pyrexia within 48 hours of surgery where no detectable infection was noted. Rest 11.5% had fever after 48 hours of surgery where the causes were UTI (7.4 %), superficial thrombophlebitis (6.8%) or SSI (4.7%). None developed chest infections or DVT.Conclusions: Fever in postoperative period is common in elective clean surgical procedures, likely due to surgical trauma in the first 2 days and patients should be closely monitored. Fever after 48 hours should be investigated for the cause and treated accordingly.

The Impact of Temperature on Critical Power Determined by a Three Minute All‐Out Test

Critical Power (CP) separates the heavy and severe exercise domains, and work above CP (defined as W′) results in an inexorable progression to maximal oxygen uptake and rise in blood lactate concentration to fatigue. The thermoregulatory demands accompanying a rise in body core temperature (Tc) compounded with the cardiovascular challenges presented by maximal exercise in a hot environment may impact CP and W′. To date, no study has explored the effects of elevated Tc and environmental temperature on CP and W′. The purpose of this study is to determine the effect of high environmental and Tc on CP and W′. CP was estimated as end test power (average of the last 30 sec) from a series of three‐min “all out” tests (3MT). Volunteers (n=7, 3F) performed a 3MT during a familiarization visit and two experimental study days (thermoneutral and hot) in a randomized crossover design. Prior to the 3MT in both experimental conditions, subjects were immersed in either thermoneutral (36°C for 30 min) or hot (40.5°C) water until Tc was ≥ 38.5°C. All 3MT were performed in an environmental chamber controlling for both temperature and humidity (18°C and 45% RH for thermoneutral; 38°C and 40% RH for hot). A paired t‐test was used for statistical analysis and data are presented as mean ± SE. Although variable, CP was similar between thermoneutral (245 ± 22W) and hot (243 ± 25; p=0.83), while W’ was only mildly reduced from thermoneutral (11 ± 1 kJ) to hot (9 ± 2) p=0.17. Total work performed was similar between thermoneutral (55 ± 5 kJ) and hot (53 ± 5) conditions (p=0.27) and peak power was similar between thermoneutral (827 ± 89W) and hot (809 ± 85) p=0.49. These preliminary data suggest that high Tc and environmental temperature, per se, appear to have no significant impact on CP as estimated by a 3‐minute all‐out test.

Risk of kidney stone among workers exposed to high occupational heat stress - A case study from southern Indian steel industry

BackgroundPredicted temperature rise is likely to increase the risks of development and progression of renal/urologic anomalies for workers engaged in physically exerting and high-heat occupations. MethodsWe conducted a cross-sectional study with 340 steelworkers engaged in moderate to heavy labour with ≥3 year's heat exposures and assessed Wet Bulb Globe Temperature (WBGT) and heat-strain indicators. We captured self-reported heat-strain and kidney symptoms using validated questionnaires and subjected 91 workers to renal ultrasound upon referral of an occupational health specialist to detect and confirm any structural renal anomalies/stones. ResultsThe results show that heat exposures (Avg.WBGT = 33.2 °C ± 3.8 °C) exceeded the Threshold Limit Value (TLV) for 220 workers. 95% of the workers reported symptoms of heat strain and dehydration and significant associations between heat exposures, rise in Core Body Temperature (CBT) (p = 0.0001) and Urine Specific Gravity (USG) (p = 0.018) were observed. Of the 91 workers subjected to renal ultrasound, 33% were positive for kidney/ureteral stones (n = 25) & other structural renal anomalies (n = 5). Renal/urologic anomalies were higher in the heat-exposed workers (AOR = 2.374; 95% C.I = 0.927 to 6.077; p = 0.072) 29% of workers were from exposed group and 4% were from unexposed group. Years of exposure to heat (≥5 vs <5) were significantly associated with the risk of renal anomalies/calculi. ConclusionThe preliminary finding concludes that high-heat stress combined with a heavy workload and chronic dehydration are high-risk factors for adverse renal health and calls for the urgent need for cooling interventions, enhanced welfare facilities, and protective labour policies to avert adverse health consequences for few million workers in the climate change scenario.

