Differences In Core Temperature Research Articles

BRACHIAL, FEMORAL, AND SKIN HAEMODYNAMIC RESPONSES TO WALKING IN HOT CONDITIONS: COMPARISON BETWEEN MALES AND FEMALES

INTRODUCTION & AIMS Heat exposure induces acute changes in arterial function, but sex differences have not been fully addressed. METHODS Participants walked (5km/h; 2% incline) in a climate chamber (42°C;50%RH) for 120mins. Cutaneous microvascular function (laser doppler flowmetry), conduit artery haemodynamics (Doppler ultrasound) and core temperature were measured at baseline, and every 30min. RESULTS 14♂ and 15♀ completed 120min. At baseline, differences in core temperature (Tc) between males and females were not significant (37.2±0.1 vs 37.0±0.1°C; P=0.06). Across all 5 timepoints, females exhibited larger Tc than males (P=0.019). At baseline, males had larger brachial (3.89±0.11 vs 3.13±0.09mm, P<0.001) and femoral (6.22±0.16 vs 5.29±0.14mm, P=0.001) diameters than females. A significant interaction (P=0.047) indicated that brachial diameter increased more in response to heat exertion than in males, whereas no sex difference was apparent in femoral diameter change. Males and females had similar baseline brachial flows (♂80.1±11.2 vs ♀57.0±7.09ml/min, P=0.087), but males had larger baseline femoral flows (♂263.0±23.9 vs ♀151.5±18.6 ml/min, P=0.010). No sex differences were apparent in the terms of the increases in brachial or femoral flows. Finally, at baseline males and females had similar skin blood flux (♂22.6±2.7 vs ♀18.3±2.9PU), but males demonstrated larger increases during heat exertion (P=0.029). CONCLUSIONS Males exhibit larger baseline artery diameters and flows in vessel beds feeding active (femoral) and inactive (brachial) limbs. In response to heat exertion, men and women exhibit similar increases in conduit diameter and flow to active muscle beds (femoral responses). In the inactive forearms, which reflect thermoregulatory responses, females had larger brachial artery diameter changes, but blood flow responses were similar between the sexes and men demonstrated larger increases in skin perfusion. These data indicate that responses to heat exertion differ in the upper and lower limbs, with sex-differences apparent in each of these territories, and at distinct levels of the arterial hierarchy.

Modeling thermoregulatory responses during high-intensity exercise in warm environments.

The six cylinder thermoregulatory model (SCTM) has been validated thoroughly for resting humans. This type of modeling is helpful to predict and develop guidance for safe performance of work and recreational activities. In the context of a warming global climate, updating the accuracy of the model for intense exercise in warm environments will help a wide range of individuals in athletic, recreational, and military settings. Three sets of previously collected data were used to determine SCTM accuracy. Dataset 1: two groups [large (LG) 91.5 kg and small (SM) 67.7 kg] of individuals performed 60 min of semirecumbent cycling in temperate conditions (25.1°C) at metabolic rates of 570-700 W. Dataset 2: two LG (100 kg) and SM (65.8 kg) groups performed 60 min of semirecumbent cycling in warm/hot environmental conditions (36.2°C) at metabolic rates of 590-680 W. Dataset 3: seven volunteers completed 8-km track trials (∼30 min) in cool (17°C) and warm (30°C) environments. The volunteers' metabolic rates were estimated to be 1,268 W and 1,166 W, respectively. For all datasets, SCTM-predicted core temperatures were found to be similar to the observed core temperatures. The root mean square deviations (RMSDs) ranged from 0.06 to 0.46°C with an average of 0.2°C deviation, which is less than the acceptance threshold of 0.5°C. Thus, the present validation shows that SCTM predicts core temperatures with acceptable accuracy during intense exercise in warm environments and successfully captures core temperature differences between large and small individuals.NEW & NOTEWORTHY The SCTM has been validated thoroughly for resting humans in warm and cold environments and during water immersion. The present study further demonstrated that SCTM predicts core temperatures with acceptable accuracy during intense exercise up to 1,300 W in temperate and warm environments and captures core temperature differences between large and small individuals. SCTM is potentially useful to develop guidance for safe operation in athletic, military, and occupational settings during exposure to warm or hot environments.

