Environmental Thermal Stress Research Articles

Fruit based diversified cropping system: an alternative approach for nutritional and economic security

Diversity of fruit crops available in the country has proved beyond doubt its potentiality for gainful diversi fication. Fruit based diversified cropping system is now considered to be the most ideal strategy to provide, food, nutrition and income security to the people particularly in view of continuous increasing population and decreasing per capita land availability which would be merely 0.68 ha by 2020. In addition to contacting land resources, national problems like environmental degradation, climate change, thermal stress, water scarcity, groundwater contamination and entry of toxic substances into the food chain are some of the other challenges for the fruit industry. Under such situation, integration of annual crops with fruit trees seems to be a viable option as it would yield multiple outputs, ensure production and income generation in a sustainable manner. Natural resources (land, solar radiation, water, soil) as well as socio economic inputs (labour, credit, power, market infrastructure) could be efficiently utilised increasing the resilience of the system over time. Integrating annual/seasonal crops with perennial fruit trees/plantation crops approach has been widely recognized by native people, obviously to achieve sustainable production ensuring ecololgical stability by growing several species together. In the recent past, several innovations and new initiatives have been made both in research and development for improving production and productivity through diversification. This paper deals with the significant achievements made in this regard in terms of different fruit based cropping system which have the potential in different agro-climatic regions of the country, particularly the fragile ecosystems of the country.

Refuge behaviour from outdoor thermal environmental stress and seasonal differences of thermal sense in tropical urban climate

Thermal sensation affects body temperature regulation. As a starting point for behavioral body temperature regulation taken to improve from a poor thermal environment to a more pleasant environment, thermal sense of thermal environment stimulus is important. The poupose of this sutudy is to use the outdoor thermal environment evaluation index ETFe to quantify effects on thermal sensations of the human body of a tropical region climate with small annual temperature differences, and to examine seasonal differences in thermal sensation. It was found temperature preferences were lower in the winter season than in the dry season, and that a tolerance for higher temperatures in the dry season than in the winter season. It was found effects of seasonal differences of the thermal environment appear in quantitative changes in thermal sensations. It was found that effects of seasonal differences of the thermal environment do not greatly affect quantitative changes in thermal comfort.

Reliability-oriented environmental thermal stress analysis of fuses in power electronics

This paper investigates the thermo-mechanical stress experienced by axial lead fuses used in power electronics. Based on some experience, the approach used in this paper is pure thermal cycling, and the found failure mechanisms have been investigated through X-ray imaging. A two-step analysis, i.e. microscopic inspection and FEM thermo-mechanical simulation have been carried out based on the real geometry, including core and isolation materials, as well as the arc quenching one, which is typically quartz sand. The failure mechanism hypothesis of higher temperature variation at the end hole of the fuse element has been confirmed thanks to the analysis performed. Finally, the fatigue analysis is presented obtained by FEM-based fatigue tool.

Epigenetic Regulation of a Heat-Activated Retrotransposon in Cruciferous Vegetables

Transposable elements (TEs) are highly abundant in plant genomes. Environmental stress is one of the critical stimuli that activate TEs. We analyzed a heat-activated retrotransposon, named ONSEN, in cruciferous vegetables. Multiple copies of ONSEN-like elements (OLEs) were found in all of the cruciferous vegetables that were analyzed. The copy number of OLE was high in Brassica oleracea, which includes cabbage, cauliflower, broccoli, Brussels sprout, and kale. Phylogenic analysis demonstrated that some OLEs transposed after the allopolyploidization of parental Brassica species. Furthermore, we found that the high copy number of OLEs in B. oleracea appeared to induce transpositional silencing through epigenetic regulation, including DNA methylation. The results of this study would be relevant to the understanding of evolutionary adaptations to thermal environmental stress in different species.

