Effects of apparent temperature on hospitalization rates for cardiovascular diseases: a case study of different rural areas in Northwest China.

Apparent temperature (AT) is a composite index that combines ambient temperature, humidity, wind speed and other meteorological factors, and reflects heat perception more accurately than raw temperature. This is the first study to investigate the association between AT and CVD in rural areas of Jiuquan and Longnan, Gansu Province, China. In this study, the distributed lag nonlinear model (DLNM) was used to examine the exposure-response relationship between AT and the 21 days relative risk (RR) of CVD admission. The results showed that the exposure risk of the gender group in Jiuquan was opposite to that of Longnan under the influence of cold effect. Under the influence of heat effect, it has a protective effect on all groups in Jiuquan area, which is harmful to males and adults in Longnan area. The results of this study can help local governments to formulate public policies.

Meteorological factors and risk of ischemic stroke, intracranial hemorrhage, and subarachnoid hemorrhage: A time-stratified case-crossover study.

BACKGROUND: Stroke risks associated with rapid climate change remain controversial due to a paucity of evidence. AIMS: To examine the risk of subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH), and ischemic stroke (IS) associated with meteorological parameters. METHODS: In this time-stratified case-crossover study, adult patients hospitalized for their first stroke between 2011 and 2020 from the insurance claims data in Taiwan were identified. The hospitalization day was designated as the case period, and three or four control periods were matched by the same day of the week and month of each case period. Daily mean and 24-h variations in ambient temperature, relative humidity, air pressure, and apparent temperature were measured. Conditional logistic regression models were applied to assess the risk of stroke associated with exposure to weather variables, using the third quintile as a reference, controlling for air pollutant levels. RESULTS: There were 7161 patients with SAH, 40,426 patients with ICH, and 107,550 patients with IS. There was an inverse linear relationship between mean daily temperature and apparent temperature with ICH. Elevated mean daily atmospheric pressure was associated with an increased risk of ICH. A greater decrease in apparent temperature over a 24-h period was associated with increased risk of ICH but decreased risk of IS (odds ratio (95% confidence interval) for the first vs. third quintile of changes in apparent temperature, 1.141 (1.053-1.237) and 0.946 (0.899-0.996), respectively). CONCLUSIONS: There were considerable differences in short-term associations between meteorological parameters and three main pathological types of strokes. DATA ACCESS STATEMENT: The authors have no permission to share the data.

The impact of apparent temperature on the emergency visits for traumatic fractures in Hangzhou, China.

BACKGROUND: Traumatic fractures occur frequently worldwide. However, research remains limited on the association between short-term exposure to temperature and traumatic fractures. This study aims to explore the impact of apparent temperature (AT) on emergency visits (EVs) due to traumatic fractures. METHODS: Based on EVs data for traumatic fractures and the contemporary meteorological data, a generalized Poisson regression model along with a distributed lag nonlinear model (DLNM) were undertaken to determine the impact of AT on traumatic fracture EVs. Subgroup analysis by gender and age and sensitivity analysis were also performed. RESULTS: A total of 25,094 EVs for traumatic fractures were included in the study. We observed a wide "J"-shaped relationship between AT and risk of traumatic fractures, with AT above 9.5 °C positively associated with EVs due to traumatic fractures. The heat effects became significant at cumulative lag 0-11 days, and the relative risk (RR) for moderate heat (95th percentile, 35.7 °C) and extreme heat (99.5th percentile, 38.8 °C) effect was 1.311 (95% CI: 1.132-1.518) and 1.418 (95% CI: 1.191-1.688) at cumulative lag 0-14 days, respectively. The cold effects were consistently non-significant on single or cumulative lag days across 0-14 days. The heat effects were higher among male and those aged 18-65 years old. The sensitivity analysis results remained robust. CONCLUSION: Higher AT is associated with cumulative and delayed higher traumatic fracture EVs. The male and those aged 18-65 years are more susceptible to higher AT.

