Keeping older individuals cool in hot and moderately humid conditions: wetted clothing with and without an electric fan

Personal Strategies to Reduce the Cardiovascular Impacts of Environmental Exposures

Ubiquitous environmental exposures increase cardiovascular disease risk via diverse mechanisms. This review examines personal strategies to minimize this risk. With regard to fine particulate air pollution exposure, evidence exists to recommend the use of portable air cleaners and avoidance of outdoor activity during periods of poor air quality. Other evidence may support physical activity, dietary modification, omega-3 fatty acid supplementation, and indoor and in-vehicle air conditioning as viable strategies to minimize adverse health effects. There is currently insufficient data to recommend specific personal approaches to reduce the adverse cardiovascular effects of noise pollution. Public health advisories for periods of extreme heat or cold should be observed, with limited evidence supporting a warm ambient home temperature and physical activity as strategies to limit the cardiovascular harms of temperature extremes. Perfluoroalkyl and polyfluoroalkyl substance exposure can be reduced by avoiding contact with perfluoroalkyl and polyfluoroalkyl substance-containing materials; blood or plasma donation and cholestyramine may reduce total body stores of perfluoroalkyl and polyfluoroalkyl substances. However, the cardiovascular impact of these interventions has not been examined. Limited utilization of pesticides and safe handling during use should be encouraged. Finally, vasculotoxic metal exposure can be decreased by using portable air cleaners, home water filtration, and awareness of potential contaminants in ground spices. Chelation therapy reduces physiological stores of vasculotoxic metals and may be effective for the secondary prevention of cardiovascular disease.

A critical review of the effectiveness of electric fans as a personal cooling intervention in hot weather and heatwaves

Health agencies worldwide have historically cautioned that electric fans accelerate body-heat gain during hot weather and heatwaves (typically in air temperatures ≥35°C). However, guidance published since 2021 has suggested that fans can still cool the body in air temperatures up to 40°C by facilitating sweat evaporation, and therefore are an inexpensive yet sustainable alternative to air conditioning. In a critical analysis of the reports cited to support this claim, we found that although fan use improves sweat evaporation, these benefits are of insufficient magnitude to exert meaningful reductions in body core temperature in air temperatures exceeding 35°C. Health agencies should continue to advise against fan use in air temperatures higher than 35°C, especially for people with compromised sweating capacity (eg, adults aged 65 years or older). Improving access to ambient cooling strategies (eg, air conditioning or evaporative coolers) and minimising their economic and environmental costs through policy initiatives, efficient cooling technology, and combined use of low-cost personal interventions (eg, skin wetting or fan use) are crucial for climate adaptation.

Experimental research in environmentally induced hyperthermic older persons: A systematic quantitative literature review mapping the available evidence

The heat-related health burden is expected to persist and worsen in the coming years due to an aging global population and climate change. Defining the breadth and depth of our understanding of age-related changes in thermoregulation can identify underlying causes and strategies to protect vulnerable individuals from heat. We conducted the first systematic quantitative literature review to provide context to the historical experimental research of healthy older adults - compared to younger adults or unhealthy age matched cases - during exogenous heat strain, focusing on factors that influence thermoregulatory function (e.g. co-morbidities). We identified 4,455 articles, with 147 meeting eligibility criteria. Most studies were conducted in the US (39%), Canada (29%), or Japan (12%), with 71% of the 3,411 participants being male. About 71% of the studies compared younger and older adults, while 34% compared two groups of older adults with and without factors influencing thermoregulation. Key factors included age combined with another factor (23%), underlying biological mechanisms (18%), age independently (15%), influencing health conditions (15%), adaptation potential (12%), environmental conditions (9%), and therapeutic/pharmacological interventions (7%). Our results suggest that controlled experimental research should focus on the age-related changes in thermoregulation in the very old, females, those with overlooked chronic heat-sensitive health conditions (e.g. pulmonary, renal, mental disorders), the impact of multimorbidity, prolonged and cumulative effects of extreme heat, evidence-based policy of control measures (e.g. personal cooling strategies), pharmaceutical interactions, and interventions stimulating protective physiological adaptation. These controlled studies will inform the directions and use of limited resources in ecologically valid fieldwork studies.

