Local Heat Stress Research Articles

Antioxidant Capacity of Thyme (Thymus vulgaris) Essential Oil and Its Effect on In Vivo Fertility of Rams Subjected to Testicle Heat Stress.

The detrimental effects of hyperthermia on the testes and the protective effect of thyme essential oil against testicular damage induced by this stress in rams were studied. Twenty-four rams of the Barbarine breed with an average weight of 62.5 ± 0.3 kg and an average age of 24 ± 0.6 months. The experiment consisted of inducing localized heat stress on the first group of rams by applying heat bags to both testicles of six rams (G s). The second group underwent the same heat stress on the testes but received orally 100 µL/day/animal of thyme essential oil (G s-he). A positive control did not undergo stress but received thyme essential oil (G he) with the same doses as the (G s-he) group, and the negative control did not undergo either stress or receive the essential oil of thyme (G c). One hundred twenty-eight adult ewes of the same breed divided into four groups of 32 ewes were used to study the effect of different treatments on the in vivo ram's fertility. Ewes are synchronized and we have applied natural mating with oestrus control, the reproduction balance sheet is calculated after lambing. The results showed that tests of heat stress (HS) negatively affect semen quality but did not cause infertility. However, neither tests for heat stress nor treatment with thyme EO significantly affected the haematological profile. The study of the effect of heat stress on the testes on fertility in vivo showed a drop in the number of females who were fertilized at the first oestrus and consequently a drop in fertility. However, the rams that suffered the same stress but were treated with EO thymus recorded an improvement in these parameters.

Future change of humid heat extremes and population exposure in Turkey

AbstractGlobal climate projections show that humid heat extremes will expand toward the higher latitudes, making the midlatitudes hotspots for these extremes. Therefore, a thorough explanation of their regional characteristics becomes crucial, given that the changes in these extremes can potentially render a large proportion of the global population at risk. Here, we perform the first analysis of historical and projected changes in the intensity and frequency of humid heat extremes and quantify the population exposure to these extremes in Turkey, using long‐term simulations from the non‐hydrostatic mesoscale model of Consortium for Small‐scale Modeling (COSMO‐CLM) under the RCP8.5 emission scenario. We portray not only the nationwide changes in the humid heat extremes and population exposure but also their regional aspects by exploiting the K‐means clustering algorithm. Our results suggest significant future increases in the intensity and frequency of these extremes over a wide geographical area, which includes the surroundings of Adana, Antalya, Izmir, Sakarya, Ordu and Diyarbakir, most of which are coastal locations. Over most of these regions, severe humid heat stress is expected to last nearly a month every year, with almost 56% of the land area is projected to experience local historical upper tail heat stress conditions for at least an additional 10 consecutive hours. Further, we explicate a significant rise in the number of people exposed to severe humid heat stress, concentrated along most coastal regions, by as much as 1.6 million person‐days. More than 20% of Turkey's population may confront severe humid heat stress for at least 1 h, with that percentage falling to 4.15% for at least five consecutive hours, which indicates that people will not only endure more intense humid heat stress but also be exposed to these conditions consecutively over a period of many hours.

Role of cholinergic agonists & hyperthermia on regional skin barriers: exposure science implications