Cardiovascular admission risk attributable to hot apparent temperature: a study in a rural area of northwest China.

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, posing a significant threat to public health. Research on the relationship between CVD and temperature has primarily focused on developed urban settings, with limited studies conducted in rural regions with lower levels of development. Additionally, compared to relative risks, attributable risks can provide more information when assessing the risk of CVD hospitalizations associated with exposure to apparent temperature (AT). Apparent temperature is a composite temperature index that takes into account both meteorological factors and temperature, providing an objective reflection of human thermal sensation. Therefore, this study investigates the impact of AT on CVD hospitalization and quantifies the burden of CVD admission in the rural areas of China. We employed the distributed lag non-linear model (DLNM) to estimate the relationship between AT and the relative risk (RR) of CVD hospitalization. Finally, we used attributable risk methods to quantify this relationship further.

Effects of apparent temperature on daily outpatient and inpatient visits for cause-specific respiratory diseases in Ganzhou, China: a time series study.

BACKGROUND: Non-optimum temperatures are associated with increased risk of respiratory diseases, but the effects of apparent temperature (AT) on respiratory diseases remain to be investigated. METHODS: Using daily data from 2016 to 2020 in Ganzhou, a large city in southern China, we analyzed the impact of AT on outpatient and inpatient visits for respiratory diseases. We considered total respiratory diseases and five subtypes (influenza and pneumonia, upper respiratory tract infection (URTI), lower respiratory tract infection (LRTI), asthma and chronic obstructive pulmonary disease [COPD]). Our analysis employed a distributed lag nonlinear model (DLNM) combined with a generalized additive model (GAM). RESULTS: We recorded 94,952 outpatients and 72,410 inpatients for respiratory diseases. We found AT significantly non-linearly associated with daily outpatient and inpatient visits for total respiratory diseases, influenza and pneumonia, and URTI, primarily during comfortable AT levels, while it was exclusively related with daily inpatient visits for LRTI and COPD. Moderate heat (32.1 °C, the 75.0th centile) was observed with a significant effect on both daily outpatient and inpatient visits for total respiratory diseases at a relative risk of 1.561 (1.161, 2.098) and 1.276 (1.027, 1.585), respectively (both P < 0.05), while the results of inpatients became insignificant with the adjustment for CO and O3. The attributable fractions in outpatients and inpatients were as follows: total respiratory diseases (24.43% and 18.69%), influenza and pneumonia (31.54% and 17.33%), URTI (23.03% and 32.91%), LRTI (37.49% and 30.00%), asthma (9.83% and 3.39%), and COPD (30.67% and 10.65%). Stratified analyses showed that children ≤5 years old were more susceptible to moderate heat than older participants. CONCLUSIONS: In conclusion, our results indicated moderate heat increase the risk of daily outpatient and inpatient visits for respiratory diseases, especially among children under the age of 5.

Exploring the relationship between land use/land cover and apparent temperature in China (1996-2020): implications for urban planning.

In recent decades, rising air temperatures (AT) and apparent temperatures (AP) have posed growing health risks. In the context of China's rapid urbanization and global climate change, it is crucial to understand the impact of urban land use/land cover (LULC) changes on AP. This study investigates the spatial distribution and long-term variation patterns of AT and AP, using data from 834 meteorological stations across China from 1996 to 2020. It also explores the relationship between AT, AP, and LULC in the urban core areas of 30 major cities. Study reveals that AT and AP exhibit overall high spatial similarity, albeit with greater spatial variance in AP. Notably, regions with significant disparities between the two have been identified. Furthermore, it's observed that the spatial range of high AP change rates is wider than that of AT. Moreover, the study suggests a potential bivariate quadratic function relationship between ΔT (the difference between AT and AP) and Wa_ratio and Ar_ratio, indicating the presence of a Least Suitable Curve (LSC), [Formula: see text]. Urban LULC planning should carefully avoid intersecting with this curve. These findings can provide valuable insights for urban LULC planning, ultimately enhancing the thermal comfort of urban residents.

