Heat stress, plasma concentrations of adrenaline, noradrenaline, 5-hydroxytryptamine and cortisol, mood state and cognitive performance

Repeated activation of preoptic area recipient neurons in posterior paraventricular nucleus mediates chronic heat-induced negative emotional valence and hyperarousal states

Mental and behavioral disorders are associated with extended period of hot weather as found in heatwaves, but the underlying neural circuit mechanism remains poorly known. The posterior paraventricular thalamus (pPVT) is a hub for emotional processing and receives inputs from the hypothalamic preoptic area (POA), the well-recognized thermoregulation center. The present study was designed to explore whether chronic heat exposure leads to aberrant activities in POA recipient pPVT neurons and subsequent changes in emotional states. By devising an air heating paradigm mimicking the condition of heatwaves and utilizing emotion-related behavioral tests, viral tract tracing, in vivo calcium recordings, optogenetic manipulations, and electrophysiological recordings, we found that chronic heat exposure for 3 weeks led to negative emotional valence and hyperarousal states in mice. The pPVT neurons receive monosynaptic excitatory and inhibitory innervations from the POA. These neurons exhibited a persistent increase in neural activity following chronic heat exposure, which was essential for chronic heat-induced emotional changes. Notably, these neurons were also prone to display stronger neuronal activities associated with anxiety responses to stressful situations. Furthermore, we observed saturated neuroplasticity in the POA-pPVT excitatory pathway after chronic heat exposure that occluded further potentiation. Taken together, long-term aberration in the POA to pPVT pathway offers a neurobiological mechanism of emotional and behavioral changes seen in extended periods of hot weather like heatwaves.

The impact of temperature changes on the health vulnerability of migrant workers: an empirical study based on the China family panel studies

Introduction

Migrant workers constitute a significant portion of China's workforce, and their health directly affects labor supply and economic stability. Health vulnerability plays a crucial role in shaping the well-being of migrant workers, yet its determinants, particularly the impact of temperature change, remain underexplored. This study, based on the socio-ecological model, investigates how temperature variations influence the health vulnerability of migrant workers in China.

Methods

Using data from 2020, this study quantifies health vulnerability and examines the impact of temperature fluctuations across different seasons. Robustness checks, including dependent variable substitutions and model modifications, ensure the reliability of the findings. Furthermore, a mechanism analysis is conducted to explore the underlying pathways through which temperature change affects health vulnerability.

Results

The findings reveal that rising temperatures in spring, summer, and winter significantly exacerbate the health vulnerability of migrant workers, while increasing autumn temperatures mitigate it. Mechanism analysis identifies heightened psychological burden as a key channel through which temperature change worsens health vulnerability. Additionally, generational differences emerge: older migrant workers are more adversely affected by elevated spring temperatures, whereas younger workers exhibit greater sensitivity to rising summer temperatures.

Discussion

These results underscore the necessity of targeted health interventions and adaptive labor protection policies. By highlighting the seasonal and generational disparities in the effects of temperature change, this study offers theoretical and empirical support for enhancing the resilience of migrant workers to climate variations. The findings provide valuable insights for policymakers in designing strategies to safeguard the health and stability of the migrant workforce.

The combined effects of sleep and extreme heat exposure on cognitive function among older adults

BACKGROUND

Extreme heat is linked to cognitive impairment. Normal sleep duration and good sleep quality can reduce cognitive impairment risks. However, the combined impact of sleep (duration and quality) and extreme heat on cognitive impairment is unclear. This study tests whether normal sleep duration and good sleep quality during a heatwave reduce cognitive impairment compared to poor sleep quality and long sleep duration in older adults.

METHODS

This study used cohort data from 9153 older adults. Extreme heat was defined as periods ≥ 3 days with daily minimum temperatures above the 92.5th percentile during the warm season. Cognitive function was assessed with the Mini-Mental State Examination (MMSE). Sleep duration was categorized as long, normal, or short, and sleep quality as good or poor. Six and four categories were used for combinations of heatwave exposure with sleep duration and quality, respectively. Cox regression models were applied for analysis.

RESULTS

Compared to those with long sleep duration during heatwaves, participants exposed to heatwaves with normal sleep duration had lower cognitive impairment risk (HR: 0.86, 95 %CI: 0.76-0.97). Those exposed to extreme heat with short sleep duration also showed lower cognitive risks (HR: 0.74, 95 %CI: 0.62-0.88). Compared to those with poor sleep quality during heatwave, participants with good sleep quality during heatwaves did not show significantly lower cognitive impairment risk (HR: 1.10, 95 %CI: 0.98-1.23).

CONCLUSION

Older adults with normal or short sleep duration during heatwaves may face lower cognitive impairment risks, highlighting the importance of sleep guidance to protect cognitive health during extreme heat.

Nature-based solutions to address anxiety disorders: A cross-sectional ecological study of green spatial patterns in Taiwan

Air pollution and heat increase the prevalence and risk of anxiety disorders, which are particularly severe under the increasing trends of climate change and urbanization. Well-designed green spaces have mediating effects on the threats posed by environmental deterioration and promote public health. However, previous research has overlooked these effects. This cross-sectional ecological study applied partial least squares structural equation modeling to data from Taiwanese cities and towns to infer the vital influences of and complex relationships among green spatial patterns (i.e., the dispersion, patch area, fragmentation, aggregation, and coverage ratio of green spaces), socioeconomic status (i.e., income and population aging), atmospheric environment (i.e., air pollution and high temperature), and anxiety disorders. The results reveal that minimizing the dispersion of green spaces and maximizing their patch area and coverage ratio are associated with reduced prevalence of anxiety disorders. Air pollution and high temperature mediate the influence of green spatial patterns on anxiety disorders. Population aging, air pollution, and high temperature are factors that increase the prevalence rate of anxiety disorders, whereas income level has a negative effect. This study identified the pathways and influences (i.e., indirect, direct, and total impacts) of green spatial pattern characteristics on anxiety disorders. These findings show that the adoption of effective greening policies may promote the development of healthy cities. Moreover, this study provides a useful methodology for clarifying complex pathways and identifying vital factors that can be applied to future research in health science and policy.

Review: Feed efficiency and metabolic flexibility in livestock

Improving the conversion of feed into product has been a key focus of genetic improvement in all livestock species. Livestock feed efficiency is the amount of product produced per unit of feed intake. Feed efficiency also depends on processes that are not directly related to economically important phenotypes, which can be considered 'waste' from a production point of view but are vital maintenance-related functions that are closely associated with environmental flexibility and adaptation. Resource allocation theory suggests that an animal's resource budget is narrowed when production efficiency is improved through an increase in productive output, along with a decrease in feed intake (capacity) and body reserves (improved leanness). The resulting trade-offs between productivity and vital functions may render the animal less capable of responding to unexpected challenges, potentially leading to negative side effects that are not directly related to economically important phenotypes. However, selection for feed efficiency may not narrow the metabolic space and result in trade-offs if the increase in feed efficiency is the result of increased metabolic flexibility in fuel substrate choice (carbohydrates, lipids, and/or proteins) and other energy-saving strategies. This review evaluates the relationship between metabolic flexibility and feed efficiency during anabolism (growth), fasting, immune activation, general stress, and heat stress, with a focus on pig production. We start with a brief overview of energy processes and substrate metabolism of carbohydrates, lipids, and protein. During muscle metabolism, the type of fuel used depends on fibre type characteristics of the muscle. Selection for improved meat production has resulted in pigs with a greater abundance of fast-twitch fibres with lower energy expenditure and higher metabolic efficiency. Metabolic flexibility for adaptation to disease, and response to regular stress implies that a more reactive immune response and reduced fear response results in higher feed efficiency. The examples presented in this review show that selection for improved feed efficiency does not necessarily narrow the metabolic space and result in trade-offs between productivity and vital functions because of energy-sparing mechanisms.

Chronic stimulation desensitizes β2-adrenergic receptor responses in natural killer cells

Adrenergic receptors (ARs) are preferentially expressed by innate lymphocytes such as natural killer (NK) cells. Here, we study the effect of epinephrine-mediated stimulation of the β2-adrenergic receptor (β2AR) on the function of human NK cells. Epinephrine stimulation inhibited early NK cell signaling events and blocked the function of the integrin LFA-1. This reduced the adhesion of NK cells to ICAM-1, explaining how NK cells are mobilized into the peripheral blood upon epinephrine release during acute stress or exercise. Additionally, epinephrine stimulation transiently reduced NK cell degranulation, serial killing, and cytokine production and affected metabolic changes upon NK cell activation via the cAMP-protein kinase A (PKA) pathway. Repeated exposure to β2AR agonists resulted in the desensitization of the β2AR via a PKA feedback loop-initiated G-protein switch. Therefore, acute epinephrine stimulation of chronically β2AR stimulated NK cells no longer resulted in inhibited signaling and reduced LFA-1 activity. Sustained stimulation by long-acting β2-agonists (LABA) not only inhibited NK cell functions but also resulted in desensitization of the β2AR. However, peripheral NK cells from LABA-treated asthma patients still reacted unchanged to epinephrine stimulation, demonstrating that local LABA administration does not result in detectable systemic effects on NK cells.