Mission-profile-based stress analysis of bond-wires in SiC power modules

This paper proposes a novel mission-profile-based reliability analysis approach for stress on bond wires in Silicon Carbide (SiC) MOSFET power modules using statistics and thermo-mechanical FEM analysis. In the proposed approach, both the operational and environmental thermal stresses are taken into account. The approach uses a two-dimension statistical analysis of the operating conditions in a real one-year mission profile sampled at time frames 5min long. For every statistical bin corresponding to a given operating condition, the junction temperature evolution is estimated by a thermal network and the mechanical stress on bond wires is consequently extracted by finite-element simulations. In the final step, the considered mission profile is translated in a stress sequence to be used for Rainflow counting calculation and lifetime estimation.

Infrared thermography based studies on the effect of age on localized cold stress induced thermoregulation in human

Thermoregulatory control of blood flow plays an important role in maintaining the human body temperature and it provides physiological resistance against extreme environmental thermal stresses. To understand the role of age on thermal signals from veins and the thermoregulatory mechanism, the dynamic variation of the vein temperature on the hands of 17 human subjects, under a localized cold stress, was studied using infrared thermography. It was observed that the vein temperature of the stimulated hand initially decreased with time up to a time interval (called ‘inversion time’), which was attributed to the localized cutaneous vasoconstriction. Beyond inversion time, a rise in the vein temperature of the stimulated hand was observed. A shift in the inversion time to higher values was observed for the older subjects, which was attributed to the reduced efficiency and responsiveness of the cutaneous vasoconstriction mechanism in these subjects. Our studies indicated that the inversion time increased linearly with subject age with strong positive Pearson’s correlation coefficient of 0.94. It was also observed that the contralateral symmetry in vasoconstriction was much lower in older subjects than the younger subjects. The absolute difference between the left and right inversion time varied between 11–118s and 5–28s for the older and younger subjects, respectively. Our study clearly demonstrated that infrared thermography is one of the most effective experimental tool for studying dynamic variation in vein pixel temperature under localized thermal stresses.

Role of Acclimatization in Weather-Related Human Mortality During the Transition Seasons of Autumn and Spring in a Thermally Extreme Mid-Latitude Continental Climate.

Human mortality is closely related to natural climate-determined levels of thermal environmental stress and the resulting thermophysiological strain. Most climate-mortality research has focused on seasonal extremes during winter and summer when mortality is the highest, while relatively little attention has been paid to mortality during the transitional seasons of autumn and spring. The body acclimatizes to heat in the summer and cold in winter and readjusts through acclimatization during the transitions between the two during which time the body experiences the thermophysiological strain of readjustment. To better understand the influences of weather on mortality through the acclimatization process, the aim here is to examine the periods that link very cold and very warms seasons. The study uses the Acclimatization Thermal Strain Index (ATSI), which is a comparative measure of short-term thermophysiological impact on the body. ATSI centers on heat exchange with the body’s core via the respiratory system, which cannot be protected. The analysis is based on data for a major city in the climatic region of the Russian Far East characterized by very hot summers and extremely cold winters. The results show that although mortality peaks in winter (January) and is at its lowest in summer (August), there is not a smooth rise through autumn nor a smooth decline through spring. A secondary peak occurs in autumn (October) with a smaller jump in May. This suggests the acclimatization from warm-to-cold produces more thermophysiological strain than the transition from cold-to-warm. The study shows that ATSI is a useful metric for quantifying the extent to which biophysical adaptation plays a role in increased strain on the body during re-acclimatization and for this reason is a more appropriate climatic indictor than air temperature alone. The work gives useful bioclimatic information on risks involved in transitional seasons in regions characterized by climatic extremes. This could be handy in planning and managing health services to the public and measures that might be used to help mitigate impacts.

Hypothalamic temperature of rats subjected to treadmill running in a cold environment.

