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Cell Stress & Chaperones Jan 2020Heat acclimation (HA) in humans promotes thermoregulatory adaptations that support management of core temperature in hot environments and reduces the likelihood of heat... (Meta-Analysis)
Meta-Analysis Review
Heat acclimation (HA) in humans promotes thermoregulatory adaptations that support management of core temperature in hot environments and reduces the likelihood of heat related illness. Another adaptation to HA is thermotolerance through induction of the heat shock protein (HSP) stress system, which provides protection against thermal insult. However, whether or not HA leads to upregulation of the intracellular HSP system, namely intracellular HSP70 (HSP70), is unclear in humans. Therefore, the purposes of this meta-analysis were to determine if HA leads to HSP70 induction among humans and to evaluate how methodological differences among HA studies influence findings regarding HA-induced HSP70 accumulation. Several databases were searched to identify studies that measured HSP70 (protein and mRNA) changes in response to HA among humans. The effect of HA on HSP70 was analyzed. Differences in the effect of HA were assessed between protein and mRNA. The moderating effect of several independent variables (HA frequency, HA duration, core temperature, exercise intensity) on HSP70 was also evaluated. Data were extracted from 12 studies including 118 participants (mean age 24 years, 98% male). There was a significant effect of HA on HSP70 expression, g = 0.97 (95% CI, 0.08-1.89). The effect of HA was different between subgroups (protein vs. mRNA), g = 1.51 (95% CI, 0.71-2.31), and g = - 0.39 (95% CI, - 1.36), respectively. The frequency of HA (in days) moderated HSP70 protein expression. There was a significant effect of heat acclimation on HSP70 induction in humans. The only factor among identified studies that may moderate this response was the frequency (number of days) of heat exposure.
Topics: Acclimatization; Animals; Body Temperature Regulation; Exercise; HSP70 Heat-Shock Proteins; Hot Temperature; Humans; Thermotolerance
PubMed: 31823288
DOI: 10.1007/s12192-019-01059-y -
Anais Da Academia Brasileira de Ciencias 2022We evaluated the influence of a 32-day camping in Antarctica on physical performance and exercise-induced thermoregulatory responses. In Brazil, before and after the...
We evaluated the influence of a 32-day camping in Antarctica on physical performance and exercise-induced thermoregulatory responses. In Brazil, before and after the Antarctic camping, the volunteers performed an incremental exercise at temperate conditions and, two days later, an exercise heat stress protocol (45-min running at 60% of maximum aerobic speed, at 31°C and 60% of relative humidity). In Antarctica, core temperature was assessed on a day of fieldwork, and average values higher than 38.5°C were reported. At pre- and post-Antarctica, physiological (whole-body and local sweat rate, number of active sweat glands, sweat gland output, core and skin temperatures) and perceptual (thermal comfort and sensation) variables were measured. The Antarctic camping improved the participants' performance and induced heat-related adaptations, as evidenced by sweat redistribution (lower in the chest but higher in grouped data from the forehead, forearm, and thigh) and reduced skin temperatures in the forehead and chest during the exercise heat stress protocol. Notwithstanding the acclimatization, the participants did not report differences of the thermal sensation and comfort. In conclusion, staying in an Antarctic camp for 32 days improved physical performance and elicited physiological adaptations to heat due to the physical exertion-induced hyperthermia in the field.
Topics: Acclimatization; Antarctic Regions; Body Temperature; Exercise; Hot Temperature; Humans; Thermotolerance
PubMed: 35239799
DOI: 10.1590/0001-3765202220210593 -
Proceedings of the National Academy of... May 2021Estimates of the global population of humans living at high altitude vary widely, and such data at the country level are unavailable. Herein, we use a geographic...
Estimates of the global population of humans living at high altitude vary widely, and such data at the country level are unavailable. Herein, we use a geographic information system (GIS)-based approach to quantify human population at 500-m elevation intervals for each country. Based on georeferenced data for population (LandScan Global 2019) and elevation (Global Multiresolution Terrain Elevation Data), 500.3 million humans live at ≥1,500 m, 81.6 million at ≥2,500 m, and 14.4 million at ≥3,500 m. Ethiopia has the largest absolute population at ≥1,500 m and ≥2,500 m, while China has the greatest at ≥3,500 m. Lesotho has the greatest percentage of its population above 1,500 m, while Bolivia has the greatest at ≥2,500 m and ≥3,500 m. High altitude presents a myriad of environmental stresses that provoke physiological responses and adaptation, and consequently impact disease prevalence and severity. While the majority of high-altitude physiology research is based upon lowlanders from western, educated, industrialized, rich, and democratic countries ascending to high altitude, the global population distribution of high-altitude residents encourages an increased emphasis on understanding high-altitude physiology, adaptation, epidemiology, and public health in the ∼500 million permanent high-altitude residents.