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

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

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.

Key Exercise Concepts in the Rehabilitation from Severe Burns

This article presents information on the benefits of exercise in counteracting the detrimental effects of bed rest, and/or severe burns. Exercise is key for maintaining physical function, lean body mass, metabolic recovery, and psychosocial health after major burn injuries. The details of an exercise training program conducted in severely burned persons are presented, as well as information on the importance of proper regulation of body temperature during exercise or physical activity. The sections on exercise and thermoregulation are followed by a section on the role of exercise in scarring and contractures. Finally, gaps in the current knowledge of exercise, thermoregulation, and contractures are presented.

Efficacy of Cooling Centers for Mitigating Physiological Strain in Older Adults during Daylong Heat Exposure: A Laboratory-Based Heat Wave Simulation

BACKGROUND

Health agencies, including the U.S. Centers for Disease Control and Prevention and the World Health Organization, recommend that heat-vulnerable older adults without home air-conditioning should visit cooling centers or other air-conditioned locations (e.g., a shopping mall) during heat waves. However, experimental evidence supporting the effectiveness of brief air-conditioning is lacking.

OBJECTIVE

We evaluated whether brief exposure to an air-conditioned environment, as experienced in a cooling center, was effective for limiting physiological strain in older adults during a daylong laboratory-based heat wave simulation.

METHODS

Forty adults 64-79 years of age underwent a 9-h simulated heat wave (heat index: 37°C) with (cooling group, n=20) or without (control group, n=20) a cooling intervention consisting of 2-h rest in an air-conditioned room (∼23°C, hours 5-6). Core and skin temperatures, whole-body heat exchange and storage, cardiovascular function, and circulating markers of acute inflammation were assessed.

RESULTS

Core temperature was 0.8°C (95% CI: 0.6, 0.9) lower in the cooling group compared with the control group at the end of the cooling intervention (p<0.001; hour 6), and it remained 0.3°C (95% CI: 0.2, 0.4) lower an hour after returning to the heat (p<0.001; hour 7). Despite this, core temperatures in each group were statistically equivalent at hours 8 and 9, within ±0.3°C (p≤0.005). Cooling also acutely reduced demand on the heart and improved indices of cardiovascular autonomic function (p≤0.021); however, these outcomes were not different between groups at the end of exposure (p≥0.58).

DISCUSSION

Brief air-conditioning exposure during a simulated heat wave caused a robust but transient reduction in core temperature and cardiovascular strain. These findings provide important experimental support for national and international guidance that cooling centers are effective for limiting physiological strain during heat waves. However, they also show that the physiological impacts of brief cooling are temporary, a factor that has not been considered in guidance issued by health agencies. https://doi.org/10.1289/EHP11651.

Climate Change and Pregnancy: Risks, Mitigation, Adaptation, and Resilience

Importance

Climate change is affecting the earth, resulting in more extreme temperatures and weather, rising sea levels, more frequent natural disasters, and displacement of populations of plants and animals, including people and insects. These changes affect food and housing security, vector-borne illnesses, and access to clean air and water, all of which influence human health.

Evidence and Results

There are a number of adverse health outcomes linked to heat, air pollution from wildfires, stress from natural disasters, and other elements of climate change. Pregnant people are especially vulnerable to the health harms resulting from climate change, namely, preterm birth, small for gestational age, hypertensive disorders of pregnancy, and other adverse reproductive health and birth outcomes. Strategies to minimize these harms include mitigation and adaptation.

Conclusions and Relevance

Physicians are in a unique position to protect the health of pregnant persons and children by advocating for policy changes that address climate change and providing clinical recommendations for patients to protect themselves from the health impacts of climate hazards.