Hormonal intrauterine devices and heat exchange during exercise.

Synthetic progestins in oral contraceptives are thought to blunt heat dissipation by reducing skin blood flow and sweating. However, whether progestin-releasing intrauterine devices (IUDs) modulate heat loss during exercise-heat stress is unknown. We used direct calorimetry to measure whole-body total (dry + evaporative) heat loss in young, physically active women (mean (SD); aged 24(4)years, 39.3(5.3) ml/kg/min) with (IUD; n=19) and without (Control; n=17) IUDs in the follicular and luteal phases of the menstrual cycle during light- and moderate-intensity exercise at fixed rates of heat production (∼175 and ∼275W/m2 ) in 30°C, ∼21% relative humidity. Between-group and -phase differences were evaluated using traditional hypothesis testing and statistical equivalence testing within pre-determined bounds (±11W/m2 ; difference required to elicit a ±0.3°C difference in core temperature over 1h) in each exercise bout. Whole-body total heat loss was statistically equivalent between groups within ±11Wm-2 (IUD-Control [90% CIs]; Light: -2 [-8, 5] W/m2 , P=0.007; Moderate: 0 [-6, 6] W/m2 , P=0.002), as were dry and evaporative heat loss (P ≤ 0.023), except for evaporative heat loss during moderate-intensity exercise (equivalence: P=0.063, difference: P=0.647). Whole-body total and evaporative heat loss were not different between phases (P≥0.267), but dry heat loss was 3 [95% CIs: 1, 5] W/m2 greater in the luteal phase (P≤0.022). Despite this, all whole-body heat loss outcomes were equivalent between phases (P≤0.003). These findings expand our understanding of the factors that modulate heat exchange in women and provide valuable mechanistic insight of the role of endogenous and exogenous female sex hormones in thermoregulation. KEY POINTS: Progestin released by hormonal intrauterine devices (IUDs) may negatively impact heat dissipation during exercise by blunting skin blood flow and sweating. However, the influence of IUDs on thermoregulation has not previously been assessed. We used direct calorimetry to show that IUD users and non-users display statistically equivalent whole-body dry and evaporative heat loss, body heat storage and oesophageal temperature during moderate- and high-intensity exercise in a warm, dry environment, indicating that IUDs do not appear to compromise exercise thermoregulation. However, within IUD users and non-users, dry heat loss was increased and body heat storage and oesophageal temperature were reduced in the luteal compared to the follicular phase of the menstrual cycle, though these effects were small and unlikely to be practically meaningful. Together, these findings expand our understanding of the factors that modulate heat exchange in women and have important practical implications for the design of future studies of exercise thermoregulation.

Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints

PurposeThe primary aim of this study was to examine whether a glycine-rich collagen peptides (CP) supplement could enhance sleep quality in physically active men with self-reported sleep complaints.MethodsIn a randomized, crossover design, 13 athletic males (age: 24 ± 4 years; training volume; 7 ± 3 h·wk1) with sleep complaints (Athens Insomnia Scale, 9 ± 2) consumed CP (15 g·day1) or a placebo control (CON) 1 h before bedtime for 7 nights. Sleep quality was measured with subjective sleep diaries and actigraphy for 7 nights; polysomnographic sleep and core temperature were recorded on night 7. Cognition, inflammation, and endocrine function were measured on night 7 and the following morning. Subjective sleepiness and fatigue were measured on all 7 nights. The intervention trials were separated by ≥ 7 days and preceded by a 7-night familiarisation trial.ResultsPolysomnography showed less awakenings with CP than CON (21.3 ± 9.7 vs. 29.3 ± 13.8 counts, respectively; P = 0.028). The 7-day average for subjective awakenings were less with CP vs. CON (1.3 ± 1.5 vs. 1.9 ± 0.6 counts, respectively; P = 0.023). The proportion of correct responses on the baseline Stroop cognitive test were higher with CP than CON (1.00 ± 0.00 vs. 0.97 ± 0.05 AU, respectively; P = 0.009) the morning after night 7. There were no trial differences in core temperature, endocrine function, inflammation, subjective sleepiness, fatigue and sleep quality, or other measures of cognitive function or sleep (P > 0.05).ConclusionCP supplementation did not influence sleep quantity, latency, or efficiency, but reduced awakenings and improved cognitive function in physically active males with sleep complaints.

