The perceived temperature – a versatile index for the assessment of the human thermal environment. Part A: scientific basics

The Perceived Temperature (PT) is an equivalent temperature based on a complete heat budget model of the human body. It has proved its suitability for numerous applications across a wide variety of scales from micro to global and is successfully used both in daily forecasts and climatological studies. PT is designed for staying outdoors and is defined as the air temperature of a reference environment in which the thermal perception would be the same as in the actual environment. The calculation is performed for a reference subject with an internal heat production of 135 W m⁻² (who is walking at 4 km h⁻¹ on flat ground). In the reference environment, the mean radiant temperature equals the air temperature and wind velocity is reduced to a slight draught. The water vapour pressure remains unchanged. Under warm/humid conditions, however, it is implicitly related to a relative humidity of 50%. Clothing is adapted in order to achieve thermal comfort. If this is impossible, cold or heat stress will occur, respectively. The assessment of thermal perception by means of PT is based on Fanger’s Predicted Mean Vote (PMV) together with additional model extensions taking account of stronger deviations from thermal neutrality. This is performed using a parameterisation based on a two-node model. In the cold, it allows the mean skin temperature to drop below the comfort value. In the heat, it assesses additionally the enthalpy of sweat-moistened skin and of wet clothes. PT has the advantages of being self-explanatory due to its deviation from air temperature and being—via PMV—directly linked to a thermo-physiologically-based scale of thermal perception that is widely used and has stood the test of time. This paper explains in detail the basic equations of the human heat budget and the coefficients of the parameterisations.     

Improvement of thermal comfort indices in agroforestry systems in the southern Brazilian Amazon

Agroforestry systems can minimize heat stress and improve cattle welfare, but the influence of the forest component in microclimatic changes in the southern Amazon remains unclear. This study aimed to compare the thermal comfort indices in grass monoculture and integrated systems. The three systems were pasture under full sunlight (PFS), integrated (triple-row) livestock-forestry (ILF_T), and integrated (single-row) livestock-forestry (ILFs), across four seasons, for two years, from June 2017 to June 2019. We assessed photosynthetically active radiation (PAR), air temperature, relative humidity, black globe temperature, and wind speed. Thermal comfort indices such as temperature-humidity index (THI), black globe temperature-humidity index (BGHI), and radiant thermal load (RTL) were calculated based on microclimate data daily-collected from 8:00 to 16:00. The ILF_T mean THI (76.8) was slightly lower than ILF_S and PFS. The BGHI and RTL values decreased as shading increased (PFS > ILFs > ILF_T). The most challenging heat stress conditions for grazing animals occurred predominately during winter and autumn. In conclusion, the presence of trees in pastures of the southern Amazon improved the microclimate and, consequently, the thermal comfort indices. Agroforestry systems can foster an environment with a more suitable thermal comfort or less restrictive to animal performance, which contribute to mitigating global climate change for forage-livestock systems in Brazilian Amazon.     

Integrated models of livestock systems for climate change studies. 2. Intensive systems

The potential impact of climate change by the year 2050 on intensive livestock systems in Britain is assessed through the use of simulation models of farming systems. The submodels comprise livestock feeding, livestock thermal balance and the thermal balance of controlled environment buildings and a stochastic weather generator. These are integrated to form system models for growing pigs and broiler chickens. They are applied to scenarios typical of SE England, which is the warmest region of the country and represents the worst case. For both species the frequency of severe heat stress is substantially increased, with a consequent risk of mortality. To offset this, it would be necessary to reduce stocking densities considerably, or to invest in improved ventilation or cooling equipment. Other effects on production are likely to be small.     

Adaptation to hot climate and strategies to alleviate heat stress in livestock production

Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.     

Thermoneutral zone for laying hens based on environmental conditions,enthalpy and thermal comfort indexes

