Heat-related illness and dementia: a study integrating epidemiological and experimental evidence.

BACKGROUND: Heat-related illness (HRI) is commonly considered an acute condition, and its potential long-term consequences are not well understood. We conducted a population-based cohort study and an animal experiment to evaluate whether HRI is associated with dementia later in life. METHODS: The Taiwan National Health Insurance Research Database was used in the epidemiological study. We identified newly diagnosed HRI patients between 2001 and 2015, but excluded those with any pre-existing dementia, as the study cohort. Through matching by age, sex, and the index date with the study cohort, we selected individuals without HRI and without any pre-existing dementia as a comparison cohort at a 1:4 ratio. We followed each cohort member until the end of 2018 and compared the risk between the two cohorts using Cox proportional hazards regression models. In the animal experiment, we used a rat model to assess cognitive functions and the histopathological changes in the hippocampus after a heat stroke event. RESULTS: In the epidemiological study, the study cohort consisted of 70,721 HRI patients and the comparison cohort consisted of 282,884 individuals without HRI. After adjusting for potential confounders, the HRI patients had a higher risk of dementia (adjusted hazard ratio [AHR] = 1.24; 95% confidence interval [CI]: 1.19-1.29). Patients with heat stroke had a higher risk of dementia compared with individuals without HRI (AHR = 1.26; 95% CI: 1.18-1.34). In the animal experiment, we found cognitive dysfunction evidenced by animal behavioral tests and observed remarkable neuronal damage, degeneration, apoptosis, and amyloid plaque deposition in the hippocampus after a heat stroke event. CONCLUSIONS: Our epidemiological study indicated that HRI elevated the risk of dementia. This finding was substantiated by the histopathological features observed in the hippocampus, along with the cognitive impairments detected, in the experimental heat stroke rat model.

Management of Heat-Related Illness and Injury in the ICU: A Concise Definitive Review.

OBJECTIVES: The increasing frequency of extreme heat events has led to a growing number of heat-related injuries and illnesses in ICUs. The objective of this review was to summarize and critically appraise evidence for the management of heat-related illnesses and injuries for critical care multiprofessionals. DATA SOURCES: Ovid Medline, Embase, Cochrane Clinical Trials Register, Cumulative Index to Nursing and Allied Health Literature, and ClinicalTrials.gov databases were searched from inception through August 2023 for studies reporting on heat-related injury and illness in the setting of the ICU. STUDY SELECTION: English-language systematic reviews, narrative reviews, meta-analyses, randomized clinical trials, and observational studies were prioritized for review. Bibliographies from retrieved articles were scanned for articles that may have been missed. DATA EXTRACTION: Data regarding study methodology, patient population, management strategy, and clinical outcomes were qualitatively assessed. DATA SYNTHESIS: Several risk factors and prognostic indicators for patients diagnosed with heat-related illness and injury have been identified and reported in the literature. Effective management of these patients has included various cooling methods and fluid replenishment. Drug therapy is not effective. Multiple organ dysfunction, neurologic injury, and disseminated intravascular coagulation are common complications of heat stroke and must be managed accordingly. Burn injury from contact with hot surfaces or pavement can occur, requiring careful evaluation and possible excision and grafting in severe cases. CONCLUSIONS: The prevalence of heat-related illness and injury is increasing, and rapid initiation of appropriate therapies is necessary to optimize outcomes. Additional research is needed to identify effective methods and strategies to achieve rapid cooling, the role of immunomodulators and anticoagulant medications, the use of biomarkers to identify organ failure, and the role of artificial intelligence and precision medicine.

Exertional Heat Illness-From Identifying Heat Rash to Treating Heat Stroke.

Heat-related illness commonly affects adolescent patients, especially as summer approaches and global temperature extremes worsen. Basic counseling on sunburn prevention can decrease the risk for future malignancies, and rapidly preventing, identifying, and treating heat stroke can prevent severe morbidity and mortality. This article will review the epidemiology of exertional heat-related illness and the variations in presentations and pathology, from heat rash and sunburn to heat exhaustion and heat stroke. By the end of this review clinicians should be able to identify and treat different heat-related illnesses in adolescents and potentially save a life. [Pediatr Ann. 2024;53(1):e17-e21.].