Investigation of neutronic and thermal–electric coupling phenomenon in a 100 kWe-level nuclear silent heat pipe-cooled reactor

Heat pipe-cooled reactors are attractive because of their compact structure, high power capacity and reliability, and inherent safety features. These reactors are distinguished by the use of high-temperature heat pipes that directly bridge the reactor core and energy conversion devices, thus creating a tightly knit modular system. However, comprehensive coupled analysis of these reactors remains challenging because of the intricate multiphysics interactions involved. To address this, the neutronic and thermoelectric coupled phenomena of heat pipe-cooled reactors are investigated in this study. Models are introduced for the point reactor kinetics, core heat transfer, channel heat transfer, two-phase two-dimensional heat pipes, thermoelectric coupling, and cold plates. The channel heat transfer is refined in a 100 kWe-level nuclear silent heat pipe-cooled reactor and a model for the three-dimensional heat transfer process in its thermoelectric matrix established, which effectively resolves the calculation distortions of the lumped model. The maximum deviation between the calculation results from the proposed model and the verification data for a full-system coupled computation is less than 10 K. The core temperature difference from the three-dimensional model is five times that of the lumped model with a maximum average fuel temperature difference of 225.7 K. The maximum and average thermoelectric conversion efficiencies are 15.56 % and 14.43 %, respectively. The failures of one, five, and nine heat pipes are analysed. The failure of a single heat pipe has negligible effects with a peak fuel temperature surge of only 121 K. In contrast, a failure involving nine heat pipes leads to a peak fuel temperature spike of 778 K and a 47.1 % increase in the maximum heat transfer power, marking a critical operational threshold. It is therefore imperative to consider the safety margin in the potential failure of multiple central heat pipes during the preliminary design stages.

Prewarming Parturients for Cesarean Section Does Not Raise Wound Temperature But Body Heat and Level of Comfort: A Randomized Trial

PurposePrewarming before cesarean section lowers the rates of surgical site infections (SSIs). We hypothesized that this effect is explained due to a higher core temperature resulting in a higher wound temperature. DesignWe conducted an open-labeled randomized study with on-term parturients scheduled for elective cesarean section under spinal anesthesia. Participants were randomized into an intervention group (prewarming) and a control group. MethodsCore and wound temperature, comfort level, and examination results were taken at defined times until discharge from the postanesthesia care unit (PACU). There was a follow-up visit and interview 1 day after the procedure. The primary outcome was a difference in wound temperature. The secondary outcomes were differences in core temperature, patient comfort, blood loss, SSI, and neonatal outcome. FindingsWe randomized a total of 60 patients, 30 per group. Prewarming lead to a significantly higher core temperature. Additionally, patient comfort was significantly higher in the prewarming group even after discharge from PACU. We did not find a difference in wound temperature, SSI, neonatal outcome, or blood loss. ConclusionsPrewarming before cesarean section under spinal anesthesia maintains core temperature and improves patient comfort but does not affect wound temperature.

Change In Core Temperature Differences Between Two Work/Rest Cycles In The Heat

Change In Core Temperature Differences Between Two Work/Rest Cycles In The Heat

Soft Wearable Thermal Devices Integrated with Machine Learning

AbstractCore body temperature (CBT) is a vital parameter that provides insight into individuals' overall health. However, existing methods to monitor CBT are mainly invasive and limited to applications in operating rooms. This work reports a soft wearable thermal device with low power operation to accurately monitor the core temperature and overcome these limitations. The thermal device comprises multiple temperature sensors separated with insulating materials of different thermal conductivities. The design provides a well‐defined thermal gradient to characterize the heat flux across the device. Thermal simulation of the devices with finite element analysis provides guidelines on the device design. Experimental studies involving tissue phantom and human subjects characterize and validate the device performance. A machine learning approach can account for heterogeneous, hard‐to‐measure parameters among individuals such as tissue thermal conductivity and heat generation rate. The machine learning algorithms can be trained to accurately quantify the core temperature in human subjects using the zero‐heat‐flux device measured temperature as a reference. The results show that the mean core temperature difference between the zero‐heat‐flux and the devices is 0.01 °C with 95% limits of agreement in the range of −0.08 °C and 0.1 °C.

