L-arginine alleviates heat stress-induced mammary gland injury through modulating CASTOR1-mTORC1 axis mediated mitochondrial homeostasis

As global warming intensifies, extreme heat is becoming increasingly frequent. These extreme heatwaves have decreased the milk production of dairy animals such as cows and goats and have caused significant damage to the entire dairy industry. It is known that heat stress (HS) can induce the apoptosis and autophagy of mammary epithelial cells (MECs), leading to a decrease in lactating MECs. L-arginine can effectively attenuate HS-induced decreases in milk yield, but the exact mechanisms are not fully understood. In this study, we found that HS upregulated the arginine sensor CASTOR1 in mouse MECs. Arginine activated mTORC1 activity through CASTOR1 and promoted mitochondrial biogenesis through the mTORC1/PGC-1α/NRF1 pathway. Moreover, arginine inhibited mitophagy through the CASTOR1/PINK1/Parkin pathway. Mitochondrial homeostasis ensures ATP synthesis and a stable cellular redox state for MECs under HS, further alleviating HS-induced damage and improving the lactation performance of MECs. In conclusion, these findings reveal the molecular mechanisms by which L-arginine relieves HS-induced mammary gland injury, and suggest that the intake of arginine-based feeds or feed additives is a promising method to increase the milk yield of dairy animals in extreme heat conditions.

Agreement between measured and self-reported physiological strain in males and females during simulated occupational heat stress

RATIONALE

Monitoring physiological strain is recommended to safeguard workers during heat exposure, but is logistically challenging. The perceptual strain index (PeSI) is a subjective estimate thought to reflect the physiological strain index (PSI) that requires no physiological monitoring. However, sex is known to influence perceptions of heat stress, potentially limiting the utility of the PeSI.

OBJECTIVES

The objective of this study was to assess whether sex modifies the relationship between PeSI and PSI.

METHODS

Thirty-four adults (15 females) walked on a treadmill (moderate intensity; ~200 W/m2) for 180 min or until termination (volitional fatigue, rectal temperature ≥39.5°C) in 16°C, 24°C, 28°C, and 32°C wet-bulb globe temperatures. Rectal temperature and heart rate were recorded to calculate PSI (0-10 scale). Rating of perceived exertion and thermal sensation were recorded to calculate PeSI (0-10 scale). Relationships between PSI and PeSI were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. Mean absolute error between measures was calculated by summing absolute errors between the PeSI and the PSI and dividing by the sample size.

FINDINGS

PSI increased with PeSI (p < 0.01) but the slope of this relation was not different between males and females (p = 0.83). Mean bias between PSI and PeSI was small (-0.4 points), but the 95% LoA (-3.5 to 2.7 points) and mean absolute error were wide (1.3 points).

IMPACT

Our findings indicate that sex does not appreciably impact the agreement between the PeSI and PSI during simulated occupational heat stress. The PeSI is not a suitable surrogate for the PSI in either male or female workers.

Projection of future heat-related morbidity in three metropolitan prefectures of Japan based on large ensemble simulations of climate change under 2 °C global warming scenarios

Recently, global warming has become a prominent topic, including its impacts on human health. The number of heat illness cases requiring ambulance transport has been strongly linked to increasing temperature and the frequency of heat waves. Thus, a potential increase in the number of cases in the future is a concern for medical resource management. In this study, we estimated the number of heat illness cases in three prefectures of Japan under 2 °C global warming scenarios, approximately corresponding to the 2040s. Based on the population composition, a regression model was used to estimate the number of heat illness cases with an input parameter of time-dependent meteorological ambient temperature or computed thermophysiological response of test subjects in large-scale computation. We generated 504 weather patterns using 2 °C global warming scenarios. The large-scale computational results show that daily amount of sweating increased twice and the core temperature increased by maximum 0.168 °C, suggesting significant heat strain. According to the regression model, the estimated number of heat illness cases in the 2040s of the three prefectures was 1.90 (95%CI: 1.35-2.38) times higher than that in the 2010s. These computational results suggest the need to manage ambulance services and medical resource allocation, including intervention for public awareness of heat illnesses. This issue will be important in other aging societies in near future.

Social interactions and heat stress mitigation among elderly people in a healthy city

BACKGROUND

Increased frequencies and duration of extreme heat events have caused severe heat stress, especially among elderly people. Despite its obvious cause and universally known preventive measures, heat stress preventive measures have not been implemented effectively at community levels. This study examined heat coping practices among elderly people and their associations with living conditions, social interactions, and community involvement.

METHODS

A self-administered questionnaire was done to assess heat-coping practices to mitigate heat stress, living conditions, and interactions with family, friends, and neighbours. Participants were 3000 randomly selected elderly people aged 65 years and older living in Owariasahi, Japan, a city that applies the 2004 Healthy City Approach. A generalised linear regression model was applied with binominal distribution to examine the association between social interactions and application of heat-coping practices. Sex and ages were adjusted in the model.

FINDINGS

Among the 2127 elderly people who completed the survey, 745 (35·0%) had heat stress during the summer of the survey year. The presence of heat stress was higher in male participants living alone and having less interaction with friends and neighbours; only interaction with friends and relatives showed difference in the occurrence of the heat-related illness in female participants. The use of ice packs, air conditioners, and the opening of windows or doors were associated with the presence of heat stress. The odds of not applying relevant preventive practices were higher in participants disconnected from relatives and friends (odds ratio 1·52 [95% CI 1·12-2·04]). Participants living alone and disconnected from their neighbours showed similar trends to the connection with relatives and friends but not significantly.

INTERPRETATION

The findings of the study indicated that heat stress mitigative measures were underused in elderly people who are socially disconnected. Heat illness prevention programmes need to focus on outreach to the disadvantaged population.

FUNDING

Japan Society for the Promotion of Science.

High-resolution projections of outdoor thermal stress in the twenty-first century: a Tasmanian case study

To adapt to Earth's rapidly changing climate, detailed modelling of thermal stress is needed. Dangerous stress levels are becoming more frequent, longer, and more severe. While traditional measurements of thermal stress have focused on air temperature and humidity, modern measures including radiation and wind speed are becoming widespread. However, projecting such indices has presented a challenging problem, due to the need for appropriate bias correction of multiple variables that vary on hourly timescales. In this paper, we aim to provide a detailed understanding of changing thermal stress patterns incorporating modern measurements, bias correction techniques, and hourly projections to assess the impact of climate change on thermal stress at human scales. To achieve these aims, we conduct a case study of projected thermal stress in central Hobart, Australia for 2040-2059, compared to the historical period 1990-2005. We present the first hourly metre-scale projections of thermal stress driven by multivariate bias-corrected data. We bias correct four variables from six dynamically downscaled General Circulation Models. These outputs drive the Solar and LongWave Environmental Irradiance Geometry model at metre scale, calculating mean radiant temperature and the Universal Thermal Climate Index. We demonstrate that multivariate bias correction can correct means on multiple time scales while accurately preserving mean seasonal trends. Changes in mean air temperature and UTCI by hour of the day and month of the year reveal diurnal and annual patterns in both temporal trends and model agreement. We present plots of future median stress values in the context of historical percentiles, revealing trends and patterns not evident in mean data. Our modelling illustrates a future Hobart that experiences higher and more consistent numbers of hours of heat stress arriving earlier in the year and extending further throughout the day.

A Novel Conceptual Model for Human Heat Tolerance

Human "heat tolerance" has no accepted definition or physiological underpinnings; rather, it is almost always discussed in relative or comparative terms. We propose to use environmental limits to heat balance accounting for metabolic rate and clothing, that is, the environments for which heat stress becomes uncompensable for a specified metabolic rate and clothing, as a novel metric for quantifying heat tolerance.

Changes in surrogate markers of intestinal epithelial injury and microbial translocation in young and older men during prolonged occupational heat stress in temperate and hot conditions

PURPOSE

Exertional heat stress can cause damage to the intestinal epithelium and disrupt gastrointestinal barrier integrity, leading to microbial translocation (MT) linked to the development of heat stroke. This study aimed to assess age-related differences in markers of intestinal epithelial injury and MT following non-heat stress and high-heat stress exercise in healthy young and older men.

METHODS

Markers of intestinal epithelial injury (intestinal fatty acid-binding protein-'IFABP') and MT (soluble cluster of differentiation 14-'sCD14'; and lipopolysaccharide-binding protein-'LBP') were assessed in healthy young (18-30 y, n = 13) and older (50-70 y) men (n = 12). Blood samples were collected before, after 180 min of moderate-intensity (metabolic rate: 200 W/m2) walking and following 60 min recovery in either a non-heat stress [temperate: 21.9 °C, 35% relative humidity (RH)] or high-heat stress (hot: 41.4 °C, 35% RH) environment.