A Review of the Links Between Work and Heart Disease in the 21st Century

This review explores the multifaceted exposures in the workplace that contribute to cardiovascular diseases (CVD), including physical, ergonomics, chemical, biological, psychosocial, and emerging occupational hazards. These well-documented occupational hazards have long been linked to heart disease. Exposures arising from these hazards present significant concerns for worker health and safety. Moreover, heat stress is an emerging and increasingly pervasive threat, exacerbated by climate change, particularly in outdoor, high-exposure industries like agriculture and construction. While the epidemiological links between heat and CVD are well established, there is a critical gap in research on the physiological impacts of heat on workers' cardiovascular health. In particular, migrant workers are especially vulnerable to these occupational hazards, particularly in the absence of targeted, equitable interventions. As global temperatures rise, addressing these occupational exposures is important for protecting the cardiovascular health of the workforce and the expanding field of occupational cardiology.

Genetic patterning in hippocampus of rat undergoing impaired spatial memory induced by long-term heat stress

The organism's normal physiological function is greatly impacted in a febrile environment, leading to the manifestation of pathological conditions including elevated body temperature, dehydration, gastric bleeding, and spermatogenic dysfunction. Numerous lines of evidence indicate that heat stress significantly impacts the brain's structure and function. Previous studies have demonstrated that both animals and humans experience cognitive impairment as a result of exposure to high temperatures. However, there is a lack of research on the effects of prolonged exposure to high-temperature environments on learning and memory function, as well as the underlying molecular regulatory mechanisms. In this study, we examined the impact of long-term heat stress exposure on spatial memory function in rats and conducted transcriptome sequencing analysis of rat hippocampal tissues to identify the crucial molecular targets affected by prolonged heat stress exposure. It was found that the long-term heat stress impaired rats' spatial memory function due to the pathological damages and apoptosis of hippocampal neurons at the CA3 region, which is accompanied with the decrease of growth hormone level in peripheral blood. RNA sequencing analysis revealed the signaling pathways related to positive regulation of external stimulation response and innate immune response were dramatically affected by heat stress. Among the verified differentially expressed genes, the knockdown of Arhgap36 in neuronal cell line HT22 significantly enhances the cell apoptosis, suggesting the impaired spatial memory induced by long-term heat stress may at least partially be mediated by the dysregulation of Arhgap36 in hippocampal neurons. The uncovered relationship between molecular changes in the hippocampus and behavioral alterations induced by long-term heat stress may offer valuable insights for the development of therapeutic targets and protective drugs to enhance memory function in heat-exposed individuals.

Plasma epinephrine and norepinephrine responses to extreme heat exposures in young and older adults

Hyperthermia is known as a hyperadrenergic state, yet there is a lack of data on the sympathetic responses to ambient heat stress in humans. Therefore, we investigated the plasma epinephrine and norepinephrine concentrations of healthy young and older adults exposed to 3 h of very hot and dry, as well as hot and humid, heat, both with accompanying activities of daily living. We hypothesized that older adults, compared with young adults, would have augmented increases in epinephrine and norepinephrine concentrations secondary to increased thermal strain. Young (n = 20) and older (n = 18) participants underwent two 3-h heat exposures on different days: very hot and dry [47°C and 15% relative humidity (RH)] and hot and humid (41°C and 40% RH). To mimic heat generation comparable to activities of daily living, participants performed seven 5-min bouts of light cycling (approximately 3 METS) dispersed throughout the heat exposure. We measured plasma concentrations of epinephrine and norepinephrine at baseline, end, and 2-h postheat exposure. There was a group-wide increase in epinephrine from baseline to the end of the heat exposure (Δ19 ± 27 pg/mL; P < 0.001) in the hot and humid condition, but not in the very hot and dry condition (Δ6 ± 19 pg/mL; P = 0.10). There were group-wide decreases in norepinephrine concentrations from baseline to the end of the heat exposure in both the very hot and dry (Δ-131 ± 169 pg/mL; P < 0.001) and the hot and humid (Δ-138 ± 157 pg/mL; P < 0.001) conditions, with both returning to near baseline at 2-h postexposure. These data suggest that ambient heating with accompanying bouts of light intermittent exercise may lead to decreases in circulating concentrations of norepinephrine.NEW & NOTEWORTHY Herein we present plasma epinephrine and norepinephrine concentrations to 3 h of very hot and dry, as well as hot and humid, heat exposures with accompanying activities of daily living in young and older participants. We found 1) increased plasma concentrations of epinephrine in young and older adults following the hot and humid, but not the very hot and dry exposures and 2) decreased concentrations of norepinephrine in both groups following exposure to both conditions.

Thrombomodulin Improves Cognitive Deficits in Heat-Stressed Mice

BACKGROUND

Thrombomodulin (TM) exerts anticoagulant and anti-inflammatory effects to improve the survival of patients with septic shock. Heat stroke resembles septic shock in many aspects. We tested whether TM would improve cognitive deficits and related causative factors in heat-stressed (HS) mice.

METHODS

Adult male mice were exposed to HS (33°C for 2 hours daily for 7 consecutive days) to induce cognitive deficits. Recombinant human soluble TM (1 mg/kg, i.p.) was administered immediately after the first HS trial and then once daily for 7 consecutive days. We performed the Y-maze, novel objective recognition, and passive avoidance tests to evaluate cognitive function. Plasma levels of lipopolysaccharide (LPS), high-mobility group box 1 (HMGB1), coagulation parameters, and both plasma and tissue levels of inflammatory and oxidative stress markers were biochemically measured. The duodenum and hippocampus sections were immunohistochemically stained. The intestinal and blood-brain barrier permeability were determined.

RESULTS

Compared with controls, HS mice treated with TM had lesser extents of cognitive deficits, exacerbated stress reactions, gut barrier disruption, endotoxemia, blood-brain barrier disruption, and inflammatory, oxidative, and coagulatory injury to heart, duodenum, and hippocampal tissues, and increased plasma HMGB1. In addition to reducing cognitive deficits, TM therapy alleviated all the abovementioned complications in heat-stressed mice.

CONCLUSIONS

The findings suggest that HS can lead to exacerbated stress reactions, endotoxemia, gut barrier disruption, blood-brain barrier disruption, hippocampal inflammation, coagulopathy, and oxidative stress, which may act as causative factors for cognitive deficits. TM, an anti-inflammatory, antioxidant, and anti-coagulatory agent, inhibited heat stress-induced cognitive deficits in mice.

The firestorm within: A narrative review of extreme heat and wildfire smoke effects on brain health

Climate change is generating increased heatwaves and wildfires across much of the world. With these escalating environmental changes comes greater impacts on human health leading to increased numbers of people suffering from heat- and wildfire smoke-associated respiratory and cardiovascular impairment. One area of health impact of climate change that has received far less attention is the effects of extreme heat and wildfire smoke exposure on human brain health. As elevated temperatures, and wildfire-associated smoke, are increasingly experienced simultaneously over summer periods, understanding this combined impact is critical to management of human health especially in the elderly, and people with dementia, and other neurological disorders. Both extreme heat and wildfire smoke air pollution (especially particulate matter, PM) induce neuroinflammatory and cerebrovascular effects, oxidative stress, and cognitive impairment, however the combined effect of these impacts are not well understood. In this narrative review, a comprehensive examination of extreme heat and wildfire smoke impact on human brain health is presented, with a focus on how these factors contribute to cognitive impairment, and dementia, one of the leading health issues today. Also discussed is the potential impact of combined heat and wildfire smoke on brain health, and where future efforts should be applied to help advance knowledge in this rapidly growing and critical field of health research.

Validity of mental and physical stress models

Different stress models are employed to enhance our understanding of the underlying mechanisms and explore potential interventions. However, the utility of these models remains a critical concern, as their validities may be limited by the complexity of stress processes. Literature review revealed that both mental and physical stress models possess reasonable construct and criterion validities, respectively reflected in psychometrically assessed stress ratings and in activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis. The findings are less robust, though, in the pharmacological perturbations' domain, including such agents as adenosine or dobutamine. Likewise, stress models' convergent- and discriminant validity vary depending on the stressors' nature. Stress models share similarities, but also have important differences regarding their validities. Specific traits defined by the nature of the stressor stimulus should be taken into consideration when selecting stress models. Doing so can personalize prevention and treatment of stress-related antecedents, its acute processing, and chronic sequelae. Further work is warranted to refine stress models' validity and customize them so they commensurate diverse populations and circumstances.