Controlling environmental conditions inside laying hens facilities systems and their effects on physiology and performance is essential in defining management strategies to alleviate the adverse effects of thermal stress in laying hens. Thus, we estimated thermoneutral zones for laying hens exposed to different heat-challenging conditions based on environmental conditions, enthalpy, and thermal comfort indexes being evaluated out in four thermal environment-controlled wind tunnels equipped with heating and air moistening function, housed in an experimental room with an area of 31.92 m². Clustering analysis and empirical models were used to estimate thermoneutral zones for laying hens based on environmental conditions, enthalpy and thermal comfort indexes, and compare them with data available in the literature through graphics. The thermoneutral zones characterizing homeostasis for laying hens based on respiration rate (RR) are as follows: from 25.9 to 29.9 °C for air dry-bulb temperature (t_db), from 67 to 75 for temperature-humidity index (THI), from 68 to 73 for black globe-humidity index (BGHI), from 45 to 56 kJ kg dry air⁻¹ for enthalpy (H) and 441.7–465.6 W for radiant heat load (RHL). Comfort limits for physiological responses cloacal temperature (t_clo), surface temperature (t_sur) and RR found in this study are 39.4–39.9 °C, 26.5 to 29.9 °C and 30 to 67 mov. min⁻¹, respectively. The number of repetitions and the use of mathematical modeling to be worked on, may directly impact the amplitude of each limit to be established for each variable of interest.     

Effects of street orientation and tree species thermal comfort within urban canyons in a hot,dry climate

Urban valleys as a primary element of the urban environment have played an undeniable role in the intensification of urban heat islands as climate change has increased in the past century. However, appropriate solutions can help improve outdoor thermal comfort (OTC) in these areas. In the present study, parameters related to thermal comfort outdoors such as air temperature (Ta), wind speed (Ws), sky view factor (SVF), mean radiant temperature (MRT) and physiological equivalent temperature (PET) in an urban street were analyzed using ENVI-met simulation. Furthermore, the influence of tree species and street orientation in the study area was also examined to improve thermal comfort conditions. Similarly, with field measurements on site, a questionnaire was used to determine the OTC range of visitors to the urban valley. The study also integrates with ENVI-met microclimatic modeling to improve thermal comfort in the urban street canyon, which was used to simulate the current situation and validated with field measurements, showing a good correlation. The results have revealed that, although SVF has been extensively used in previous studies, it is not an exact indicator to determine the amount of radiation and OTC conditions. The simulation study expressed that orientations' effect on thermal comfort is less prominent than tree cover. However, significant changes in orientation have a remarkable effect on improving OTC in the urban valley.     

Livestock production system management responses to thermal challenges

The adaptive capabilities of animals and livestock production systems have been emphasized in this report. Biometeorology has a key role in rational management to meet the challenges of thermal environments. While the focus is primarily on cattle in warm or hot climates, the importance of dynamic animal responses to environmental challenges applies to all species and climates. Methods used to mitigate environmental challenges focus on heat loss/heat production balance. Under cold stress, reduction of heat loss is the key. Under heat stress, reduction of heat load or increasing heat loss are the primary management tools, although heat-tolerant animals are also available. In general, livestock with health problems and the most productive animals (e.g., highest growth rate or milk production) are at greatest risk of heat stress, thereby requiring the most attention. Risk management, by considering perceived thermal challenges, then assessing the potential consequences and acting accordingly, will reduce the impact of such challenges. Appropriate actions include: shade, sprinkling, air movement, or active cooling. Summarizing, the most important element of proactive environmental management to reduce risk is preparation: be informed, develop a strategic plan, observe and recognize animals in distress, and take appropriate tactical action.     

Review of the physiology of human thermal comfort while exercising in urban landscapes and implications for bioclimatic design

This review comprehensively examines scientific literature pertaining to human physiology during exercise, including mechanisms of heat formation and dissipation, heat stress on the body, the importance of skin temperature monitoring, the effects of clothing, and microclimatic measurements. This provides a critical foundation for microclimatologists and biometeorologists in the understanding of experiments involving human physiology. The importance of the psychological aspects of how an individual perceives an outdoor environment are also reviewed, emphasizing many factors that can indirectly affect thermal comfort (TC). Past and current efforts to develop accurate human comfort models are described, as well as how these models can be used to develop resilient and comfortable outdoor spaces for physical activity. Lack of suitable spaces plays a large role in the deterioration of human health due to physical inactivity, leading to higher rates of illness, heart disease, obesity and heat-related casualties. This trend will continue if urban designers do not make use of current knowledge of bioclimatic urban design, which must be synthesized with physiology, psychology and microclimatology. Increased research is required for furthering our knowledge on the outdoor human energy balance concept and bioclimatic design for health and well-being in urban areas.     