Regional differences in skin barrier properties are common in mammals, as some exterior surfaces are fairly impermeable and others are leakier. Neural-induced changes in skin physiology and temperature have the potential to alter skin barrier properties, but the circumstances and mechanisms are unclear. We hypothesized that increasing methylcholine (MCh) or acetylcholine (ACh) concentration would decrease the transepithelial resistance (an index of the skin barrier) measured across mouse paw pad skin jacketed at neutral skin (32°C) or internal (37°C) temperature. Additionally, we hypothesized that paw pads would have lower transepithelial resistance compared to mouse tail skin, and subjecting samples to 40°C (local cutaneous heat stress) would lower transepithelial resistance compared to paw pad skin tested at 32°C. 30 C57BL/6 mouse rear paw pads (containing sweat glands) and 7 mouse tail skins (no sweat glands) were dissected and mounted into a vertical Ussing chamber filled with Kreb’s bicarbonate buffer, gassed with 95% O₂ & 5% CO₂, and encased in a temperature jacket. Transepithelial resistance utilized a current clamp and was measured with Ag-AgCl2 electrodes placed in both epidermal and hypodermal baths during hypodermal-side-only cholinergic dosing (5 min/dose). ACh (0, 0.0833, 0.1666, 0.2499, 0.4166, 0.58323, and 0.74989 M) significantly decreased transepithelial resistance in paw pads clamped at 37°C in a dose-dependent manner. Tail skin had significantly higher transepithelial resistance than paw pad skin. However, transepithelial resistance decreased significantly with MCh (same dosing as ACh) at both skin sites. Increasing jacket temperature to 40°C did not alter the magnitude of decrease in transepithelial resistance to MCh in paw pads compared to 32°C. Transepithelial resistance observations were similar when data were expressed as absolute or relative changes to baseline. Increased ion movement in murine skin (signifying a leakier epithelium) occurred with cholinergic stimulation but not with local hyperthermia, suggesting that neural influences can suffciently affect skin function to directly alter regional skin barriers. P30ES026529 with additional support from TL1TR001997 and R25ES027684. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Climate walking and linear mixed model statistics for the seasonal outdoor thermophysiological comfort assessment in Lisbon

To measure urban outdoor pedestrian thermophysiological comfort mobile roving missions were conducted in all seasons of the year during the day and at night. Six routes were chosen, representing areas of the city with varying urban morphological layouts. The thermal comfort conditions were analysed using the Local Climate Zone spatial scale. This enabled the identification of typologies of areas where pedestrians might feel (un)comfortable. To achieve the proposed objectives, quantitative and qualitative analysis were run, namely a Linear Mixed-Effect Model. This model was useful to understand the thermal behaviour of the roved areas by comparison to a reference area. The city was found to be generally cooler, except at night when it can have a 44% increased UTCI. Most collected values throughout the year had ‘no thermal stress’, except in the summer when ‘moderate’ and ‘strong heat stress’ was predominant. Compact and large low rise urban areas were found to be the most uncomfortable. Significant amplitudes were found in some LCZs, reaching as high as 7 °C in some scenarios. Sparsely wooded areas exhibited higher values in all seasons and at night, except in the summer. This showed that for a local heat stress analysis a higher resolution scale is needed.

Locally applied heat stress during exercise training may promote adaptations to mitochondrial enzyme activities in skeletal muscle

There is some evidence for temperature-dependent stimulation of mitochondrial biogenesis; however, the role of elevated muscle temperature during exercise in mitochondrial adaptation to training has not been studied in humans in vivo. The purpose of this study was to determine the role of elevating muscle temperature during exercise in temperate conditions through the application of mild, local heat stress on mitochondrial adaptations to endurance training. Eight endurance-trained males undertook 3 weeks of supervised cycling training, during which mild (~ 40 °C) heat stress was applied locally to the upper-leg musculature of one leg during all training sessions (HEAT), with the contralateral leg serving as the non-heated, exercising control (CON). Vastus lateralis microbiopsies were obtained from both legs before and after the training period. Training-induced increases in complex I (fold-change, 1.24 ± 0.33 vs. 1.01 ± 0.49, P = 0.029) and II (fold-change, 1.24 ± 0.33 vs. 1.01 ± 0.49, P = 0.029) activities were significantly larger in HEAT than CON. No significant effects of training, or interactions between local heat stress application and training, were observed for complex I–V or HSP70 protein expressions. Our data provides partial evidence to support the hypothesis that elevating local muscle temperature during exercise augments training-induced adaptations to mitochondrial enzyme activity.