Short-term ambient temperature variations and incidence of preterm birth: A systematic review and meta-analysis

This study aimed to determine the short-term effects of ambient temperature variations exposures on the incidence of preterm birth (PTB) for each single lag day (lag0 to lag6) and cumulative lag days (lag0-1 to lag0-6) up to a week before birth. To find relevant publications, online databases, including Web of Science, PubMed, and Scopus were searched with appropriate keywords and Mesh terms from their inception to October 25, 2023. Overall, the number of 39 observational studies with 12.5 million pregnant women and 700.000 cases of PTB met our eligibility criteria. The associations of temperature variations with the incidence of PTB were investigated with two different meta-analyses, including the percentile meta-analysis (comparing different percentiles (P1 to P99) with a referent percentile (P50)), and the linear meta-analysis (per 5 °C increment of the temperature levels). For the percentile meta-analysis, we observed both extreme cold (P1, only lag 0) and heat (P95 and P99 with the highest risk at lag1 and lag0-6) exposures can be significantly associated with a higher risk of PTB. The pooled RR (95 % CI) per 5 °C increase in the temperature levels at lag0-6 was estimated as 1.038 (1.018, 1.058) for the overall analysis. Subgroup analysis based on the season shows a significant association in the warm season (RR = 1.082 and 95 % CI = 1.036, 1.128) at all lag days but not the cold season. For the single lag day, we observed the risk of PTB is the highest at lag1 and decreased with moving to lag6. In sum, we suppose there is a nearly V-shape non-linear association between air temperature levels and the incidence of PTB with the linear relationship for each unit increase (also decrease) in the temperature levels above (also below) moderate temperature limits. Future studies should investigate possible association of occupational heat and cold exposure during pregnancy on the incidence of adverse birth outcomes such as PTB.

Long-term effect of extreme temperature on cognitive function of middle-aged and older adults in China

BACKGROUND

Several studies have explored the association between temperature and cognitive function. However, few studies have examined the effect of extreme temperature on cognitive function. In this study, we aimed to quantify the long-term effect of extreme temperature (e.g., heat waves, cold spells, and hot night excess (HNE)) on cognitive performance in middle-aged and older people in China.

METHOD

We investigated 7915 aged >45 years people from the China Health and Retirement Longitudinal Study (CHARLS), surveyed in 2011 and 2015. A structured questionnaire was utilized to assess cognitive function, including four dimensions: episodic memory, attention, orientation, and visuo-construction. Hourly ambient temperature from the ERA5-Land datasets were used to calculate variables indicating extreme temperature. We performed difference-in-difference (DID) models to assess the potential causal relationship between extreme temperature and cognitive function.

RESULTS

Non-linear analyses suggested that both sustained increases in temperature and excessive variability in temperature increased the risk of cognitive decline. Meanwhile, we observed the extra risk of global cognitive function decline was 2.3% (95% Confidence interval (95% CI): 0.2%, 4.4%) for heat waves (one unit increase) and 5.9% (95% CI: 0.6%, 11.6%) for HNE (one unit increase), while the association for cold spells was insignificant. Two cognitive dimensions, episodic memory and visuo-construction, were sensitive to these two heat-related factors.

CONCLUSION

Extreme temperature was inversely related to cognitive performance in middle-aged and older adults, which was substantial for heat waves and HNE particularly. The effect size varied by cognitive dimensions.

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.

Physiological responses to 9 hours of heat exposure in young and older adults. Part III: Association with self-reported symptoms and mood state

Older adults are at greater risk of heat-related morbidity and mortality during heat waves, which is commonly linked to impaired thermoregulation. However, little is known about the influence of increasing age on the relation between thermal strain and perceptual responses during daylong heat exposure. We evaluated thermal and perceptual responses in 20 young (19-31 yr) and 39 older adults (20 with hypertension and/or type 2 diabetes; 61-78 yr) resting in the heat for 9 h (heat index: 37°C). Body core and mean skin temperature areas under the curve (AUC, hours 0-9) were assessed as indicators of cumulative thermal strain. Self-reported symptoms (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were assessed at end-heating (adjusted for prescores). Body core temperature AUC was 2.4°C·h [1.0, 3.7] higher in older relative to young adults (P < 0.001), whereas mean skin temperature AUC was not different (-0.5°C·h [-4.1, 3.2] P = 0.799). At end-heating, self-reported symptoms were not different between age groups (0.99-fold [0.80, 1.23], P = 0.923), with or without adjustment for body core or mean skin temperature AUC (both P ≥ 0.824). Mood disturbance was 0.93-fold [0.88, 0.99] lower in older, relative to young adults (P = 0.031). Older adults with and without chronic health conditions experienced similar thermal strain, yet those with these conditions reported lower symptom scores and mood disturbance compared with young adults and their age-matched counterparts (all P ≤ 0.026). Although older adults experienced heightened thermal strain during the 9-h heat exposure, they did not experience greater self-reported symptoms or mood disturbance relative to young adults.NEW & NOTEWORTHY Despite experiencing greater cumulative thermal strain during 9 h of passive heat exposure, older adults reported similar heat-related symptoms and lower mood disturbance than young adults. Furthermore, self-reported symptoms and mood disturbance were lower in older adults with common age-associated health conditions than young adults and healthy age-matched counterparts. Perceptual responses to heat in older adults can underestimate their level of thermal strain compared with young adults, which may contribute to their increased heat vulnerability.

Au/Pt@ZIF-90 Nanoenzyme Capsule-Based "Explosive" Signal Amplifier for "All-in-Tube" POCT

The sensitive, convenient, and visual detection of low-concentration disease markers in biological samples has always been a priority in disease diagnosis. However, existing research has been problematic due to complex operation and unsatisfactory sensitivity. Consequently, an "explosive" signal amplification platform based on Au/Pt@ZIF-90 was developed for sensitive visual detection of disease markers. In this study, a controllable and explosively released Au/Pt nanoparticles (NPs) "nanoenzyme capsule" was prepared by encapsulating Au/Pt NPs with excellent peroxidase activity in ZIF-90. This was achieved by adjusting the particle size of ZIF-90 and the encapsulation amount of Au/Pt NPs. Using the prepared capsules as the signal output module and aptamer as the target recognition module, an "All-in-Tube" portable point-of-care (POC) platform was constructed by integrating the Au/Pt@ZIF-90/filter paper and TMB/strips into an Eppendorf (EP) tube. By utilizing specific competitive binding of targets to aptamers, the platform enabled the sensitive and convenient measurement of small molecular disease markers. Taking adenosine as the proof of concept, the portable detection achieved excellent sensitivity. Moreover, the platform can achieve universal detection of various targets by varying the aptamer sequence. This signal amplification strategy provides a design pattern for the detection of low-concentration targets in biological samples and holds significant potential in the fields of disease diagnosis and environmental monitoring.

Effects of heat and personal protective equipment on thermal strain in healthcare workers: part B-application of wearable sensors to observe heat strain among healthcare workers under controlled conditions

PURPOSE

As climate change accelerates, healthcare workers (HCW) are expected to be more frequently exposed to heat at work. Heat stress can be exacerbated by physical activity and unfavorable working requirements, such as wearing personal protective equipment (PPE). Thus, understanding its potential negative effects on HCW´s health and working performance is becoming crucial. Using wearable sensors, this study investigated the physiological effects of heat stress due to HCW-related activities.

METHODS

Eighteen participants performed four experimental sessions in a controlled climatic environment following a standardized protocol. The conditions were (a) 22 °C, (b) 22 °C and PPE, (c) 27 °C and (d) 27 °C and PPE. An ear sensor (body temperature, heart rate) and a skin sensor (skin temperature) were used to record the participants´ physiological parameters.

RESULTS

Heat and PPE had a significant effect on the measured physiological parameters. When wearing PPE, the median participants' body temperature was 0.1 °C higher compared to not wearing PPE. At 27 °C, the median body temperature was 0.5 °C higher than at 22 °C. For median skin temperature, wearing PPE resulted in a 0.4 °C increase and higher temperatures in a 1.0 °C increase. An increase in median heart rate was also observed for PPE (+ 2/min) and heat (+ 3/min).

CONCLUSION

Long-term health and productivity risks can be further aggravated by the predicted temperature rise due to climate change. Further physiological studies with a well-designed intervention are needed to strengthen the evidence for developing comprehensive policies to protect workers in the healthcare sector.