Skin temperature response to thermal stimulus in patients with hyperhidrosis: A comparative study

Primary hyperhidrosis (HH), the excessive sweating exceeding physiological demand, has been associated to a complex dysfunction of the autonomic nervous system which may explain the disfunction in sweating but may also cause unrevealed alterations in skin blood flow regulation. In fact, HH patients present a sympathetic over-function with less reflex bradycardia in response to the Valsalva maneuver and higher sympathetic skin responses. We aimed to identify response patterns to room thermal stimulus in HH patients compared to a control group in order to investigate putative differences in blood flow assuming that skin temperature in glabrous (non-hairy) areas reflect the sympathetic tone in arteriovenous anastomoses (AVAs). Infrared thermography images were obtained from a cohort of patients diagnosed with HH, followed at a hospital pediatric surgical department and to a sex- and age-matched control group of patients admitted for other surgical procedures. With the participants in Fowler's position, a set of 3 images were captured simultaneously and 44 regions of interest were analyzed, distributed on the palms of the hands, soles of the feet, axilla, and inner canthus. After an acclimatization period at 20 °C, the room temperature was increased to 24, 28 and 32 °C to obtain similar sets of thermograms. A total of 37 patients with HH and 16 participants in the control group were included in the study. At baseline (20 °C), body core temperature (measured in the inner canthus) was significantly higher in the HH patients compared to the controls (p = 0.019 and p = 0.003 in right and left inner canthi, respectively), without any significant differences in the other thermograms. When room temperature was increased, differences in core temperature disappeared, while differences appeared in axilla and palms of the hands with HH patients presenting significantly lower temperature at the three thermal stimulus stages. Patients with HH presented a lower thermoregulatory response when submitted to room temperature increase, which may reflect a vasomotor sympathetic over-function in AVAs.

Both caffeine and Capsicum annuum fruit powder lower blood glucose levels and increase brown adipose tissue temperature in healthy adult males.

Using a combination of respiratory gas exchange, infrared thermography, and blood glucose (BGL) analysis, we have investigated the impact of Capsicum annuum (C. annuum) fruit powder (475 mg) or caffeine (100 mg) on metabolic activity in a placebo controlled (lactose, 100 mg) double-blinded three-way cross-over-design experiment. Metabolic measurements were made on day 1 and day 7 of supplementation in eight adult male participants (22.2 ± 2 years of age, BMI 23 ± 2 kg/m2, x̅ ± SD). Participants arrived fasted overnight and were fed a high carbohydrate meal (90 g glucose), raising BGL from fasting baseline (4.4 ± 0.3 mmol/L) to peak BGL (8.5 ± 0.3 mmol/L) 45 min after the meal. Participants consumed the supplement 45 min after the meal, and both caffeine and C. annuum fruit powder restored BGL (F (8,178) = 2.2, p = 0.02) to near fasting levels within 15 min of supplementation compared to placebo (120 min). In parallel both supplements increased energy expenditure (F (2, 21) = 175.6, p < 0.001) over the 120-min test period (caffeine = 50.74 ± 2 kcal/kg/min, C. annuum fruit = 50.95 ± 1 kcal/kg/min, placebo = 29.34 ± 1 kcal/kg/min). Both caffeine and C. annuum fruit powder increased supraclavicular fossa temperature (F (2,42) = 32, p < 0.001) on both day 1 and day 7 of testing over the 120-min test period. No statistical difference in core temperature or reference point temperature, mean arterial pressure or heart rate was observed due to supplementation nor was any statistical difference seen between day 1 and day 7 of intervention. This is important for implementing dietary ingredients as potential metabolism increasing supplements. Together the results imply that through dietary supplements such as caffeine and C. annuum, mechanisms for increasing metabolism can be potentially targeted to improve metabolic homeostasis in people.