Topics: Acclimatization; Adaptation, Physiological; Altitude; Altitude Sickness; Bolivia; China; Ethiopia; Female; Humans; Lesotho; Male; Population Surveillance
PubMed: 33903258
DOI: 10.1073/pnas.2102463118 -
International Journal of Sports Medicine Jun 2024Inducing a heat-acclimated phenotype via repeated heat stress improves exercise capacity and reduces athletes̓ risk of hyperthermia and heat illness. Given the... (Review)
Review
Inducing a heat-acclimated phenotype via repeated heat stress improves exercise capacity and reduces athletes̓ risk of hyperthermia and heat illness. Given the increased number of international sporting events hosted in countries with warmer climates, heat acclimation strategies are increasingly popular among endurance athletes to optimize performance in hot environments. At the tissue level, completing endurance exercise under heat stress may augment endurance training adaptation, including mitochondrial and cardiovascular remodeling due to increased perturbations to cellular homeostasis as a consequence of metabolic and cardiovascular load, and this may improve endurance training adaptation and subsequent performance. This review provides an up-to-date overview of the metabolic impact of heat stress during endurance exercise, including proposed underlying mechanisms of altered substrate utilization. Against this metabolic backdrop, the current literature highlighting the role of heat stress in augmenting training adaptation and subsequent endurance performance will be presented with practical implications and opportunities for future research.
Topics: Humans; Endurance Training; Heat-Shock Response; Acclimatization; Physical Endurance; Heat Stress Disorders; Adaptation, Physiological
PubMed: 38401534
DOI: 10.1055/a-2251-3170 -
Experimental Physiology Jan 2021What is the central question of this study? We assessed the utility of a new metric for quantifying ventilatory acclimatization to high altitude, derived from...
NEW FINDINGS
What is the central question of this study? We assessed the utility of a new metric for quantifying ventilatory acclimatization to high altitude, derived from differential ascent and descent steady-state cardiorespiratory variables (i.e. hysteresis). Furthermore, we aimed to investigate whether the magnitude of cardiorespiratory hysteresis was associated with the development of acute mountain sickness. What is the main finding and its importance? Hysteresis in steady-state cardiorespiratory variables quantifies ventilatory acclimatization to high altitude. The magnitude of cardiorespiratory hysteresis during ascent to and descent from high altitude was significantly related to the development of symptoms of acute mountain sickness. Hysteresis in steady-state chemoreflex drive can provide a simple, non-invasive method of tracking ventilatory acclimatization to high altitude.
ABSTRACT
Maintenance of arterial blood gases is achieved through sophisticated regulation of ventilation, mediated by central and peripheral chemoreflexes. Respiratory chemoreflexes are important during exposure to high altitude owing to the competing influence of hypoxia and hypoxic hyperventilation-mediated hypocapnia on steady-state ventilatory drive. Inter-individual variability exists in ventilatory acclimatization to high altitude, potentially affecting the development of acute mountain sickness (AMS). We aimed to quantify ventilatory acclimatization to high altitude by comparing differential ascent and descent values (i.e. hysteresis) in steady-state cardiorespiratory variables. We hypothesized that: (i) the hysteresis area formed by cardiorespiratory variables during ascent and descent would quantify the magnitude of ventilatory acclimatization; and (ii) larger hysteresis areas would be associated with lower AMS symptom scores during ascent. In 25 healthy, acetazolamide-free trekkers ascending to and descending from 5160 m, cardiorespiratory hysteresis was measured in the partial pressure of end-tidal CO , peripheral oxygen saturation, minute ventilation, chemoreceptor stimulus index (end-tidal CO /peripheral oxygen saturation) and the calculated steady-state chemoreflex drive (SS-CD; minute ventilation/chemoreceptor stimulus index) using portable devices (capnograph, peripheral pulse oximeter and respirometer, respectively). Symptoms of AMS were assessed daily using the Lake Louise questionnaire. We found that: (i) ascent-descent hysteresis was present in all cardiorespiratory variables; (ii) SS-CD is a valid metric for tracking ventilatory acclimatization to high altitude; and (iii) the highest AMS scores during ascent exhibited a significant, moderate and inverse correlation with the magnitude of SS-CD hysteresis (r = -0.408, P = 0.043). We propose that ascent-descent hysteresis is a new and feasible way to quantify ventilatory acclimatization in trekkers during high-altitude exposure.