Prediction of air temperature for thermal comfort of people in outdoor environments

Current thermal comfort indices do not take into account the effects of wind and body movement on the thermal resistance and vapor resistance of clothing. This may cause public health problem, e.g. cold-related mortality. Based on the energy balance equation and heat exchanges between a clothed body and the outdoor environment, a mathematical model was developed to determine the air temperature at which an average adult, wearing a specific outdoor clothing and engaging in a given activity, attains thermal comfort under outdoor environment condition. The results indicated low clothing insulation, less physical activity and high wind speed lead to high air temperature prediction for thermal comfort. More accurate air temperature prediction is able to prevent wearers from hypothermia under cold conditions.     

Biological role of melatonin during summer season related heat stress in livestock

Heat stress can cause a significant financial burden to livestock producers by decreasing all productive functions in livestock. The major strategies associated with relieving heat stress in livestock are through use of sheds, fans, or evaporative cooling. Such practices are not possible where the animals are reared in a semi-intensive system. This necessitates developing other strategies to counteract the adverse effects of heat stress. A new strategy involving the feeding of melatonin (MEL) has been evaluated by a few researchers. Melatonin has hypothermic and antioxidant effects and may counter the detrimental effect of heat stress on livestock production. The aim of the paper is to review evidence for and against the use of MEL as an anti-heat stress agent. The early suggestion of a functional antagonism between the pineal and the adrenal gland became additionally reinforced by experimental and clinical findings indicating that MEL may be able to protect the organism against heat stress-induced damages. Melatonin effectively protects against heat stress, by a variety of mechanisms. As animals in tropical countries are exposed to heat stress during much of the year, MEL with its potential beneficial effects may be useful as an anti-heat stress agent to prevent the loss of production.     

Thermal parameters for assessing thermal properties of clothing

1. The thermal parameters for describing clothing were summarized first (i.e., clo and tog unit, permeability index, evaporative transmissibility, permeation efficiency factor, index of water permeability). Their applications were then outlined for the calculation of heat exchange between human body and its environment, and for the prediction of the physiological variables under heat stress conditions.2. Nevertheless, the human body is not frequently exposed under steady-state condition, instead it is subjected to changes in environmental variables, clothing and activity. The transient thermal response of the human-clothing system plays a major role during transients. The heat exchange between the body and the environment may be affected significantly by the dynamic response of the clothing. The thermal comfort property of a clothing system during dynamic conditions should be assessed based on moisture vapor pressure alteration within the clothing, surface temperature of the clothing and heat loss from the body.3. There is a trend to develop overall thermal parameter to describe the transient thermal and moisture transfer properties of clothing system.     

Regional differences in temperature sensation and thermal comfort in humans

Sensations evoked by thermal stimulation (temperature-related sensations) can be divided into two categories, "temperature sensation" and "thermal comfort." Although several studies have investigated regional differences in temperature sensation, less is known about the sensitivity differences in thermal comfort for the various body regions. In the present study, we examined regional differences in temperature-related sensations with special attention to thermal comfort. Healthy male subjects sitting in an environment of mild heat or cold were locally cooled or warmed with water-perfused stimulators. Areas stimulated were the face, chest, abdomen, and thigh. Temperature sensation and thermal comfort of the stimulated areas were reported by the subjects, as was whole body thermal comfort. During mild heat exposure, facial cooling was most comfortable and facial warming was most uncomfortable. On the other hand, during mild cold exposure, neither warming nor cooling of the face had a major effect. The chest and abdomen had characteristics opposite to those of the face. Local warming of the chest and abdomen did produce a strong comfort sensation during whole body cold exposure. The thermal comfort seen in this study suggests that if given the chance, humans would preferentially cool the head in the heat, and they would maintain the warmth of the trunk areas in the cold. The qualitative differences seen in thermal comfort for the various areas cannot be explained solely by the density or properties of the peripheral thermal receptors and thus must reflect processing mechanisms in the central nervous system.     

Stress biomarkers and proteomics alteration to thermal stress in ruminants: A review