Investigating ferro-liquid flow in a rotating and stretching deformed cone

The motion of a hydro-ferro-liquid in a rotating and stretching deformed cone is investigated in this study. We use the similarity variable for velocity and temperature distribution to simplify and dimensionalize the governing equations of ferrohydrodynamic flow. The finite element technique in COMSOL Multiphysics is employed to numerically work out the reduced similarity equations for velocity and temperature. Magnetic viscosity is generated in the flow as a result of the cone rotating under the influence of the magnetic field. We examine the velocity and temperature fields for various values of ferromagnetic interaction numbers, cone deformation rate, and Eckert number. Furthermore, we look at how these variables affect local heat transfer and stress on the cone’s surface. The current findings may be applied realistically to enhance the spinning shaft’s sealing. Controlling the heat in electronic devices can also benefit from the current behavior of ferrohydrodynamic flow.

Aging is associated with impaired triggering of TRPV3-mediated cutaneous vasodilation: a crucial process for local heat exposure.

Sensing temperature is vitally important to adapt our body to environmental changes. Local warm detection is required to initiate regulation of cutaneous blood flow, which is part of the peripheral thermoregulatory mechanisms, and thus avoid damage to surrounding tissues. The mechanisms mediating cutaneous vasodilation during local heat stress are impaired with aging. However, the impact of aging on the ability of the skin to detect subtle thermal changes is unknown. Among heat-activated cation channels, transient receptor potential vanilloid 3 (TRPV3) is a thermo-sensor predominantly expressed on keratinocytes and involved in local vascular thermoregulatory mechanisms of the skin in young mice. In the present study, using a murine in vivo model of local heat exposure of the skin, we showed that heat-induced vasodilation was reduced in old mice associated with reduced expression of TRPV3 channels. We also found a decrease in expression and activity of TRPV3 channel, as well as reduced TRPV3-dependent adenosine tri-phosphate release in human primary keratinocytes from old donors. This study shows that aging alters the epidermal TRPV3 channels, which might delay the detection of changes in skin temperature, thereby limiting the mechanisms triggered for local vascular thermoregulation in the old skin.

Towards local sustainability: A case study to evaluate outdoor urban spaces in Baghdad using physiological equivalent temperature index

Improving environmental quality to promote outdoor activities, which also aims at providing social benefits, is an extensively researched field of study. In this study, a sustainable urban solution is evaluated as a prototype using the physiological equivalent temperature (PET) index. The literature demonstrated the local deficit of increasing social qualities through the development of a prototype that performs as a mitigation strategy to improve the urban thermal environment. To fill this gap, the aim of this experimental study is to create a neutral outdoor thermal comfort area that is suitable for social gatherings while minimizing local heat stress. We investigated six selected sites using ENVI-met 4.4 software, and we validated them with the observed data by two types of validation metrics. The sites were located near the Tigris River in Baghdad. The conditions at the sites were analyzed between 8:00 and 24:00. The simulation findings revealed the possibility of achieving thermal comfort during most of the working hours. A reduction in thermal stress by ∼18.4 °C was observed with a drop of 36.4% of PET results. The urban solution contributed to a decrease in the temperature by four degrees from the existing situation, which promotes a sustainable outdoor urban area. In hot climates, any outdoor activity between 12:00–16:00 is generally discouraged, whereas (8:00–10:00 & 18:00–00:00) hours are suitable for social interaction. However, multistoried buildings with sufficient orientation and shading could be ideal for achieving local sustainability, whereas the river's presence and its low albedo significantly raise the mean radiant temperature (MRT) by ∼7–8 °C, which proves its importance in heat reduction. The hybrid fabric altered the traditional courtyard's climatic characteristics, exacerbating its heat stress. The largest dip in PET in the courtyard area occurred at 17:00, with a drop of 13.6 °C, which was smaller than the rest of the areas. The additional sustainable prototype had a significant impact on influencing the microclimate and played a decisive role in determining thermal comfort. The prototype's high- albedo materials and dense, selective local trees have a direct effect on reducing the local air temperature and MRT. This, together with the physical characteristics of the surrounding area, helped to minimize PET outcomes and improve the local thermal environment. The findings of this study serve urban designers by verifying the success of the modelled design prototype spatially and environmentally.