Topics: Acclimatization; Adult; Altitude; Altitude Sickness; Humans; Hypoxia; Lung; Oxygen; Oxygen Saturation
PubMed: 32421248
DOI: 10.1113/EP088488 -
Journal of Applied Physiology... Jun 2024
Topics: Climate Change; Humans; Acclimatization; Hot Temperature; Animals
PubMed: 38836542
DOI: 10.1152/japplphysiol.00265.2024 -
The Journal of Physiology Mar 2023High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea level (SL)...
High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea level (SL) and after 14 days acclimatization to 4300 m (chronic HA) in Cerro de Pasco (CdP), Péru (HA), against sex-, age- and body mass index-matched healthy highlanders (n = 9) native to CdP (lifelong HA). Venous blood was assayed for serum proteins reflecting NVU integrity, in addition to free radicals and nitric oxide (NO). Regional cerebral blood flow (CBF) was examined in conjunction with cerebral substrate delivery, dynamic cerebral autoregulation (dCA), cerebrovascular reactivity to carbon dioxide (CVR ) and neurovascular coupling (NVC). Psychomotor tests were employed to examine cognitive function. Compared to lowlanders at SL, highlanders exhibited elevated basal plasma and red blood cell NO bioavailability, improved anterior and posterior dCA, elevated anterior CVR and preserved cerebral substrate delivery, NVC and cognition. In highlanders, S100B, neurofilament light-chain (NF-L) and T-tau were consistently lower and cognition comparable to lowlanders following chronic-HA. These findings highlight novel integrated adaptations towards regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia. KEY POINTS: High-altitude (HA) hypoxia has the potential to alter the structural-functional integrity of the neurovascular unit (NVU) in humans. For the first time, we examined to what extent chronic and lifelong hypoxia impacts multimodal biomarkers reflecting NVU structure and function in lowlanders and native Andean highlanders. Despite lowlanders presenting with a reduction in systemic oxidative-nitrosative stress and maintained cerebral bioenergetics and cerebrovascular function during chronic hypoxia, there was evidence for increased axonal injury and cognitive impairment. Compared to lowlanders at sea level, highlanders exhibited elevated vascular NO bioavailability, improved dynamic regulatory capacity and cerebrovascular reactivity, comparable cerebral substrate delivery and neurovascular coupling, and maintained cognition. Unlike lowlanders following chronic HA, highlanders presented with lower concentrations of S100B, neurofilament light chain and total tau. These findings highlight novel integrated adaptations towards the regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia.
Topics: Humans; Male; Altitude Sickness; Carbon Dioxide; Altitude; Hypoxia; Acclimatization; Oxidation-Reduction; Nitric Oxide; Homeostasis
PubMed: 36633375
DOI: 10.1113/JP283362 -
The Journal of Experimental Biology Jul 2022Temperature is a key driver of metabolic rates. So far, we know little about potential physiological adjustments of subtropical corals to seasonal temperature changes...
Temperature is a key driver of metabolic rates. So far, we know little about potential physiological adjustments of subtropical corals to seasonal temperature changes (>8°C) that substantially exceed temperature fluctuation experienced by their counterparts in the tropics. This study investigated the effect of temperature reductions on Montastraea cavernosa and Porites astreoides in Bermuda (32°N; sea surface temperature ∼19-29°C) over 5 weeks, applying the following treatments: (i) constant control temperature at 28°C, and (ii) temperature reduction (0.5°C day-1) followed by constant temperature (20 days; acclimatization period) at 24°C and (iii) at 20°C. Both species decreased photosynthesis and respiration during temperature reduction as expected, which continued to decrease during the acclimatization period, indicating adjustment to a low energy turnover rather than thermal compensation. Trajectories of physiological adjustments and level of thermal compensation, however, differed between species. Montastraea cavernosa zooxanthellae metrics showed a strong initial response to temperature reduction, followed by a return to close to control values during the acclimatization period, reflecting a high physiological flexibility and low thermal compensation. Porites astreoides zooxanthellae, in contrast, showed no initial response, but an increase in pigment concentration per zooxanthellae and similar photosynthesis rates at 24°C and 20°C at the end of the experiment, indicating low acute thermal sensitivity and the ability for thermal compensation at the lowest temperature. Respiration decreased more strongly than photosynthesis, leading to significant build-up of biomass in both species (energy reserves). Results are important in the light of potential poleward migration of corals and of potential latitudinal and species-specific differences in coral thermal tolerance.