Effects of wetted inner clothing on thermal strain in young and older males while wearing ventilation garments

The present study examined the effect of wearing a water-soaked inner t-shirt with a ventilation garment on thermal and cardiovascular strain in eight young (26 ± 4 years) and eight older (67 ± 3 years) men undertaking moderate-intensity work (metabolic rate: 200-230 W m^-2) in a hot environment (37°C, 50% RH, 2.8 kPa). While intermittent walking in hot conditions for 60 min, as a control (CON), the subject wore a dry inner t-shirt (long-sleeved) without fanning of a ventilation jacket (single-layered cotton, 0.21 clo). On separate days, under a fanned ventilation jacket, the subject wore a dry inner t-shirt (DRY) or an inner t-shirt soaked with 350 mL of tap water (WET). In the young group, increases in rectal temperature from pre-exercise baseline in the WET trial (0.7°C ± 0.2°C) were lower than in the CON (1.3°C ± 0.3°C) and DRY (1.1°C ± 0.2°C) (both p < 0.05) trials during exercise in hot conditions. In the older group, the increases were also attenuated in WET (0.7°C ± 0.4°C) compared with CON (1.3°C ± 0.4°C) and DRY (1.1°C ± 0.4°C) (both p < 0.05) without differences between age groups. Heart rate and whole-body sweat loss were lowest in the WET, followed by DRY, and then CON conditions in both groups (all p < 0.05). These findings demonstrate that wearing a water-soaked inner t-shirt while using a ventilation garment is an effective and practical cooling strategy to mitigate thermal and cardiovascular strains in young and older individuals during moderate-intensity work in hot conditions.

Heat Illness Requiring Emergency Care for People Experiencing Homelessness: A Case Study Series

Extreme heat and hot weather has a negative impact on human health and society. Global warming has resulted in an increase in the frequency and duration of heatwaves. Heat-related illnesses are a significant negative consequence of high temperatures and can be life-threatening medical emergencies. The severity of the symptoms can depend on the pre-existing medical conditions and vary from mild headaches to severe cases that can lead to coma and death. The risk of heat-related illness may be higher for people experiencing homelessness due to a lack of access to cool places and water, and the complex interactions between mental illness, medications and substance use disorder. This paper presents two cases of people experiencing homelessness who were admitted to the emergency department of a hospital in Sydney, Australia during a heatwave in November 2020. Both cases were adult males with known risk factors for heat-related illness including hypertension and schizophrenia (Case One) and hepatitis C, cirrhosis, and alcohol use disorder (Case Two). These cases show that severe weather can not only be detrimental to homeless people's health but can also cause a significant economic toll, evident by the $70,184 AUD expenditure on the care for these two cases. This case report highlights the requirement to determine the risk of heat-related illness to people experiencing homelessness and need to protect this vulnerable population from weather-related illness and death.

Efficiency of three cooling methods for hyperthermic military personnel linked to water availability

PURPOSE

Three feasible cooling methods for treatment of hyperthermic individuals in the military, that differed considerably in water volume needed (none to ~80 L), were evaluated.

METHODS

Ten male soldiers were cooled following exercise-induced hyperthermia (rectal temperature (T_re) ∼39.5 °C) using ventilation by fanning (1.7 m s^-1), ventilation by fanning (1.7 m s^-1) while wearing a wet t-shirt (250 mL-27 °C water) and tarp assisted cooling with oscillations (80 L of 27.2 ± 0.5 °C water; TACO).

RESULTS

Cooling rates were higher using TACO (0.116 ± 0.032 °C min^-1) compared to ventilation (0.065 ± 0.011 °C min^-1, P<0.001) and ventilation in combination with a wet t-shirt (0.074 ± 0.020 °C min^-1, P=0.002). Time to cool (TTC) to T_re=38.2 °C for TACO was shorter (14 ± 4 min) compared to ventilation only (20 ± 5 min; P=0.018), but not to ventilation while wearing a wet t-shirt (18 ± 6 min; P=0.090).

CONCLUSIONS

TACO may be an acceptable, efficient and feasible cooling method in case of exertional heat stroke. However, in case of limited water availability, transportat should be prioritized, and cooling of any form should be implemented while waiting for and during transport.

Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis

The present comprehensive review (i) summarizes the current knowledge on the impacts of occupational heat stress on outdoor workers, (ii) provides a historical background on this issue, (iii) presents a meta-analysis of published data, (iv) explores inter-individual and intra-individual factors, (v) discusses the available heat mitigation strategies, (vi) estimates physical work capacity, labour productivity, and metabolic rate for the year 2030, and (vii) provides an overview of existing policy and legal frameworks on occupational heat exposure. Meta-analytic findings from 38 field studies that involved monitoring 2,409 outdoor workers across 41 jobs in 21 countries suggest that occupational heat stress increases the core (r = 0.44) and skin (r = 0.44) temperatures, as well as the heart rate (r = 0.38) and urine specific gravity (r = 0.13) of outdoor workers (all p < 0.05). Moreover, it diminishes the capacity of outdoor workers for manual labour (r = -0.82; p < 0.001) and is responsible for more than two thirds of the reduction in their metabolic rate. Importantly, our analysis shows that physical work capacity is projected to be highly affected by the ongoing anthropogenic global warming. Nevertheless, the metabolic rate and, therefore, labour productivity are projected to remain at levels higher than the workers' physical work capacity, indicating that people will continue to work more intensely than they should to meet their financial obligations for food and shelter. In this respect, complementary measures targeting self-pacing, hydration, work-rest regimes, ventilated garments, and mechanization can be adopted to protect outdoor workers.

Quantifying the impact of heat on human physical work capacity; part II: the observed interaction of air velocity with temperature, humidity, sweat rate, and clothing is not captured by most heat stress indices

Increasing air movement can alleviate or exacerbate occupational heat strain, but the impact is not well defined across a wide range of hot environments, with different clothing levels. Therefore, we combined a large empirical study with a physical model of human heat transfer to determine the climates where increased air movement (with electric fans) provides effective body cooling. The model allowed us to generate practical advice using a high-resolution matrix of temperature and humidity. The empirical study involved a total of 300 1-h work trials in a variety of environments (35, 40, 45, and 50 °C, with 20 up to 80% relative humidity) with and without simulated wind (3.5 vs 0.2 m∙s^-1), and wearing either minimal clothing or a full body work coverall. Our data provides compelling evidence that the impact of fans is strongly determined by air temperature and humidity. When air temperature is ≥ 35 °C, fans are ineffective and potentially harmful when relative humidity is below 50%. Our simulated data also show the climates where high wind/fans are beneficial or harmful, considering heat acclimation, age, and wind speed. Using unified weather indices, the impact of air movement is well captured by the universal thermal climate index, but not by wet-bulb globe temperature and aspirated wet-bulb temperature. Overall, the data from this study can inform new guidance for major public and occupational health agencies, potentially maintaining health and productivity in a warming climate.

Extreme Heat and Cardiovascular Health: What a Cardiovascular Health Professional Should Know

As global temperatures continue to rise, extreme heat events are becoming more frequent and intense. Extreme heat affects cardiovascular health as it is associated with a greater risk of adverse cardiovascular events, especially for adults with preexisting cardiovascular diseases. Nonetheless, the pathophysiology underlying the association between extreme heat and cardiovascular risk remains understudied. Furthermore, specific recommendations to mitigate the effects of extreme heat on cardiovascular health remain limited to guide clinical practice within the context of a warming climate. The overall objective of this review article is to raise awareness that extreme heat poses a risk for cardiovascular health. Specifically, the review discusses why cardiovascular healthcare professionals should care about extreme heat, how extreme heat affects cardiovascular health, and recommendations to minimise the cardiovascular consequences of extreme heat. Future research directions are also provided to further our understating of the cardiovascular health consequences of extreme heat. A better awareness and understanding of the cardiovascular consequences of extreme heat will help cardiovascular health professionals assess the risk and optimise the care of their patients exposed to an increasingly warm climate.

Reducing the health effects of hot weather and heat extremes: from personal cooling strategies to green cities

Heat extremes (ie, heatwaves) already have a serious impact on human health, with ageing, poverty, and chronic illnesses as aggravating factors. As the global community seeks to contend with even hotter weather in the future as a consequence of global climate change, there is a pressing need to better understand the most effective prevention and response measures that can be implemented, particularly in low-resource settings. In this Series paper, we describe how a future reliance on air conditioning is unsustainable and further marginalises the communities most vulnerable to the heat. We then show that a more holistic understanding of the thermal environment at the landscape and urban, building, and individual scales supports the identification of numerous sustainable opportunities to keep people cooler. We summarise the benefits (eg, effectiveness) and limitations of each identified cooling strategy, and recommend optimal interventions for settings such as aged care homes, slums, workplaces, mass gatherings, refugee camps, and playing sport. The integration of this information into well communicated heat action plans with robust surveillance and monitoring is essential for reducing the adverse health consequences of current and future extreme heat.