Regional Differences in Human Skin Responses to Receptor Agonists: Implications for Differing Facial vs. Forearm Innervation

There is not yet consensus on the precise differences between non-glabrous and facial skin characteristics. Our lab identified similar responses to local heat stress in forearm and facial skin, while others identified differing responses to autonomic stressors within facial regions. Anatomical differences, such as the thinner nature of facial skin and specifically its thinner stratum corneum, may also impact facial autonomic responses. Considering this layer is a protective barrier, facial skin may be more sensitive to perturbations like drug administration. While non-glabrous skin is innervated by spinal nerves, facial skin is innervated by cranial nerves. Because of these anatomical and physiological differences between non-glabrous and facial skin, it is possible that their differing neural and receptor characteristics impact a key autonomic end-organ response: cutaneous blood flow. In this pilot experiment, we investigated possible regional differences between the forehead and forearm in response to adrenergic and cholinergic agonists. We hypothesized that drugs targeting adrenergic (phenylephrine, clonidine, and isoproterenol) and cholinergic (acetylcholine) cutaneous receptors would elicit similar vasomotor effects in both locations. One female subject underwent forearm and forehead iontophoresis of each agonist using adaptations of published protocols, as well as a control protocol using deionized water (vehicle) alone. We recorded blood flow via laser-Doppler flowmetry (Moor Instruments) and beat-by-beat arterial blood pressure via finger photoplethysmography (ADInstruments). We calculated baseline cutaneous vascular conductance (CVC) and plateau 43°C CVC to determine the change in skin blood flow resulting from drug administration. Our results indicate that while phenylephrine administration caused vasodilation, opposing our hypothesis, administration of all other drugs caused responses in agreement with our expectations. Thus, these pilot data suggest that facial and non-glabrous skin may respond similarly to adrenergic or cholinergic agonists. These findings imply a potential use for topical dermatological drug treatments utilized on the trunk/extremities to benefit cutaneous facial diseases.

A Multi-Segmented Human Bioheat Model for Asymmetric High Temperature Environments.

In workplaces such as steel, power grids, and construction, firefighters and other workers often encounter non-uniform high-temperature environments, which significantly increase the risk of local heat stress and local heat discomfort for the workers. In this paper, a multi-segment human bioheat model is developed to predict the human thermal response in asymmetric high-temperature environments by considering the sensitivity of the modeling to angular changes in skin temperature and the effects of high temperatures on human thermoregulatory and physiological responses simultaneously. The extended model for asymmetric high-temperature environments is validated with the current model results and experimental data. The result shows that the extended model predicts the human skin temperature more accurately. Under non-uniform high-temperature conditions, the local skin temperature predictions are highly consistent with the experimental data, with a maximum difference of 2 °C. In summary, the proposed model can accurately predict the temperature of the human core and skin layers. It has the potential to estimate human physiological and thermoregulatory responses under uniform and non-uniform high-temperature environments, providing technical support for local heat stress and local thermal discomfort protection.

Visualising and quantifying microvascular structure and function in patients with heart failure using optical coherence tomography.

Heart failure (HF) is characterised by abnormal conduit and resistance artery function in humans. Microvascular function in HF is less well characterised, due in part to the lack of tools to image these vessels in vivo. The skin microvasculature is a surrogate for systemic microvascular function and health and plays a key role in thermoregulation, which is dysfunctional in HF. We deployed a novel optical coherence tomography (OCT) technique to visualise and quantify microvascular structure and function in 10 subjects with HF and 10 age‐ and sex‐matched controls. OCT images were obtained from the ventral aspect of the forearm, at baseline (33°C) and after 30 min of localised skin heating. At rest, OCT‐derived microvascular density (20.3 ± 8.7%, P = 0.004), diameter (35.1 ± 6.0 μm, P = 0.006) and blood flow (82.9 ± 41.1 pl/s, P = 0.021) were significantly lower in HF than CON (27.2 ± 8.0%, 40.4 ± 5.8 μm, 110.8 ± 41.9 pl/s), whilst blood speed was not significantly lower (74.3 ± 11.0 μm/s vs. 81.3 ± 9.9 μm/s, P = 0.069). After local heating, the OCT‐based density, diameter, blood speed and blood flow of HF patients were similar (all P > 0.05) to CON. Although abnormalities exist at rest which may reflect microvascular disease status, patients with HF retain the capacity to dilate cutaneous microvessels in response to localised heat stress. This is a novel in vivo human observation of microvascular dysfunction in HF, illustrating the feasibility of OCT to directly visualise and quantify microvascular responses to physiological stimuli in vivo. Key points Microvessels in the skin are critical to human thermoregulation, which is compromised in participants with heart failure (HF).We have developed a powerful new non‐invasive optical coherence tomography (OCT)‐based approach for the study of microvascular structure and function in vivo.Our approach enabled us to observe and quantify abnormal resting microvascular function in participants with HF.Patients with HF were able to dilate skin microvessels in response to local heat stress, arguing against an underlying structural abnormality. This suggests that microvascular functional regulation is the primary abnormality in HF.OCT can be used to directly visualise and quantify microvascular responses to physiological stimuli in vivo.