Occupational heat stress induced health impacts: A cross-sectional study from South Indian working population

Rising temperature and heat stress risks in the changing climate scenario might potentially affect workers globally, especially the ones with strenuous workload in tropical settings. We used a cross-sectional study design to profile the heat exposures of ∼1900 workers from eight industrial sectors using a QuesTemp Wet Bulb Globe Temperature (WBGT) monitor, quantified select heat-strain indicators viz., rise in Core Body Temperature, Sweat Rate, and Urine Specific Gravity and evaluated the perceived health impacts of heat stress using a structured questionnaire. Heat exposures (average WBGT: 30.1 ± 2.6 °C) exceeded the Threshold Limit Value for 67% workers and was positively associated with the rise in Core Body Temperature >1 °C in 13% and elevated Urine Specific Gravity >1.020 in 9% workers. Heat-related health concerns were reported by 86% workers, and the heat-exposed workers had 2.3 times higher odds of adverse health outcomes compared to unexposed workers (p < 0.0001). Exposure to higher WBGT and adverse renal health among salt-pan workers were significantly associated (p = 0.004), and steel workers had 9% prevalence of kidney stones. Evidence presented clearly points to heat stress as a health and productivity risk factor that could have long-term and irreversible health impacts. In-depth assessments are urgently needed to develop scientifically sound preventative interventions and protective labor policies to avert the adverse occupational health and productivity consequences for millions of workers globally, thereby aiding poverty reduction.

Using Non-Invasive Monitoring Technologies to Capture Behavioural, Physiological and Health Responses of Dairy Calves to Different Nutritional Regimes during the First Ten Weeks of Life.

Simple SummaryRecent research has debated the effects of milk and forage feeding regimes in the first weeks of life on the future performance of dairy calves. However, little is known about how feeding regime can affect behavioural and physiological responses, which have the potential to impact on calf health and well-being. Traditional methods of assessing calf health and welfare such as behavioural observations and blood sampling can be time consuming and impractical for producers and invasive for animals involved. Developments in technology have increased the availability of on-farm non-invasive devices which allow automatic and remote collection of behavioural and physiological data linked to animal health and welfare. This study aimed to use devices to measure lying behaviour, heart rate, heart rate variability and infrared temperature of calves offered high or low levels of milk replacer and different types of forage throughout the first ten weeks of life. Calves displayed changes in lying behaviour and heart rate variability as a result of changes in milk replacer feeding frequency. Additionally, infrared temperature changes were detected during periods of vaccination which corresponded with a rise in core body temperature. Results have highlighted that these sensors can provide important and useable data regarding overall calf well-being on commercial farms.This study aimed to examine the use of non-invasive monitoring technologies as a means of capturing behavioural, physiological and health responses of calves allocated to different nutritional regimes. Seventy-four Holstein Friesian calves were individually penned and allocated to receive either high (HML) or conventional (CML) milk replacer (MR) levels between 5–70 days of age. Additionally calves were allocated to one of four forage treatments: (i) chopped straw offered between 14–70 days of age (CS14), (ii) chopped straw offered between 56–70 days of age (CS56), (iii) grass silage offered between 56–70 days of age (GS56), and (iv) no forage in the pre-wean period (NF). A representative sample of calves from each treatment were fitted with activity sensors and heart rate monitors throughout the experimental period to examine lying behaviour and heart rate variability, respectively. Thermal images of the eye and rectal area of each calf were taken 5 days/week between 5–77 days of age. Faecal and respiratory scoring of each individual calf was carried out on a daily basis throughout the experimental period. Milk replacer feeding level had limited effects on measures of calf health, although HML calves tended to have an increased likelihood for receiving treatment for scour than CML calves. Daily lying time (min/d) was lower in HML calves following reduction in MR feeding frequency at 43 days of age and weaning at 71 days of age when compared with CML calves. Additionally, HML calves displayed a lower heart rate variability following weaning, this suggestive of increased stress load. There were limited effects of forage treatment, however, CS14 calves displayed a greater daily lying time following MR step-down at 68 days of age, this potentially indicating increased rumination. Results of the present study highlight the benefits of using remote monitoring technologies as a means of detecting behavioural and physiological changes as a result of nutritional management strategy in individually housed dairy calves.