Menstrual Cycle Modulates the Contribution of Dry Heat Loss to Total Heat Loss During Exercise in Warm‐Dry Conditions in Young, Recreationally Active Females: Preliminary Findings

The mid‐luteal phase of the menstrual cycle is characterized by an upward shift in basal body core temperature secondary to elevated circulating estradiol and progesterone levels as compared to the early‐follicular phase. This elevation in body core temperature, perhaps together with increased estradiol‐mediated cutaneous vasodilation, may increase convective and radiative (dry) heat loss by improving core‐to‐skin heat transfer. This increase in dry heat loss may, in turn, reduce the need for sweat secretion (evaporative heat loss) without necessarily altering the relative contribution of these avenues to total heat exchange. Thus, the purpose of this study was to evaluate the hypothesis that females in the mid‐luteal phase would exhibit a greater contribution of dry heat loss to total heat loss as compared to the early‐follicular phase during exercise in warm‐dry conditions.Seven young, recreationally active, ovulating females (3 using hormonal intrauterine devices, mean (SD), 24 (3) years, V̇O2peak 40.5 (3.4) mL kg‐1 min‐1) completed two 45‐min bouts of semi‐recumbent cycling at a low (175 W m‐2; ~40% V̇O2peak) and high (275 W m‐2; ~65% V̇O2peak) rate of metabolic heat production, interspersed by 15‐min rest, in warm‐dry conditions (30.0 (0.2) °C, (25 (9) % relative humidity) in the early‐follicular (cycle days 2‐6) and mid‐luteal phase (days 19‐23). Metabolic heat production and dry and evaporative heat loss were measured via indirect and direct calorimetry, respectively. The contribution of dry heat loss was expressed as a percentage of total heat loss. Body core temperature (esophageal, n=6) and mean skin temperature (8 sites) were measured continuously. Averages of the final 5‐min of exercise in each heat load were compared between phases using dependent, two‐tailed t‐tests.As anticipated, resting body core temperature in the mid‐luteal phase was 0.2 °C [95% CI: 0.1, 0.3] higher than in the early‐follicular phase (p&lt;0.001). Core temperature remained 0.2 °C [0.1, 0.5] higher at the low heat load (37.8 (0.2) vs. 37.6 (0.3) °C, p&lt;0.01), but initial differences in core temperature were not observed in the high heat load (38.4 (0.3) vs. 38.3 (0.4) °C, p=0.83). Skin temperature and core‐to‐skin gradient were similar between phases throughout (all p≥0.21). Total heat loss was not different between phases at the low (162 (8) vs. 162 (13) W m‐2, p=0.93) or high (255 (10) vs. 252 (7) W m‐2, p=0.39) heat loads. However, the contribution of dry heat loss to total heat loss was 3% [1, 4] greater in the mid‐luteal phase at the low heat load (20 (8) vs. 17 (9) %, p&lt;0.01). This difference was not observed at the high heat load (12 (8) vs. 10 (9) %, p=0.16).In this preliminary analysis, females in the mid‐luteal phase exhibited a higher body core temperature and greater contribution of dry heat loss to total heat loss at low exercise‐induced heat loads in warm‐dry conditions. However, these differences were not observed at higher heat loads. These data provide novel mechanistic insight into the shifts in the contribution of the main avenues of heat loss in ovulating females across the menstrual cycle.