RESULTS

There were no differences in IFABP and sCD14 between the young and older groups in the temperate condition, while LBP was greater in the older group (+ 0.66 ug/mL; + 0.08 to + 1.24 ug/mL). In the hot condition, the older group experienced greater increases in IFABP compared to the young group (+ 712 pg/mL/hr; + 269 to + 1154 pg/mL/hr). However, there were no clear between-group differences for sCD14 (+ 0.24 ug/mL/hr, - 0.22 to + 0.70 ug/mL/hr) or LBP (+ 0.86 ug/mL/hr, - 0.73 to + 2.46 ug/mL/hr).

CONCLUSION

While older men may experience greater intestinal epithelial injury following exercise in the heat; this did not lead to a greater magnitude of microbial translocation relative to their younger counterparts.

Protective effects of Lactobacillus on heat stress-induced intestinal injury in finisher broilers by regulating gut microbiota and stimulating epithelial development

Heat stress (HS) is a critical challenge in broilers due to the high metabolic rate and lack of sweat glands. Results from this study show that implementing a cyclic chronic HS (34 °C for 7 h/d) to finisher broilers decreased the diversity of cecal microbiota and impaired intestinal barrier, resulting in gut leak and decreased body weight (both P < 0.05). These alterations might be related to inflammatory outbursts and the retarded proliferation of intestinal epithelial cells (IECs) according to the transcriptome analysis. Considering the potential beneficial properties of Lactobacillus on intestinal development and function, the protective effects of Lactobacillus rhamnosus (L. rhamnosus) on the intestine were investigated under HS conditions in this study. Orally supplemented L. rhamnosus improved the composition of cecal microbiota and upregulated the transcription of tight junction proteins in both duodenum and jejunum, with a consequent suppression in intestinal gene expressions of pro-inflammatory cytokines and facilitation in digestive capability. Meanwhile, the jejunal villus height of the birds that received L. rhamnosus was significantly higher compared with those treated with the broth (P < 0.05). The expression abundances of genes related to IECs proliferation and differentiation were increased by L. rhamnosus, along with upregulated mRNA levels of Wnt3a and β-catenin in jejunum. In addition, L. rhamnosus attenuated enterocyte apoptosis as indicated by decreased caspase-3 and caspase-9 gene expressions. The results indicated that oral administration with L. rhamnosus mitigated HS-induced dysfunction by promoting intestinal development and epithelial maturation in broilers and that the effects of L. rhamnosus might be dependent of Wnt/β-catenin signaling.

Muscle Cooling Before and in the Middle of a Session: There Are Benefits on Subsequent Localized Endurance Performance in a Warm Environment

ABSTRACT

Baláš, J, Kodejška, J, Procházková, A, Knap, R, and Tufano, JJ. Muscle cooling before and in the middle of a session: there are benefits on subsequent localized endurance performance in a warm environment. J Strength Cond Res 38(3): 533-539, 2024-Localized cold-water immersion (CWI) has been shown to facilitate recovery in the middle of a session of exhaustive repeated forearm contractions. However, it has been suggested that these benefits may be attributed to "precooling" the muscle before an activity, as opposed to cooling a previously overheated muscle. Therefore, this study aimed to determine how precooling and mid-cooling affects localized repeated muscular endurance performance in a warm environment. Nineteen subjects completed a familiarization session and 3 laboratory visits, each including 2 exhaustive climbing trials separated by 20 minutes of recovery: PRE CWI (CWI, trial 1; passive sitting [PAS], trial 2); MID CWI (PAS, trial 1; CWI, trial 2); and CONTROL (PAS, trial 1; PAS, trial 2). Climbing trial 1 in PRE CWI was 32 seconds longer than in CONTROL ( p = 0.013; d = 0.46) and 47 seconds longer than in MID CWI ( p = 0.001; d = 0.81). The time of climbing trial 2 after PAS (PRE CWI and CONTROL) was very similar (312 vs. 319 seconds) irrespective of the first trial condition. However, the time of the second trial in MID CWI was 43 seconds longer than in PRE CWI ( p < 0.001; d = 0.63) and 50 seconds longer than in CONTROL ( p < 0.001; d = 0.69). In warm environments, muscle precooling and mid-cooling can prolong localized endurance performance during climbing. However, the effectiveness of mid-cooling may not be as a "recovery strategy" but as a "precooling" strategy to decrease muscle temperature before subsequent performance, delaying the onset of localized heat-induced neuromuscular fatigue.

Elevated brain temperature under severe heat exposure impairs cortical motor activity and executive function

BACKGROUND

Excessive heat exposure can lead to hyperthermia in humans, which impairs physical performance and disrupts cognitive function. While heat is a known physiological stressor, it is unclear how severe heat stress affects brain physiology and function.

METHODS

Eleven healthy participants were subjected to heat stress from prolonged exercise or warm water immersion until their rectal temperatures (Tre) attained 39.5°C, inducing exertional or passive hyperthermia, respectively. In a separate trial, blended ice was ingested before and during exercise as a cooling strategy. Data were compared to a control condition with seated rest (normothermic). Brain temperature (Tbr), cerebral perfusion, and task-based brain activity were assessed using magnetic resonance imaging techniques.

RESULTS

Tbr in motor cortex was found to be tightly regulated at rest (37.3°C ± 0.4°C (mean ± SD)) despite fluctuations in Tre. With the development of hyperthermia, Tbr increases and dovetails with the rising Tre. Bilateral motor cortical activity was suppressed during high-intensity plantarflexion tasks, implying a reduced central motor drive in hyperthermic participants (Tre = 38.5°C ± 0.1°C). Global gray matter perfusion and regional perfusion in sensorimotor cortex were reduced with passive hyperthermia. Executive function was poorer under a passive hyperthermic state, and this could relate to compromised visual processing as indicated by the reduced activation of left lateral-occipital cortex. Conversely, ingestion of blended ice before and during exercise alleviated the rise in both Tre and Tbr and mitigated heat-related neural perturbations.

CONCLUSION

Severe heat exposure elevates Tbr, disrupts motor cortical activity and executive function, and this can lead to impairment of physical and cognitive performance.

Facial fanning reduces heart rate but not tolerance to a simulated hemorrhagic challenge following exercise heat stress in young healthy humans

We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 yr) exercised at ∼63% V̇o2max until core temperature had increased ∼1.5°C before undergoing LBNP to presyncope either with fanning to return face skin temperature to baseline (Δ-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg·min). Before LBNP, whole body and face skin temperatures were elevated from baseline in both trials (38.0 ± 0.5°C and 36.3 ± 0.5°C, respectively, both P < 0.001). During LBNP, face skin temperature decreased in the Fan trial (30.9 ± 1.0°C) but was unchanged in the No Fan trial (36.1 ± 0.6°C, between trials P < 0.001). Mean arterial pressure was not different between trials (P = 0.237) and was similarly reduced at presyncope in both trials (from 82 ± 7 to 67 ± 8 mmHg, P < 0.001). During LBNP, heart rate was attenuated in the Fan trial at Mid LBNP (146 ± 16 vs. 158 ± 12 beats/min, P = 0.036) and at peak heart rate (158 ± 15 vs. 170 ± 15 beats/min; P < 0.001). LBNP tolerance was not different between trials (321 ± 248 vs. 328 ± 115 mmHg·min, P = 0.851). In exercise heat-stressed individuals, lowering face skin temperature to normothermic values suppressed heart rate thereby altering cardiovascular control during a simulated hemorrhagic challenge without reducing tolerance.

NINJ1 mediates inflammatory cell death, PANoptosis, and lethality during infection conditions and heat stress

Innate immunity provides the first line of defense through multiple mechanisms, including pyrogen production and cell death. While elevated body temperature during infection is beneficial to clear pathogens, heat stress (HS) can lead to inflammation and pathology. Links between pathogen exposure, HS, cytokine release, and inflammation have been observed, but fundamental innate immune mechanisms driving pathology during pathogen exposure and HS remain unclear. Here, we use multiple genetic approaches to elucidate innate immune pathways in infection or LPS and HS models. Our results show that bacteria and LPS robustly increase inflammatory cell death during HS that is dependent on caspase-1, caspase-11, caspase-8, and RIPK3 through the PANoptosis pathway. Caspase-7 also contributes to PANoptosis in this context. Furthermore, NINJ1 is an important executioner of this cell death to release inflammatory molecules, independent of other pore-forming executioner proteins, gasdermin D, gasdermin E, and MLKL. In an in vivo HS model, mortality is reduced by deleting NINJ1 and fully rescued by deleting key PANoptosis molecules. Our findings suggest that therapeutic strategies blocking NINJ1 or its upstream regulators to prevent PANoptosis may reduce the release of inflammatory mediators and benefit patients.