Heat stress may adversely affect physiochemical and immune responses of livestock and alter biological functions. The comfort or thermoneutral zone for livestock, which has long been a subject of research, mainly depends on species, breed, and health. Heat stress is associated with impaired livestock productivity due to reductions in feed intake, growth rates and immunity and changes in blood constituents and biological pathways. In ruminants, elevated temperatures have deleterious consequences on protein synthesis. Exposure of ruminant animals to elevated temperatures may induce release of heat shock proteins (HSPs); HSPs usually enter the blood circulation during tissue damage and causes cell necrosis or death. Additionally, hyperthermia is associated with augmented production of cellular reactive oxygen species (ROS), which cause protein degradation and further decrease protein synthesis by preventing protein translation. Moreover, it has been suggested that high environmental temperatures lead to increased inflammatory signalling in tissues via activation of the nuclear factor kappa B (NF-κB) and tumor necrosis factor alpha (TNF-α) pathways as well as via alteration of skin colour gene (melanocortin 1 receptor (MC1R) and premelanosome protein (PMEL)) expression. Previous proteomics analyses have suggested that heat stress can reduce adenosine triphosphate (ATP) synthesis, alter gluconeogenesis precursor supply, and induce lipid accumulation in the liver with subsequent disturbance of liver structure. This review focuses on the scientific evidence regarding the impact of heat stress on immune and inflammatory responses, antioxidant status, stress biomarkers, skin colour gene (PMEL and MC1R) expression and proteomic profiles in ruminants.     

Environmental profile and critical temperature effects on milk production of Holstein cows in desert climate

The environmental profile of central Arizona is quantitatively described using meteorological data between 1971 and 1986. Utilizing ambient temperature criteria of hours per day less than 21° C, between 21 and 27° C, and more than 27° C, the environmental profile of central Arizona consists of varying levels of thermoneutral and heat stress periods. Milk production data from two commercial dairy farms from March 1990 to February 1991 were used to evaluate the seasonal effects identified in the environmental profile. Overall, milk production is lower during heat stress compared to thermoneutral periods. During heat stress, the cool period of hours per day with temperature less than 21° C provides a margin of safety to reduce the effects of heat stress on decreased milk production. Using minimum, mean and maximum ambient temperatures, the upper critical temperatures for milk production are 21, 27 and 32° C, respectively. Using the temperature-humidity index as the thermal environment indicator, the critical values for minimum, mean and maximum THI are 64, 72 and 76, respectively.     

Assessment of human bioclimate based on thermal response

To assess the thermal component of human climate, the adequacy of two body-environment energy balance models is tested. Requirements are that these models should include the full range of atmospheric variables using a system which embraces both the attributes of those exposed and the functional attributes of the environment. They should also account for thermal stress on the body as well as the feedback thermophysiological responses as a result of that stress, and produce a unitary thermal index. Based on detailed field assessment, the study provides an interpretation of index values in terms of thermal sensation and pleasantness using standardised verbal scales. Detailed statistical analysis shows that the associations between index values and thermal sensation votes are strong giving correlation coefficients in the order of 0.86 which is considerably larger than those from comparable results reported in the literature. Optimal thermal conditions for sedentary activity appear to be located in the zone of vasomotor regulation against heat, subjectly interpreted as slightly warm, rather than precisely at the point of minimum heat stress. Sensitivity of model output and thermal sensation are greater in the zone of heat stress than in the zone of cold stress.     

A study on body temperature regulation and residential thermal environments of the elderly—I. whole country survey of residential thermal environment and evaluation methods: RTE-index

1. 1. As part of “research on environmental comfort,” that is, research which aims to make people's living environment more comfortable, we attempted to clarify the relation between the living environment of elderly people and physiological and psychological factors. We carried out a comprehensive study with a view to establishing comfort standards for the residential thermal environment, and for creating evaluation and control systems.

2. 2. The comfort of the living environment is closely related to the thermal environment and the temperature-regulation ability of the human body. This ability of the body to regulate temperature develops during childhood and recedes as the adult ages.

3. 3. We therefore carried out: (a) experiments on body-temperature regulation and on special characteristics of the body-temperature regulation of elderly people, (b) a nationwide survey of the actual residential thermal environments of elderly people and (c) a survey of the daily activities of elderly people, and how elderly people's physiological and psychological conditions change when they are engaged in these activities.

4. 4. As a result of these experiments and surveys, we were able to: (d) formulate standards for evaluation of the residential thermal environment and (e) numerically express the results of systematic evaluation of residential thermal environments of elderly people, by means of a RTE-index.

Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans.

Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface (Tsk) temperatures are known afferent inputs to the thermoregulatory system, the relative contributions of Tc and Tsk to thermal comfort are unknown. We independently altered Tc and Tsk in human subjects while measuring thermal comfort, vasomotor changes, metabolic heat production, and systemic catecholaminergic responses. Multiple linear regression was used to determine the relative Tc/Tsk contribution to thermal comfort and the autonomic thermoregulatory responses, by using the ratio of regression coefficients for Tc and Tsk. The Tc/Tsk contribution ratio was relatively lower for thermal comfort (1:1) than for vasomotor changes (3:1; P = 0.008), metabolic heat production (3.6:1; P = 0.001), norepinephrine (1.8:1; P = 0.03), and epinephrine (3:1; P = 0.006) responses. Thus Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses.     