Field temperature performances of in-use permeable sidewalks and asphalt vehicle roads and the potential impacts on apparent temperature and land surface temperature.

Permeable pavements help reduce surface temperatures and have been widely implemented in urban areas. This study utilized an in-use permeable pavement sidewalk in front of a mass rapid transit station in the Taipei city center of Taiwan to determine the actual pavement surface temperature performance. A neighboring asphalt road and impervious pavement were also monitored. With a full year of continuous monitoring, the results showed that the temperature of permeable pavement was 3.7 °C lower than that of impervious pavement and 4.5 °C lower than that of asphalt pavement in the hot season. The frequent rainfall in spring resulted in the smallest temperature differences between the different pavement types. The cooling effects of permeable pavement differed at the different air temperatures. At air temperatures lower than 15 °C, the differences among pavement surface temperatures were noticeable. However, when the air temperature was higher than 35 °C, the surface temperature of permeable pavement was not different from that of impervious pavement and was greater than 55 °C. Field observations were carried out to determine the effects on the apparent temperature and the future surface temperature of climate change scenarios. The results showed that permeable pavement could reduce the average apparent temperature to near the air temperature, and asphalt pavement could increase the apparent temperature by 1.2 °C, assuming that the pavement temperature completely affects the air temperature. With the good prediction ability of the machine learning approach and 15 environmental factors, the preliminary prediction showed the projected surface temperature change in Taipei city in 2033. In the worst-case scenario, the average impervious pavement temperature is as high as 39.12 °C, whereas the average permeable pavement temperature is 32.50 °C.

Ozone, Heat Wave, and Cardiovascular Disease Mortality: A Population-Based Case-Crossover Study.

A case-crossover study among 511,767 cardiovascular disease (CVD) deaths in Jiangsu province, China, during 2015-2021 was conducted to assess the association of exposure to ambient ozone (O3) and heat wave with CVD mortality and explore their possible interactions. Heat wave was defined as extreme high temperature for at least two consecutive days. Grid-level heat waves were defined by multiple combinations of apparent temperature thresholds and durations. Residential O3 and heat wave exposures were assessed using grid data sets (spatial resolution: 1 km × 1 km for O3; 0.0625° × 0.0625° for heat wave). Conditional logistic regression models were applied for exposure-response analyses and evaluation of additive interactions. Under different heat wave definitions, the odds ratios (ORs) of CVD mortality associated with medium-level and high-level O3 exposures ranged from 1.029 to 1.107 compared with low-level O3, while the ORs for heat wave exposure ranged from 1.14 to 1.65. Significant synergistic effects on CVD mortality were observed for the O3 and heat wave exposures, which were generally greater with higher levels of the O3 exposure, higher temperature thresholds, and longer durations of heat wave exposure. Up to 5.8% of the CVD deaths were attributable to O3 and heat wave. Women and older adults were more vulnerable to the exposure to O3 and heat wave exposure. Exposure to both O3 and heat wave was significantly associated with an increased odds of CVD mortality, and O3 and heat wave can interact synergistically to trigger CVD deaths.

Fluctuations in Seminal Quality throughout the Year: How do Temperature, Humidity and Atmospheric Pressure Impact on Human Sperm Quality?