Electric fan use for cooling during hot weather: a biophysical modelling study

BACKGROUND

In hot weather, electric fans can potentially provide effective cooling for people, with lower greenhouse gas emissions and cost than air conditioning. However, international public health organisations regularly discourage fan use in temperatures higher than 35°C, despite little evidence. We aimed to determine humidity-dependent temperature thresholds at which electric fans would become detrimental in different age groups.

METHODS

We used biophysical modelling to determine the upper humidity-dependent temperature thresholds at which fan use would become detrimental (ie, worsen heat stress) for healthy young adults (aged 18-40 years), healthy older adults (aged ≥65 years), and older adults taking anticholinergic medication. We also obtained hourly environmental data for the period Jan 1, 2007, to Dec 31, 2019, for 108 populous cities to determine the number of days fan use would be effective for cooling, standardised to a 31-day hot weather month. We established simplified temperature thresholds for future fan use recommendations on the basis of temperatures below which fan use would never have been detrimental between Jan 1, 2007, and Dec 31, 2019, across all prevailing levels of ambient humidity.

FINDINGS

According to our model, fan use would have been beneficial on 30·0 (96·6%) of 31 hot weather days for healthy young adults and 29·4 (94·9%) of 31 hot weather days for both older adults and older adults taking anticholinergic medication between Jan 1, 2007, and Dec 31, 2019. Adherence to the current WHO recommendation of fan use below temperatures of 35°C only, fan use would have been recommended on 27·2 days (87·7%) of 31 hot weather days. According to our simplified thresholds for fan use (at temperatures <39·0°C for healthy young adults, <38·0°C for healthy older adults, and <37·0°C for older adults taking anticholinergic medication), fan use would have been recommended on 29·6 (95·5%) of 31 hot weather days in healthy young adults, 29·4 (94·8%) days in healthy older adults, and 28·8 (93·0%) days in older adults taking anticholinergic medication between Jan 1, 2007, and Dec 31, 2019.

INTERPRETATION

Electric fan use, particularly for healthy young adults, would not have worsened heat stress on the majority of study days between 2007 and 2019. Our newly proposed thresholds for fan use provide simple guidelines that improve future heatwave fan use recommendations.

FUNDING

None.

Extreme Weather and Climate Change: Population Health and Health System Implications

Extreme weather and climate events, such as heat waves, cyclones, and floods, are an expression of climate variability. These events and events influenced by climate change, such as wildfires, continue to cause significant human morbidity and mortality and adversely affect mental health and well-being. Although adverse health impacts from extreme events declined over the past few decades, climate change and more people moving into harm's way could alter this trend. Long-term changes to Earth's energy balance are increasing the frequency and intensity of many extreme events and the probability of compound events, with trends projected to accelerate under certain greenhouse gas emissions scenarios. While most of these events cannot be completely avoided, many of the health risks could be prevented through building climate-resilient health systems with improved risk reduction, preparation, response, and recovery. Conducting vulnerability and adaptation assessments and developing health system adaptation plans can identify priority actions to effectively reduce risks, such as disaster risk management and more resilient infrastructure. The risks are urgent, so action is needed now.

The requirement for physical effort reduces voluntary cooling behavior during heat exposure in humans