Different strategies for cooling the body prior to or during physical exercise have been shown to improve prolonged performance. Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies. Therefore, our first aim sought to measure the hypothalamic temperature (Thyp) of rats subjected to treadmill running in a cold environment. Moreover, evidence suggests that Thyp and abdominal temperature (Tabd) are regulated by different physiological mechanisms. Thus, this study also investigated the dynamics of exercise-induced changes in Thyp and Tabd at two ambient temperatures: 25°C (temperate environment) and 12°C (cold). Adult male Wistar rats were used in these experiments. The rats were implanted with a guide cannula in the hypothalamus and a temperature sensor in the abdominal cavity. After recovery from this surgery, the rats were familiarized with running on a treadmill and were then subjected to the two experimental trials: constant-speed running (20 m/min) at 12°C and 25°C. Both Thyp and Tabd increased during exercise at 25°C. In contrast, Thyp and Tabd remained unchanged during fatiguing exercise at 12°C. The temperature differential (i.e., Thyp - Tabd) increased during the initial min of running at 25°C and thereafter decreased toward pre-exercise values. Interestingly, external cooling prevented this early increase in the temperature differential from the 2nd to the 8th min of running. In addition, the time until volitional fatigue was higher during the constant exercise at 12°C compared with 25°C. Together, our results indicate that Thyp and Tabd are regulated by different mechanisms in running rats and that external cooling affected the relationship between both temperature indexes observed during exercise without environmental thermal stress. Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

Effect of severe environmental thermal stress on redox state in salmon

Fish are exposed to many kinds of environmental stressors and the chances of succumbing to infectious diseases may be increased a result. For example, an acute increase in temperature can induce numerous physiological changes in the body. In the present study, we examined the redox state in response to a severe acute stress resulting from heat shock in teleost coho salmon (Oncorhynchus kisutch). The plasma lipid peroxides levels in fish gradually increased after heat shock treatment. By 2.5 h post-heat stress, plasma glutathione (GSH) levels had decreased, but they had returned to basal levels by 17.5 h post-stress. Plasma superoxide dismutase activities in stressed fish were significantly increased compared with those in control fish at 17.5 h post-stress, but had returned to basal levels by 48 h post-stress. Expression levels of hepatic GSH and heat shock protein 70 gradually increased after heat shock treatment. These results concerning the changing patterns of multiple important redox-related biomarkers suggest that severe thermal stressors can affect the redox state and induce oxidative stress in ectothermal animals, such as fish, in vivo. Hence, manipulation of appropriate thermal treatment may possibly be useful to control fish fitness.

Season-Induced Changes in Bovine Sperm Motility Following a Freeze-Thaw Procedure

Decreased conception rate of dairy cows in the summer is mainly associated with the deleterious effects of environmental thermal stress on the female reproductive tract. Here, we suggest that decreased reproductive performance might be partially due to inferior-quality semen. Semen from five representative bulls was collected in summer (August to September) and winter (December to January) and evaluated with a computerized sperm-quality analyzer for bulls (SQA-Vb). No seasonal effect was found in fresh ejaculate, but sperm examined post-thawing showed lower velocity, motility and progressive motility (P<0.04) in summer vs. winter samples. Element concentrations in the seminal plasma, determined by inductively coupled plasma-atomic emission spectrometry, differed between seasons, with higher (P<0.01) concentration values of K, Mg, Na and S elements in winter vs. summer samples. Therefore, season-induced alterations in seminal plasma element concentration should be taken into account when using an extender for cryopreservation. Acrosome integrity was assessed by a triple-fluorescence test using Hoechst 33342, fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA) and propidium iodide. Acrosome reaction was examined by a one-step staining method using FITC-PSA. The proportion of sperm cells with a damaged acrosome post-thawing tended to be higher (P<0.07) in semen collected during the summer vs. winter. Such alterations suggest that seasonal reductions in sperm function might also be involved in the decreased conception rate of dairy cows in summer.

Using the product threshold model for estimating separately the effect of temperature on male and female fertility1

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.