Albedo on cropland: Field-scale effects of current agricultural practices in Northern Europe

Agricultural land use and management affect land surface albedo and thus the climate. Increasing the albedo of cropland could enhance reflection of solar radiation, counteracting the radiative forcing (RF) of greenhouse gases (GHGs) and local warming. However, knowledge is lacking on how agricultural practices affect albedo under local conditions, and on the benefits of individual practices. In this study, field measurements were made in 15 paired plots at a site in Northern Europe to determine albedo, net shortwave irradiance and RF impacts under various common crops, cultivation intensities and tillage practices. Field data for 2019-2020 were compared with satellite-based albedo for the surrounding region in 2010-2020. At regional level, different combinations of soil type, yearly weather and agricultural practices led to great variability in the albedo of individual crops, despite similar pedo-climatic conditions. At field level within years, albedo differences were determined mainly by crop type, species-specific phenology and post-harvest management. Annual albedo was higher with perennial ley (0.20-0.22) and winter-sown crops (0.18-0.22) than with spring-sown crops (0.16-0.18) and bare soil (0.13). Barley had the highest albedo among winter and spring cereals. In summer, when increased albedo could alleviate local heat stress, oats reduced net shortwave irradiance at the surface by 0.8-5.8 Wm−2 compared with other cereals, ley, peas or rapeseed. Delayed or reduced tillage gave high local cooling potential (up to -13.6 Wm−2) in late summer. Potential benefits for global mean climate as GWP100 per hectare and year reached -980 kg CO2e for avoiding black fallow, -578 kg CO2e for growing a winter-sown variety and -288 kg CO2e for delayed tillage. Thus realistic albedo increases on cropland could have important effects on local temperatures and offset a substantial proportion of the RF deriving from field-scale GHG emissions on short time-scales.

Recent changes in heatwaves and maximum temperatures over a complex terrain in the Himalayas

The temperature response to anthropogenic global warming and forest cover changes is dependent on regional climatic characteristics. It is challenging to segregate the impacts of the two anthropogenic changes on local temperatures and heatwaves over complex mountainous regions. Here we present estimates of regional and local heat stress responses to the recent global climate change and local forest cover loss in complex terrain in the Himalayas using a satellite-based high-resolution land-surface temperature dataset. We find large-scale decreasing trends in the observed frequency of heatwaves and heat days, and localized increases in urbanized and high-elevation regions. Our results show large-scale significant decreasing trends in annual maximum and mean surface temperatures over the period 2003–2019. In locations that have witnessed large-scale forest losses, the declines in the surface temperatures were steeper compared to no-loss regions.We develop a regional multiple linear regression model to estimate the regional and local temperature responses to global climatic change and to segregate them from the response to forest cover losses. Our model estimates a regional decrease of about 2.0 °C in annual maximum temperature over the recent 2003–2019 period, which is locally modulated by the extent of urbanization, forest cover, and elevation. At the locations of intense deforestation, our model successfully predicts a steeper decrease in maximum surface temperature, and estimates the temperature response due to forest loss, after controlling for elevation and initial forest cover. The local cooling effect due to deforestation was reaffirmed by comparing the regions with contrasting forest cover losses. The results suggest that forest clearing amplifies the anthropogenic climate change over the region.