Augmented human thermal discomfort in urban centers of the Arabian Peninsula

Anthropogenic climate change has amplified human thermal discomfort in urban environments. Despite the considerable risks posed to public health, there is a lack of comprehensive research, evaluating the spatiotemporal changes in human thermal discomfort and its characteristics in hot-hyper arid regions, such as the Arabian Peninsula (AP). The current study analyzes spatiotemporal changes in human thermal discomfort categories and their characteristics in AP, using the newly developed high-resolution gridded ERA5-HEAT (Human thErmAl comforT) dataset for the period 1979-2022. In addition, the study assesses the interplay between the Universal Thermal Climate Index (UTCI) and El Niño-Southern Oscillation (ENSO) indices for the study period. The results reveal a significant increase in human thermal discomfort and its characteristics, with higher spatial variability in the AP region. The major urban centers in the southwestern, central, and southeastern parts of AP have experienced significant increases in human thermal discomfort (0.4-0.8 °C), with higher frequency and intensity of thermal stress during the study period. The temporal distribution demonstrates a linear increase in UTCI indices and their frequencies and intensities, particularly from 1998 onward, signifying a transition towards a hotter climate characterized by frequent, intense, and prolonged heat stress conditions. Moreover, the UTCI and ENSO indices exhibit a dipole pattern of correlation with a positive (negative) pattern in the southwestern (eastern parts) of AP. The study's findings suggest that policymakers and urban planners need to prioritize public health and well-being in AP's urban areas, especially for vulnerable groups, by implementing climate change adaptation and mitigation strategies, and carefully designing future cities to mitigate the effects of heat stress.

Assessing heatwave effects on disabled persons in South Korea

This study investigated the risk of heatwaves for people with disabilities and other socioeconomic attributes using Health Care Bigdata in South Korea. The Health Care Bigdata provides detailed information on heat-related illness (HRI) patients in 2011-2020 from seven major cities. We employed the Distributed Lag Nonlinear Model (DLNM) to measure heat waves' relative risk. Our findings are four-fold. First, the relative risk (RR) of disabled people was 5.075 (95% confidence interval 4.476-5.674), significantly surpassing that of non-disabled people, 3.296 (2.517-4.075). Second, among various personal characteristics studied, disability influenced RR the most, exceeding impacts from elderly (4.457: 3.748-5.166), low-income (3.909: 3.004-4.813), and outdoor (4.052: 2.940-5.164). Third, the disabled young group (5.305: 4.414-6.195) was more vulnerable than the non-disabled elderly group (4.287: 3.576-4.999). Lastly, no significant difference in relative risk was observed between the mild (4.413: 3.855-4.971) and severe disabled groups (4.013: 3.121-4.905).

Investigation of Climate Effects on the Physiological Parameters of Dairy Livestock (Cow vs. Buffalo)

Nowadays climate change is affecting the planet's biodiversity, and livestock practices must adapt themselves to improve production without affecting animal welfare. This work investigates the influence that some climatic parameters such as Environment Temperature, Relative Humidity, Thermal excursion and Temperature-Humidity Index (THI), can have on milk quantity and quality in two different dairy species (buffaloes and cows) raised on the same farm. A further aim was to understand if THI threshold used for cows could also be used for buffaloes. The climatic parameters were recorded daily through a meteorological station located inside the farm. Milk quantity (converted into ECM) and quality (Fat Percentage-FP; Protein Percentage-PP; Somatic Cell Count-SCC) were measured. Data were analyzed with Spearman's correlation index, separately for buffaloes and cows. The results indicate a greater sensitivity of cows to heat stress and a strong negative correlation of the ECM with meteorological data (p < 0.01). The results of this study may stimulate the use of integrated technologies (sensors, software) in the dairy sector, since the IoT (sensors, software) helps to enhance animal well-being and to optimize process costs, with a precision livestock farming approach.

No large effects on cognitive performance in high versus low solar green-flag WBGT conditions

Excessive solar radiation negatively affects cognitive performance. Occupational guidelines typically combine environmental components into one value, such as wet-bulb globe temperature (WBGT). Here, we evaluated cognitive performance in two similar 28.6 °C WBGT-effective (WBGTeff) that were designed differently; using high or low levels of solar radiation. Eight soldiers were exposed to a virtual-reality environment in a climate chamber set to high (900 Wm-2) or low solar radiation conditions (300 Wm-2). Soldiers walked 3 x 30 min at 5 kmh-1. Cognitive performance was evaluated using a virtual-reality scenario and a computerised test battery. There was no statistically significant effect of condition on the cognitive tasks (p > 0.05). Associations were found between mean body temperature (Tb) and visual detection (P ≤ 0.01). Differences in solar radiation with similar WBGTeff (28.6 °C) do not cause large systematic differences in cognitive performance. Certain aspects of cognitive performance (i.e. response inhibition) seem to be partly associated with Tb rather than solar radiation.Practitioner summary: Cognitive performance was evaluated in two similar WBGT conditions that were designed differently; using high or low levels of solar radiation. Differences in solar radiation with similar WBGT do not cause systematic differences in cognitive performance. Certain aspects of cognition were partly associated with mean body temperature rather than solar radiation.

Cross-adaptation from heat stress to hypoxia: A systematic review and exploratory meta-analysis

Cross-adaptation (CA) refers to the successful induction of physiological adaptation under one environmental stressor (e.g., heat), to enable subsequent benefit in another (e.g., hypoxia). This systematic review and exploratory meta-analysis investigated the effect of heat acclimation (HA) on physiological, perceptual and physical performance outcome measures during rest, and submaximal and maximal intensity exercise in hypoxia. Database searches in Scopus and MEDLINE were performed. Studies were included when they met the Population, Intervention, Comparison, and Outcome criteria, were of English-language, peer-reviewed, full-text original articles, using human participants. Risk of bias and study quality were assessed using the COnsensus based Standards for the selection of health status Measurement INstruments checklist. Nine studies were included, totalling 79 participants (100 % recreationally trained males). The most common method of HA included fixed-intensity exercise comprising 9 ± 3 sessions, 89 ± 24-min in duration and occurred within 39 ± 2 °C and 32 ± 13 % relative humidity. CA induced a moderate, beneficial effect on physiological measures at rest (oxygen saturation: g = 0.60) and during submaximal exercise (heart rate: g = -0.65, core temperature: g = -0.68 and skin temperature: g = -0.72). A small effect was found for ventilation (g = 0.24) and performance measures (peak power: g = 0.32 and time trial time: g = -0.43) during maximal intensity exercise. No effect was observed for perceptual outcome measures. CA may be appropriate for individuals, such as occupational or military workers, whose access to altitude exposure prior to undertaking submaximal activity in hypoxic conditions is restricted. Methodological variances exist within the current literature, and females and well-trained individuals have yet to be investigated. Future research should focus on these cohorts and explore the mechanistic underpinnings of CA.

Multi-tissue metabolic and transcriptomic responses to a short-term heat stress in swine

BACKGROUND

Heat stress (HS) is an increasing threat for pig production with a wide range of impacts. When submitted to high temperatures, pigs will use a variety of strategies to alleviate the effect of HS. While systemic adaptations are well known, tissue-specific changes remain poorly understood. In this study, thirty-two pigs were submitted to a 5-day HS at 32 °C.

RESULTS

Transcriptomic and metabolomic analyses were performed on several tissues. The results revealed differentially expressed genes and metabolites in different tissues. Specifically, 481, 1774, 71, 1572, 17, 164, and 169 genes were differentially expressed in muscle, adipose tissue, liver, blood, thyroid, pituitary, and adrenal glands, respectively. Regulatory glands (pituitary, thyroid, and adrenal) had a lower number of regulated genes, perhaps indicating an earlier sensitivity to HS. In addition, 7, 8, 2, and 8 metabolites were differentially produced in muscle, liver, plasma, and urine, respectively. The study also focused on the oxidative stress pathway in muscle and liver by performing a correlation analysis between genes and metabolites.

CONCLUSIONS

This study has identified various adaptation mechanisms in swine that enable them to cope with heat stress (HS). These mechanisms include a global decrease in energetic metabolism, as well as changes in metabolic precursors that are linked with protein and lipid catabolism and anabolism. Notably, the adaptation mechanisms differ significantly between regulatory (pituitary, thyroid and adrenal glands) and effector tissues (muscle, adipose tissue, liver and blood). Our findings provide new insights into the comprehension of HS adaptation mechanisms in swine.

