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Experimental Physiology Jan 2016At high altitude the barometric pressure falls, challenging oxygen delivery to the tissues. Thus, whilst hypoxia is not the only physiological stress encountered at high... (Review)
Review
At high altitude the barometric pressure falls, challenging oxygen delivery to the tissues. Thus, whilst hypoxia is not the only physiological stress encountered at high altitude, low arterial P(O2) is a sustained feature, even after allowing adequate time for acclimatization. Cardiac and skeletal muscle energy metabolism is altered in subjects at, or returning from, high altitude. In the heart, energetic reserve falls, as indicated by lower phosphocreatine-to-ATP ratios. The underlying mechanism is unknown, but in the hypoxic rat heart fatty acid oxidation and respiratory capacity are decreased, whilst pyruvate oxidation is also lower after sustained hypoxic exposure. In skeletal muscle, there is not a consensus. With prolonged exposure to extreme high altitude (>5500 m) a loss of muscle mitochondrial density is seen, but this was not observed in a simulated ascent of Everest in hypobaric chambers. At more moderate high altitude, decreased respiratory capacity may occur without changes in mitochondrial volume density, and fat oxidation may be downregulated, although this is not seen in all studies. The underlying mechanisms, including the possible role of hypoxia-signalling pathways, remain to be resolved, particularly in light of confounding factors in the high-altitude environment. In high-altitude-adapted Tibetan natives, however, there is evidence of natural selection centred around the hypoxia-inducible factor pathway, and metabolic features in this population (e.g. low cardiac phosphocreatine-to-ATP ratios, increased cardiac glucose uptake and lower muscle mitochondrial densities) share similarities with those in acclimatized lowlanders, supporting a possible role for the hypoxia-inducible factor pathway in the metabolic response of cardiac and skeletal muscle energy metabolism to high altitude.
Topics: Acclimatization; Air Pressure; Altitude; Animals; Energy Metabolism; Heart; Humans; Muscle, Skeletal; Myocardium
PubMed: 26315373
DOI: 10.1113/EP085317 -
Clinical Autonomic Research : Official... Aug 2018Ascent to high-altitude elicits compensatory physiological adaptations in order to improve oxygenation throughout the body. The brain is particularly vulnerable to the... (Review)
Review
Ascent to high-altitude elicits compensatory physiological adaptations in order to improve oxygenation throughout the body. The brain is particularly vulnerable to the hypoxemia of terrestrial altitude exposure. Herein we review the ventilatory and cerebrovascular changes at altitude and how they are both implicated in the maintenance of oxygen delivery to the brain. Further, the interdependence of ventilation and cerebral blood flow at altitude is discussed. Following the acute hypoxic ventilatory response, acclimatization leads to progressive increases in ventilation, and a partial mitigation of hypoxemia. Simultaneously, cerebral blood flow increases during initial exposure to altitude when hypoxemia is the greatest. Following ventilatory acclimatization to altitude, and an increase in hemoglobin concentration-which both underscore improvements in arterial oxygen content over time at altitude-cerebral blood flow progressively decreases back to sea-level values. The complimentary nature of these responses (ventilatory, hematological and cerebral) lead to a tightly maintained cerebral oxygen delivery while at altitude. Despite this general maintenance of global cerebral oxygen delivery, the manner in which this occurs reflects integration of these physiological responses. Indeed, ventilation directly influences cerebral blood flow by determining the prevailing blood gas and acid/base stimuli at altitude, but cerebral blood flow may also influence ventilation by altering central chemoreceptor stimulation via central CO washout. The causes and consequences of the integration of ventilatory and cerebral blood flow regulation at high altitude are outlined.