Effect of prewarming on body temperature in short-term bladder or prostatic transurethral resection under general anesthesia: A randomized, double-blind, controlled trial

Perioperative hypothermia causes postoperative complications. Prewarming reduces body temperature decrease in long-term surgeries. We aimed to assess the effect of different time-periods of prewarming on perioperative temperature in short-term transurethral resection under general anesthesia. Randomized, double-blind, controlled trial in patients scheduled for bladder or prostatic transurethral resection under general anesthesia. Eligible patients were randomly assigned to receive no-prewarming or prewarming during 15, 30, or 45 min using a forced-air blanket in the pre-anesthesia period. Tympanic temperature was used prior to induction of anesthesia and esophageal temperature intraoperatively. Primary outcome was the difference in core temperature among groups from the induction of general anesthesia until the end of surgery. Repeated measures multivariate analysis of covariance modeled the temperature response at each observation time according to prewarming. We examined modeled contrasts between temperature variables in subjects according to prophylaxis. We enrolled 297 patients and randomly assigned 76 patients to control group, 74 patients to 15-min group, 73 patients to 30-min group, and 74 patients to the 45-min group. Temperature in the control group before induction was 36.5 ± 0.5 °C. After prewarming, core temperature was significantly higher in 15- and 30-min groups (36.8 ± 0.5 °C, p = 0.004; 36.7 ± 0.5 °C, p = 0.041, respectively). Body temperature at the end of surgery was significantly lower in the control group (35.8 ± 0.6 °C) than in the three prewarmed groups (36.3 ± 0.6 °C in 15-min, 36.3 ± 0.5 °C in 30-min, and 36.3 ± 0.6 °C in 45-min group) (p < 0.001). Prewarming prior to short-term transurethral resection under general anesthesia reduced the body temperature drop during the perioperative period. These time-periods of prewarming also reduced the rate of postoperative complications.Study Registration Registered at ClinicalTrials.gov (Identifier: NCT03630887).

Analysis on passive residual heat removal system with heat pipes for longterm decay heat removal of small lead-based reactor

.A lead-based reactor with employing heat pipes as passive residual heat removal system (PRHRS) for longterm decay heat removal was designed. Three-dimensional computational fluid dynamics (CFD) software FLUENT was adopted to simulate the thermal-hydraulic characteristics of the PRHRS under Station-Black-Out (SBO) accident condition. The results showed that heat in the core could be removed smoothly by the PRHRS, and the core temperature difference is less than 20 K.

Menstrual cycle effects on cardiovascular drift and maximal oxygen uptake during exercise heat stress.

Compared to other modulators of physiological strain associated with exercise heat stress, hyperthermia results in the greatest magnitude of cardiovascular (CV) drift and associated decrements in maximal oxygen uptake ([Formula: see text]). To determine if elevated core temperature in the luteal phase (LP) of the menstrual cycle results in greater CV drift and reductions in [Formula: see text] versus the follicular phase (FP). Seven women performed 15- and 45-min cycling bouts on separate occasions (60% [Formula: see text], 35°C) followed by a [Formula: see text] test during the FP and LP. CV drift was measured between 15 and 45min during the 45-min bout, and the 15-min bout was for measuring [Formula: see text] over the same time interval that CV drift occurred. Core temperature during LP was ~ 0.3°C higher than FP (P < 0.05), but changes from rest during exercise were similar between phases (all P > 0.05). Heart rate increased significantly over time but was not different between phases (P = 0.78). Stroke volume decreased more over time during LP compared to FP (P = 0.02), but the values were similar at the end of exercise between phases (both time points P > 0.05). [Formula: see text] decrements for FP (13%) and LP (16%) were also comparable (P = 0.97). The LP-FP difference in core temperature in this study was not sufficient to amplify CV strain and decrements in [Formula: see text]. Greater differences in core temperature may be required to independently modulate CV drift and accompanying decrements in [Formula: see text] during prolonged exercise heat stress.