Assessing local heat stress and air quality with the use of remote sensing and pedestrian perception in urban microclimate simulations

Cities are increasingly confronted with multiple environmental and climatic stressors. Especially during heatwaves, street canyons are both producers and sufferers of air pollution and urban heat island (UHI) effects, with severe risks on public health. To better design mitigation measures, it is important to consider both the microclimate behaviors as well as the perceptions of the local population. Therefore, this study examined pedestrian perceptions and microclimate modelings to understand outdoor thermal comfort conditions and air pollution dispersion in the case study neighborhood of Dortmund Marten, Germany. A field survey with measurement points at two street canyons for climatic variables and questionnaires on subjective thermal comfort and air pollution was conducted on a hot day during the heatwave period in August 2020. As a cost-effective method for modeling input generation, we extracted spatial and spectral data like albedo, roof materials and tree locations out of remote sensing imageries. Finally, we compared the modeling results of the physiological equivalent temperature (PET) index, particulate matter concentrations and air temperatures with empirical field measurement data and the questionnaire responses. Results indicate that during hot summer days with light winds from the east, the north-south orientated street canyon with tree arrangements tends to act as a tunnel for particulate matter accumulation. Coincidently, pedestrians show less thermal discomfort than calculated PET values in that particular area during morning and daytime, which underlines the dichotomy of such places. On the other hand, the low rise east-west orientated street canyon shows higher PET votes than predicted by the model. However, particulate matter concentrations were considerably underestimated by the model, while air temperature predictions provided meaningful results. The proposed workflow shows the potential to accelerate future preparations of input data for microclimate modelings, while the results can enhance wind-sensitive planning procedures and heat stress resilience in mid-latitude urban neighborhoods.

Spatial correlation length of summer extreme heat stress over eastern China

AbstractThis study attempts to measure the spatial correlation length (SCL) of summer extreme heat stress in any location by using a characterized scale identification method. Daily datasets of multiple meteorological variables from 2,134 observation stations over eastern China during 1961–2010 were used. Three types of heat indexes (a total of seven indexes) were applied to characterize the heat stress. The first type used a single variable, that is, daily maximum temperature (Tmax) or daily minimum temperature (Tmin), while the second used mean temperature (T) and relative humidity, and the third used T, vapour pressure, and 10‐m wind speed. A 90th percentile of the climatology of local heat stress was applied to identify hot days. The SCLs of heat stress were analysed in three regions: North China (NC), the Yangtze River Valley (YRV), and South China (SC). Results showed that the trend changes in heat stress had obvious temporal and geographical characteristics, especially in NC and YRV. Generally, the SCLs of heat stress in NC were the largest, reaching more than 440 km for Tmax, with YRV second, about 350 km, and SC the smallest, only about 185 km. This phenomenon could be found for almost all indexes. Moreover, the SCLs of the first two types of heat indexes (except Tmin) for the three regions were greater than that of the third one, particularly in NC and YRV, which was related to inconsistent changes in the variables used and the primary role of which one characterized the heat stress. The spatial distributions of high SCLs for all indexes were in line with that of the major urban agglomeration in eastern China. The SCL of heat stress for a location was related not only to the changes themselves, but also to the surroundings, involving the number and spatial distribution of hot days.

Seminal Plasma Analysis of Oxidative Stress in Different Genitourinary Topographical Regions Involved in Reproductive Tract Disorders Associated with Genital Heat Stress.