The effects of heatwave on cognitive impairment among older adults: Exploring the combined effects of air pollution and green space

The association between heatwaves and cognitive impairment in older adults, especially the joint effect of air pollution and green space on this association, remains unknown. The present cohort study used data from waves of the Chinese Longitudinal Healthy Longevity Survey (CLHLS) from 2008 to 2018. Heatwaves were defined as having daily maximum temperature ≥ 92.5th, 95th and 97.5th percentile that continued at least two, three and four days, measured as the one-year heatwave days prior to the participants' incident cognitive impairment. Data on the annual average air pollutant concentrations of fine particulate matter (PM2.5) and ozone (O3) as well as green space exposure (according to the Normalized Difference Vegetation Index (NDVI)) were collected. Time-varying Cox proportional hazards models were constructed to examine the independent effect of heatwaves on cognitive impairment and the combined effect of heatwaves, air pollution, and green space on cognitive impairment. Potential multiplicative interactions were examined by adding a product term of air pollutants and NDVI with heatwaves in the models. The relative excess risk due to interaction (RERI) was calculated to reflect additive interactions. We found that heatwave exposure was associated with higher risks of cognitive impairment, with hazard ratios (HRs) and 95 % confidence intervals (CIs) ranging from 1.035 (95 % CI: 1.016-1.055) to 1.058 (95 % CI: 1.040-1.075). We observed a positive interaction of PM2.5 concentrations, O3 concentrations, lack of green space, and heatwave exposure on a multiplicative scale (HRs for product terms >1). Furthermore, we found a synergistic interaction of PM2.5 concentrations, O3, lack of green space, and heatwave exposure on an additive scale, with RERIs >0. These results suggest that extreme heat exposure may be a potential risk factor for cognitive impairment in older adults. Additionally, coexposure to air pollution and lack of green space exacerbated the adverse effects of heatwaves on cognitive function.

High temperatures are associated with reduced cognitive performance in wild southern pied babblers

Global temperatures are increasing rapidly. While considerable research is accumulating regarding the lethal and sublethal effects of heat on wildlife, its potential impact on animal cognition has received limited attention. Here, we tested wild southern pied babblers (Turdoides bicolor) on three cognitive tasks (associative learning, reversal learning and inhibitory control) under naturally occurring heat stress and non-heat stress conditions. We determined whether cognitive performance was explained by temperature, heat dissipation behaviours, individual and social attributes, or proxies of motivation. We found that temperature, but not heat dissipation behaviours, predicted variation in associative learning performance. Individuals required on average twice as many trials to learn an association when the maximum temperature during testing exceeded 38°C compared with moderate temperatures. Higher temperatures during testing were also associated with reduced inhibitory control performance, but only in females. By contrast, we found no temperature-related decline in performance in the reversal learning task, albeit individuals reached learning criterion in only 14 reversal learning tests. Our findings provide novel evidence of temperature-mediated cognitive impairment in a wild animal and indicate that its occurrence depends on the cognitive trait examined and individual sex.

Core Body Temperatures in Intermittent Sports: A Systematic Review

BACKGROUND

Hyperthermia (and associated health and performance implications) can be a significant problem for athletes and teams involved in intermittent sports. Quantifying the highest thermal strain (i.e. peak core body temperature [peak Tc]) from a range of intermittent sports would enhance our understanding of the thermal requirements of sport and assist in making informed decisions about training or match-day interventions to reduce thermally induced harm and/or performance decline.

OBJECTIVE

The objective of this systematic review was to synthesise and characterise the available thermal strain data collected in competition from intermittent sport athletes.

METHODS

A systematic literature search was performed on Web of Science, MEDLINE, and SPORTDiscus to identify studies up to 17 April 2023. Electronic databases were searched using a text mining method to provide a partially automated and systematic search strategy retrieving terms related to core body temperature measurement and intermittent sport. Records were eligible if they included core body temperature measurement during competition, without experimental intervention that may influence thermal strain (e.g. cooling), in healthy, adult, intermittent sport athletes at any level. Due to the lack of an available tool that specifically includes potential sources of bias for physiological responses in descriptive studies, a methodological evaluation checklist was developed and used to document important methodological considerations. Data were not meta-analysed given the methodological heterogeneity between studies and therefore were presented descriptively in tabular and graphical format.

RESULTS

A total of 34 studies were selected for review; 27 were observational, 5 were experimental (2 parallel group and 3 repeated measures randomised controlled trials), and 2 were quasi-experimental (1 parallel group and 1 repeated measures non-randomised controlled trial). Across all included studies, 386 participants (plus participant numbers not reported in two studies) were recruited after accounting for shared data between studies. A total of 4 studies (~ 12%) found no evidence of hyperthermia, 24 (~ 71%) found evidence of 'modest' hyperthermia (peak Tc between 38.5 and 39.5 °C), and 6 (~ 18%) found evidence of 'marked' hyperthermia (peak Tc of 39.5 °C or greater) during intermittent sports competition.

CONCLUSIONS

Practitioners and coaches supporting intermittent sport athletes are justified to seek interventions aimed at mitigating the high heat strain observed in competition. More research is required to determine the most effective interventions for this population that are practically viable in intermittent sports settings (often constrained by many competing demands). Greater statistical power and homogeneity among studies are required to quantify the independent effects of wet bulb globe temperature, competition duration, sport and level of competition on peak Tc, all of which are likely to be key modulators of the thermal strain experienced by competing athletes.

REGISTRATION

This systematic review was registered on the Open Science Framework ( https://osf.io/vfb4s ; https://doi.org/10.17605/OSF.IO/EZYFA , 4 January 2021).

Delayed metabolic disturbances in the myocardium after exertional heat stroke: contrasting effects of exertion and thermal load

Epidemiological studies report higher risks of cardiovascular disease in humans exposed to heat stroke earlier in life. Previously, we explored mechanistic links between heat stroke and developing cardiac abnormalities using a preclinical mouse model of exertional heat stroke (EHS). Profound metabolic abnormalities developed in the ventricles of females but not males after 2 wk of recovery. Here we tested whether this lack of response in males could be attributed to the lower exercise performances or reduced thermal loads they experienced with the same running protocol. We systematically altered environmental temperature (Te) during EHS to manipulate heat exposure and exercise performance in the males. Three groups of adult C57BL/6 male mice were studied: "EHS-34" (Te = 34°C), "EHS-41" (Te = 41°C), and "EHS-39.5" (Te = 39.5°C). Mice ran until symptom limitation (unconsciousness), reaching max core temperature (Tc,max). After a 2-wk recovery, the mice were euthanized, and the ventricles were removed for untargeted metabolomics. Results were compared against age-matched nonexercise controls. The EHS-34 mice greatly elevated their exercise performance but reached lower Tc,max and lower thermal loads. The EHS-41 mice exhibited equivalent thermal loads, exercise times, and Tc,max compared with EHS-39.5. The ventricles from EHS-34 mice exhibited the greatest metabolic disturbances in the heart, characterized by shifts toward glucose metabolism, reductions in acylcarnitines, increased amino acid metabolites, elevations in antioxidants, altered TCA cycle flux, and increased xenobiotics. In conclusion, delayed metabolic disturbances following EHS in male myocardium appear to be greatly amplified by higher levels of exertion in the heat, even with lower thermal loads and max core temperatures.NEW & NOTEWORTHY Epidemiological data demonstrate greater cardiovascular risk in patients with previous heat stroke exposure. Using a preclinical mouse model of exertional heat stroke, male mice were exposed to one of three environmental temperatures (Te) during exercise. Paradoxically, after 2 wk, the mice in the lowest Te, exhibiting the largest exercise response and lowest heat load, had the greatest ventricular metabolic disturbances. Metabolic outcomes resemble developing left ventricular hypertrophy or stress-induced heart disease.

Indoor overheating influences self-reported symptoms and mood-state in older adults during a simulated heatwave: Effects of mid-day cooling centre use

Public health agencies recommend that older adults without home air-conditioning visit cooling centres to mitigate physiological strain from high ambient temperatures during heat waves. However, there is little evidence regarding their influence on self-reported environmental symptoms and mood-state after returning to the heat.

METHODS

Forty adults (64-79 years) underwent a daylong laboratory-based indoor overheating simulation (9-hours, heat index: 37 °C) with (cooling, n = 20) or without (control, n = 20) a 2-hour air-conditioning intervention (hours 5-6). Mean skin and core temperature areas under the curve (AUC, hours 0-9) were used to assess cumulative thermal strain. Group differences in total symptom scores and subjective heat illness (68-item environmental symptoms questionnaire) as well as total mood disturbance and energy index (40-item profile of mood states questionnaire) were evaluated at end-heating (adjusted for pre-exposure scores).

RESULTS

Cooling reduced mean skin and core temperature AUCs by 4.0 [0.1, 0.8] and 1.6 [0.4, 2.8] °C·hour compared to control (both p < 0.048). However, at end-heating neither mean skin nor core temperatures differed between groups (both p > 0.999). Total symptom scores and subjective heat illness were 0.58-fold [0.44, 0.77] and 0.56-fold [0.40, 0.78] lower in the cooling compared to control group (both p < 0.001). Mood disturbance was 0.91-fold [0.83, 0.99] lower for cooling than control (p = 0.036), although energy index was not different between groups (p = 0.141).

CONCLUSION

Cooling centres can have sustained positive effects on perceived thermal strain and mood-state in older adults after returning to the heat. However, continued vigilance and use of appropriate countermeasures to mitigate physiological strain from indoor overheating should be encouraged as body temperatures can rapidly return to pre-cooling levels.