We tested the hypothesis that cool-seeking behavior during heat exposure is attenuated when physical effort is required. Twelve healthy adults (mean(SD), 24(4) years, four women) underwent three experimental trials during two hours of exposure to 41(1) °C, 20(0)% relative humidity in which subjects undertook intermittent exercise alternating between seated rest and cycling exercise at ~4 metabolic equivalents every 15 min. In all trials, subjects wore a water perfused suit top. In the control trial (Control), no water perfused the suit. In the other trials, subjects were freely able to perfuse 2.1(0.2) °C water through the suit. In one cooling trial, subjects received two minutes of cooling by pressing a button (Button). The other cooling trial permitted cooling by engaging in isometric handgrip exercise at 15% of maximal grip strength (Handgrip), with cooling maintained throughout the duration the required force was produced or until two minutes elapsed. In both Button and Handgrip, a one-minute washout proceeded cooling. Core temperature increased over time in all trials (P<0.01) and there were no differences between trials (P = 0.32). Mean skin temperature at the end of heat exposure was lowest in Button [34.2(1.5) °C] compared to Handgrip [35.6(0.8) °C, P = 0.03] and Control [36.9(0.7) °C, P<0.01]. The total number of behaviors [8(3) vs. 10(5), P = 0.04] and cumulative cooling time [850(323) vs. 1230(616) seconds, P = 0.02] were lower in Handgrip compared to Button. These data indicate that when physical effort is required, the incidence and duration of cooling behavior during heat exposure is attenuated compared to when behaving requires minimal physical effort.

The elderly's physiological and perceptual responses to cooling during simulated activities of daily living in UK summer climatic conditions

OBJECTIVES

The elderly are the most at-risk population for heat-related illness and mortality during the periods of hot weather. However, evidence-based elderly-specific cooling strategies to prevent heat-illness are limited. The aim of this investigation was to quantify the elderly's physiological and perceptual responses to cooling through cold water ingestion (COLD) or an L-menthol mouth rinse (MENT) during simulated activities of daily living in UK summer climatic conditions.

STUDY DESIGN

Randomised, controlled repeated measures research design.

METHODS

A total of ten participants (men n = 7, women n = 3: age; 69 ± 3 yrs, height; 168 ± 10 cm, body mass; 68.88 ± 13.72 kg) completed one preliminary and three experimental trials; control (CON), COLD and MENT. Experimental trials consisted of 40 min rest followed by 30 min of cycling exercise at 6 metabolic equivalents and a 6-min walk test (6MWT), within a 35 °C, 50% relative humidity environment. Experimental interventions (every 10 min); cold water (4 °C) ingestion (total of 1.5L) or menthol (5 ml mouth swill for 5 s, menthol concentration of 0.01%).

RESULTS

Peak rectal temperature (T_re) was significantly (P < 0.05) lower in COLD compared with CON (-0.34 ± 0.16 °C) and MENT (-0.36 ± 0.20 °C). End exercise heart rate (HR) decreased in COLD compared with CON (-7 ± 9 b min^-1) and MENT (-6 ± 7 b min^-1). There was no difference in end exercise thermal sensation (TS) (CON; 6.1 ± 0.4, COLD; 6.0 ± 0.4, MENT; 6.4 ± 0.6) or thermal comfort (TC) (CON; 4 ± 1, COLD; 4 ± 1, MENT; 4 ± 1) between trials. The participants walked significantly further during the COLD 6MWT compared with CON (40 m ± 40 m) and MENT (40 m ± 30 m). There was reduced physiological strain in the COLD 6MWT compared with CON (T_re; -0.21 ± 0.24 °C, HR; -7 ± 8 b min^-1) and MENT (T_re; -0.23 ± 0.24 °C, HR; -4 ± 7 b min^-1).

CONCLUSION

The elderly have reduced physiological strain (T_re and HR) during activities of daily living and a 6MWT in hot UK climatic conditions, when they drink cold water. Furthermore, the elderly's perception (TS and TC) of the hot environment did not differ from CON at the end of exercise with COLD or MENT interventions. Menthol provided neither perceptual benefit to exercise in the heat nor functional gain. The TS data indicate that elderly may be at increased risk of heat illness, due to not feeling hot and uncomfortable enough to implement physiological strain reducing strategies such as cold-water ingestion.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Dietary nitrate supplementation does not influence thermoregulatory or cardiovascular strain in older individuals during severe ambient heat stress

NEW FINDINGS

What is the central question of this study? Does dietary nitrate supplementation with beetroot juice attenuate thermoregulatory and cardiovascular strain in older adults during severe heat stress? What is the main finding and its importance? A 7-day nitrate supplementation regimen lowered resting mean arterial pressure in thermoneutral conditions. During heat stress, core and mean skin temperatures, vasodilatory responses, sweat loss, heart rate and left ventricular function were unchanged, and mean arterial pressure was only transiently reduced, post-supplementation. These data suggest nitrate supplementation with beetroot juice does not mitigate thermoregulatory or cardiovascular strain in heat-stressed older individuals.