Self-Pacing as a Protective Mechanism against the Effects of Heat Stress

Self-pacing or avoidance of physiological strain by adjustment of work rate may be an important protective behaviour for manual workers in severe thermal conditions. Data were gathered at a number of industrial sites in the United Arab Emirates to assess whether self-pacing takes place in these workers. Heart rate and aural temperature were monitored in 150 subjects for 12 h daily over 2 consecutive days. Environmental parameters were measured for quantification of heat stress by the thermal work limit. There was no evidence of an effect of variation in environmental thermal stress on either average working heart rate or aural temperature. These studies provide evidence that self-pacing is a protective response to working in heat which does not require a highly informed workforce; recognition of this should form part of a holistic approach to management of heat stress in hot climates.

The incidence of heat casualties in sprint triathlon: The tale of two Melbourne race events

Triathlon is a popular participation sport combining swimming, cycling and running into a single event. The Triathlon Australia medical policy advocates the use of wet bulb globe temperature as the criterion for altering race distance and an ambient temperature of 35 degrees C as a criterion for consideration of cancellation of an event, but there is little empirical evidence detailing the effectiveness of this policy. Nor has the impact of environmental thermal stress on triathletes in shorter duration events been determined. During an injury surveillance investigation of a triathlon race series over the 2006/2007 seasons, two events with similar environmental conditions were completed. One thousand eight hundred and eighty-four participants competed in event 1 (December 2006) and 2000 competed in event 2 (February 2007). Maximum dry bulb (DBT), minimum vapour pressure (VP) and minimum relative humidity (RH) for event 1 were 37 degrees C DBT, 0.56 kPa VP and 9% RH measured by the Bureau of Meteorology. Fifty-three participants presented for medical aid, 15 due to heat-related collapse. The conditions measured for event 2 were 33 degrees C DBT, 1.16 kPa VP and 24% RH and there were no heat illness presentations despite 38 individuals presenting for medical aid. These observations suggest that the risk of heat-related collapse is greatest when high-environmental temperatures occur early in the competitive season when participants may be inadequately prepared and have not yet acquired natural acclimatisation to heat. Any Triathlon Australia policy revision could place stronger emphasis on the use of ambient temperature as a limiting criterion for race organisers.

Expression of the GM-CSF receptor in ovine spermatozoa: GM-CSF effect on sperm viability and motility of sperm subpopulations after the freezing–thawing process

The granulocyte–macrophage colony stimulating factor (GM-CSF) is a pleiotropic cytokine capable of stimulating proliferation, maturation and function of haematopoietic cells. Receptors for this cytokine are composed of two subunits, alpha and beta, and are expressed in myeloid progenitors and mature mononuclear phagocytes, monocytes, eosinophils and neutrophils, as well as in other non-haematopoietic cells. We have previously demonstrated that bull spermatozoa express functional GM-CSF receptors that signal for increased glucose and vitamin-C uptake and enhance several parameters of sperm motility in the presence of glucose or fructose substrates. In this study, we have analyzed the expression of GM-CSF receptors in ovine spermatozoa and studied the effect of GM-CSF on sperm viability and motility after the freezing–thawing process. Immunolocalization and immunoblotting analyses demonstrated that ovine spermatozoa (Xisqueta race) expressed GM-CSF receptors. In addition, GM-CSF partially counteracted the impairing action of freezing/thawing on the percentage of total motility, as well as on the specific motility patterns of each of the separate, motile sperm subpopulations of ram ejaculates subjected to this protocol. These results suggest that GM-CSF can play a role in the resistance of ram spermatozoa to environmental thermal stress.