Contribution of wetted clothing to body energy exchange and heat stress

Quantifying the impact of clothing thermal and evaporation resistance is essential to providing representative boundary conditions for physiological modeling. In many models, sweat is assumed to drip off the skin surface to the environment and is not captured in clothing. In high metabolic rate and high temperature and humidity conditions the sweat produced by the body has the potential to saturate semipermeable clothing ensembles, changing the assumptions of the model. Workers, athletes and soldiers commonly wear encapsulating versions of such clothing to protect against environmental hazards. A saturated clothing model is proposed based on the ASHRAE two-node model using a saturated spot element in parallel with the existing method to account for sweat absorbed in the clothing. The work uses fundamental heat and mass transfer principles, modifying the existing formula using clothing measurements and basic assumptions. The effectiveness of the model is demonstrated by comparing the predictions of the original and proposed models, to the results of 21 soldiers exercising. The soldiers wore combat pants and shirt, helmet, gloves, shoes, socks, and underwear, and walked in a thermal chamber for 2 h at 42.2 °C dry bulb temperature, 54.4 °C wet bulb temperature, 20% relative humidity, and airspeed of 2 m/s. Core temperature, seven skin temperatures, heart rate, and total sweat loss were measured. The original model provides an average core temperature difference compared with the human subject results of 1.31 °C (SD = 0.557 °C) while the modified model improves the final prediction of core temperature to within an average of 0.15 °C (SD = 0.383 °C). The new model shows an improvement in the prediction of human core temperature under the tested conditions where dripping sweat will saturate clothing. The format can be used in multi-segmented thermal models and can continue to be developed and improved as more information on wetted clothing properties become available.

Experimental evidence that stripes do not cool zebras

There are as many as 18 theories for the possible functions of the stripes of zebras, one of which is to cool the animal. We performed field experiments and thermographic measurements to investigate whether thermoregulation might work for zebra-striped bodies. A zebra body was modelled by water-filled metal barrels covered with horse, cattle and zebra hides and with various black, white, grey and striped patterns. The barrels were installed in the open air for four months while their core temperature was measured continuously. Using thermography, the temperature distributions of the barrel surfaces were compared to those of living zebras. The sunlit zebra-striped barrels reproduced well the surface temperature characteristics of sunlit zebras. We found that there were no significant core temperature differences between the striped and grey barrels, even on many hot days, independent of the air temperature and wind speed. The average core temperature of the barrels increased as follows: white cattle, grey cattle, real zebra, artificial zebra, grey horse, black cattle. Consequently, we demonstrate that zebra-striped coats do not keep the body cooler than grey coats challenging the hypothesis of a thermoregulatory role of zebra stripes.

Modeling of Gender Differences in Thermoregulation.

In January 2013, the Department of Defense lifted a ban that had prevented women from holding combat positions in the military. However, innate differences in physical traits and physiology between men and women likely will result in differences in physical performance. Sex differences in thermoregulation is a key area that needs to be examined due to the potential impact on physical performance. Therefore, we expanded our previously developed thermoregulation model (TRM) to include the effects of gender. Women have been found to have a lower sweat output in heat stress and lesser shivering in cold stress than men; therefore, the equations for sweat mass loss rate and shivering heat generation were modified for women accordingly. The updated TRM showed good agreement with female data collected from exercise in cool to hot conditions, cold air exposure, and cold water immersion. Gender differences in sweat evaporation appear minimal except for sufficiently high exercise-heat combinations. Gender differences in core temperature and heat generation during cold stress are significant. The expanded TRM can be used to assess gender-specific thermal response with future application to predicting performance differences and optimizing warfighter effectiveness for a wide range of military relevant tasks.

Core Temperature in Service Members With and Without Traumatic Amputations During a Prolonged Endurance Event.

Service members with traumatic amputations may be at an increased risk of elevated core body temperature, since their ability to dissipate heat may decrease with the reduction in body surface area (BSA) after injury. Elevated core temperature can impair physical performance during combat operations potentially putting the service members and their teams at risk. The purpose of this study was to compare core temperature between individuals with and without amputations during a prolonged endurance event. Twenty healthy male military service members (10 with amputations, 10 without) participated in the Bataan Memorial Death March 26.2-mile event on March 27, 2011. Data collected include BSA, body mass index, body composition, body weight before and after the event, core temperature during the event, and postevent hydration status. Body composition was measured by dual-energy X-ray absorptiometry. Body weight was measured by digital scale. Core temperature was measured by ingestible sensor. Hydration was measured by urine specific gravity. The Walter Reed Army Medical Center Institutional Review Board approved this study and participants provided written informed consent. Three participants' data were not included in the analyses. No significant differences in core temperature were found between participants in both groups, and no correlation was found between core temperature and either BSA or hydration status. There was no significant difference in maximal core temperature between the groups (p = 0.27). Nearly all participants (8 control, 6 amputation) reached 38.3°C, the threshold for increased risk of heat exhaustion. No subjects reached 40.0°C, the threshold for increased risk of heat stroke. Time spent above the 38.3°C threshold was not significantly different between groups, but varied widely by participant in relation to the duration of the event. Participants without amputations finished the event faster than participants with amputations (7.9 ± 1.4 vs. 9.6 ± 0.96, p < 0.01), possibly indicating that participants with amputations self-selected a slower pace to attenuate increased core temperature. Until conclusive evidence is accumulated, it is prudent for military leaders, trainers, and military service members to closely monitor this population during physical activity to prevent heat injuries.