Elephantopus scaber L. Polysaccharides Alleviate Heat Stress-Induced Systemic Inflammation in Mice via Modulation of Characteristic Gut Microbiota and Metabolites

Elephantopus scaber L. (ESL) is a Chinese herb that is used both as a food and medicine, often being added to soups in summer in south China to relieve heat stress (HS), but its exact mechanism of action is unknown. In this study, heat-stressed mice were gavaged with ESL polysaccharides (ESLP) at 0, 150, 300, and 450 mg/kg/d-1 (n = 5) for seven days. The gut microbiota composition, short-chain fatty acids (SCFAs), seven neurotransmitters in faeces, expression of intestinal epithelial tight junction (TJ) proteins (Claudin-1, Occludin), and serum inflammatory cytokines were measured. The low dose of ESLP (ESLL) improved the adverse physiological conditions; significantly reduced the cytokines (TNF-α, IL-1β, IL-6) and lipopolysaccharide (LPS) levels (p < 0.05); upregulated the expression of Claudin-1; restored the gut microbiota composition including Achromobacter and Oscillospira, which were at similar levels to those in the normal control group; significantly increased beneficial SCFAs like butyric acid and 5-HT levels in the faeces of heat-stressed mice; and significantly decreased the valeric acid and glutamic acid level. The level of inflammatory markers significantly correlated with the above-mentioned indicators (p < 0.05). Thus, ESLL reduced the HS-induced systemic inflammation by optimizing gut microbiota (Achromobacter, Oscillospira) abundance, increasing gut beneficial SCFAs like butyric acid and 5-HT levels, and reducing gut valeric and glutamic acid levels.

Estimating the effects of vegetation and increased albedo on the urban heat island effect with spatial causal inference

The urban heat island effect causes increased heat stress in urban areas. Cool roofs and urban greening have been promoted as mitigation strategies to reduce this effect. However, evaluating their efficacy remains a challenge, as potential temperature reductions depend on local characteristics. Existing methods to characterize their efficacy, such as computational fluid dynamics and urban canopy models, are computationally burdensome and require a high degree of expertise to employ. We propose a data-driven approach to overcome these hurdles, inspired by recent innovations in spatial causal inference. This approach allows for estimates of hypothetical interventions to reduce the urban heat island effect. We demonstrate this approach by modeling evening temperature in Durham, North Carolina, using readily retrieved air temperature, land cover, and satellite data. Hypothetical interventions such as lining streets with trees, cool roofs, and changing parking lots to green space are estimated to decrease evening temperatures by a maximum of 0.7-0.9   [Formula: see text], with reduced effects on temperature as a function of distance from the intervention. Because of the ease of data access, this approach may be applied to other cities in the U.S. to help them come up with city-specific solutions for reducing urban heat stress.

Heat and cold stress increases the risk of paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is a common arrhythmia in adults. Its occurrence depends on the presence of the reentry circuit and the trigger of the paroxysm. Stress, emotional factors, and comorbidities favour the occurrence of such an episode. We hypothesized that the occurrence of PSVT follows extreme thermal episodes. The retrospective analysis was based on the data collected from three hospital emergency departments in Poland (Olsztyn, Radom, and Wroclaw) involving 816 admissions for PSVT in the period of 2016-2021. To test the hypothesis, we applied the Universal Climate Thermal Index (UTCI) to objectively determine exposure to cold or heat stress. The risk (RR) for PSVT increased to 1.37 (p = 0.006) in cold stress and 1.24 (p = 0.05) in heat stress when compared to thermoneutral conditions. The likelihood of PSVT during cold/heat stress is higher in women (RR = 1.59, p< 0.001 and RR = 1.36, p = 0.024, respectively) than in men (RR = 0.64 at p = 0.088 and RR = 0.78, p = 0.083, respectively). The susceptibility for PSVT was even higher in all groups of women after exclusion of perimenopausal group of women, in thermal stress (RR = 1.74, p< 0.001, RR = 1.56, p = 0.029, respectively). Females, particularly at the perimenopausal stage and men irrespective of age were less likely to develop PSVT under thermal stress as compared to thermoneutral conditions. Progress in climate change requires searching for universal methods and tools to monitor relationships between humans and climate. Our paper confirms that the UTCI is the universal tool describing the impact of thermal stress on the human body and its high usefulness in medical researches.

Effects of preconditioning with heat stress on acute exercise-induced intracellular signaling in male rat gastrocnemius muscle

Heat stress (HS) induces Akt/mTOR phosphorylation and FoxO3a signaling; however, whether a prior increase in heat shock protein 72 (HSP72) expression affects intracellular signaling following eccentric exercise remains unclear. We analyzed the effects of HS pretreatment on intramuscular signaling in response to acute exercise in 10-week-old male Wistar rats (n = 24). One leg of each rat was exposed to HS and the other served as an internal control (CT). Post-HS, rats were either rested or subjected to downhill treadmill running. Intramuscular signaling responses in the red and white regions of the gastrocnemius muscle were analyzed before, immediately after, or 1 h after exercise (n = 8/group). HS significantly increased HSP72 levels in both deep red and superficial white regions. Although HS did not affect exercise-induced mTOR signaling (S6K1/ERK) responses in the red region, mTOR phosphorylation in the white region was significantly higher in CT legs than in HS legs after exercise. Thr308 phosphorylation of Akt showed region-specific alteration with a decrease in the red region and an increase in the white region immediately after downhill running. Overall, a prior increase in HSP72 expression elicits fiber type-specific changes in exercise-induced Akt and mTOR phosphorylation in rat gastrocnemius muscle.

Applicability of thermography as a potential non-invasive technique to assess the body-thermal status of heat-stressed and water-deprived goats (Capra hircus)

To evaluate the use of infrared thermography to assess the thermal status of heat-stressed and water-deprived Capra hircus, full-body surface temperature (TS) and six other body-thermal variables [core, rectal (TR), and skin (TSK) temperatures, respiratory and heart rates, and total body-thermal gradient (core-to-ambient, BTG)] were measured after three days of euhydration (EU), dehydration (DE), and rehydration (RE). Results revealed that the combined effect of heat stress and water deprivation had affected all tested variables including the TS, and once these animals gained access to water in the RE stage variables returned to their EU levels. Moreover, there were positive correlations between TS and all variables with the exception of BTG. From these six variables, only three variables (i.e. the TR, TSK, and BTG) during the DE stage and two variables (i.e. the TSK and BTG) throughout the experimental stages showed higher constancy (R2 ≥ 0 75, P < 0 001; agreement intervals ±1 96 95 % CI) with TS. However, BTG appeared more closely correlated with TS, representing the body-thermal status more realistically than other variables. In effect, the mean and thresholds of the BTG were predicted using the recorded TS and were within 0.02 °C of original estimates. Collectively, these findings show that infrared thermography is appropriate for assessing body-thermal status, and thus the welfare, of these animals under the three conditions studied, and conclude that full-body TS can be a surrogate proxy for BTG in these animals. Further experiments are needed to adequately examine the reproducibility of these results under biometeorologically-simulated environments and natural habitats.

The intensity-dependent effects of exercise and superimposing environmental heat stress on autophagy in peripheral blood mononuclear cells from older men

Autophagy is a vital cellular process, essential to maintaining cellular function during acute physiological stressors including exercise and heat stress. We previously showed that autophagy occurs during exercise in an intensity-dependent manner in peripheral blood mononuclear cells (PBMCs) from young men, with elevated responses in the heat. However, given autophagy declines with age, it is unclear whether a similar pattern of response occurs in older adults. Therefore, we evaluated autophagy and the cellular stress response [i.e., apoptosis, inflammation, and the heat shock response (HSR)] in PBMCs from 10 healthy older men [mean (SD): aged 70 yr (5)] in response to 30 min of semirecumbent cycling at low, moderate, and vigorous intensities [40, 55, and 70% maximal oxygen consumption (V̇o2max), respectively] in a temperate (25°C) environment, with an additional vigorous-intensity bout (70% of V̇o2max) performed in a hot environment (40°C). Responses were evaluated before and after exercise, as well as throughout a 6-h seated recovery period performed in the same environmental conditions as the respective exercise bout. Proteins were assessed via Western blot. Although we observed elevations in mean body temperature with each increase in exercise intensity, autophagy was only stimulated during vigorous-intensity exercise, where we observed elevations in LC3-II (P < 0.05). However, when the same exercise was performed in the heat, the LC3-II response was attenuated, which was accompanied by significant p62 accumulation (P < 0.05). Altogether, our findings demonstrate that older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot environments, potentially underlying heat-induced cellular vulnerability in older men.NEW & NOTEWORTHY We demonstrate that autophagic stimulation occurs in response to short-duration (30-min) vigorous-intensity exercise in peripheral blood mononuclear cells from older adults; however, no changes in autophagy occur during low- or moderate-intensity exercise. Moreover, older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot ambient conditions. When paired with an attenuated heat shock response, as well as elevated apoptotic responses, older men may exhibit greater cellular vulnerability to exertional heat stress.

Impact of heat stress on thermal balance, hydration and cortical response among outdoor workers in hot environment - an exploratory report from North East India

OBJECTIVE

The objective of our study was to assess the impact of heat stress on hydration and cognition among outdoor workers in hot environment.

METHODS

Area heat stress assessments were measured using Quest Temp WBGT monitor. Sweat rate for dehydration and reaction time for acute cognitive processing were recorded using standard procedures.