Exertional Rhabdomyolysis Among Active Component Members of the U.S. Armed Forces, 2018-2022.

Exertional rhabdomyolysis is a pathologic muscle breakdown associated with strenuous physical activity. A largely preventable condition, it persists as an occupational hazard of military training and operations, especially in high heat environments among individuals exerting themselves to endurance limits. During the 5-year surveillance period, unadjusted incidence rates of exertional rhabdomyolysis among U.S. service members declined by approximately 15%, from 43.1 cases per 100,000 person-years (p-yrs) in 2018 to 36.5 cases per 100,000 p-yrs in 2022. Consistent with prior reports, subgroup- specific rates in 2022 were highest among men, those younger than 20 years, non-Hispanic Black service members, Marine Corps or Army members, and those in combat-specific and "other" occupations. Recruit trainees had the highest rates of exertional rhabdomyolysis in 2021 and 2022, with incidence rates 10 times higher than all other service members. Prompt recognition of the symptoms of exertional rhabdomyolysis (muscular pain or swelling, limited range of motion, or the excretion of darkened urine after strenuous physical activity, especially in hot, humid weather) by health care providers is crucial to avoid the most severe consequences of this potentially life-threatening condition.

Exertional Hyponatremia Among Active Component Members of the U.S. Armed Forces, 2007-2022.

Exertional hyponatremia occurs either during or following periods of heavy exertion, when losses of water and electrolytes due to the body's normal cooling mechanisms are replaced only with water. Hyponatremia can lead to death or serious morbidity if left untreated. Between 2007 and 2022, there were 1,690 diagnoses of exertional hyponatremia among active component service members, for an overall incidence rate of 7.9 cases per 100,000 person-years (p-yrs). Those younger than 20 years or older than 40, non-Hispanic White service members, Marine Corps members, and recruit trainees had higher overall rates of exertional hyponatremia diagnoses. Between 2007 and 2022, annual rates of incident exertional hyponatremia diagnoses peaked (12.7 per 100,000 p-yrs) in 2010 and then decreased to a low of 5.3 cases per 100,000 p-yrs in 2013. During the last 9 years of the surveillance period, rates fell between a range of 6.1 and 8.6 cases per 100,000 p-yrs. Service members and their supervisors must know the dangers of excessive water consumption and prescribed limits for water intake during prolonged physical activity, such as field training exercises, personal fitness training, as well as recreational activities, particularly in hot, humid weather.

[Heat illness]. / Hitteziekte.

Thermoregulation keeps the normal body temperature of humans at approximately 37 °C. However, as a result of heat load - both endogenous and exogenous heat - it can occur that the body is unable to dissipate excess heat, leading to an increase in the core body temperature. This can result in various heat illnesses, ranging from mild, non-life-threatening conditions, such as heat rash, heat edema, heat cramps, heat syncope and exercise associated collapse to life-threatening conditions, namely exertional heatstroke and classic heatstroke. Exertional heatstroke is the result of strenuous exercise in a (relatively) hot environment, whereas classic heatstroke is caused by environmental heat. Both forms result in a core temperature of > 40 °C in combination with a lowered or altered consciousness. Early recognition and treatment are critical in reducing morbidity and mortality. Cornerstone of treatment is cooling.

Acute in-competition medical care at the Tokyo 2020 Olympics: a retrospective analysis.