Ambient temperatures associated with reduced cognitive function in older adults in China

The cognitive function status of older adults determines the social function and living quality of older adults, which is related to the healthy development and stability of the society. However, the impact of high or low ambient temperature on cognitive function in older adults remains unclear. Based on data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), we comprehensively assessed the impact of ambient temperature on the cognitive function of older adults in this study. The findings exhibited that for each 1 °C ascent in monthly temperature of high temperature, the examination score of global cognitive function of older adults decreased by 0.48 (95% CI 0.21-0.74), which was greater than that of 0.14 (95% CI 0.06-0.25) for each 1 °C reduction in low temperature. Overall, the detrimental effect of high temperature on cognitive function in older adults was more significant than that of low temperature, including on the five sub-cognitive functions involved. Our research provides vital technical guidance and reference for the health protection and prevention of cognitive function of older adults in specific external environmental conditions under the current climatic variation and temperature rise.

Seasonal influence on cognitive and psycho-physiological responses to a single 11-h day of work in outdoor mine industry workers

This study investigated the seasonal effects that working outdoors had on various parameters in mining industry workers over the course of a work-shift. Workers (n = 27) were assessed in summer (33.3 ± 4.2°C, 38 ± 18% RH; n = 13, age = 46 ± 14 y, BMI = 29.1 ± 5.7 kg/m2) and winter (23.6 ± 5.1°C, 39 ± 20% RH; n = 14, age = 44 ± 12 y, BMI = 31.2 ± 4.1 kg/m2). Core temperature and heart-rate were measured continuously (analyzed at five time points), while perceptual measures, cognitive and manual dexterity performance were assessed at various times over an 11-h shift at the start of a 14-day swing. Hydration was assessed (urine specific gravity) pre- and post-shift. Working memory was impaired in summer compared to winter (-10%; p = 0.039), however did not change throughout the shift. Processing efficiency was significantly reduced at 12 pm (-12%; p = 0.005) and 5 pm (-21%; p < 0.001) compared to 9 am, irrespective of season (p > 0.05). Manual dexterity (dominant-hand) improved over the shift (+13%, p = 0.002), but was not different between seasons. Perceived fatigue had no main effect of season or shift. Core temperature, heart-rate, thermal sensation and rating of perceived exertion increased throughout the shift, with only core temperature and thermal sensation showing a seasonal effect (summer: +0.33°C, +18%, respectively; p < 0.002). Notably, 23% of workers in summer and 64% in winter started work significantly dehydrated, with 54% and 64% in summer and winter, respectively, finishing work with significant to serious dehydration. Impairment in working memory in summer combined with high levels of dehydration over the work-shift reinforces the need for workplace education on the importance of hydration and risk of occupation heat stress. Abbreviations: Core temperature: Tc; Fly-in fly-out: FIFO; Ratings of perceived exertion: RPE; Relative humidity: RH; Urinary specific gravity: USG; Wet bulb globe temperature: WBGT.

Heat stress associated with aerosol PPE and its impact

BACKGROUND

Aerosol personal protective equipment (PPE) is subjectively reported to negatively impact healthcare workers' performance and well-being, but this has not been assessed objectively.

AIMS

This randomized controlled crossover study aimed to quantify the heat stress associated with aerosol PPE and to investigate its impact upon mood, cognitive and motor function, and task performance.

METHODS

Sixteen healthy, young, lean participants (eight males) undertook an exercise protocol, which simulated the metabolic expenditure of hospital work: once wearing aerosol PPE (PPE visit) and once wearing standard surgical attire (control visit). Participants walked on a treadmill for 2 h followed by 30-min rest. Core temperature, heart rate, urine specific gravity, weight, grip strength, mood (Bond-Lader scale) and task performance (Intubation of a Manikin) were recorded. Values are between-visit mean (standard deviation) differences.

RESULTS

On the PPE visit core temperature (+0.2 (0.3)°C; P < 0.01), heart rate (+12 (13) bpm; P < 0.001), urine specific gravity (+0.003 (0.005); P < 0.05) and intubation task time (+50 (81) s; P < 0.01) were greater than on the control visit; and alertness (-14 (21) mm; P < 0.001), contentment (-14 (15) mm; P < 0.001) and grip strength (-4 (4) N; P < 0.01) were less.

CONCLUSIONS

This study demonstrates that wearing aerosol PPE in a simulated hospital environment results in heat exhaustion and has a negative impact upon mood, motor function, and task performance. Whilst wearing PPE is important to prevent disease transmission, strategies should be developed to limit its impact upon healthcare workers' performance and well-being.

Risk factors for heat-related illnesses during the Hajj mass gathering: an expert review

Human exposure to a hot environment may result in various heat-related illnesses (HRIs), which range in severity from mild and moderate forms to life-threatening heatstroke. The Hajj is one of the largest annual mass gatherings globally and has historically been associated with HRIs. Hajj attracts over two million Muslim pilgrims from more than 180 countries to the holy city of Makkah, Kingdom of Saudi Arabia. Several modifiable and non-modifiable factors render Hajj pilgrims at increased risk of developing HRIs during Hajj. These include characteristics of the Hajj, its location, population, and rituals, as well as pilgrims' knowledge of HRIs and their attitude and behavior. Makkah is characterized by a hot desert climate and fluctuating levels of relative humidity. Pilgrims are very diverse ethnically and geographically, with different adaptations to heat. Significant proportions of the Hajj population are elderly, obese, and with low levels of fitness. In addition, many have underlying health conditions and are on multiple medications that can interfere with thermoregulation. Other factors are inherent in the Hajj and its activities, including crowding, physically demanding outdoor rituals, and a high frequency of infection and febrile illness. Pilgrims generally lack awareness of HRIs, and their uptake of preventive measures is variable. In addition, many engage in hazardous behaviors that increase their risk of HRIs. These include performing rituals during the peak sunshine hours with no sun protection and with suboptimal sleep, nutrition, and hydration, while neglecting treatment for their chronic conditions. HRIs preventive plans for Hajj should incorporate measures to address the aforementioned factors to reduce the burden of these illnesses in future Hajj seasons. Lessons from the Hajj can be used to inform policy making and HRIs preventive measures in the general population worldwide.

Sex differences in response to exercise heat stress in the context of the military environment

Women can now serve in ground close combat (GCC) roles, where they may be required to operate alongside men in hot environments. However, relative to the average male soldier, female soldiers are less aerobically fit, with a smaller surface area (A _D), lower mass (m) with higher body fat and a larger A _D/m ratio. This increases cardiovascular strain, reduces heat exchange with the environment and causes a greater body temperature increase for a given heat storage, although a large A _D/m ratio can be advantageous. Physical employment standards for GCC roles might lessen the magnitude of fitness and anthropometric differences, yet even when studies control for these factors, women sweat less than men at high work rates. Therefore, the average female soldier in a GCC role is likely to be at a degree of disadvantage in many hot environments and particularly during intense physical activity in hot-arid conditions, although heat acclimation may mitigate some of this effect. Any thermoregulatory disadvantage may be exacerbated during the mid-luteal phase of the menstrual cycle, although the data are equivocal. Likewise, sex differences in behavioural thermoregulation and cognition in the heat are not well understood. Interestingly, there is often lower reported heat illness incidence in women, although the extent to which this is influenced by behavioural factors or historic differences in role allocation is unclear. Indeed, much of the extant literature lacks ecological validity and more work is required to fully understand sex differences to exercise heat stress in a GCC context.

Worsening of Primary Raynaud's Phenomenon During Episodes of Pyrexia and Rigors in SARS-CoV-2 Infection

Acute SARS-CoV-2 infection is associated with several cutaneous manifestations, including vasculitic digital ischemia. The reversal of digital ischemia in the primary Raynaud phenomenon (RP) arises from endothelial hypersensitivity to circulating adrenaline and noradrenaline and diminished vasodilatory innervation. SARS-CoV-2 can infect endothelial cells and be associated with raised adrenaline levels, reduced microvascular dilatory responses, and exaggerated clotting mechanisms. We report worsened RP in a patient with previously mild winter-time primary RP during the periods of fever and rigors from an acute SARS-CoV-2 infection contracted in a warm summer period. This reverted to the mild phenotype after recovery, and we discussed possible mechanisms for the brief exacerbation.

Effect of Heat Stress on Hippocampal Neurogenesis: Insights into the Cellular and Molecular Basis of Neuroinflammation-Induced Deficits

Heat stress is known to result in neuroinflammation, neuronal damage, and disabilities in learning and memory in animals and humans. It has previously been reported that cognitive impairment caused by neuroinflammation may at least in part be mediated by defective hippocampal neurogenesis, and defective neurogenesis has been linked to aberrantly activated microglial cells. Moreover, the release of cytokines within the brain has been shown to contribute to the disruption of cognitive functions in several conditions following neuroinflammation. In this review, we summarize evolving evidence for the current understanding of inflammation-induced deficits in hippocampal neurogenesis, and the resulting behavioral impairments after heat stress. Furthermore, we provide valuable insights into the molecular and cellular mechanisms underlying neuroinflammation-induced deficits in hippocampal neurogenesis, particularly relating to cognitive dysfunction following heat stress. Lastly, we aim to identify potential mechanisms through which neuroinflammation induces cognitive dysfunction, and elucidate how neuroinflammation contributes to defective hippocampal neurogenesis. This review may therefore help to better understand the relationship between hippocampal neurogenesis and heat stress.