RESULTS

Heat stress measurements ranged from 23.8 °C - 42 °C. More than 50 % of the workers had high sweat rate (>1.2 L/h) when exposed to high environmental temperatures. Positive correlation was obtained between WBGT, sweat rate and reaction time which indicates that hyperthermia has an impact on neural network processing. Heart rate and reaction time also increased with rise in WBGT and heavy physical activity.

CONCLUSIONS

There was impairment of cognitive functions (reaction time) under heat stress conditions. Hence, reaction time can be used to assess the short-term impact of heat stress on neural modulation and will help to plan effective intervention strategies to reduce morbidity and mortality among workers.

Validation of a temperature-humidity index (Humidex) in evaluating heat stress at a tile factory in Iran

BACKGROUND

Several heat indices have been developed in industrial health, but each has its limitations.

OBJECTIVE

The objective of this article is to determine the validity and applicability of a temperature-humidity index, named Humidex compared with the Standard Wet-Bulb Globe Temperature (WBGT) index (ISO 7243).

METHOD

This cross-sectional study was conducted in the summer of 2019, in a tile factory in the west of Iran. 59 measurements were performed in 8 different workstations. Environmental parameters including natural wet bulb temperature (Tnw), dry bulb temperature (Ta), globe bulb temperature (Tg), and heat stress (WBGT) were measured. Humidex was calculated according to an equation. SPSS software (version 16) was used for data analysis.

RESULTS

There was a high correlation between Humidex and WBGT in the estimation of heat stress (R=0.912, P<0.001). The Kappa Coefficient between Humidex and WBGT was 0.298, P=0.001.

CONCLUSION

Humidex is highly correlated with WBGT. Humidex can be used instead of the WBGT index, especially in hot and humid environments.

Characteristic of bioclimatic conditions in Poland based on Physiologically Equivalent Temperature

The aim of the study was to characterise bioclimatic conditions in Poland in the times of progressing warming. This type of research permits the verification whether the progressing climate warming also translates into a change in bioclimatic conditions. This study was based on data obtained for the period 1966-2021 from 37 synoptic stations located in Poland. All the data series were uniform and obtained from the data base of the Institute of Meteorology and Water Management-National Research Institute (IMGW-PIB). The study revealed high variability of bioclimatic conditions in Poland both in spatial and in temporal terms. The lowest mean annual PET values were recorded in the north and north-east of the country and the highest in the south-west of Poland. The study revealed changes in the frequency of occurrence of days with cold and heat stress, as well as days with no thermal stress. The most intensive changes were determined for days with cold stress. A decrease in the number of days in this category translated into an increase in the number of days with no thermal stress and days with heat stress.

Change of Seasons: Boston Marathon Wet Bulb Globe Temperature Index in October

INTRODUCTION

The importance of providing wet bulb globe temperature (WBGT) heat stress flag category measurements in real time is well recognized by road race directors, and it is bound to become even more important with the rise of extreme weather and pandemic outbreaks. The purpose of this paper is to describe the WBGT index and its components measured during the 125th running of the Boston Marathon on October 11, 2021, for qualitative comparison to measurements made similarly on its traditional April date, 2014 to 2019.

METHODS

Monitoring occurred at the 7 km, 18 km, and 32 km marks of the race in the towns of Ashland, Natick-Wellesley, and Newton. The outdoor WBGT index was calculated from direct hourly measurements of the dry bulb, black globe, and natural wet bulb temperatures from 0900 to 1500 h.

RESULTS

The WBGT index was not different among towns; thus, the average hourly values for the 3 towns were compared to historical data averaged identically. Although the black globe temperature fluctuated considerably in response to changing cloud cover, on average, partly cloudy skies kept the solar load comparable to what has been observed in April. Dry bulb and wet bulb temperatures were higher than those on most April dates shown, which resulted in a yellow (or amber) flag day for most of the race.

CONCLUSIONS

The historic October Boston Marathon was among the warmest in recent history. Like the impact of COVID-19 on the 2021 Boston Marathon, future climate challenges around outdoor activities could necessitate rescheduling; they underscore the importance of real-time WBGT index measures.

Association between thermal stress and cardiovascular mortality in the subtropics

Hazardous thermal conditions resulting from climate change may play a role in cardiovascular disease development. We chose the Universal Thermal Climate Index (UTCI) as the exposure metric to evaluate the relationship between thermal conditions and cardiovascular mortality in Shenzhen, China. We applied quasi-Poisson regression non-linear distributed lag models to evaluate the exposure-response associations. The findings suggest that cardiovascular mortality risks were significantly increased under heat and cold stress, and the adverse effects of cold stress were stronger than heat stress. Referencing the 50th percentile of UTCI (25.4°C), the cumulative risk of cardiovascular mortality was 75% (RRlag0-21 =1.75, 95%CI: 1.32, 2.32) higher in the 1st percentile (3.5°C), and 40% (RRlag0-21=1.40, 95%CI: 1.09, 1.80) higher in the 99th percentile (34.1°C). We observed that individuals older than 65 years were more vulnerable to both cold and heat stress, and females were identified as more susceptible to heat stress than males. Moreover, increased mortality risks of hypertensive disease and cerebrovascular disease were observed under cold stress, while heat stress was related to higher risks of mortality for hypertensive disease and ischemic heart disease. We also observed a stronger relationship between cold stress and ischemic heart disease mortality during the cold season, as well as a significant impact of heat stress on cerebrovascular disease mortality in the warm season when compared to the analysis of the entire year. These results confirm the significant relationship between thermal stress and cardiovascular mortality, with age and sex as potential effect modifiers of this association. Providing affordable air conditioning equipment, increasing the amount of vegetation, and establishing comprehensive early warning systems that take human thermoregulation into account could all help to safeguard the well-being of the public, particularly vulnerable populations, in the event of future extreme weather.

Optimal low-cost cooling strategies for infant strollers during hot weather

The current study aimed to identity the optimal low-cost stroller cooling strategies for use in hot and moderately humid summer weather. A commercially available stroller was instrumented to assess the key parameters of the thermal environment. The cooling efficacy of eight different stroller configurations was examined in a counterbalanced order across 16 hot summer days (air temperature (Ta) = 33.3 ± 4.1 °C; relative humidity = 36.7 ± 15%; black globe temperature = 43.9 ± 4.6 °C). Compared with a standard-practice stroller configuration, combining a moist muslin draping with a battery-operated clip-on fan provided optimal in-stroller cooling, reducing the end-trial air temperature by 4.7 °C and the wet bulb globe temperature (WBGT) by 1.4 °C. In contrast, in-stroller temperatures were substantially increased by draping a dry muslin (Ta = +2.6 °C; WBGT = +0.9 °C) or flannelette (Ta = +3.7 °C; WBGT = +1.4 °C) cloth over the stroller carriage. These findings provide empirical evidence which may inform guidance aimed at protecting infants during hot weather.Practitioner summary: This study examined the efficacy of traditional and novel stroller cooling strategies for use in hot and moderately humid weather. Covering the carriage with a dry muslin cloth substantially increased stroller temperatures and should be avoided. Evaporative cooling methods reduced in-stroller temperatures. A moist muslin cloth draping combined with a fan provided optimal stroller cooling.

Analysis of heatwaves based on the universal thermal climate index and apparent temperature over mainland Southeast Asia

Heatwaves have caused significant damage to human health, infrastructure, and economies in recent decades, and the occurrences of heatwaves are becoming more frequent and severe across the globe under climate change. The previous studies on heatwaves have primarily focused on air temperature, neglecting other variables like wind speed, relative humidity, and radiation, which could lead to a serious underestimation of the adverse effects of heatwaves. To address this issue, this study proposed to the use of more sophisticated thermal indices, such as universal thermal climate index (UTCI) and apparent temperature (AT), to define heatwaves and carry out a comprehensive heatwave assessment over mainland southeast Asia (MSEA) from 1961 to 2020. The traditional temperature-based method was also compared. The results of the study demonstrate that the annual maximum temperature in heatwave days (HWA) and the annual average temperature in heatwave days (HWM) are significantly underestimated if only air temperature is considered. However, UTCI and AT tend to predict a lower frequency of yearly heatwave occurrences and shorter durations. Trend analysis indicates a general increase in heatwave occurrences across MSEA under all thermal indices in the past six decades, particularly in the last 30 years. This study's approach and findings provide a holistic view of heatwave characteristics based on thermal indices and highlight the risk of intensified heat stress during heatwaves in MSEA.