OBJECTIVE: To analyse injuries and illnesses during the 2020 Tokyo Olympic Summer Games. METHODS: This retrospective descriptive study included 11 420 athletes from 206 National Olympic Committees and 312 883 non-athletes. Incidences of injuries and illnesses during the competition period from 21 July to 8 August 2021 were analysed. RESULTS: A total of 567 athletes (416 injuries, 51 non-heat-related illnesses and 100 heat-related illnesses) and 541 non-athletes (255 injuries, 161 non-heat-related illnesses and 125 heat-related illnesses) were treated at the competition venue clinic. Patient presentation and hospital transportation rates per 1000 athletes were 50 and 5.8, respectively. Marathons and race walking had the highest incidence of injury and illness overall (17.9%; n=66). The highest incidence of injury (per participant) was noted in boxing (13.8%; n=40), sport climbing (12.5%; n=5) and skateboarding (11.3%; n=9), excluding golf, with the highest incidence of minor injuries. Fewer infectious illnesses than previous Summer Olympics were reported among the participants. Of the 100 heat-related illnesses in athletes, 50 occurred in the marathon and race walking events. Only six individuals were transported to a hospital due to heat-related illness, and none required hospital admission. CONCLUSION: Injuries and heat-related illnesses were lower than expected at the 2020 Tokyo Olympic Summer Games. No catastrophic events occurred. Appropriate preparation including illness prevention protocols, and treatment and transport decisions at each venue by participating medical personnel may have contributed to these positive results.

Development of a Prototype Observatory of Heat-Related Occupational Illnesses and Injuries through the Collection of Information from the Italian Press, as Part of the WORKLIMATE Project.

Exposure to heat is a recognized occupational risk factor. Deaths and accidents at work caused by high temperatures are underestimated. With the aim of detecting and monitoring heat-related illnesses and injuries, a prototype database of occupational events attributable to critical thermal conditions reported in Italian newspapers was created. Information was analyzed from national and local online newspapers using a web application. The analysis was conducted from May to September during the three-year period 2020-2022. Articles concerning 35 occupational heat-related illnesses and injuries were selected; 57.1% of the events were reported in 2022, and 31.4% of total accidents occurred in the month of July 2022, when the Universal Thermal Climate Index daily mean values corresponded to "moderate heat stress" (51.0%) and "strong heat stress" (49.0%). Fatal heat-related illnesses were the most frequent conditions described. In most cases, workers had been involved in outdoor activities in the construction sector. A comprehensive report was created by compiling all relevant newspaper articles to enhance awareness of this issue among relevant stakeholders and promote heat-risk prevention strategies in the current context where heatwaves are becoming increasingly frequent, intense and long-lasting.

Climate change and nephrology.

Climate change should be of special concern for the nephrologist, as the kidney has a critical role in protecting the host from dehydration, but it is also a favorite target of heat stress and dehydration. Here we discuss how rising temperatures and extreme heat events may affect the kidney. The most severe presentation of heat stress is heat stroke, which can result in severe electrolyte disturbance and both acute and chronic kidney disease (CKD). However, lesser levels of heat stress also have multiple effects, including exacerbating kidney disease and precipitating cardiovascular events in subjects with established kidney disease. Heat stress can also increase the risk for kidney stones, cause multiple electrolyte abnormalities and induce both acute and chronic kidney disease. Recently there have been multiple epidemics of CKD of uncertain etiology in various regions of the world, including Mesoamerica, Sri Lanka, India and Thailand. There is increasing evidence that climate change and heat stress may play a contributory role in these conditions, although other causes, including toxins, could also be involved. As climate change worsens, the nephrologist should prepare for an increase in diseases associated with heat stress and dehydration.

The serum irisin response to prolonged physical activity in temperate and hot environments in older men with hypertension or type 2 diabetes.