ABSTRACT

This study tested the hypothesis that dietary nitrate supplementation with concentrated beetroot juice attenuates thermoregulatory and cardiovascular strain in older individuals during environmental heat stress. Nine healthy older individuals (six females, three males; aged 67 ± 5 years) were exposed to 42.5 ± 0.1°C and 34.0 ± 0.5% relative humidity conditions for 120 min before (CON) and after 7 days of dietary nitrate supplementation with concentrated beetroot juice (BRJ; 280 ml, ∼16.8 mmol of nitrate daily). Core and skin temperatures, body mass changes (indicative of whole-body sweat loss), skin blood flow and cutaneous vascular conductance, forearm blood flow and vascular conductance, heart rate, arterial blood pressures and indices of cardiac function were measured. The 7-day beetroot juice regimen increased plasma nitrate/nitrite levels from 27.4 ± 15.2 to 477.0 ± 102.5 μmol l^-1 (P < 0.01) and lowered resting mean arterial pressure from 90 ± 7 to 83 ± 10 mmHg at baseline under thermoneutral conditions (P = 0.02). However, during subsequent heat stress, no differences in core and skin temperatures, skin blood flow and vascular conductance, forearm blood flow and vascular conductance, whole-body sweat loss, heart rate, and echocardiographic indices of systolic function and diastolic filling were evident following nitrate supplementation (all P > 0.05). Mean arterial pressure was lower in BRJ vs. CON during heat stress (treatment-by-time interaction: P = 0.02). Overall, these findings suggest that dietary nitrate supplementation with concentrated beetroot juice does not attenuate thermoregulatory or cardiovascular strain in older individuals exposed to severe ambient heat stress.

COVID-19 and thermoregulation-related problems: Practical recommendations

The COVID-19 pandemic started in the cold months of the year 2020 in the Northern hemisphere. Concerns were raised that the hot season may lead to additional problems as some typical interventions to prevent heat-related illness could potentially conflict with precautions to reduce coronavirus transmission. Therefore, an international research team organized by the Global Health Heat Information Network generated an inventory of the specific concerns about this nexus and began to address the issues. Three key thermal and covid-19 related topics were highlighted: 1) For the general public, going to public cool areas in the hot season interferes with the recommendation to stay at home to reduce the spread of the virus. Conflicting advice makes it necessary to revise national heat plans and alert policymakers of this forecasted issue. 2) For medical personnel working in hot conditions, heat strain is exacerbated due to a reduction in heat loss from wearing personal protective equipment to prevent contamination. To avoid heat-related injuries, medical personnel are recommended to precool and to minimize the increase in body core temperature using adopted work/rest schedules, specific clothing systems, and by drinking cold fluids. 3) Fever, one of the main symptoms of COVID-19, may be difficult to distinguish from heat-induced hyperthermia and a resting period may be necessary prior to measurement to avoid misinterpretation. In summary, heat in combination with the COVID-19 pandemic leads to additional problems; the impact of which can be reduced by revising heat plans and implementing special measures attentive to these compound risks.

Impairments to Thermoregulation in the Elderly During Heat Exposure Events

Heat waves represent a public health risk to elderly people, and typically result in an increased rate of hospital admissions and deaths. Studies of thermoregulation in this cohort have generally focused on single elements such as sweating capacity. Sweating capacity and skin blood flow reduce with age, reducing ability to dissipate heat. Perception of effort during heat exposure is emerging as an area that needs further investigation as the elderly appear to lack the ability to adequately perceive increased physiological strain during heat exposure. The role of the gut and endotoxemia in heat stress has received attention in young adults, while the elderly population has been neglected. This shortcoming offers another potential avenue for identifying effective integrated health interventions to reduce heat illnesses. Increasing numbers of elderly individuals in populations worldwide are likely to increase the incidence of heat wave-induced deaths if adequate interventions are not developed, evaluated, and implemented. In this narrative-style review we identify and discuss health-related interventions for reducing the impact of heat illnesses in the elderly.