A comprehensive evaluation of heat stress and heat strain in a sample of sugarcane cutters in Brazil

Sugarcane cutters are vulnerable to extreme heat and are at risk for heat-related illness and chronic kidney disease, potentially due to high heat strain. We performed a comprehensive assessment of the physiological demands of sugarcane cutters via measurements of metabolic, thermal, and cardiovascular responses. In addition, we assessed cross-shift changes in markers of kidney function. Nine male sugarcane cutters were monitored while working during the spring harvest season in Brazil. Core temperature (Tcore) and heart rate (HR) were continuously recorded, and oxygen consumption was measured during the work shift. Urine and blood samples were collected pre- and postwork shifts. Total sweat loss was calculated using body weight changes and adjusting for water ingestion and urine output. A wet-bulb globe temperature (WBGT) station was used to monitor environmental heat stress. WBGT was ≥30°C on 7 of the 8 study days. Mean and peak Tcore during the work shift were 37.96 ± 0.47°C and 38.60 ± 0.41°C, respectively, with all participants surpassing a Tcore of 38°C. Mean and peak HR during the work shift were 137 ± 14 and 164 ± 11 beats/min, respectively. Percent of maximal oxygen consumption was, on average, 53 ± 11%. Workers had a total sweat loss of 7.63 ± 2.31 L and ingested 6.04 ± 1.95 L of fluid. Kidney function (estimated glomerular filtration rate) was reduced from pre- to postwork shift (Δ -20 ± 18 mL·min·1.73 m2). We demonstrated that sugarcane cutters performing prolonged work during a period of high environmental heat stress display high levels of heat strain, high water turnover, and reduced kidney function.NEW & NOTEWORTHY We demonstrate that a shift of sugarcane cutting performed outdoors during the spring harvest season results in a high level of heat strain. In fact, all the studied workers sustained core temperatures above 38°C and heart rates above 75% of the measured maximum heart rate. Additionally, workers displayed a high water turnover with sweat loss close to 10% of their body weight. Finally, we report elevated muscle damage and reductions in kidney function following the work shift.

Measuring Heat Stress for Human Health in Cities: A Low-Cost Prototype Tested in a District of Valencia, Spain

Nowadays, the measurement of heat stress indices is of principal importance due to the escalating impact of global warming. As temperatures continue to rise, the well-being and health of individuals are increasingly at risk, which can lead to a detrimental effect on human performance and behavior. Hence, monitoring and assessing heat stress indices have become necessary for ensuring the safety and comfort of individuals. Thermal comfort indices, such as wet-bulb globe temperature (WBGT), Tropical Summer Index (TSI), and Predicted Heat Strain (PHS), as well as parameters like mean radiant temperature (MRT), are typically used for assessing and controlling heat stress conditions in working and urban environments. Therefore, measurement and monitoring of these parameters should be obtained for any environment in which people are constantly exposed. Modern cities collect and publish this relevant information following the Smart City concept. To monitor large cities, cost-effective solutions must be developed. This work presents the results of a Heat Stress Monitoring (HSM) system prototype network tested in the Benicalap-Ciutat Fallera district in Valencia, Spain. The scope of this work is to design, commission, and test a low-cost prototype that is able to measure heat stress indices. The Heat Stress Monitoring system comprises a central unit or receiver and several transmitters communicating via radiofrequency. The transmitter accurately measures wind speed, air temperature, relative humidity, atmospheric pressure, solar irradiation, and black globe temperature. The receiver has a 4G modem that sends the data to an SQL database in the cloud. The devices were tested over one year, showing that radio data transmission is reliable up to 700 m from the receiver. The system's power supply, composed of a Photovoltaic panel and Lithium-ion batteries, provided off-grid capabilities to the transmitter, with a tested backup autonomy of up to 36 days per charge. Then, indicators such as WBGT, TSI, and MRT were successfully estimated using the data collected by the devices. The material cost of a 12-point network is around EUR 2430 with a competitive price of EUR 190 per device.

Vitexin Regulates Heat Shock Protein Expression by Modulating ROS Levels Thereby Protecting against Heat-Stress-Induced Apoptosis

Heat stress due to high temperatures can cause heat stroke, pyrexia, heat cramps, heart disease, and respiratory diseases, which seriously affect human health. Vitexin has been shown to alleviate heat stress; however, its mechanism of action remains unclear. Therefore, in this study, we used Caco-2 cells to establish a heat stress model and vitamin C as a positive control to investigate the regulatory effects of vitexin on heat-stress-induced apoptosis and the related mechanisms using Cell Counting Kit-8, flow cytometry, real-time quantitative polymerase chain reaction, and Western blot. The results showed that the mRNA expressions of Hsp27, Hsp70, and Hsp90 induced by heat stress could be effectively inhibited at vitexin concentrations as low as 30 μM. After heat stress prevention and heat stress amelioration in model cells based on this concentration, intracellular reactive oxygen species (ROS) levels and the mRNA level and the protein expression of heat shock proteins (Hsp70 and Hsp90) and apoptotic proteins were reduced. In addition, compared with the heat stress amelioration group, the expression of BCL2 mRNA and its protein (anti-apoptotic protein Bcl-2) increased in the heat stress prevention group, while the expression of BAX, CYCS, CASP3, and PARP1 mRNAs and their proteins (apoptotic proteins Bax, Cytochrome C, cle-Caspase-3, and cle-PARP1) were decreased. In summary, the heat-stress-preventive effect of vitexin was slightly better than its heat-stress-ameliorating effect, and its mechanism may be through the inhibition of intracellular ROS levels and thus the modulation of the expressions of Hsp70 and Hsp90, which in turn protects against heat-stress-induced apoptosis. This study provides a theoretical basis for the prevention and amelioration of heat stress using vitexin.

Cardiac autonomic modulation in individuals with controlled and uncomplicated hypertension during exercise-heat stress

TAKE-HOME MESSAGE

During short bouts of light-to-vigorous exercise in the heat, controlled and uncomplicated hypertension did not significantly modulate HRV in physically active individuals. These findings can be used to refine guidance on use of exercise for hypertension management in the heat.

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

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

Upper-Body versus Lower-Body Cooling in Individuals with Paraplegia during Arm-Crank Exercise in the Heat

PURPOSE

For wheelchair users with a spinal cord injury, the lower body may be a more convenient cooling site than the upper body. However, it remains unknown if leg cooling reduces thermal strain in these individuals. We compared the impact of upper-body versus lower-body cooling on physiological and perceptual outcomes during submaximal arm-crank exercise under heat stress in individuals with paraplegia.

METHODS

Twelve male participants with paraplegia (T4-L2, 50% complete lesion) performed a maximal exercise test in temperate conditions, and three heat stress tests (32°C, 40% relative humidity) in which they received upper-body cooling (COOL-UB), lower-body cooling (COOL-LB), or no cooling (CON) in a randomized counterbalanced order. Each heat stress test consisted of four exercise blocks of 15 min at 50% of peak power output, with 3 min of rest in between. Cooling was applied using water-perfused pads, with 14.8-m tubing in both COOL-UB and COOL-LB.

RESULTS

Gastrointestinal temperature was 0.2°C (95% confidence interval (CI), 0.1°C to 0.3°C) lower during exercise in COOL-UB versus CON (37.5°C ± 0.4°C vs 37.7°C ± 0.3°C, P = 0.009), with no difference between COOL-LB and CON ( P = 1.0). Heart rate was lower in both COOL-UB (-7 bpm; 95% CI, -11 to -3 bpm; P = 0.01) and COOL-LB (-5 bpm; 95% CI, -9 to -1 bpm; P = 0.049) compared with CON. The skin temperature reduction at the cooled skin sites was larger in COOL-LB (-10.8°C ± 1.1°C) than in COOL-UB (-6.7°C ± 1.4°C, P < 0.001), which limited the cooling capacity in COOL-LB. Thermal sensation of the cooled skin sites was improved and overall thermal discomfort was lower in COOL-UB ( P = 0.01 and P = 0.04) but not in COOL-LB ( P = 0.17 and P = 0.59) compared with CON.

CONCLUSIONS

Upper-body cooling more effectively reduced thermal strain than lower-body cooling in individuals with paraplegia, as it induced greater thermophysiological and perceptual benefits.

Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance

As heatwaves become more frequent, intense, and longer-lasting due to climate change, the question of breaching thermal limits becomes pressing. A wet-bulb temperature (Tw) of 35 °C has been proposed as a theoretical upper limit on human abilities to biologically thermoregulate. But, recent-empirical-research using human subjects found a significantly lower maximum Tw at which thermoregulation is possible even with minimal metabolic activity. Projecting future exposure to this empirical critical environmental limit has not been done. Here, using this more accurate threshold and the latest coupled climate model results, we quantify exposure to dangerous, potentially lethal heat for future climates at various global warming levels. We find that humanity is more vulnerable to moist heat stress than previously proposed because of these lower thermal limits. Still, limiting warming to under 2 °C nearly eliminates exposure and risk of widespread uncompensable moist heatwaves as a sharp rise in exposure occurs at 3 °C of warming. Parts of the Middle East and the Indus River Valley experience brief exceedances with only 1.5 °C warming. More widespread, but brief, dangerous heat stress occurs in a +2 °C climate, including in eastern China and sub-Saharan Africa, while the US Midwest emerges as a moist heat stress hotspot in a +3 °C climate. In the future, moist heat extremes will lie outside the bounds of past human experience and beyond current heat mitigation strategies for billions of people. While some physiological adaptation from the thresholds described here is possible, additional behavioral, cultural, and technical adaptation will be required to maintain healthy lifestyles.