The pathophysiological mechanisms responsible for male subfertility/infertility caused by or complicated by genital heat stress remains unclear in many respects. Because seminal plasma creates the environment for the proper functioning of spermatozoa, in this study, we verified the associations among standard spermiograms, seminal biochemical parameters (neutral alpha-glucosidase, fructose, and citric acid) and oxidative stress markers (total antioxidant capacity, catalase activity, superoxide dismutase activity, and malondialdehyde concentration) in distinct entities associated with male infertility with and without long-time exposure to local hyperthermia. We demonstrated that men exposed to prolonged environmental or clinically recognized local heat stress in adulthood may suffer from dysregulation of seminal antioxidant components, which can be directly associated with epididymal and prostate function. The comparative analysis of the studied parameters showed numerous correlations among all biochemical parameters (particularly neutral alpha-glucosidase) with low standard semen quality in almost all the investigated infertile groups. In light of the data obtained in this originally designed study, we conclude that more attention should be paid to the epididymis and accessory gland function in subfertile and infertile men exposed to genital heat stress, especially in the context of novel treatment algorithms (targeted therapies).

Impact of repeated local heat stress on skeletal muscle structure and function in humans

IntroductionShort‐term exposure to heat stress has been shown to enhance muscle strength and elicit mitochondrial adaptations in human skeletal muscle. We recently documented that exposure to five sessions of heat therapy (HT) accelerates the recovery of fatigue resistance following exercise‐induced muscle damage in humans. However, the long‐term impact of repeated exposure to local heat stress on contractile function and skeletal muscle structure remains unknown. The purpose of the present study was to examine the effects of 8 weeks of daily treatment with local HT on muscle strength, fatigability, fiber size and mitochondrial content in humans.MethodsTwelve healthy young adults (23.6±1.4 years, BMI 24.9±0.9 kg/m2) had one randomly selected thigh treated with daily HT for 8 consecutive weeks while the opposite thigh served as a control. A water‐circulating garment perfused with water at ~52ºC was used to apply HT for 90 min daily. Knee extensor strength (single peak torque during 3 repetition maximums at 180°/s and 60°/s) and fatigue resistance (total work during 40 repetition maximums at 180°/s) were assessed using isokinetic dynamometry before and after 4 and 8 weeks of treatment. Biopsies were obtained from the vastus lateralis muscle for the determination of myofiber cross‐sectional area and maximal citrate synthase activity.ResultsTreatment with HT elicited an increase in thigh skin temperature (39.8±0.1ºC), while skin temperature remained at baseline levels in the control thigh (32.4± 0.1ºC). A significant treatment effect was observed for the changes from baseline in peak isokinetic torque at 180º/s (p=0.04). On average, the changes in peak isokinetic torque from baseline for HT were ~2 fold higher than control at week 4 (Control: 4.1±3.7 Nm vs. HT: 9±4.6 Nm) and ~4 fold higher at week 8 (Control: 1.7±2.7 Nm vs. HT: 7.7±2.9 Nm). There were no differences between treatments for peak isokinetic torque at 60º/s, myofiber cross‐sectional area and citrate synthase activity.ConclusionThese results indicate that daily exposure to HT for 8 weeks enhances muscle strength in humans. Local HT may be a practical therapeutic approach to improve muscle function in individuals with limited mobility and skeletal muscle weakness.Support or Funding InformationSupport: American College of Sports Medicine Research EndowmentThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Differences in serum IL-6 response after 1 °C rise in core body temperature in individuals with spinal cord injury and cervical spinal cord injury during local heat stress

Objectives: Passive rise in core body temperature achieved by head-out hot water immersion (HHWI) results in acute increases in serum interleukin (IL)-6 but no change in plasma adrenaline in patients with cervical spinal cord injury (CSCI). The purpose of the present study was to determine the mechanism of heat stress-induced increase in serum IL-6.Setting: A cross-sectional study.Methods: The study subjects were nine with CSCI, ten with thoracic and lumbar spinal cord injury (TLSCI) and eight able-bodied (AB) subjects. Time since injury was 16.1 ± 3.4 years in TLSCI and 16.4 ± 4.1 years in CSCI. Subjects were subjected to lower-body heat stress (LBH) by wearing a hot water-perfused suit until 1 °C increase in core temperature. The levels of serum IL-6, plasma adrenaline, tumour necrosis factor (TNF)-α, C-reactive protein (CRP), and counts of blood cells were measured at normothermia and after LBH.Results: Serum IL-6 concentrations increased significantly immediately after LBH in all the three groups. ΔIL-6% was lower in CSCI subjects compared with AB subjects. Plasma adrenaline concentrations significantly increased after LBH in AB and TLSCI subjects, but did not change throughout the study in CSCI subjects. Cardiac output and heart rate increased at the end of LBH in all three groups.Conclusions: Under a similar increase in core temperature, ΔIL-6% was lower in the CSCI group compared with the AB group. These findings suggest that the observed rise in IL-6 during hyperthermia is mediated, at least in part, by plasma adrenaline.