Current labor demographics are changing, with the number of older adults increasingly engaged in physically demanding occupations expected to continually rise, which are often performed in the heat. Given an age-related decline in whole-body heat loss, older adults are at an elevated risk of developing heat injuries that may be exacerbated by hypertension (HTN) and type 2 diabetes (T2D). Elevated irisin production may play a role in mitigating the excess oxidative stress and acute inflammation associated with physically demanding work in the heat. However, the effects of HTN and T2D on this response remain unclear. Therefore, we evaluated serum irisin before and after 3-h of moderate intensity exercise (metabolic rate: 200 W/m2) and at the end of 60-min of post-exercise recovery in a temperate (wet-bulb globe temperature (WBGT) 16 °C) and high-heat stress (WBGT 32 °C) environment in 12 healthy older men (mean ± SD; 59 ± 4 years), 10 men with HTN (60 ± 4 years), and 9 men with T2D (60 ± 5 years). Core temperature (Tco) was measured continuously. In the heat, total exercise duration was significantly lower in older men with HTN and T2D (both, p ≤ 0.049). Despite Tco not being different between groups, Tco was higher in the hot compared to the temperate condition for all groups (p < 0.001). Similarly, serum irisin concentrations did not differ between groups under either condition but were elevated relative to the temperate condition during post-exercise and end-recovery in the heat (+93.9 pg/mL SEM 26 and + 70.5 pg/mL SEM 38 respectively; both p ≤ 0.014). Thus, our findings indicate similar irisin responses in HTN and T2D compared to healthy, age-matched controls, despite reduced exercise tolerance during prolonged exercise in the heat. Therefore, older workers with HTN and T2D may exhibit greater cellular stress during prolonged exercise in the heat, underlying greater vulnerability to heat-induced cellular injury.

[Research progress of heatstroke warning system].

With global warming and frequent heat waves, the incidence of heat-related-illness has gradually increased, and heatstroke is the most serious clinical syndrome, with high mortality and incidence of sequelae. Effective heatstroke warning aims to reduce the incidence and the harm of heatstroke by monitoring certain parameters and forecasting the possibility of suffering heat illness, however, there is no unified summary of the heatstroke early warning system at present. The occurrence of heatstroke involves two key aspects: climate environment and individual susceptibility, and individual susceptibility is manifested as the difference in heat tolerance ability. This article represents the current early warning system of heatstroke from climate environment, such as effective temperature, heat index, wet bulb globe temperature (WBGT) index, somatosensory temperature, etc., and individual susceptibility, for the reference of research and development in this field.

Update: Exertional rhabdomyolysis, active component, U.S. Armed Forces, 2017-2021.

Among active component service members in 2021, there were 513 incident cases of exertional rhabdomyolysis, for an unadjusted incidence rate of 38.6 cases per 100,000 person-years (p-yrs). Subgroup-specific rates in 2021 were highest among males, those less than 20 years old, non-Hispanic Black service members, Marine Corps or Army members, recruits, and those in "other" and combat-specific occupations. During 2017­2021, crude rates of exertional rhabdomyolysis reached a peak of 43.1 per 100,000 p-yrs in 2018 after which the rate decreased to 38.4 and 38.6 per 100,000 p-yrs in 2020 and 2021, respectively. Compared to those in other race/ethnicity groups, non-Hispanic Black service members had the highest overall rate of exertional rhabdomyolysis in every year of the period. Overall and annual rates were highest among Marine Corps members, intermediate among those in the Army, and lowest among those in the Air Force and Navy. Most cases of exertional rhabdomyolysis were diagnosed at installations that support basic combat/recruit training or major ground combat units of the Army or the Marine Corps. Medical care providers should consider exertional rhabdomyolysis in the differential diagnosis when service members (particularly recruits) present with muscular pain or swelling, limited range of motion, or the excretion of darkened urine after strenuous physical activity, especially in hot, humid weather.

The Role of Seminal Oxidative Stress Scavenging System in the Pathogenesis of Sperm DNA Damage in Men Exposed and Not Exposed to Genital Heat Stress.