The effect of exercise-induced fatigue and heat exposure on soccer-specific decision-making during high-intensity intermittent exercise

Global warming and the globalisation of sport has increased the prevalence of sports competitions being held in hot environments. However, there is currently limited research investigating the impact of the heat on soccer-specific decision-making skills during exercise reflective of the physical demands of match-play. Therefore, the effects of heat exposure on physical and soccer-specific decision-making performance, biological markers (i.e., metanephrines), appraisal (i.e., challenge vs. threat) and affective states, during prolonged high-intensity intermittent exercise were investigated. Nine well-trained male soccer players completed a 92-min cycling intermittent sprint protocol (CISP), whilst simultaneously responding to a series of soccer-specific decision-making trials at various time points, in two temperature conditions: hot (32°C, 50%rh) and temperate (18°C, 50%rh). Results showed that decision-making score (p = .030) was impaired in the hot compared to the temperate condition. There was a reduced workload in the second half during the hot condition (p = .016), which coincided with a heightened threat state (p = .007) and more unpleasant feelings (p = .008) experienced in the hot, compared to temperate, condition. Furthermore, plasma normetanephrine (NMET) was higher at half-time (p = .012) and post-CISP (p ≤ .001). Also, plasma metanephrine (MET) was higher post-CISP (p = .009) in the hot compared to temperate condition, reflecting a heightened stress response. Our findings highlight the need for practitioners to consider the detrimental effects heat exposure can have on both physical and decision-making performance when looking to facilitate performance in hot conditions.

Responses of soccer players performing repeated maximal efforts in simulated conditions of the FIFA World Cup Qatar 2022: A holistic approach

This study aimed to assess the capacity for repeated maximal effort (RME) of soccer players in the thermo-natural conditions (NC) and in simulated conditions for the 2022 FIFA World Cup in Qatar (QSC). Twenty-four semi-professional soccer players participated in the study. The exercise test consisted of ten 6-second maximal efforts on a cycloergometer. A 90-second passive rest interval was used. The test was performed in a Weiss Technik WK-26 climate test chamber in two different conditions: 1) thermo-neutral conditions (NC-20.5°C; 58.7% humidity); and 2) simulated conditions for the 2022 World Cup in Qatar (QSC-28.5 ± 1.92°C; 58.7 ± 8.64% humidity). Power-related, physiological, psychomotor, blood, and electrolyte variables were recorded. Results showed that (1) players achieved higher peak power (max 1607,46 ± 192,70 [W] - 3rd rep), needed less time to peak power (min 0,95 ± 0,27 [s] - 3rd rep), and had a higher fatigue slope (max 218,67 ± 59,64 [W/sek] - 7th rep) in QSC than in NC (in each repetition of study protocol); (2) between the 1st repetition and subsequent repetitions a number of significants in among physiological, blood-related, and electrolyte variables were noted, but their direction was similar in both simulated conditions (e.g. V'O2/kg 37,59 ± 3,96 vs 37,95 ± 3,17 [ml/min/kg] - 3rd rep, LAC 13,16 ± 2,61 vs 14,18 ± 3,13 [mg/dl] - 10th rep or K 4,54 ± 0,29 vs 4,79 ± 0,36 [mmol/l] - 2nd rep when compare QCS and NC respectively); (3) an 8°C of temperature difference between the climatic conditions did not significantly affect the soccer players' physical and physiological responses in RME. The study results can be used in the design of training programs aimed to increase players' physiological adaptations by simulating soccer-specific conditions of play in terms of anaerobic capacity, in particular, repetitive maximal efforts. These findings will be useful during the upcoming 2022 World Cup in Qatar and in locations where high ambient temperatures are customary.

Effects of Elevated Body Temperature on Selected Physiological Indices and Thermal Stress in Athletes and Non-Athletes

The purpose of this study was to determine the effects of active and passive overheating. A group of athletes (A) and non-athletic men (N) underwent an exercise stress test at elevated ambient temperature and sauna bathing until an increase in rectal temperature of 1.2°C was observed. It was shown that group A performed physical exercise for a longer period of time, which elicited significantly higher amounts of work performed in the stress test. Both forms of overheating caused a significant decrease in BM and a significant change in plasma volume, while greater dehydration was observed after active overheating. Changes observed in group A were higher than in group N. MCV levels were initially higher in group A. The levels in both groups decreased after sauna bathing, although in non-athletes the decrease was greater. Both forms of overheating increased Hb, HCT, and SBP, while only the non-athletic group showed a decrease in DBP after the exercise stress test. However, a decrease in DBP was observed in both groups after sauna bathing. The PSI increased after both tests, yet to a higher extent after the stress test than after sauna bathing. The PSI was negatively correlated with VO2max in both groups. The increase in cortisol concentration was higher after sauna bathing. There was a correlation between cortisol levels and the work performed during the stress test in group A. Endurance training resulted in more efficient thermoregulatory mechanisms in athletes.

Association between sequential extreme precipitation-heatwaves events and hospitalizations for schizophrenia: The damage amplification effects of sequential extremes

OBJECTIVES

In the context of frequent global extreme weather events, there are few studies on the effects of sequential extreme precipitation (EP) and heatwaves (HW) events on schizophrenia. We aimed to quantify the effects of the events on hospitalizations for schizophrenia and compare them with EP and HW alone to explore the amplification effect of successive extremes on health loss.

METHODS

A time-series Poisson regression model combined with a distributed lag non-linear model was applied to estimate the association between sequential EP and HW events (EP-HW) and schizophrenia hospitalizations. The effects of EP-HW with different intervals and intensities on the admission of schizophrenia were compared. In addition, we calculated the mean attributable fraction (AF) and attributable numbers (AN) per exposure of extreme events to reflect the amplification effect of sequential extreme events on health hazards compared with individual extreme events.

RESULTS

EP-HW increased the risk of hospitalization for schizophrenia, with significant effects lasting from lag0 (RR and 95% CI: 1.150 (1.041-1.271)) to lag11 (1.046 (1.000-1.094)). Significant associations were found in the subgroups of male, female, married people, and those aged≥ 40 years old. Shorter-interval (0-3days) or higher-intensity EP-HW (both precipitation ≥ P97.5 and mean temperature ≥ P97.5) had a longer lag effect compared to EP-HW with longer intervals or lower intensity. We found that the mean AF and AN caused by each exposure to EP-HW (AF: 0.074% (0.015%-0.123%); AN: 4.284 (0.862-7.118)) were higher than those induced by each exposure to HW occurring alone (AF:0.032% (0.004%-0.058%); AN:1.845 (0.220-3.329)).

CONCLUSIONS

Sequential extreme precipitation-heatwaves events significantly increase the risk of hospitalizations for schizophrenia, with greater impact and disease burden than independently occurring extremes. The impact of consecutive extremes is supposed to be considered in local sector early warning systems for comprehensive public health decision-making.

Influence of Heat Exposure on Motor Control Performance and Learning as Well as Physiological Responses to Visuomotor Accuracy Tracking Task

This study aimed to determine whether heat exposure attenuates motor control performance and learning, and blunts cardiovascular and thermoregulatory responses to visuomotor accuracy tracking (VAT) tasks. Twenty-nine healthy young adults (22 males) were divided into two groups performing VAT tasks (5 trials × 10 blocks) in thermoneutral (NEUT: 25 °C, 45% RH, n = 14) and hot (HOT: 35 °C, 45% RH, n = 15) environments (acquisition phase). One block of the VAT task was repeated at 1, 2, and 4 h after the acquisition phase (retention phase). Heat exposure elevated skin temperature to ~3 °C with a marginally increased core body temperature. VAT performance (error distance of curve tracking) was more attenuated overall in HOT than in NEUT in the acquisition phase without improvement in magnitude alteration. Heat exposure did not affect VAT performance in the retention phase. The mean arterial blood pressure and heart rate, but not for sweating and cutaneous vascular responses to VAT acquisition trials, were more attenuated in HOT than in NEUT without any retention phase alternations. We conclude that skin temperature elevation exacerbates motor control performance and blunts cardiovascular response during the motor skill acquisition period. However, these alternations are not sustainable thereafter.