Global patterns and impacts of El Niño events on coral reefs: A meta-analysis.

Impacts of global climate change on coral reefs are being amplified by pulse heat stress events, including El Niño, the warm phase of the El Niño Southern Oscillation (ENSO). Despite reports of extensive coral bleaching and up to 97% coral mortality induced by El Niño events, a quantitative synthesis of the nature, intensity, and drivers of El Niño and La Niña impacts on corals is lacking. Herein, we first present a global meta-analysis of studies quantifying the effects of El Niño/La Niña-warming on corals, surveying studies from both the primary literature and International Coral Reef Symposium (ICRS) Proceedings. Overall, the strongest signal for El Niño/La Niña-associated coral bleaching was long-term mean temperature; bleaching decreased with decreasing long-term mean temperature (n = 20 studies). Additionally, coral cover losses during El Niño/La Niña were shaped by localized maximum heat stress and long-term mean temperature (n = 28 studies). Second, we present a method for quantifying coral heat stress which, for any coral reef location in the world, allows extraction of remotely-sensed degree heating weeks (DHW) for any date (since 1982), quantification of the maximum DHW, and the time lag since the maximum DHW. Using this method, we show that the 2015/16 El Niño event instigated unprecedented global coral heat stress across the world's oceans. With El Niño events expected to increase in frequency and severity this century, it is imperative that we gain a clear understanding of how these thermal stress anomalies impact different coral species and coral reef regions. We therefore finish with recommendations for future coral bleaching studies that will foster improved syntheses, as well as predictive and adaptive capacity to extreme warming events.

The Effect of Being Aerobically Active vs. Inactive on Cutaneous Vascular Conductance during Local Heat Stress in an Older Population.

Objective: To test the hypothesis that long- term aerobically trained elderly individuals have a greater amount of bioavailable nitric oxide (NO) and have a larger cutaneous vasodilation during local heat stress compared to their inactive elderly counterparts.Methods: Eight aerobically trained and 8 inactive older men (>60 years old) participated in this study. NO bioavailability in blood and intradermal dialysate were measured with an ozone based chemiluminescence NO analyzer. Cutaneous vasodilator response to local heating was obtained using laser Doppler velocimetry.Results: Whole blood NO were similar in older- trained and inactive subjects (0.75 ± 0.56 and 0.38 ± 0.32 μM, respectively; Mann–Whitney, p = 0.153), as was intradermal dialysate NO before (7.82 ± 6.32 and 4.18 ± 1.89 μM, respectively) and after local heating (7.16 ± 6.27 and 5.88 ± 3.97 μM, respectively, p = 0.354). The cutaneous vasodilator response of the older- inactive group was smaller than the older- trained group [Group-Time interaction, F(24, 264) = 12.0, p < 0.0001]. When compared to a young group the peak vasodilator response of the older- trained subjects was similar. However, the time to initial dilation was 3.1 and 2.2 times longer (p < 0.05) in older- inactive and older- trained subjects, respectively, compared to young subjects.Conclusions: Our data support the hypothesis that the age-related reductions in cutaneous vasodilation can possibly be restored by maintaining an aerobic training regimen (at least 3 years). However, some residual effects of aging remain, specifically a delayed cutaneous vasodilator response to local heating is still present in active older adults. We found no evidence for an increase in systemic or local NO-bioavailability with an extended commitment to aerobic fitness.