Hormonal responses to opioid receptor blockade: during rest and exercise in cold and hot environments

Opioid receptors appear to modulate a variety of physiological and metabolic homeostatic responses to stressors such as exercise and thermally extreme environments. To more accurately determine the role of the naloxone (NAL) sensitive opioid receptor system during rest and exercise, subjects were subjected to concomitant environmental thermal stress. Fifteen untrained men rested or performed low intensity (60% VO2peak) or high intensity (80% VO2peak) exercise on a cycle ergometer for 60 min in an environmental chamber during cold (0 degrees C) hot (35 degrees C) air exposure while receiving an infusion of normal saline (SAL) or NAL (0.1 mg kg(-1)). Plasma adrenocorticotropin hormone (ACTH), immunoreactive beta-endorphin (IBE), cortisol and growth hormone were measured at baseline and every 15 min while in the chamber. Time to exhaustion was significantly reduced during high intensity exercise in the heat (P<0.0001). NAL significantly (P=0.0004) reduced the time to exhaustion (38.3+/-2.1 min) during high intensity exercise in the heat compared to SAL (49.4+/-2.1 min). ACTH and IBE increased during hot conditions and cold attenuated this response. Plasma concentrations of IBE, ACTH, and growth hormone increased significantly with NAL during high intensity exercise in the heat compared to SAL. Cold attenuated the response of ACTH, IBE and cortisol to NAL. NAL administration exaggerates plasma hormone concentration during high intensity exercise in the heat, but not cold. These results support a regulatory effect of the opioid receptor system on physiological responses during exercise in thermally stressful environments. Future research should be directed to more clearly defining the effect of environmental temperature on the mechanism of hypothalamic-pituitary-adrenal hormonal release during exercise and hot environmental temperatures.

Placental angiogenesis in sheep models of compromised pregnancy.

Because the placenta is the organ that transports nutrients, respiratory gases and wastes between the maternal and fetal systems, development of its vascular beds is essential to normal placental function, and thus in supporting normal fetal growth. Compromised fetal growth and development have adverse health consequences during the neonatal period and throughout adult life. To establish the role of placental angiogenesis in compromised pregnancies, we first evaluated the pattern of placental angiogenesis and expression of angiogenic factors throughout normal pregnancy. In addition, we and others have established a variety of sheep models to evaluate the effects on fetal growth of various factors including maternal nutrient excess or deprivation and specific nutrients, maternal age, maternal and fetal genotype, increased numbers of fetuses, environmental thermal stress, and high altitude (hypobaric) conditions. Although placental angiogenesis is altered in each of these models in which fetal growth is adversely affected, the specific effect on placental angiogenesis depends on the type of 'stress' to which the pregnancy is subjected, and also differs between the fetal and maternal systems and between genotypes. We believe that the models of compromised pregnancy and the methods described in this review will enable us to develop a much better understanding of the mechanisms responsible for alterations in placental vascular development.

Insect population differentiation in response to enviromental thermal stress

Numerous studies reported the adaptation strategies adopted by ecthotherms to survive under environmental thermal stress. Geographic and seasonal variations in the thermal stress tolerance, which is closely associated with species' climatic adaptation and allopatric speciation, have been extensively investigated in insects. The variation patterns suggest directional selection for species' adaptive straits, and are used to predict the origin, distribution and dynamics of insect populations. These studies are becoming more and more important in the context of global warming. This paper discusses the process of adaptation to environmental thermal stress and the mechanisms underlying the differentiation in related adaptive straits of insect populations.

Heat storage rate and acute fatigue in rats.

Thermal environmental stress can anticipate acute fatigue during exercise at a fixed intensity (%VO2max). Controversy exists about whether this anticipation is caused by the absolute internal temperature (Tint, degrees C), by the heat storage rate (HSR, cal/min) or by both mechanisms. The aim of the present study was to study acute fatigue (total exercise time, TET) during thermal stress by determining Tint and HSR from abdominal temperature. Thermal environmental stress was controlled in an environmental chamber and determined as wet bulb globe temperature ( degrees C), with three environmental temperatures being studied: cold (18 degrees C), thermoneutral (23.1 degrees C) or hot (29.4 degrees C). Six untrained male Wistar rats weighing 260-360 g were used. The animals were submitted to exercise at the same time of day in the three environments and at two treadmill velocities (21 and 24 m/min) until exhaustion. After implantation of a temperature sensor and treadmill adaptation, the animals were submitted to a Latin square experimental design using a 2 x 3 factorial scheme (velocity and environment), with the level of significance set at P<0.05. The results showed that the higher the velocity and the ambient temperature, the lower was the TET, with these two factors being independent. This result indicated that fatigue was independently affected by both the increase in exercise intensity and the thermal environmental stress. Fatigue developed at different Tint and HSR showed the best inverse relationship with TET. We conclude that HSR was the main anticipating factor of fatigue.