Physiological mechanisms of the impact of heat during pregnancy and the clinical implications: review of the evidence from an expert group meeting

Many populations experience high seasonal temperatures. Pregnant women are considered vulnerable to extreme heat because ambient heat exposure has been linked to pregnancy complications including preterm birth and low birthweight. The physiological mechanisms that underpin these associations are poorly understood. We reviewed the existing research evidence to clarify the mechanisms that lead to adverse pregnancy outcomes in order to inform public health actions. A multi-disciplinary expert group met to review the existing evidence base and formulate a consensus regarding the physiological mechanisms that mediate the effect of high ambient temperature on pregnancy. A literature search was conducted in advance of the meeting to identify existing hypotheses and develop a series of questions and themes for discussion. Numerous hypotheses have been generated based on animal models and limited observational studies. There is growing evidence that pregnant women are able to appropriately thermoregulate; however, when exposed to extreme heat, there are a number of processes that may occur which could harm the mother or fetus including a reduction in placental blood flow, dehydration, and an inflammatory response that may trigger preterm birth. There is a lack of substantial evidence regarding the processes that cause heat exposure to harm pregnant women. Research is urgently needed to identify what causes the adverse outcomes in pregnancy related to high ambient temperatures so that the impact of climate change on pregnant women can be mitigated.

Effects of heat strain on cognitive function among a sample of miners

Heat stress is associated with workplace injuries, likely through a combination of fatigue, reduced cognitive function, and thermal discomfort. The purpose of this study was to evaluate four cognitive tasks for sensitivity to heat stress. Eight participants performed treadmill exercise followed by assessments of serial reaction time (RT), Stroop effect, verbal delayed memory, and continuous performance working memory in an environmental chamber. A control (21.1 °C) trial, and "Hot 1" and "Hot 2" (both 37.8 °C) trials were run sequentially on two separate days to evaluate the four cognitive tasks. Heat strain (comparing Hot 1 and Hot 2 with the control trial) resulted in impairments in the serial RT test response and Stroop accuracy. Delayed memory was impacted only in the Hot 2 trial compared with the control trial. Given the demonstrated impact of heat on cognitive processes relevant to workers' real-world functioning in the workplace, understanding how to assess and monitor vigilant attention in the workplace is essential.

Explore the Benefits of Natural Air: New Insights from Field and Chamber Tests on Cognitive Performance

Exposure to natural environments has a range of health benefits, including enhancing psychological restoration and cognitive development. While there are various explanations on the causes for the benefits of the natural exposure, such as less air pollution and noise, more physical activity, stronger social interactions, or even more diverse microbial community, etc., this study has zeroed in on the air quality of the natural environment. In addition to low-level pollution, what makes the natural air superior remains unclear. To this end, we conducted a series of psychological evaluation and cognitive tests on a couple of subjects in a national forest park in southwest China. Based on the results, we built an artificial chamber where selected air parameters can be independently manipulated and carried out similar tests in the chamber. We came to the following conclusion. (1) Exposure to real natural environment demonstrated tangible benefits for cognitive performances and mental states and the benefits can be obtained to some extent in the artificial environment by creating air qualities similar to the air in the natural environment. (2) Scents in natural environments may be one of the key beneficial factors. (3) Adopting proper cognitive test is critical for distinguishing the differences made by the natural exposure. Working memory showed marked responses to the natural exposure.

Alteration in cerebral blood flow, kynurenines with respect to mood profile in freshly recruited armed forces personnel

The present study is conducted to understand the association of mood profile with the kynurenine pathway (KP) metabolites, and cerebral hemodynamics in freshly recruited central armed forces personnel. Profile of Mood States questionnaire was utilized to assess mood profile, and Total Mood Disturbance (TMD) score was calculated. Transcranial Doppler was used to record blood flow velocity bilaterally of the middle cerebral artery. Chromatographic profile of the kynurenine metabolites was obtained in serum. Further, personnel were stratified according to sociodemographic variables (gender, age and diet) to observe the changes in their KP metabolic status. An activation of the kynurenic acid branch of the KP and the reduction in the mean blood flow velocity, and an increase in Gosling pulsatility index (PI) were observed in females having high TMD score. On gender comparative analysis, kynurenine metabolites of quinolinic acid branch and serotonin were significantly high in males. In males, with increase in age, a significant increase in the quinolinic acid branch of the KP was observed. Furthermore, a significant difference in level metabolites of the KP among the vegetarian and non-vegetarian groups was also observed. In conclusion we observed that increased TMD score was associated with cerebral hypoperfusion and higher vascular resistance along with activation of the KP. Our findings highlighted the importance of multi-facet brain function to showcase the close interaction of various dimensionalities and true picture of the assessee.

Heat exposure and workers' health: a systematic review

OBJECTIVES

Several studies on the health effects of heat exposure on workers have been reported; however, only few studies have summarized the overall and systematic health effects of heat exposure on workers. This study aims to review the scientific reports on the health status of workers exposed to high temperatures in the workplace.

METHODS

We reviewed literature from databases such as PubMed and Google Scholar, using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines to identify studies that address health effects of heat exposure among workers.

RESULTS

In total, 459 articles were identified, and finally, 47 articles were selected. Various health effects of heat exposure on workers have been reported, such as heat-related diseases, deaths, accidents or injuries, effects on the urinary system, reproductive system, and on the psychological system.

CONCLUSIONS

Our review suggests that many workers are vulnerable to heat exposure, and this has a health effect on workers.

The Influence of a Competitive Field Hockey Match on Cognitive Function

Despite the known positive effects of acute exercise on cognition, the effects of a competitive team sport match are unknown. In a randomized crossover design, 20 female and 17 male field hockey players (19.7 ± 1.2 years) completed a battery of cognitive tests (Visual Search, Stroop, Corsi Blocks, and Rapid Visual Information Processing) prior to, at half-time, and immediately following a competitive match (or control trial of seated rest); with effect sizes (ES) presented as raw ES from mixed effect models. Blood samples were collected prior to and following the match and control trial, and analyzed for adrenaline, noradrenaline, brain derived neurotrophic factor (BDNF), cathepsin B, and cortisol. The match improved response times for a simple perception task at full-time (ES = –14 ms; P < 0.01) and response times on the complex executive function task improved at half-time (ES = –44 ms; P < 0.01). Working memory declined at full-time on the match (ES = –0.6 blocks; P < 0.01). The change in working memory was negatively correlated with increases in cortisol (r = –0.314, P = 0.01; medium), as was the change in simple perception response time and the change in noradrenaline concentration (r = –0.284, P = 0.01; small to medium). This study is the first to highlight the effects a competitive hockey match can have on cognition. These findings have implications for performance optimization, as understanding the influence on specific cognitive domains across a match allows for the investigation into strategies to improve these aspects.

Psychological, Physical, and Heat Stress Indicators Prior to and after a 15-Minute Structural Firefighting Task

Firefighters work in strenuous conditions for prolonged periods wearing up to 20 kg of personal protective equipment. This often contributes to significant heat and cardiovascular strain. This study examined the relationships between psychological and physical measures taken prior to undertaking a 15 min firefighting task, and the occurrence of heat stress and high levels of fatigue following the task. Nine qualified firefighters completed a 15 min “live burn” scenario designed to mimic a fire started by a two-seater couch in a lounge room and completed simulated tasks throughout the duration. Logical reasoning, speed and accuracy, general motivation and fatigue, and physical and mental effort were recorded pre-scenario, and at 0- and 20-min post-scenario. General motivation and fatigue scores at 0- and 20-min post-scenario were highly correlated with each other (rs = 0.90; p = 0.001). The general motivation and fatigue scores, at 0- and 20-min post-scenario, were also strongly related to pre-task logic/reasoning test scores (Post 0 rs = −0.77, p = 0.016; Post 20 rs = −0.87, p = 0.002). Firefighters with lower logical reasoning and speed and accuracy scores were more susceptible to fatigue and impaired cognition when exposed to rises in core temperature and heat stress.

Simultaneous assessment of motor and cognitive tasks reveals reductions in working memory performance following exercise in the heat

This study tested the hypothesis that, following exercise in the heat, motor task performance will be impaired when assessed simultaneously with a cognitive task. In a randomized, crossover and counterbalanced design, twelve healthy adults (23 ± 2 years, 5 women) completed four 10-minute exercise circuits involving upper and lower body exercise in a moderate (18.1 ± 1.7°C, 38 ± 10% relative humidity) and a hot (40.3 ± 1.1°C, 26 ± 5% relative humidity) environment. Experimental testing was completed in a temperate thermal environment before exercise (~25°C) and in either the moderate or hot environment following exercise. The 3 Back test (a test of working memory) was used as the cognitive task and postural sway was used as the motor task. Cognitive and motor task performance assessments were conducted both individually (solo) and simultaneously (dual). At the end of exercise, core temperature (by 0.4 ± 0.3°C, P < 0.001), heart rate (by 12 ± 18 bpm, P = 0.025), and mean skin temperature (by 7.6 ± 0.8°C, P < 0.001) were higher in the Hot trial compared to Moderate. During solo testing, postural sway increased from pre- to post-exercise in the Hot (P ≤ 0.028), but not the Moderate (P ≥ 0.261) trial. During dual testing, postural sway did not differ between trials (P ≥ 0.065) or over time (P ≥ 0.094). During solo testing, 3 Back performance did not differ between trials (P = 0.810) or over time (P = 0.707), but during dual testing 3 Back performance following exercise was reduced in the Hot compared to the Moderate trial (P = 0.028). Simultaneous assessment of motor and cognitive tasks reveals that motor performance is reduced following exercise in the heat. .