Autonomic changes induced by provocative motion in rats bred for high (HAB) and low (LAB) anxiety-related behavior: Paradoxical responses in LAB animals

In humans, associations between anxiety and nausea (including motion-induced) are reported but the underlying mechanisms are not known. Hypothermia is proposed to be an index of nausea in rats. Utilising hypothermia and heart rate as outcome measures we investigated the response to provocative motion in rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviors and in non-selected (NAB) rats to further elucidate the potential relationship between hypothermia and nausea-like state. Core temperature and electrocardiogram were monitored in each group (n=10 per group) using telemetry, with or without circular motion (40min; 0.75Hz) and vehicle or diazepam (2mg/kg, i.p.) pre-treatment. Heart rate and time- and frequency-domain parameters of heart rate variability were derived from the electrocardiogram. There was no baseline difference in core temperature between the three groups (mean 38.0±0.1°C), but HAB animals had a significantly lower resting heart rate (330±7bpm) compared to LAB (402±5bpm) and NAB (401±9bpm). Animals in all groups exhibited hypothermia during motion (HAB: 36.3±0.1°C; NAB: 36.4±0.1°C; LAB: 34.9±0.2°C) with the magnitude (area under the curve, AUC) of the response during 40-min motion being greater in LAB compared to NAB and HAB rats, and this was also the case for the motion-induced bradycardia. Diazepam had minimal effects on baseline temperature and heart rate in all groups, but significantly reduced the hypothermia response (AUC) to motion in all groups by ~30%. Breeding for extremes in anxiety-related behavior unexpectedly selects animals with low trait anxiety that have enhanced bradycardia and hypothermic responses to motion; consequently, this animal model appears to be not suitable for exploring relationships between anxiety and autonomic correlates of nausea. Thermal and cardiovascular responses to motion were little different between HAB and NAB rats indicating that either hypothermia is not an index of a nausea-like state in rats, or that the positive correlation between anxiety and nausea demonstrated in humans does not exist in rats. The mechanism underlying the enhanced physiological responses in LAB requires more detailed study and may provide a novel model to investigate factors modulating motion sensitivity.

Transgenic sickle cell trait mice do not exhibit abnormal thermoregulatory and stress responses to heat shock exposure

There remains controversy over whether individuals with sickle cell trait (SCT) are vulnerable to health risks during physical activity in high temperatures. We examined thermoregulatory and stress-related responses to heat exposure in SCT and wild-type (WT) mice. No significant differences in core temperature (Tc) were observed between SCT and WT mice during heat exposure. There was no correlation between peak Tc during heat exposure and levels of hemoglobin S in SCT mice. Basal levels of circulating inflammatory and stress-related markers were not significantly different between SCT and WT mice. Although heat exposure caused significant increases in plasma interleukins 1β and 6, and 8-isoprostane in SCT and WT mice, no differences were found between SCT and WT mice with similar thermal response profiles during heat exposure. SCT mice had significantly higher expression of heat shock protein 72 in heart, liver and gastrocnemius muscle than WT mice under control and post-heat conditions. In conclusion, there is neither thermoregulatory dysfunction nor abnormal stress-related response in SCT mice exposed to moderate heat. The hemoglobin variant in mice is associated with altered tissue stress protein homeostasis.