Plasma measurements of the dual sugar test reveal carbohydrate immediately alleviates intestinal permeability caused by exertional heat stress

The aim of this set of randomised cross-over studies was to determine the impact of progressive heat exposure and carbohydrate or protein feeding during exertional stress on small intestine permeability using a dual sugar test. In our previous work, and typically in the field, recovery of lactulose and l-rhamnose is measured cumulatively in urine. This follow-up study exploits our novel high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) protocol to accurately quantify the sugars in plasma. Endurance-trained participants completed experimental trial A (ET-A; n = 8), consisting of 2 h running at 60%V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ in temperate, warm and hot ambient conditions, and/or experimental trial B (ET-B; n = 9), consisting of 2 h running at 60%V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ in the heat while consuming water, carbohydrate or protein. Blood samples were collected and plasma lactulose (L) and l-rhamnose (R) appearance, after dual sugar solution ingestion at 90 min of exercise, was quantified by HPAEC-PAD to measure plasma L/R and reveal new information about intestinal permeability immediately post-exercise and during recovery. In ET-A, plasma L/R increased immediately post-exercise in hot compared with temperate and warm conditions, while, in ET-B, carbohydrate alleviated this, and this information was otherwise missed when measuring urine L/R. Consuming carbohydrate or protein before and during exercise attenuated small intestine permeability throughout recovery from exertional heat stress. We recommend using the dual sugar test with quantification of plasma sugars by HPAEC-PAD at intervals to maximise intestinal permeability data collection in exercise gastroenterology research, as this gives additional information compared to urinary measurements. KEY POINTS: Intestinal permeability is typically assessed using a dual sugar test, by administering a drink containing non-metabolisable sugars (e.g. lactulose (L) and l-rhamnose (R)) that can enter the circulation by paracellular translocation when the epithelium is compromised, and are subsequently measured in urine. We demonstrate that our recently developed ion chromatography protocol can be used to accurately quantify the L/R ratio in plasma, and that measuring L/R in plasma collected at intervals during the post-exercise recovery period reveals novel acute response information compared to measuring 5-h cumulative urine L/R. We confirm that exercising in hot ambient conditions increases intestinal epithelial permeability immediately after exercise, while consuming carbohydrate or protein immediately before and during exercise attenuates this. We recommend using our dual sugar absorption test protocol to maximise intestinal epithelial permeability data collection in exercise gastroenterology research and beyond.

Genetic parameters for automatically-measured vaginal temperature, respiration efficiency, and other thermotolerance indicators measured on lactating sows under heat stress conditions

BACKGROUND

Genetic selection based on direct indicators of heat stress could capture additional mechanisms that are involved in heat stress response and enable more accurate selection for more heat-tolerant individuals. Therefore, the main objectives of this study were to estimate genetic parameters for various heat stress indicators in a commercial population of Landrace × Large White lactating sows measured under heat stress conditions. The main indicators evaluated were: skin surface temperatures (SST), automatically-recorded vaginal temperature (TV), respiration rate (RR), panting score (PS), body condition score (BCS), hair density (HD), body size (BS), ear size, and respiration efficiency (Reff).

RESULTS

Traits based on TV presented moderate heritability estimates, ranging from 0.15 ± 0.02 to 0.29 ± 0.05. Low heritability estimates were found for SST traits (from 0.04 ± 0.01 to 0.06 ± 0.01), RR (0.06 ± 0.01), PS (0.05 0.01), and Reff (0.03 ± 0.01). Moderate to high heritability values were estimated for BCS (0.29 ± 0.04 for caliper measurements and 0.25 ± 0.04 for visual assessments), HD (0.25 ± 0.05), BS (0.33 ± 0.05), ear area (EA; 0.40 ± 0.09), and ear length (EL; 0.32 ± 0.07). High genetic correlations were estimated among SST traits (> 0.78) and among TV traits (> 0.75). Similarly, high genetic correlations were also estimated for RR with PS (0.87 ± 0.02), with BCS measures (0.92 ± 0.04), and with ear measures (0.95 ± 0.03). Low to moderate positive genetic correlations were estimated between SST and TV (from 0.25 ± 0.04 to 0.76 ± 0.07). Low genetic correlations were estimated between TV and BCS (from - 0.01 ± 0.08 to 0.06 ± 0.07). Respiration efficiency was estimated to be positively and moderately correlated with RR (0.36 ± 0.04), PS (0.56 ± 0.03), and BCS (0.56 ± 0.05 for caliper measurements and 0.50 ± 0.05 for the visual assessments). All other trait combinations were lowly genetically correlated.

CONCLUSIONS

A comprehensive landscape of heritabilities and genetic correlations for various thermotolerance indicators in lactating sows were estimated. All traits evaluated are under genetic control and heritable, with different magnitudes, indicating that genetic progress is possible for all of them. The genetic correlation estimates provide evidence for the complex relationships between these traits and confirm the importance of a sub-index of thermotolerance traits to improve heat tolerance in pigs.

Variability of heat stress using the UrbClim climate model in the city of Seville (Spain): mitigation proposal

Climate change is creating an increase in temperatures, which is harming the quality of life of people all over the world, particularly those with minimal financial resources. While 30% of the world's population is now vulnerable to extreme heat, estimates show that ratio will rise to 74% in the next 20 years, according to forecasts. Using the UrbClim climate model, this study examines the space-time variability of the heat stress index (HI) in different local climate zones (LCZs), as well as how heat wave conditions might affect this index based on land use and land cover. To that end, Seville, in Southern Spain, was investigated during the summer of 2017, when it had four heat waves. The following indices were considered for each urban sub-area: Normalized Difference Vegetation, Proportion Vegetation, Normalized Difference Built, and Urban Index. The goal is to conduct a statistical analysis of the link between the aforementioned elements and the heat stress index in order to recommend mitigation and resilience techniques. Our findings showed that compact and industrial LCZs (2, 3, and 10) are less resistant to HI than open and rural regions (5, 6, B, D, and G), which are more resistant to HI due to higher vegetation rates. The heat wave condition exacerbates the HI in all LCZs. As a result, initiatives such as enhancing open space, increasing green space, or using green roofs and façades might alleviate heat stress and improve people's quality of life.

Distribution of upper limit of the prescriptive zone values for acclimatized and unacclimatized individuals

Heat stress has an adverse impact on worker health and well-being, and the effects will increase with more frequent and severe heat events associated with global warming. Acclimatization to heat stress is widely considered to be a critical mitigation strategy and wet bulb globe temperature- (WBGT-) based occupational standards and guidelines contain adjustments for acclimatization. The purpose here was to 1) compare the mean values for the upper limit of the prescriptive zone (ULPZ, below which the rise in core temperature is minimal) between unacclimatized and acclimatized men and women; 2) demonstrate that the change in the occupational exposure limit (ΔOEL) due to acclimatization is independent of metabolic rate; 3) examine the relation between ΔOEL and body surface area (BSA); and 4) compare the exposure-response curves between unacclimatized and acclimatized populations. Empirically derived ULPZ data for unacclimatized participants from Pennsylvania State University (PSU) and acclimatized participants from University of South Florida (USF) were used to explore the difference between unacclimatized and acclimatized heat exposure limits. The findings provide support for a constant 3°C WBGT OEL decrease to account for unacclimatized workers. Body surface area explained part of the difference in ULPZ values between men and women. In addition, the pooled PSU and USF data provide insight into the distribution of individual values for the ULPZ among young, healthy unacclimatized and acclimatized populations in support of occupational heat stress guidelines.NEW & NOTEWORTHY Occupational exposure limit guidelines using wet bulb globe temperature (WBGT) distinguish between acclimatized and unacclimatized workers with about a 3°C difference between them. For the first time, empirical data from two laboratories provide support for acclimatization state adjustments. Using a constant difference rather than increasing differences with metabolic rate better describes the limit for unacclimatized participants. Furthermore, the lower upper limit of the prescriptive zone (ULPZ) values set forth for women do not relate to fitness level but are partly explained by their smaller body surface area (BSA). An examination of individual ULPZ values suggests that many unacclimatized individuals should be able to sustain safe work at the exposure limit for acclimatized workers.