A single day of high-fat diet feeding induces lipid accumulation and insulin resistance in brown adipose tissue in mice

Brown adipose tissue (BAT) catabolizes glucose and fatty acids to produce heat and thereby contributes to energy expenditure. Long-term high-fat diet (HFD) feeding results in so-called 'whitening' of BAT characterized by increased lipid deposition, mitochondrial dysfunction, and reduced fat oxidation. The aim of the current study was to unravel the rate and related mechanisms by which HFD induces BAT whitening and insulin resistance. Wild-type mice were fed a HFD for 0, 1, 3, or 7 days. Within 1 day of HFD, BAT weight and lipid content were increased. HFD also immediately reduced insulin-stimulated glucose uptake by BAT, indicating rapid induction of insulin resistance. This was accompanied by a tendency toward a reduced uptake of triglyceride-derived fatty acids by BAT. Mitochondrial mass and Ucp1 expression were unaltered, whereas after 3 days of HFD, markers of mitochondrial dynamics suggested induction of a more fused mitochondrial network. Additionally, HFD also increased macrophage markers in BAT after 3 days of HFD. Counterintuitively, the switch to HFD was accompanied by an acute rise in core body temperature. We showed that a single day of HFD feeding is sufficient to induce the first signs of whitening and insulin resistance in BAT, which reduces the uptake of glucose and triglyceride-derived fatty acids. BAT whitening and insulin resistance are likely sustained by reduced mitochondrial oxidation due to changes in mitochondrial dynamics and macrophage infiltration, respectively. Likely, the switch to HFD swiftly induces thermogenesis in other metabolic organs, which allows attenuation of BAT thermogenesis.

Divers risk accelerated fatigue and core temperature rise during fully-immersed exercise in warmer water temperature extremes

ABSTRACTPhysiological responses to work in cold water have been well studied but little is known about the effects of exercise in warm water; an overlooked but critical issue for certain military, scientific, recreational, and professional diving operations. This investigation examined core temperature responses to fatiguing, fully-immersed exercise in extremely warm waters. Twenty-one male U.S. Navy divers (body mass, 87.3 ± 12.3 kg) were monitored during rest and fatiguing exercise while fully-immersed in four different water temperatures (Tw): 34.4, 35.8, 37.2, and 38.6°C (Tw34.4, Tw35.8, Tw37.2, and Tw38.6 respectively). Participants exercised on an underwater cycle ergometer until volitional fatigue or core temperature limits were reached. Core body temperature and heart rate were monitored continuously. Trial performance time decreased significantly as water temperature increased (Tw34.4, 174 ± 12 min; Tw35.8, 115 ± 13 min; Tw37.2, 50 ± 13 min; Tw38.6, 34 ± 14 min). Peak core body temperature during work was significantly lower in Tw34.4 water (38.31 ± 0.49°C) than in warmer temperatures (Tw35.8, 38.60 ± 0.55°C; Tw37.2, 38.82 ± 0.76°C; Tw38.6, 38.97 ± 0.65°C). Core body temperature rate of change increased significantly with warmer water temperature (Tw34.4, 0.39 ± 0.28°C·h−1; Tw35.8, 0.80 ± 0.19°C·h−1; Tw37.2, 2.02 ± 0.31°C·h−1; Tw38.6, 3.54 ± 0.41°C·h−1). Physically active divers risk severe hyperthermia in warmer waters. Increases in water temperature drastically increase the rate of core body temperature rise during work in warm water. New predictive models for core temperature based on workload and duration of warm water exposure are needed to ensure warm water diving safety.