Evaluation of hydration status, thermal stress and energy cost during volleyball training sessions

A sudorese (Ts) é o principal mecanismo dissipador de calor durante o exercício em ambientes quentes. Recomenda-se a ingestão de água (H2O) suficiente para repor a perda hídrica pela sudorese e evitar os efeitos adversos da desidratação no rendimento esportivo. No entanto, as recomendações não quantificam o custo calórico (CAL) e os fatores ambientais (IBUTG) em situações esportivas reais. Este estudo mediu a capacidade aeróbica ( V 0 2PiCo)* a H20, o CAL, a freqüência cardíaca (FC), a Ts, o fluxo urinário (Vu), a coloração (Ucor) e a gravidade específica da urina (Du) e o IBUTG durante sessões de treinamento (Streino) de uma equipe juvenil (média de 18 anos) masculina de voleibol. O CAL de uma Strein0= 650 ± 99 kcal.h (55% do V 0 2Pico)&gt; a FC média = 133 ± 9 bat.min'1 A Ts média = 15 ± 4 ml.min'1 (1,5 litros, total), com uma ingestão de água = 8,9 ± 3,7 ml.min"1 (0,9 litros total). O Vu = 0,8 ± 0,4 ml.min'1 (0,08 litros total), e a Ucor = “2” no início e “3” no final. A Du inicial = 1024 ± 4 e a final = 1026 ± 6. O IBUTG variou entre termoneutro e moderadamente quente (20,1 a 24,6 °C). Concluiu-se que, as Streino foram de intensidade moderada e o ambiente classificado como risco moderado para hipertermia. Os atletas terminaram as sessões com -0,9% da massa corporal e eu-hidratados de acordo com a gravidade específica e coloração da urina.

Racial Differences in Hemodynamic Responses to Environmental Thermal Stress Among Adolescents

Previous studies by our laboratory and others have shown that blood pressure (BP) responses to many short-term laboratory stressors are greater in black than in white children. We sought to determine the cardiac and vascular contributions to these differences in BP reactivity and whether racial differences in vascular reactivity involve excessive vasoconstriction or deficient vasodilation. We evaluated BP, heart rate, and impedance cardiographic measures of preejection period (PEP) and total peripheral resistance (TPR) in healthy black (n=76) and white (n=60) adolescents (mean age, 14.8 years) during passive exposure to a vasoconstrictive cold chamber (8 degrees C to 10 degrees C) and a vasodilatory heat chamber (40 degrees C to 42 degrees C). Results indicated greater decreases in PEP and increases in TPR in blacks than whites during cold exposure (P<0.05) but no group differences during heat exposure. Covariance analyses indicated that the racial differences during cold exposure probably reflected greater beta-adrenergic cardiac reactivity and alpha-adrenergic vasoconstrictive reactivity in blacks than whites. Blacks and whites exhibited comparable myocardial and vasodilatory responses to heat stress, but blacks exhibited heightened myocardial and vasoconstrictive reactivity to cold stress. These results suggest that the locus of racial differences in vascular reactivity involves vasoconstrictive rather than vasodilatory function. The pattern of racial differences during cold stress raises the possibility that both myocardial and vasoconstrictive mechanisms may contribute to the increased risk of hypertension in blacks.