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

A digital heat early warning system for older adults

Extreme heat events lead to considerable health burden and are becoming more severe and frequent, calling for the development of effective population-based and individualised heat early warning systems. We developed an individualised heat early warning system and tested it in 78 older adults' ( ≥ 65 years) homes in Southeast Queensland, Australia. Quantitative and qualitative data from this proof-of-concept testing study showed that the Ethos system performed well on a standard usability scale (mean score of 78 on the System Usability Scale). Following a summer-time use of this early warning system, there were increases in heat preparedness (P < 0.001, marginal homogeneity tests) but no significant increases in heat health risk perception or the uptake of low-cost cooling measures (e.g., hand/forearm bath, fans). This proof-of-concept research demonstrated the usability of this tailored, actionable, real-time digital heat early warning system, although the effectiveness of the system remains to be evaluated in a robust trial design.

Effect of fluid temperature on the relation and agreement between perceptual and physiological strain during simulated work in a hot environment

BACKGROUND

Cold fluid ingestion is recommended during work to maintain hydration status and physiological function. While monitoring the physiological strain index (PSI) during work in the heat is recommended, it is logistically challenging. Subjective estimates, i.e., perceptual strain index (PeSI), are thought to reflect PSI. However, it remains unclear if cold fluid influences an individual's perception of heat strain.

METHODS

Twenty young adults (10 females) performed four 15-min bouts of moderate-intensity (200 W/m2) cycling in the heat (40°C, 13% RH), each separated by 15-min rest. On separate days, participants consumed 2 boluses consisting of 5.2 g/kg of cold (0°C) or warm fluid (37.5°C) before the first and third work bout. Rectal temperature (Tc) and heart rate (HR) were recorded to calculate PSI (0-10 scale). Rating of perceived exertion (RPE) and thermal sensation (TS) were recorded to calculate PeSI (0-10 scale). Tc, HR, TS, and RPE were compared between experimental trials and across work bouts via two-way ANOVAs. Relation between PSI, PeSI and fluid temperature were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis.

FINDINGS

Tc, HR, TS and RPE were not influenced by fluid temperature (P ≥ 0.09), nor was the relation between PeSI and PSI (P = 0.11). Mean bias [95% LoA] between PSI and PeSI was greater in cold (-2.1 [-5.7 - 1.5]) compared to the warm fluid condition (-1.8 [-4.8 - 1.2], P = 0.008).

CONCLUSION

While the relation between PeSI and PSI was not influenced by beverage temperature the agreement between measures was worsened following cold fluid ingestion.

"Sadness smile" curve: Processing emotional information from social network for evaluating thermal comfort perception

Thermal comfort is a subjective perception, hence conventional evaluation using meteorological factors faces a technical challenge in precise assessment. Human beings have the nature to differentiate expressions of facial emotions when varied thermal environments are perceived. Facial expression scores can be taken as a predictor of perceived thermal comfort which can be precisely assessed using deep learning against physical factors. In this study, a total of 8314 facial photos were obtained from volunteers in 82 parks of 49 cities via social network. Facial expressions were analyzed to happy, sad, and neutral emotion scores using a professional instrument. Temperature-responsive changes in sadness score (SS) can be fit by a U-shaped curve which was called as the 'sadness smile'. The stationary point of second-order derivative was identified to predict the-most-comfort temperature (22.84 °C), across which a tangent line framed the range of comfort temperatures based on two intersections with first-order derivatives (14.62-31.06 °C). Critical temperature points were identified along a positively correlated line of modified temperature-humidity index against increasing temperatures, which were negatively correlated with SS in autumn and winter. The ResNet model was demonstrated to excellently predict emotion-based thermal comfort perceptions in validation set (R2 > 0.5). A nation-wide mapping suggested that many cities of Northwest and North China had local environments that can be perceived with comfort assessed by SS against thermal and cooling temperatures in summer and winter, respectively.

Foot immersion with and without neck cooling reduces self-reported environmental symptoms in older adults exposed to simulated indoor overheating

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

Indoor overheating: A review of vulnerabilities, causes, and strategies to prevent adverse human health outcomes during extreme heat events

The likelihood of exposure to overheated indoor environments is increasing as climate change is exacerbating the frequency and severity of hot weather and extreme heat events (EHE). Consequently, vulnerable populations will face serious health risks from indoor overheating. While the relationship between EHE and human health has been assessed in relation to outdoor temperature, indoor temperature patterns can vary markedly from those measured outside. This is because the built environment and building characteristics can act as an important modifier of indoor temperatures. In this narrative review, we examine the physiological and behavioral determinants that influence a person's susceptibility to indoor overheating. Further, we explore how the built environment, neighborhood-level factors, and building characteristics can impact exposure to excess heat and we overview how strategies to mitigate building overheating can help reduce heat-related mortality in heat-vulnerable occupants. Finally, we discuss the effectiveness of commonly recommended personal cooling strategies that aim to mitigate dangerous increases in physiological strain during exposure to high indoor temperatures during hot weather or an EHE. As global temperatures continue to rise, the need for a research agenda specifically directed at reducing the likelihood and impact of indoor overheating on human health is paramount. This includes conducting EHE simulation studies to support the development of consensus-based heat mitigation solutions and public health messaging that provides equitable protection to heat-vulnerable people exposed to high indoor temperatures.

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.