The Comparison between Different types of Cold Fluid Ingestion towards Endurance Exercise in Hot and Humid Condition

The rise in body core temperature associated with continuous exercise in hot and humid environments is known to possess a particularly stressful challenge to the maintenance of normal body temperature and fluid homeostasis. Recent evidence has shown that internal cooling methods, such as drinking cold fluids, are able to lower core temperature and enhance endurance performance in the heat. Pre-cooling (before exercise) and per-cooling (during exercise) methods were use, as ingesting cold fluids is easily implemented on site and provides additional benefit of hydration for athletes. Therefore, this study examines the effectiveness of pre-cooling and per-cooling methods on endurance exercise towards heart rate, rectal temperature, sweat rate, and power output of athletes ingesting different types of cold fluids. 3 female high-performance cyclists were asked to complete a 30km time trial on a cycle ergometer. The familiarisation and experimental sessions were identical, however application of fluid ingestion at 4-5°C before and during exercise differs (plain water = PW, Guava juice = GJ, isotonic drink = ID). Fluid is ingested every 15 minutes during the exercise sessions. As different athletes possess different work intensities, results showed that there is no significant difference on the effects of different types of cold fluid ingestion towards thermoregulation of the body as each fluid succeeded in enhancing athletes’ performance. Therefore, it is suggested that the consumption of any types of fluid at cold temperature could help in body thermoregulation as well as enhancing continuous exercise performance.

Heat Strain Decision Aid (HSDA) accurately predicts individual-based core body temperature rise while wearing chemical protective clothing

PurposeWe examined the accuracy of the Heat Strain Decision Aid (HSDA) as a predictor of core body temperature in healthy individuals wearing chemical protective clothing during laboratory and field exercises in hot and humid conditions. MethodsThe laboratory experiment examined three chemical protective clothing ensembles in eight male volunteers (age 24 ± 6 years; height 178 ± 5 cm; body mass 76.6 ± 8.4 kg) during intermittent treadmill marching in an environmental chamber (air temperature 29.3 ± 0.1 °C; relative humidity 56 ± 1%; wind speed 0.4 ± 0.1 m s−1). The field experiment examined four different chemical protective clothing ensembles in twenty activity military volunteers (26 ± 5 years; 175 ± 8 cm; 80.2 ± 12.1 kg) during a prolonged road march (26.0 ± 0.5 °C; 55 ± 3%; 4.3 ± 0.7 m s−1). Predictive accuracy and precision were evaluated by the bias, mean absolute error (MAE), and root mean square error (RMSE). Additionally, accuracy was evaluated using a prediction bias of ±0.27 °C as an acceptable limit and by comparing predictions to observations within the standard deviation (SD) of the observed data. ResultsCore body temperature predictions were accurate for each chemical protective clothing ensemble in laboratory (Bias −0.10 ± 0.36 °C; MAE 0.28 ± 0.24 °C; RMSE 0.37 ± 0.24 °C) and field experiments (Bias 0.23 ± 0.32 °C; MAE 0.30 ± 0.25 °C; RMSE 0.40 ± 0.25 °C). From all modeled data, 72% of all predictions were within one standard deviation of the observed data including 92% of predictions for the laboratory experiment (SD ± 0.64 °C) and 67% for the field experiment (SD ± 0.38 °C). Individual-based predictions showed modest errors outside the SD range with 98% of predictions falling <1 °C; while, 81% of all errors were within 0.5 °C of observed data. ConclusionThe HSDA acceptably predicts core body temperature when wearing chemical protective clothing during laboratory and field exercises in hot and humid conditions.

Differences in serum IL-6 response after 1 °C rise in core body temperature in individuals with spinal cord injury and cervical spinal cord injury during local heat stress

Objectives: Passive rise in core body temperature achieved by head-out hot water immersion (HHWI) results in acute increases in serum interleukin (IL)-6 but no change in plasma adrenaline in patients with cervical spinal cord injury (CSCI). The purpose of the present study was to determine the mechanism of heat stress-induced increase in serum IL-6.Setting: A cross-sectional study.Methods: The study subjects were nine with CSCI, ten with thoracic and lumbar spinal cord injury (TLSCI) and eight able-bodied (AB) subjects. Time since injury was 16.1 ± 3.4 years in TLSCI and 16.4 ± 4.1 years in CSCI. Subjects were subjected to lower-body heat stress (LBH) by wearing a hot water-perfused suit until 1 °C increase in core temperature. The levels of serum IL-6, plasma adrenaline, tumour necrosis factor (TNF)-α, C-reactive protein (CRP), and counts of blood cells were measured at normothermia and after LBH.Results: Serum IL-6 concentrations increased significantly immediately after LBH in all the three groups. ΔIL-6% was lower in CSCI subjects compared with AB subjects. Plasma adrenaline concentrations significantly increased after LBH in AB and TLSCI subjects, but did not change throughout the study in CSCI subjects. Cardiac output and heart rate increased at the end of LBH in all three groups.Conclusions: Under a similar increase in core temperature, ΔIL-6% was lower in the CSCI group compared with the AB group. These findings suggest that the observed rise in IL-6 during hyperthermia is mediated, at least in part, by plasma adrenaline.