Prophylactic influences of prebiotics on gut microbiome and immune response of heat-stressed broiler chickens

Climatic changes and elevated ambient temperature are significant environmental stressors with a negative impact on birds' physiological, immunological, and behavioral status, increasing their susceptibility to stressors and immunosuppression and consequently increasing intestinal permeability (leaky gut). Prebiotics have been utilized to stop or diminish the harmful effects of stress in chickens. We aimed to evaluate the role of mannan-oligosaccharides, and beta-D-glucan prebiotics supplements in drinking water against experimentally induced heat stress (HS) on broiler chickens and study their impact on birds' performance, gut microbiome, and immune response. A total of 120 1-day-old Ross broiler chicks were allocated into four groups (30 birds/group), and each group was subdivided into triplicates (10 birds each). The experimental groups were classified as follows; the 1st (G1) control birds, the 2nd (G2) birds exposed experimentally to HS, the 3rd (G3) birds administered prebiotics in drinking water without exposure to HS, and the 4th (G4) birds exposed to HS and administered prebiotics in drinking water. After each vaccination, blood samples and serum samples were collected to evaluate the birds' immune status. Fecal samples were also collected for the molecular evaluation of the gut microbiome based on the genetic analyses and sequencing of 16S rRNA gene. The results showed that HS has reduced the birds' performance and badly affected the birds' immune response and gut microbiome. However, the addition of prebiotics to drinking water, with or without stress, enhanced the growth rate, maintained a normal gut microbiome, and improved immune parameters. Moreover, the usage of prebiotics improved the chicken gut microbiome and alleviated the negative effect of heat stress. Administering prebiotics significantly (p < 0.05) increased the relative abundance of beneficial bacteria and eradicated pathogenic ones in the birds' gut microbiome. Prebiotics showed a positive effect on the gut microbiome and the immune status of chickens under HS in addition to their efficacy as a growth promoter.

Transcriptome analysis of multiple tissues reveals the potential mechanism of death under acute heat stress in chicken

BACKGROUND

Acute heat stress could induce high mortality and cause huge economic losses in the poultry industry. Although many studies have revealed heat stress-induced injuries of multiple tissues, the main target tissue and molecular mechanism of death under acute heat stress was largely unknown. This study systematically compared the transcriptome data of five main visceral tissues in chickens to reveal the response of multiple tissues to acute heat stress and determine the main target tissue of acute heat stress, further revealing the injuries of main target tissue and their potential mechanism by combing pathological section and qRT-PCR technologies.

RESULTS

The transcriptome data of five visceral tissues revealed that acute heat stress broadly caused inflammatory response and damaged tissues metabolic homeostasis. Among the five tested visceral tissues, the number of differentially expressed genes in the lung was the highest, and their fold changes were the greatest, indicating that the lung was the main target tissue of acute heat stress. The results of pathological section revealed severe inflammation, emphysema and pulmonary hemorrhage in the lung under acute heat stress. Our study found that some pro-inflammatory genes, including CNTFR, FURIN, CCR6, LIFR and IL20RA, were significantly up-regulated both in the heat-stress and heat-death groups, and their fold changes in the heat-death group were significantly greater than that in the heat-stress group. We also found an anti-inflammatory gene, AvBD9, exhibiting an extremely high expression in the heat-stress group but a low expression in the heat-death group.

CONCLUSIONS

Our study found that acute heat stress caused multiple tissue injuries broadly and the lung was the main target tissue of acute heat stress in chicken. Acute heat stress caused a severe inflammatory response, emphysema, and pulmonary haemorrhage, The severe inflammatory response in the heat-death group was related to the up-regulation of pro-inflammatory genes and down-regulation of anti-inflammatory genes.

Predicting climate-change induced heat-related illness risk in Grand Canyon National Park visitors

BACKGROUND

The climate crisis is the greatest public health threat of the 21st century. Excessive heat is responsible for more deaths than any other extreme weather event, and the frequency, intensity, and duration of extreme heat events are increasing globally due to climate change. Exposure to excessive heat can result in heat related illnesses (HRIs) and long-term poor health outcomes. Physical exertion, sudden exposure to excessive heat, and the lack of physical or behavioral adaptation resources are all associated with greater HRI risk, which is expected to increase for visitors to Grand Canyon National Park (GCNP) and other public lands as climate change worsens.

OBJECTIVES

Our objectives were to understand 1) the relationship between weather and HRI in GCNP visitors, 2) how future HRI rates may change, and 3) how land management agencies can update risk mitigation strategies to match changing risk and better manage an increased HRI burden.

METHODS

We utilized previously published data on HRI in GCNP visitors, and records of daily visitation, temperatures, and maximum and minimum daily humidity from the same study period to develop a model estimate for HRI risk. We then used future climate projections from the World Climate Research Programme's Coupled Model Intercomparison Project phase 5 multi-model dataset to model future HRI risk under different climate scenarios.

RESULTS

The incidence of HRI was significantly associated with maximum daily temperature and minimum relative humidity, and was more common in the shoulder season months. We estimated that HRI will increase 29%-137% over 2004-2009 levels through 2100, assuming no change in visitation.

DISCUSSION

Climate change will continue to increase HRI risk for GCNP visitors and poses risks to public land managers' mission to provide for safe recreation experiences for the benefit of this and future generations in places like GCNP. Excessive risk during the shoulder season months presents an opportunity to increase preventative search and rescue and education efforts to mitigate increased risk.

Blood Transcriptomic Analyses Reveal Functional Pathways Associated with Thermotolerance in Pregnant Ewes Exposed to Environmental Heat Stress

Environmental heat stress triggers a series of compensatory mechanisms in sheep that are dependent on their genetic regulation of thermotolerance. Our objective was to identify genes and regulatory pathways associated with thermotolerance in ewes exposed to heat stress. We performed next-generation RNA sequencing on blood collected from 16 pregnant ewes, which were grouped as tolerant and non-tolerant to heat stress according to a physiological indicator. Additional samples were collected to measure complete blood count. A total of 358 differentially expressed genes were identified after applying selection criteria. Gene expression analysis detected 46 GO terms and 52 KEGG functional pathways. The top-three signaling pathways were p53, RIG-I-like receptor and FoxO, which suggested gene participation in biological processes such as apoptosis, cell signaling and immune response to external stressors. Network analysis revealed ATM, ISG15, IRF7, MDM4, DHX58 and TGFβR1 as over-expressed genes with high regulatory potential. A co-expression network involving the immune-related genes ISG15, IRF7 and DXH58 was detected in lymphocytes and monocytes, which was consistent with hematological findings. In conclusion, transcriptomic analysis revealed a non-viral immune mechanism involving apoptosis, which is induced by external stressors and appears to play an important role in the molecular regulation of heat stress tolerance in ewes.

Broad Scale Spatial Modelling of Wet Bulb Globe Temperature to Investigate Impact of Shade and Airflow on Heat Injury Risk and Labour Capacity in Warm to Hot Climates

While shade and air flow are recognised factors that reduce outdoor heat exposure, the level of reduction in terms of labour capacity at varying air temperature and humidity levels is poorly understood. This study investigated cooling effects on the commonly used heat index, wet bulb globe temperature (WBGT), and subsequent impact on labour capacity, for a range of air flow and shade conditions in warm to hot climates. We modelled heat exposure using a physics-based method to map WBGT for a case study region which experiences a range of heat categories with varying levels of health risks for outdoor workers. Continent-scale modelling confirmed significant spatial variability in the effect of various shade and wind speed scenarios across a range of real-world mid-summer daytime conditions. At high WBGTs, increasing shade or air flow for outdoor workers lowered heat exposure and increases labour capacity, with shade giving the greatest benefit, but cooling varied considerably depending upon underlying air temperature and humidity. Shade had the greater cooling effect; reducing incident radiation by 90% decreased WBGT by 2-6 °C depending on location. Wind had a lower cooling effect in the hottest regions, with a decreasing exponential relationship between wind speed and WBGT observed.

The effects of betaine supplementation on fluid balance and heat tolerance during passive heat stress in men

INTRODUCTION

Consuming intracellular osmolytes, like betaine (BET), may attenuate symptoms of heat stress. The purpose of this study was to examine the effects of BET supplementation on fluid balance and heat tolerance after a 7-day loading period and during passive heat exposure.

METHODS

A double-blind, placebo controlled, crossover study compared BET or placebo consumption (50 mg·kg-1 , twice daily) for 7 days in young, recreationally active men (N = 11).

RESULTS

During the loading period, no significant interactions were found for any marker of fluid balance between or within conditions. During heat exposure, significant time effects but no condition x time interactions, were found for plasma characteristics (i.e., volume, osmolality, sodium, albumin, and total protein). Plasma volume was significantly increased by min 30 in both conditions (PLA: +6.9. ± 5.0%, BET: +10.2 ± 7.4%) and remained elevated for the remainder of the experimental trial, but was not significantly different between conditions. After 60 min of passive heat exposure, both conditions experienced a similar increase in core temperature (PLA: +0.32 ± 0.22°C, BET: +0.31 ± 0.21°C; p = 0.912).

CONCLUSIONS

Supplemental BET did not improve markers of fluid balance or heat tolerance during 7 days of loading or during passive heat exposure.