Responding to the need for the verification of some experimental animal studies showing the involvement of oxidative stress in germ cell damage in the heat-induced testis, we investigated the possibility of a direct relationship between seminal oxidative stress markers (total antioxidant capacity, catalase activity, superoxide dismutase activity, and malondialdehyde concentration) and ejaculated sperm chromatin/DNA integrity (DNA fragmentation and chromatin condensation abnormalities) in distinct groups of men exposed and not exposed to prolonged scrotal hyperthermia. A statistical increase in the proportion of sperm with DNA fragmentation was observed in all the studied subgroups compared to the fertile men. In turn, the groups subjected to heat stress as professional drivers or infertile men with varicocele presented greater disturbances in the oxidative stress scavenging system than men not exposed to genital heat stress. Based on the comparative analysis of the studied parameters, we can conclude that alterations in the seminal oxidative stress scavenging system are directly engaged in the pathogenesis of ejaculated sperm DNA damage regardless of the intensity of the impact of thermal insult. To the best of our knowledge, this study, for the first time, revealed the co-existence of oxidative stress and sperm DNA damage in the semen of professional drivers.

Markers of kidney tubular and interstitial injury and function among sugarcane workers with cross-harvest serum creatinine elevation.

OBJECTIVES: Serum creatinine (SCr) is a routine marker of kidney injury but also increases with dehydration and muscular work. This study was to elucidate whether increase in SCr is associated with more specific markers of kidney tubular and interstitial injury and function, during prolonged heat stress among workers at high risk of chronic kidney disease of non-traditional origin (CKDnt). METHODS: Urine monocyte chemoattractant protein-1 (MCP-1), kidney injury molecule-1 (KIM-1), calbindin, glutathione S-transferase-π (GST-π), clusterin, interleukin 18 and albumin, fractional excretion of potassium (FEK), blood haemoglobin, serum potassium, ferritin and erythropoietin were measured before and after harvest in a sample of 30 workers with a ≥0.3 mg/dL SCr increase across harvest (cases), and 53 workers with stable SCr (controls). RESULTS: Urine MCP-1 (p for differential cross-harvest trend <0.001), KIM-1 (p=0.002), calbindin (p=0.02), GST-π (p=0.04), albumin (p=0.001) and FEK (p<0.001) increased in cases, whereas blood haemoglobin (p<0.001) and serum erythropoietin (p<0.001) decreased. CONCLUSION: Several markers of tubular and interstitial injury and function changed as SCr increased across a harvest season, supporting the use of SCr as an indicator of kidney injury in physically active workers regularly exposed to heat stress. Repeated injury similar to that described here, and continued work under strenuous and hot conditions with similarly elevated injury markers is likely to worsen and possibly initiate CKDnt.

Heat illness experience at BMH Shaibah, Basra, during Operation TELIC: May-July 2003.

This is an observational study of heat-related illness in UK Service Personnel deployed into summer conditions in Northern Kuwait and Southern Iraq. Among 622 hospitalisations reported during a 9-week period at the historical British Military Hospital, Shaibah, 303 consecutive admissions are reviewed in detail. Several clinical syndromes attributable to thermal stress were observed. These ranged from self-limiting debility to life-threatening failures of homeostasis, with 5.0% developing a critical care requirement. Hyponatraemia was a commonly occurring electrolyte disturbance by which, relative to the local reference range, a majority of heat-attributed admissions were affected. Reductions in measured serum sodium could be profound (<125 mmol/L in 20.1% of all heat-related casualties). Hypokalaemia was observed in half of cases, though only a minority were affected by severely low potassium (<2.5 mmol/L in 4.0%). Despite preventive measures prescribed on hospital discharge, illness and significant biochemical derangements could recur upon return to duties in the heat. We reiterate the need for primary prevention of heat illness wherever possible and importance of early, effective interventions to treat and protect Service Personnel from secondary injury. We also highlight the requirement for comprehensive assessment to inform prognostication and occupational decision-making in relation to extreme climatic heat, including aeromedical evacuation. We draw additional attention to the contribution of psychological factors in select cases and identify research questions to improve understanding of environment-induced incapacitation in general.

Update: Exertional rhabdomyolysis, active component, U.S. Armed Forces, 2016-2020.