Examining the Influence of Exercise Intensity and Hydration on Gastrointestinal Temperature in Collegiate Football Players.

DeMartini-Nolan, JK, Martschinske, JL, Casa, DJ, Lopez, RM, Stearns, RL, Ganio, MS, and Coris, E. Examining the influence of exercise intensity and hydration on gastrointestinal temperature in collegiate football players. J Strength Cond Res 32(10): 2888-2896, 2018-Debate exists regarding the influence of intensity and hydration on body temperature during American football. The purpose of this study was to observe body core temperature responses with changes in intensity and hydration. Twenty-nine male football players (age = 21 ± 1 year, height = 187 ± 9 cm, mass = 110.1 ± 23.5 kg, body mass index [BMI] = 31.3 ± 5.0, and body surface area [BSA] = 2.34 ± 0.27 m) participated in 8 days of practice in a warm environment (wet bulb globe temperature: 29.6 ± 1.6° C). Participants were identified as starters (S; n = 12) or nonstarters (n = 17) and linemen (L; n = 14) or nonlinemen (NL; n = 15). Variables of interest included core body temperature (T), hydration status, and physical performance characteristics as measured by a global positioning system. Intensity measures of average heart rate (138 ± 9 bpm), low-velocity movement (4.2 ± 1.7%), high-velocity movement (0.6 ± 0.6%), and average velocity (0.36 ± 0.10 m·s) accounted for 42% of the variability observed in T (38.32 ± 0.34° C, r = 0.65, p = 0.01). Hydration measures (percent body mass loss = -1.56 ± 0.80%, urine specific gravity [Usg] = 1.025 ± 0.006, and urine color [Ucol] = 6 ± 1) did not add to the prediction of T (p = 0.83). Metrics of exercise intensity accounted for 39% of the variability observed in maximum T (38.83 ± 0.42° C, r = 0.62, p = 0.02). Hydration measures did not add to this prediction (p = 0.40). Low-velocity movement, high-velocity movement, average velocity, BMI, and BSA were significantly different (p = 0.002, p < 0.001, p = 0.02, p < 0.001, p < 0.001, respectively) between L vs. NL. Heart rate and T were not different between L and NL (p > 0.05). Exercise intensity primarily accounted for the rise in core body temperature. Although L spent less time at higher velocities, T was similar to NL, suggesting that differences in BMI and BSA added to thermoregulatory strain.

TRPV1 antagonism by piperazinyl-aryl compounds: A Topomer-CoMFA study and its use in virtual screening for identification of novel antagonists

Transient Receptor Potential Vanilloid, member 1 (TRPV1), is a non-selective cation channel belonging to the transient receptor potential (TRP) family of ion channels. It occurs in the peripheral and central nervous system, activated by a variety of exogenous and endogenous stimuli, thus playing a key role in transmission of pain. This has been a target for chronic pain since more than a decade and a number of antagonists that progressed into clinical trials have failed due to the unexpected side effect of core body temperature rise, thus halting progress in this field. Of late, there has been an upsurge in research on this target, with the rat TRPV1 structure being determined, many new antagonists discovered that are temperature-neutral and many new therapeutic avenues being discovered for TRPV1, including diseases of respiratory and digestive systems, skin and bladder. Towards identifying diverse compounds to decipher the role of this target in various indications, here we report a 3D-QSAR model built using the new topomer-CoMFA methodology on a series of piperazinyl-aryl TRPV1 antagonists and the use of this model, along with a pharmacophore model and the shape of one of the potent compounds of this series, to virtually screen a subset of the ZINC database to find novel and diverse hits. These can serve as starting points to develop modality-selective antagonists for chronic pain and to elucidate the critical role of TRPV1 in the various new therapeutic areas.