Thermal bioclimatic conditions and patterns of behaviour in an urban park in Göteborg,Sweden

People in urban areas frequently use parks for recreation and outdoor activities. Owing to the complexity of the outdoor environment, there have only been a few attempts to understand the effect of the thermal environment on people's use of outdoor spaces. This paper therefore seeks to determine the relationship between the thermal environment, park use and behavioural patterns in an urban area of Sweden. The methods used include structured interviews, unobtrusive observations of the naturally occurring behaviour and simultaneous measurements of thermal comfort variables, i.e., air temperature, air humidity, wind speed and global radiation. The thermal environment is investigated through the mean radiant temperature (T_mrt) and the predicted mean vote (PMV) index. The outcome is compared to the subjective behaviour and thermal sensation of the interviewees. It is found that the thermal environment, access and design are important factors in the use of the park. In order to continue to use the park when the thermal conditions become too cold or too hot for comfort, people improve their comfort conditions by modifying their clothing and by choosing the most supportive thermal opportunities available within the place. The study also shows that psychological aspects such as time of exposure, expectations, experience and perceived control may influence the subjective assessment. Comparison between the thermal sensation of the interviewees and the thermal sensation assessed by the PMV index indicates that steady-state models such as the PMV index may not be appropriate for the assessment of short-term outdoor thermal comfort, mainly because they are unable to analyse transient exposure.     

A methodology for mapping current and future heat stress risk in pigs

Heat stress is a global issue constraining pig productivity, and it is likely to intensify under future climate change. Technological advances in earth observation have made tools available that enable identification and mapping livestock species that are at risk of exposure to heat stress due to climate change. Here, we present a methodology to map the current and likely future heat stress risk in pigs using R software by combining the effects of temperature and relative humidity. We applied the method to growing-finishing pigs in Uganda. We mapped monthly heat stress risk and quantified the number of pigs exposed to heat stress using 18 global circulation models and projected impacts in the 2050s. Results show that more than 800 000 pigs in Uganda will be affected by heat stress in the future. The results can feed into evidence-based policy, planning and targeted resource allocation in the livestock sector.     

Effects of Methionine Supplementation on the Expression of Protein Deposition-Related Genes in Acute Heat Stress-Exposed Broilers

The objective of this study was to evaluate the effect of heat stress and methionine supplementation on the gene expression of insulin-like growth factor I (IGF-I), growth hormone receptor (GHR), phosphatidylinositol 3-kinase, and regulatory 1 (PI3KR1) in the liver, as well as the expression of the atrogin 1 and cathepsin L2 (CTSL2) genes in the breast muscle of broilers. Broilers from 1–21 and 22–42 days of age were divided into three treatments related to methionine supplementation as follows: without methionine supplementation (MD), recommended level of methionine (DL1), and excess supplementation of methionine (DL2). The animals were either maintained at a thermal comfort temperature or exposed to heat stress (HS) (38°C for 24 hours, starting on day 20 or day 41 for experiments 1 and 2, respectively). The heat stress increased the body temperature at both ages. Starter period: The HS animals presented increased plasma creatinine content (P<0.0001) and the highest CTSL2 gene expression (P<0.0001). The methionine supplementation increased the IGF-I (P = 0.0144) and GHR (P = 0.0011) gene expression and decreased the CTSL2 (P = 0.0004) and atrogin 1 (P = 0.0012) gene expression. Grower period: Significant effects for the interaction between supplementation and environment were observed for GHR (P = 0.0252) and CTSL2 (P = 0.0011) gene expression. The highest GHR expression was observed in animals that remained in thermal comfort on the DL2 diet, and the lowest expression occurred in the HS animals fed the MD diet. For CTSL2, the HS animals fed the MD diet presented the highest CTSL2 gene expression, and the lowest expression was observed in the animals maintained at thermal comfort on DL1 and DL2 diets. Only methionine supplementation had effect on atrogin-1 gene expression (P<0.0001), with higher methionine content in the diet lower atrogin-1 gene expression was observed. Our results suggest that heat stress induces greater protein degradation and that methionine supplementation could induce protein deposition because methionine increased the expression of genes related to protein synthesis and decreased the expression of genes related to protein breakdown.