Background: Most studies evaluating the possible seasonal variation of semen quality have considered temperature as the only causal factor. Aims: To assess possible seasonality in sperm quality and associations between semen parameters and several meteorological variables (temperature, humidity, apparent temperature and atmospheric pressure) in a large cohort of andrological patients. Settings and Design: This was a retrospective, cross-sectional and correlational/descriptive study. Materials and Methods: Patients (n: 15665) were categorised into four groups (summer, winter, spring and autumn) according to the date of assistance at the fertility centre. Daily values of temperature, apparent temperature, humidity and atmospheric pressure were provided by the National Weather System and were calculated as the average of the 74 days previous to semen collection (spermatogenic cycle). Statistical Analysis Used: As appropriate, the results were analysed by analysis of variance/Kruskal-Wallis, Chi-square test, t-test/Mann-Whitney, forward conditional regression model and Spearman/Pearson's correlations. Results: We detected seasonality effects on sperm count, total sperm count and total motile sperm count, with the highest values in winter and the lowest in summer. Correlation analysis showed that temperature, apparent temperature and humidity negatively correlated with semen parameters, being humidity the most powerful predictive meteorological variable. Conclusion: Sperm quality is influenced by seasons; increased environmental temperature and humidity negatively affect semen quality.

Association between apparent temperature and hypertension hospital admissions: a case study in rural areas in western China.

INTRODUCTION AND OBJECTIVE: Although it has previously been shown that temperature is associated with cardiovascular disease, no investigations exploring the association between apparent temperature (AT) and hypertension in farmers in Zhangye and Longnan, Gansu Province, China, have been undertaken. As hypertension is a commonly known risk factor for cardiovascular disease, the relationship between apparent temperature (AT) and hypertension is examined in Zhangye and Longnan to provide advice to local governments on preventive measures. MATERIAL AND METHODS: Daily data and weather conditions were collected in Zhangye and Longnan from 2014-2015. The Poisson generalized linear model and the distributed lag nonlinear model (DLNM) were combined to investigate the relationship between AT and hypertension in hospital admissions in the study areas. RESULTS: A non-linear relationship between AT and hypertension in hospital admissions in both Zhangye and Longnan were recorded. The cold effects were stronger in Zhangye than that in Longnan for both study group and subgroups. The heat effects were more deleterious for the entire study group, female subgroup and adult subgroup in Longnan, but stronger for the male subgroup and elderly subgroup in Zhangye. CONCLUSIONS: This investigation indicates that AT has adverse impacts on hypertension hospital admissions in Zhangye and Longnan, especially under low AT exposure levels. The results from this study may promote the formulation of further prevention measures for hypertension disease.

Changes in Thermal Stress in Korea Using Climate-Based Indicators: Present-Day and Future Projections from 1 km High Resolution Scenarios.

Among the various thermal stress indices, apparent temperature (AT) is closely related to public health indicators, and consequently is widely used by weather agencies around the world. Therefore, in this paper we estimate the changes in AT and contributing components in Korea as a whole and in five major cities (Seoul, Gwanju, Daegu, Daejeon, and Busan) using national standard climate scenarios based on the coupled model inter-comparison project (CMIP6). In the present day, high AT occurs in major cities due to high temperature (TAS) and relative humidity (RH). Our findings reveal that even when TAS is relatively low, large AT occurs with higher humidity. Notably, in future warmer climate conditions, high AT may first appear in the five major cities and then extend to the surrounding areas. An increase in TAS and RH during the pre-hot season (March to June) may lead to earlier occurrence of thermal risks in future warmer climate conditions and more frequent occurrence of high thermal stress events. Our study can serve as a reference for future information on thermal risk changes in Korea. Considering those who have not adapted to high temperature environments, our findings imply that thermal risks will become more serious and that heat adaptation strategies will be needed during the pre-hot season under future warmer climate conditions.

Spatio-temporal interpolation and delineation of extreme heat events in California between 2017 and 2021.

Robust spatio-temporal delineation of extreme climate events and accurate identification of areas that are impacted by an event is a prerequisite for identifying population-level and health-related risks. In prior research, attributes such as temperature and humidity have often been linearly assigned to the population of the study unit from the closest weather station. This could result in inaccurate event delineation and biased assessment of extreme heat exposure. We have developed a spatio-temporal model to dynamically delineate boundaries for Extreme Heat Events (EHE) across space and over time, using a relative measure of Apparent Temperature (AT). Our surface interpolation approach offers a higher spatio-temporal resolution compared to the standard nearest-station (NS) assignment method. We show that the proposed approach can provide at least 80.8 percent improvement in identification of areas and populations impacted by EHEs. This improvement in average adjusts the misclassification of about one million Californians per day of an extreme event, who would be either unidentified or misidentified under EHEs between 2017 and 2021.