Topics: Acclimatization; Animals; Anthozoa; Coral Reefs; Hot Temperature; Seasons; Symbiosis; Temperature
PubMed: 35702952
DOI: 10.1242/jeb.244196 -
Biological Reviews of the Cambridge... Apr 2022Elucidating the physiological mechanisms that underlie thermal stress and discovering how species differ in capacities for phenotypic acclimatization and evolutionary...
Elucidating the physiological mechanisms that underlie thermal stress and discovering how species differ in capacities for phenotypic acclimatization and evolutionary adaptation to this stress is critical for understanding current latitudinal and vertical distribution patterns of species and for predicting their future state in a warming world. Such mechanistic analyses require careful choice of study systems (species and temperature-sensitive traits) and design of laboratory experiments that reflect the complexities of in situ conditions. Here, we critically review a wide range of studies of intertidal molluscs that provide mechanistic accounts of thermal effects across all levels of biological organization - behavioural, organismal, organ level, cellular, molecular, and genomic - and show how temperature-sensitive traits govern distribution patterns and capacities for coping with thermal stress. Comparisons of congeners from different thermal habitats are especially effective means for identifying adaptive variation. We employ these mechanistic analyses to illustrate how species differ in the severity of threats posed by rising temperature. Counterintuitively, we show that some of the most heat-tolerant species may be most threatened by increases in temperatures because of their small thermal safety margins and minimal abilities to acclimatize to higher temperatures. We discuss recent molecular biological and genomic studies that provide critical foundations for understanding the types of evolutionary changes in protein structure, RNA secondary structure, genome content, and gene expression capacities that underlie adaptation to temperature. Duplication of stress-related genes, as found in heat-tolerant molluscs, may provide enhanced capacity for coping with higher temperatures. We propose that the anatomical, behavioural, physiological, and genomic diversity found among intertidal molluscs, which commonly are of critical importance and high abundance in these ecosystems, makes this group of animals a highly appropriate study system for addressing questions about the mechanistic determinants of current and future distribution patterns of intertidal organisms.
Topics: Acclimatization; Adaptation, Physiological; Animals; Climate Change; Ecosystem; Mollusca; Temperature
PubMed: 34713568
DOI: 10.1111/brv.12811 -
Nutrients Mar 2021The aim of this study was to assess the history of exertional heat illness (EHI), heat preparation, cooling strategies, heat related symptoms, and hydration during an...
The aim of this study was to assess the history of exertional heat illness (EHI), heat preparation, cooling strategies, heat related symptoms, and hydration during an ultra-endurance running event in a warm and humid environment. This survey-based study was open to all people who participated in one of the three ultra-endurance races of the Grand Raid de la Réunion. Ambient temperature and relative humidity were 18.6 ± 5.7 °C (max = 29.7 °C) and 74 ± 17%, respectively. A total of 3317 runners (56% of the total eligible population) participated in the study. Overall, 78% of the runners declared a history of heat-related symptoms while training or competing, and 1.9% reported a previous diagnosis of EHI. Only 24.3% of study participants living in temperate climates declared having trained in the heat before the races, and 45.1% of all respondents reported a cooling strategy during the races. Three quarter of all participants declared a hydration strategy. The planned hydration volume was 663 ± 240 mL/h. Fifty-nine percent of the runners had enriched their food or drink with sodium during the race. The present study shows that ultra-endurance runners have a wide variability of hydration and heat preparation strategies. Understandings of heat stress repercussions in ultra-endurance running need to be improved by specific field research.
Topics: Acclimatization; Adult; Drinking; Female; Heat Stress Disorders; Hot Temperature; Humans; Humidity; Male; Marathon Running; Middle Aged; Water
PubMed: 33810371
DOI: 10.3390/nu13041085