Temperature最新文献

Our body temperature is normally kept within a narrow range of 1°C. For example, if our body temperature rises, such as in a hot environment or due to strenuous exercise, our thermoregulatory system will trigger a powerful heat defense response with vasodilation, sweating, and lowered metabolism. During fever, which often involves body temperatures of up to 41°C, this heat defense mechanism is apparently inhibited; otherwise, the rising body temperature would be immediately combated, and fever would not be allowed to develop. New evidence suggests how and where this inhibition takes place. In two consecutive studies from Cheng et al. and Xu et al., it has been shown that prostaglandin E₂, which generates fever by acting on thermosensory neurons in the preoptic hypothalamus, also acts on neurons in the brainstem parabrachial nucleus, which receive temperature information from temperature-activated spinal cord neurons and relay this information to the thermoregulatory center in the hypothalamus to either induce cold or heat defenses. By acting on the same type of prostaglandin E₂ receptor that is critical for fever generation in the preoptic hypothalamus, the EP₃ receptor, prostaglandin E₂ inhibits the signaling of the heat-responsive parabrachial neurons, while stimulating the cold-responsive neurons. These novel findings thus show that prostaglandin E₂, by binding to the same receptor subtype in the parabrachial nucleus as in the preoptic hypothalamus, adjusts the sensitivity of the thermosensory system in a coordinated manner to allow the development of febrile body temperatures.

While foot immersion and neck cooling have been recommended for protecting heat-vulnerable groups, recent evidence does not support their efficacy for mitigating increases in physiological heat strain in older adults. However, their influence on self-reported environmental symptoms and mood-state remains unclear. Seventeen older adults (nine females, median [interquartile range] age: 72 [69-74]) completed three randomized heat exposures (6-h; 38°C, 35% relative humidity) with no cooling (control), foot immersion to mid-calf in 20°C water for the final 40-min of each hour (foot immersion), or foot immersion with a wet towel (20°C) around the neck (foot immersion with neck cooling). Core temperature, skin temperature, and heart rate areas under the curve (AUC) were assessed as indicators of cumulative physiological strain. Environmental symptom scores (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were evaluated at end-heating (adjusted for pre-exposure). Core temperature AUC was not different between conditions (p = 0.418). However, the skin temperature and heart rate AUCs were 11.8°C · h [95% confidence interval: 8.1, 15.5] and 12.5 bpm · h [0.1, 24.8] lower for foot immersion and 16.6°C · h [12.9, 20.3] and 19.6 bpm · h [7.2, 32.0] lower for foot immersion with neck cooling compared to control (p ≤ 0.032). Environmental symptom scores were 0.8-fold [0.6, 1.0] lower for both foot immersion with and without neck cooling, compared to control (both p = 0.036). Mood disturbance was not different between conditions (both p ≥ 0.275). Foot immersion with and without neck cooling reduces self-reported environmental symptoms in older adults despite having little effect on physiological heat strain.

Wet bulb globe temperature (WBGT) is a commonly used measure to predict heat strain in workers. Different combinations of environmental conditions can create equivalent WBGT, yet it remains unknown whether biophysical, physiological, and perceptual responses vary when working in different but equivalent hot conditions. The purpose of the study was to compare body heat storage and physiological and perceptual strain during walking in hot-dry and warm-wet conditions of the same WBGT. Twelve subjects (age: 22 ± 2 y) walked for 90 min at 60% maximum heart rate in a 27.8°C WBGT environment of hot-dry (HD: 40°C, 19% relative humidity) or warm-wet (WW: 30°C, 77% relative humidity) conditions. Partitional calorimetry was used to estimate heat storage. Core temperature at 90 min (HD: 38.5 ± 0.5°C; WW: 38.4 ± 0.3°C, p = 0.244) and cumulative heat storage (HD: 115 ± 531 Kj; WW: 333 ± 269 Kj, p = 0.242) were not different. At 90 min, heart rate was not different (HD: 160 ± 19 bpm; WW: 154 ± 15 bpm, p = 0.149) but skin temperature (HD: 36.6 ± 0.9°C; WW: 34.7 ± 0.6°C, p < 0.001), thirst (HD: 6.8 a.u.; WW: 5.3 a.u. p = 0.043), and sweat rate (HD: 15.1 ± 4.4 g·min^-1; WW: 10.0 ± 4.1 g·min^-1, p < 0.001) were greater in HD compared to WW. Hot environments of equivalent 27.8°C WBGT created equivalent core temperature despite differences in physiological strain during exercise, including earlier onset of cardiovascular strain, greater sweat rate, and higher skin temperature compared to a WW environment. ClinicalTrials.gov ID NCT04624919.

The International Olympic Committee recently introduced a consensus statement on recommendations for outdoor sports in the heat. However, indoor sports such as fencing whereby athletes are required to wear full body protective clothing when competing have received no recommendations. Such scenarios could cause high thermoregulatory demands particularly as competition progresses into latter rounds (direct elimination; DE). Therefore, the aim of this study was to determine the thermoregulatory responses of épée fencing across different phases of competition (Poule and DE). Seven well-trained fencers competed in a simulated competition comprising of seven Poule and seven DE fights. Gastrointestinal temperature (T_gast), skin temperature (T_skin), mask temperature (T_mask), heart rate (HR), thermal sensation, differentiated ratings of perceived exertion (RPE), and movement characteristics were collected for all fights. There was a moderate thermoregulatory demand during Poule rounds shown by post-fight T_gast (38.1 ± 0.4°C), T_skin (34.4 ± 0.7°C), and thermal sensation ratings (6 ± 1). A greater thermoregulatory and perceptual demand observed during DE rounds evidenced by T_gast (38.7 ± 0.3°C post fight), T_skin (35.1 ± 0.7°C), thermal sensation (7 ± 1), increases in T_mask across DE rounds (~1.1°C), and RPE (~15). Furthermore, a significant (p < 0.05) reduction in distance covered from DE 1 to DE 7 suggests a thermoregulatory based impact on performance. This is the first study demonstrating the thermoregulatory demands of épée fencing, highlighting the need to develop heat exertion guidelines within fencing.

Impaired thermoregulatory function is a clinical feature of many health conditions that affect triathletes using wheelchairs and consequently, individual athlete performances may fluctuate according to environmental temperature. We aimed to determine the effect of 1) water temperature on wheelchair triathlon swim time and 2) air temperature on handcycle and wheelchair run (push) time. Published race records from 2017 to 2023 (n = 49 events) were extracted from the World Triathlon website. Bayesian negative binomial regression was used to separately model the nonlinear relationships between water temperature and swim time, and air temperature and handcycle and push time. Age, sex, sport class, whether wetsuits were worn (swim model), and swim time (handcycle and push model) were included as fixed effects. Over the observed water temperature range of 15.7-30.5°C, male swim time (mm:ss) improved from 14:13 (95% credible interval [CrI] = 12:27, 16:09) to 12:35 (95% CrI = 11:00, 14:19). Female swim time improved from 15:33 (95% CrI = 13:24, 17:55) to 12:46 (95% CrI = 11:03, 14:38). It was unclear whether handcycle and push time slowed over the observed air temperature range of 14-33°C. Warmer water temperatures, up to 30.5°C, were associated with faster swim times. It was unclear whether combined handcycle and push time slowed with increases in air temperature, up to 33°C. The integration of information on athlete impairment type and severity with performance data is needed to better understand the extent to which individual athlete performances fluctuate across environmental conditions.