Exploring the Association between Ambient Temperature and Daily Hospital Admissions for Diarrhea in Mopani District, Limpopo Province, South Africa.

Diarrhea contributes significantly to global morbidity and mortality. There is evidence that diarrhea prevalence is associated with ambient temperature. This study aimed to determine if there was an association between ambient temperature and diarrhea at a rural site in South Africa. Daily diarrheal hospital admissions (2007 to 2016) at two large district hospitals in Mopani district, Limpopo province were compared to average daily temperature and apparent temperature (Tapp, 'real-feel' temperature that combined temperature, relative humidity, and wind speed). Linear regression and threshold regression, age-stratified to participants ≤5 years and >5 years old, considered changes in daily admissions by unit °C increase in Tapp. Daily ranges in ambient temperature and Tapp were 2-42 °C and -5-34 °C, respectively. For every 1 °C increase in average daily temperature, there was a 6% increase in hospital admissions for diarrhea for individuals of all ages (95% CI: 0.04-0.08; p < 0.001) and a 4% increase in admissions for individuals older than 5 years (95% CI: 0.02-0.05; p < 0.001). A positive linear relationship between average daily Tapp and all daily diarrheal admissions for children ≤5 years old was not statistically significant (95% CI: -0.00-0.03; p = 0.107). Diarrhea is common in children ≤5 years old, however, is more likely triggered by factors other than temperature/Tapp, while it is likely associated with increased temperature in individuals >5 years old. We are limited by lack of data on confounders and effect modifiers, thus, our findings are exploratory. To fully quantify how temperature affects hospital admission counts for diarrhea, future studies should include socio-economic-demographic factors as well as WASH-related data such as personal hygiene practices and access to clean water.

Short-term effect of apparent temperature on daily hospitalizations for osteoporotic fractures in Beijing, China: A retrospective observational study.

BACKGROUND: Studies on the associations between temperature and osteoporotic fractures (OF) hospitalizations are limited. This study aimed to assess the short-term effect of apparent temperature (AT) on the risk of OF hospitalizations. METHODS: This retrospective observational study was conducted in Beijing Jishuitan Hospital from 2004 to 2021. Daily OF hospitalizations, meteorological variables and fine particulate matter were collected. A Poisson generalized linear regression model combined with a distributed lag non-linear model was applied to analyze the lag-exposure-response relationship between AT and the number of OF hospitalizations. Subgroup analysis by gender, age and fracture type was also conducted. RESULTS: Total daily hospitalization visits for OF during the studied period were 35,595. The exposure-response curve of AT and OF presented a non-linear relationship, with optimum apparent temperature (OAT) at 28.40 °C. Taking OAT as the reference, the cold effect (-10.58 °C, 2.5th percentage) on single lag day had statistical significance from the current day of exposure (RR = 1.18, 95 % CI: 1.08-1.28) to lag 4 day (RR = 1.04, 95 % CI: 1.01-1.08), while the cumulative cold effect increased the risk of OF hospitalization visits from lag 0 to 14 days, with the maximum RR over lag 0-14 days (RR = 1.84, 95 % CI: 1.21-2.79). There were no significant risks of OF hospitalizations for warm effects (32.53 °C, 97.5th percentage) on single or cumulative lag days. The cold effect might be more evident among females, patients aged 80 years or older, and patients with hip fractures. CONCLUSION: Exposure to cold temperatures is associated with an increased risk of OF hospitalizations. Females, patients aged 80 years or older and patients with hip fractures might be more vulnerable to the cold effect of AT.

Maternal apparent temperature during pregnancy on the risk of offspring asthma and wheezing: effect, critical window, and modifiers.