Effect of non-optimum ambient temperature on cognitive function of elderly women in Germany

Non-optimum ambient temperature has been associated with a variety of health outcomes in the elderly population. However, few studies have examined its adverse effects on neurocognitive function. In this study, we explored the temperature-cognition association in elderly women. We investigated 777 elderly women from the German SALIA cohort during the 2007-2010 follow-up. Cognitive function was evaluated using the CERAD-Plus test battery. Modelled data on daily weather conditions were assigned to the residential addresses. The temperature-cognition association over lag 0-10 days was estimated using multivariable regression with distributed lag non-linear model. The daily mean temperature ranged between -6.7 and 26.0 °C during the study period for the 777 participants. We observed an inverse U-shaped association in elderly women, with the optimum temperature (15.3 °C) located at the 68th percentile of the temperature range. The average z-score of global cognitive function declined by -0.31 (95%CI: 0.73, 0.11) for extreme cold (the 2.5th percentile of temperature range) and -0.92 (95%CI: 1.50, -0.33) for extreme heat (the 97.5th percentile of temperature range), in comparison to the optimum temperature. Episodic memory was more sensitive to heat exposure, while semantic memory and executive function were the two cognitive domains sensitive to cold exposure. Individuals living in an urban area and those with a low educational level were particularly sensitive to extreme heat. In summary, non-optimum temperature was inversely associated with cognitive function in elderly women, with the effect size for heat exposure particularly substantial. The strength of association varied by cognitive domains and individual characteristics.

Carbohydrate ingestion attenuates cognitive dysfunction following long-duration exercise in the heat in humans

INTRODUCTION

To determine if electrolyte or carbohydrate supplementation vs. water would limit the magnitude of dehydration and decline in cognitive function in humans following long-duration hyperthermic-exercise.

METHODS

24 subjects performed 3 visits of 2 h walking (3mph/7% grade) in an environmental chamber (33 °C/10% relative humidity). In random order, subjects consumed water (W), electrolytes (Gatorade Zero; E), or electrolytes+carbohydrates (Gatorade; E+C). Throughout exercise (EX), subjects carried a 23 kg pack and drank ad-libitum. Pre-and post-EX, body mass (BM) and plasma osmolality (pOsm) were measured. Physiological Strain Index (PSI) and core temperature (T_C) were recorded every 15 min. Plasma glucose (GLU) was measured every 30 min. Cognitive processing (SCWT) was measured post-EX and compared to baseline (BL). A subset of 8 subjects performed a normothermic (N) protocol (21 °C/ambient humidity) to ascertain how the exercise stimulus influenced hydration status and cognition without heat.

RESULTS

There were no significant differences between fluid conditions (W, E, E+C) for BM loss (Δ2.5 ± 0.2, 2.5 ± 0.2, 2.3 ± 0.2 kg), fluid consumption (1.9 ± 0.2, 1.9 ± 0.2, 1.8 ± 0.2L), pOsm (Δ1.5 ± 2.7, 2.2 ± 2.4, 2.0 ± 1.5 mmol/L), peak-PSI (7.5 ± 0.4, 7.0 ± 0.6, 7.9 ± 0.5), and peak-T_C (38.7 ± 0.1, 38.6 ± 0.2, 38.8 ± 0.2 °C). GLU decreased significantly in W and E, whereas it increased above BL in E+C at 60, 90, and 120 min (P < 0.05). Compared to BL values (43.6 ± 26 ms), SCWT performance significantly decreased in all conditions (463 ± 93, 422 ± 83, 140 ± 52 ms, P < 0.05). Importantly, compared to W and E, the impairment in SCWT was significantly attenuated in E+C (P < 0.05). As expected, when compared to the heat-stress protocol (W, E, E+C), N resulted in lower BM loss, fluid consumption, and peak-PSI (1.1 ± 0.1 kg, 1.2 ± 0.7L, 4.8, respectively), and improved SCWT performance.

CONCLUSIONS

These data are the first to suggest that, independent of supplementation variety, cognitive processing significantly decreases immediately following long-duration exercise in the heat in healthy humans. Compared to water and fluids supplemented with only electrolytes, fluids supplemented with carbohydrates significantly blunts this decrease in cognitive function.

Proposed framework for forecasting heat-effects on motor-cognitive performance in the Summer Olympics

Heat strain impairs performance across a broad spectrum of sport disciplines. The impeding effects of hyperthermia and dehydration are often ascribed to compromised cardiovascular and muscular functioning, but expert performance also depends on appropriately tuned sensory, motor and cognitive processes. Considering that hyperthermia has implications for central nervous system (CNS) function and fatigue, it is highly relevant to analyze how heat stress forecasted for the upcoming Olympics may influence athletes. This paper proposes and demonstrates the use of a framework combining expected weather conditions with a heat strain and motor-cognitive model to analyze the impact of heat and associated factors on discipline- and scenario-specific performances during the Tokyo 2021 games. We pinpoint that hyperthermia-induced central fatigue may affect prolonged performances and analyze how hyperthermia may impair complex motor-cognitive performance, especially when accompanied by either moderate dehydration or exposure to severe solar radiation. Interestingly, several short explosive performances may benefit from faster cross-bridge contraction velocities at higher muscle temperatures in sport disciplines with little or no negative heat-effect on CNS fatigue or motor-cognitive performance. In the analyses of scenarios and Olympic sport disciplines, we consider thermal impacts on “motor-cognitive factors” such as decision-making, maximal and fine motor-activation as well as the influence on central fatigue and pacing. From this platform, we also provide perspectives on how athletes and coaches can identify risks for their event and potentially mitigate negative motor-cognitive effects for and optimize performance in the environmental settings projected.

Is there an association between hot weather and poor mental health outcomes? A systematic review and meta-analysis

BACKGROUND

Mental health is an important public health issue globally. A potential link between heat exposure and mental health outcomes has been recognised in the scientific literature; however, the associations between heat exposure (both high ambient temperatures and heatwaves) and mental health-related mortality and morbidity vary between studies and locations.

OBJECTIVE

To fill gaps in knowledge, this systematic review aims to summarize the epidemiological evidence and investigate the quantitative effects of high ambient temperatures and heatwaves on mental health-related mortality and morbidity outcomes, while exploring sources of heterogeneity.

METHODS

A systematic search of peer-reviewed epidemiological studies on heat exposure and mental health outcomes published between January 1990 and November 2020 was conducted using five databases (PubMed, Embase, Scopus, Web of Science and PsycINFO). We included studies that examined the association between high ambient temperatures and/or heatwaves and mental health-related mortality and morbidity (e.g. hospital admissions and emergency department visits) in the general population. A range of mental health conditions were defined using ICD-10 classifications. We performed random effects meta-analysis to summarize the relative risks (RRs) in mental health outcomes per 1 °C increase in temperature, and under different heatwaves definitions. We further evaluated whether variables such as age, sex, socioeconomic status, and climate zone may explain the observed heterogeneity.

RESULTS

The keyword search yielded 4560 citations from which we identified 53 high temperatures/heatwaves studies that comprised over 1.7 million mental health-related mortality and 1.9 million morbidity cases in total. Our findings suggest associations between heat exposures and a range of mental health-related outcomes. Regarding high temperatures, our meta-analysis of study findings showed that for each 1 °C increase in temperature, the mental health-related mortality and morbidity increased with a RR of 1.022 (95%CI: 1.015-1.029) and 1.009 (95%CI: 1.007-1.015), respectively. The greatest mortality risk was attributed to substance-related mental disorders (RR, 1.046; 95%CI: 0.991-1.101), followed by organic mental disorders (RR, 1.033; 95%CI: 1.020-1.046). A 1 °C temperature rise was also associated with a significant increase in morbidity such as mood disorders, organic mental disorders, schizophrenia, neurotic and anxiety disorders. Findings suggest evidence of vulnerability for populations living in tropical and subtropical climate zones, and for people aged more than 65 years. There were significant moderate and high heterogeneities between effect estimates in overall mortality and morbidity categories, respectively. Lower heterogeneity was noted in some subgroups. The magnitude of the effect estimates for heatwaves varied depending on definitions used. The highest effect estimates for mental health-related morbidity was observed when heatwaves were defined as "mean temperature ≥90th percentile for ≥3 days" (RR, 1.753; 95%CI: 0.567-5.421), and a significant effect was also observed when the definition was "mean temperature ≥95th percentile for ≥3 days", with a RR of 1.064 (95%CI: 1.006-1.123).

CONCLUSIONS

Our findings support the hypothesis of a positive association between elevated ambient temperatures and/or heatwaves and adverse mental health outcomes. This problem will likely increase with a warming climate, especially in the context of climate change. Further high-quality studies are needed to identify modifying factors of heat impacts.