Among active component service members in 2020, there were 501 incident cases of exertional rhabdomyolysis, for an unadjusted incidence rate of 37.8 cases per 100,000 person-years (p-yrs). Subgroup-specific rates in 2020 were highest among males, those less than 20 years old, non-Hispanic Black service members, Marine Corps or Army members, and those in combatspecific occupations. During 2016-2020, crude rates of exertional rhabdomyolysis reached a peak of 42.9 per 100,000 p-yrs in 2018 after which the rate decreased to a low of 37.8 per 100,000 p-yrs in 2020. Most cases of exertional rhabdomyolysis were diagnosed at installations that support basic combat/ recruit training or major ground combat units of the Army or the Marine Corps. Medical care providers should consider exertional rhabdomyolysis in the differential diagnosis when service members (particularly recruits) present with muscular pain or swelling, limited range of motion, or the excretion of darkened urine after strenuous physical activity, especially in hot, humid weather.

Heat stress during late pregnancy of sows influences offspring longissimus dorsi muscle growth at weaning.

In pregnant sows, heat stress (HS) not only affects sows, but also has long-term effects on offspring growth. However, it is still unclear how HS in pregnant sows influences offspring skeletal muscle development. In this study, 12 sows with similar body conditions were assigned into either a control (CON) or an HS group. The CON sows were housed at 18-22 ℃, and the sows in the HS group were housed at 28-32 ℃ from day 85 to 114 of pregnancy. The results showed that maternal HS decreased the total protein content (P < 0.05) and prolactin level (P < 0.05), yet increased the triglyceride content (P < 0.05) of milk. The piglets of both groups had similar body weight and longissimus dorsi (LD) muscle weight at birth, but body weight (P < 0.05) and LD weight (P < 0.05) was significantly lower at weaning age in the HS group. Increased expression of myostatin (MSTN) (P < 0.05) and its receptor (P < 0.05) in the LD of HS piglets was observed at weaning. The following decreased in HS piglets: expression of serine/threonine-specific protein kinase (P < 0.05), the mammalian target of rapamycin (P < 0.05), and glycogen synthase kinase-3ß (P < 0.05) signal pathway-involved proteins. The results indicated that maternal HS during late pregnancy influenced offspring LD muscle growth via the activated MSTN pathway. This effect may be related to sow's milk composition.

Burn Injury Does Not Exacerbate Heat Strain during Exercise while Wearing Body Armor.

INTRODUCTION: Although evaporative heat loss capacity is reduced in burn-injured individuals with extensive skin grafts, the thermoregulatory strain due to a prior burn injury during exercise-heat stress may be negligible if the burn is located underneath protective clothing with low vapor permeability. PURPOSE: This study aimed to test the hypothesis that heat strain during exercise in a hot-dry environment while wearing protective clothing would be similar with and without a simulated torso burn injury. METHODS: Ten healthy individuals (8 men/2 women) underwent three trials wearing: uniform (combat uniform, tactical vest, and replica torso armor plates), uniform with a 20% total body surface area simulated torso burn (uniform + burn), or shorts (and sports bra) only (control). Exercise consisted of treadmill walking (5.3 km·h; 3.7% ± 0.9% grade) for 60 min at a target heat production of 6.0 W·kg in 40.0°C ± 0.1°C and 20.0% ± 0.6% relative humidity conditions. Measurements included rectal temperature, heart rate, ratings of perceived exertion (RPE), and thermal sensation. RESULTS: No differences in rectal temperature (P ≥ 0.85), heart rate (P ≥ 0.99), thermal sensation (P ≥ 0.73), or RPE (P ≥ 0.13) occurred between uniform + burn and uniform trials. In the control trial, however, core temperature, heart rate, thermal sensation, and RPE were lower compared with the uniform and uniform + burn trials (P ≤ 0.04 for all). CONCLUSIONS: A 20% total body surface area simulated torso burn injury does not further exacerbate heat strain when wearing a combat uniform. These findings suggest that the physiological strain associated with torso burn injuries is not different from noninjured individuals when wearing protective clothing during an acute exercise-heat stress.