The objective of this study was to explore the impact of maternal AT during pregnancy on childhood asthma and wheezing, as well as the potential effect modifiers in this association. A cross-sectional study was implemented from December 2018 to March 2019 in Jinan to investigate the prevalence of childhood asthma and wheezing among aged 18 months to 3 years. Then, we conducted a case-control study based on population to explore the association between prenatal different AT exposure levels and childhood asthma and wheezing. The association was assessed by generalized additive models and logistic regression models, and stratified analyses were performed to explore potential effect modifiers. A total of 12,384 vaccinated children participated in screening for asthma and wheezing, 236 cases were screened, as well as 1445 controls were randomized. After adjusting for the covariates, childhood asthma and wheezing were significantly associated with cold exposure in the first trimester, with OR 1.731 (95% CI: 1.117-2.628), and cold exposure and heat exposure in the third trimester, with ORs 1.610 (95% CI: 1.030-2.473) and 2.039 (95% CI: 1.343-3.048). In the third trimester, enhanced impacts were found among girls, children whose distance of residence was close to the nearest main traffic road, and children whose parents have asthma. The study indicates that exposure to extreme AT during the first and third trimesters could increase the risk of childhood asthma and wheezing.

Heat Acclimation Knowledge among Recreational Runners.

Heat acclimation (HA) is the foremost method of preventing exertional heat illness during exercise in hot and humid environments. However, the prevalence of HA training and its associated knowledge is not currently known in recreational running populations. The purpose of this study was to determine the knowledge of recreational runners toward HA. A survey consisting of 38 questions that required approximately 10-15 min to complete was disseminated to running clubs throughout the Southeastern United States. Questions were designed to collect data on participant demographics, yearly training habits, and HA knowledge. Recreational runners (N = 125) demonstrated a lack of knowledge toward proper HA training and its associated benefits. Participants largely received HA advice from their peers (31.2%) and reported no professional guidance in their training (79.2%). Finally, participants' beliefs toward proper HA training differed among training groups with moderate and high groups perceiving greater frequency, miles/wk, and min/wk as appropriate for HA compared to the low group (p ≤ 0.05). Due to the warmer temperatures and higher relative humidity experienced in the southeastern, southwestern, and mid-Atlantic locations of the United States and throughout certain regions of the European Union, governing bodies in sport and exercise science should develop more educational initiatives to convey the importance and advantages of HA, especially when runners are training for major marathons that are typically held in the late spring and early fall seasons.

Long-Term Apparent Temperature, Extreme Temperature Exposure, and Depressive Symptoms: A Longitudinal Study in China.

Temperature is increasingly understood to impact mental health. However, evidence of the long-term effect of temperature exposure on the risk of depressive symptoms is still scarce. Based on the China Health and Retirement Longitudinal Study (CHARLS), this study estimated associations between long-term apparent temperature, extreme temperature, and depressive symptoms in middle-aged and older adults. Results showed that a 1 °C increase or decrease from optimum apparent temperature (12.72 °C) was associated with a 2.7% (95% CI: 1.3%, 4.1%) and 2.3% (95% CI: 1.1%, 3.5%) increased risk of depressive symptoms, respectively. This study also found that each percent increase in annual change in ice days, cool nights, cool days, cold spell durations, and tropical nights was associated with higher risk of depressive symptoms, with HRs (95%CI) of 1.289 (1.114-1.491), 2.064 (1.507-2.825), 1.315 (1.061-1.631), 1.645 (1.306-2.072), and 1.344 (1.127-1.602), respectively. The results also indicated that people living in northern China have attenuated risk of low apparent temperature. Older people were also observed at higher risk relating to more cool nights. Middle-aged people, rural residents, and people with lower household income might have higher related risk of depressive symptoms due to increased tropical nights. Given the dual effect of climate change and global aging, these findings have great significance for policy making and adaptive strategies for long-term temperature and extreme temperature exposure.

Reconstruction of the hourly fine-resolution apparent temperature (Humidex) with the aerodynamic parameters.

Apparent temperature is the preferred measure of hotness or coldness expressed to depict the human sense. Spatially explicit measurement of the hourly apparent temperature is essential for capturing the threats to bioclimatic comfort and preventing potential mortality/morbidity risk from heat or cold. However, existing apparent temperature products only provide daily observations at the spatial resolution of several dozen kilometers, resulting in some substantial underestimations for some life-threatening thermal stresses highly localized in space and time. Furthermore, some data-driven models lack mechanical constraints on the turbulent exchange between the surface and the atmosphere, making some unsatisfactory accuracy. Here, we propose Humidex reconstruction model incorporating atmospheric dynamics theory and aerodynamic parameters (i.e., heat and momentum roughness lengths for natural surfaces and three urban canopy geometry parameters for artificial surfaces), capable of developing an hourly dataset at fine-grained spatial resolution (0.01° × 0.01°). In this study, a total of 2952 h in four seasons were selected to test the seasonal performance of this model, taking the Yangtze River Delta as an example. The results show that the Humidex products from this model generally outperform the existing comparable products, with the hourly population root mean square error (RMSE) ranging from 1 to 2 °C in winter and autumn and 2-3 °C in spring and summer. Moreover, the constraint of aerodynamic parameters can reduce RMSE with a significant margin for each season, up to 2 °C, especially in areas with dense woodlands or buildings. In addition, the results demonstrate the excellent performance of this model in capturing short-lived thermal health threats, which are easily overlooked when observed data only provides a daily variation. This indicates that the model can allow researchers and practitioners investigate the fine-grained spatial and temporal evolution of thermal stress and its impact on public health, tourism, learning, and work performance.

Predicting fatal heat and humidity using the heat index model.

A unique wet-bulb temperature of 35°C is often used as the threshold for human survivability, but recent experiments have shown that a person's core temperature starts to rise at a wide range of critical wet-bulb temperatures. Here, it is shown that the model underlying the heat index correctly predicts those critical wet-bulb temperatures, explaining 95% of the variance in the values observed in laboratory heat-stress experiments. This is the first time the heat-index model has been validated against physiological data from laboratory experiments. For light and moderate exertion in an indoor setting, the heat index model predicts that the critical wet-bulb temperature ranges from 20°C to 32°C, depending on the relative humidity, consistent with experimental results. For the same setting and exertion, the heat index model predicts fatal wet-bulb temperatures ranging from 24°C to 37°C.NEW & NOTEWORTHY Recent experiments have identified the critical combinations of heat and humidity, in an indoor setting, above which an individual is unable to maintain a standard core temperature, indicating severe heat stress. It is shown here why this state of severe heat stress cannot be predicted using the wet-bulb temperature. Instead, it is shown that the recently extended heat index model can explain nearly all of the variance in the observed critical combinations of temperature and humidity, and can be used to calculate fatal combinations.

Temperature modifies the association between air pollution and respiratory disease mortality in Cape Town, South Africa.

The aim of this 10-year study was to investigate whether and how temperature modifies the association between daily ambient PM10, NO2, SO2 air pollution and daily respiratory disease mortality in Cape Town. A time-stratified case-crossover epidemiological design was applied. Susceptibility by sex and age groups (15-64 years and ≥65 years) was also investigated. On days with medium Tapp levels, NO2 displayed a stronger association with respiratory mortality than PM10 or SO2. Females appeared to be more susceptible to NO2 at medium Tapp levels to males. The 15-64-year-old age group seemed to be more vulnerable to NO2 and PM10 at medium Tapp levels compared to the elderly (≥65 years). At high Tapp levels, females were more susceptible to PM10. The 15-64-year-old group were more vulnerable to NO2 and SO2. The results can be used in present-day early warning systems and in risk assessments to estimate the impact of increased air pollution and temperature.