Topics: Acclimatization; Altitude; Cerebrovascular Circulation; Humans; Hypoxia; Respiration
PubMed: 29574504
DOI: 10.1007/s10286-018-0522-2 -
Acta Physiologica (Oxford, England) Jul 2017
Topics: Acclimatization; Altitude; Altitude Sickness; Humans
PubMed: 28498559
DOI: 10.1111/apha.12894 -
Molecular Aspects of Medicine Apr 2022In mammals and other air-breathing vertebrates that live at high altitude, adjustments in convective O transport via changes in blood hemoglobin (Hb) content and/or Hb-O... (Review)
Review
In mammals and other air-breathing vertebrates that live at high altitude, adjustments in convective O transport via changes in blood hemoglobin (Hb) content and/or Hb-O affinity can potentially mitigate the effects of arterial hypoxemia. However, there are conflicting views about the optimal values of such traits in hypoxia, partly due to the intriguing observation that hypoxia-induced acclimatization responses in humans and other predominantly lowland mammals are frequently not aligned in the same direction as evolved phenotypic changes in high-altitude natives. Here we review relevant theoretical and empirical results and we highlight experimental studies of rodents and humans that provide insights into the combination of hematological changes that help attenuate the decline in aerobic performance in hypoxia. For a given severity of hypoxia, experimental results suggest that optimal values for hematological traits are conditional on the states of other interrelated phenotypes that govern different steps in the O-transport pathway.
Topics: Acclimatization; Altitude; Animals; Hemoglobins; Humans; Hypoxia; Oxygen; Oxygen Consumption
PubMed: 34879970
DOI: 10.1016/j.mam.2021.101052 -
Comparative Biochemistry and... Oct 2023The fields of biological anthropology and exercise physiology are closely related and can provide mutually beneficial insights into human performance. These fields often... (Review)
Review
The fields of biological anthropology and exercise physiology are closely related and can provide mutually beneficial insights into human performance. These fields often use similar methods and are both interested in how humans function, perform, and respond in extreme environments. However, these two fields have different perspectives, ask different questions, and work within different theoretical frameworks and timescales. Biological anthropologists and exercise physiologists can greatly benefit from working together when examining human adaptation, acclimatization, and athletic performance in the extremes of heat, cold, and high-altitude. Here we review the adaptations and acclimatizations in these three different extreme environments. We then examine how this work has informed and built upon exercise physiology research on human performance. Finally, we present an agenda for moving forward, hopefully, with these two fields working more closely together to produce innovative research that improves our holistic understanding of human performance capacities informed by evolutionary theory, modern human acclimatization, and the desire to produce immediate and direct benefits.
Topics: Humans; Acclimatization; Adaptation, Physiological; Altitude; Anthropology; Extreme Environments
PubMed: 37423419
DOI: 10.1016/j.cbpa.2023.111476 -
Comparative Biochemistry and... 2021One of the principal goals of comparative biology is the elucidation of mechanisms by which organisms adapt to different environments. The study of enzyme structure,... (Review)
Review
One of the principal goals of comparative biology is the elucidation of mechanisms by which organisms adapt to different environments. The study of enzyme structure, function, and stability has contributed significantly to this effort, by revealing adaptation at a molecular level. Comparative biochemistry, including enzymology, necessarily pursues a reductionist approach in describing the function and structure of biomolecules, allowing more straightforward study of molecular systems by removing much of the complexity of their biological milieu. Although this reductionism has allowed a remarkable series of discoveries linking chemical processes to metabolism and to whole-organism function in the context of the environment, it also has the potential to mislead when careful consideration is not made of the simplifying assumptions inherent to such research. In this review, a brief history of the growth of enzymology, its reliance on a reductionist philosophy, and its contributions to our understanding of biological systems is given. Examples then are provided of research techniques, based on a reductionist approach, that have advanced our knowledge about enzyme adaptation to environmental stresses, including stability assays, enzyme kinetics, and the impact of solute composition on enzyme function. In each case, the benefits of the reductionist nature of the approach is emphasized, notable advances are described, but potential drawbacks due to inherent oversimplification of the study system are also identified.
Topics: Acclimatization; Animals; Enzymes; Humans
PubMed: 33600949
DOI: 10.1016/j.cbpb.2021.110574 -
Journal of Basic Microbiology Oct 2018Cyanobacteria are among the oldest living organisms on this planet, existing since more than 3 billion years. They are ideal organisms for investigating biological... (Review)
Review
Cyanobacteria are among the oldest living organisms on this planet, existing since more than 3 billion years. They are ideal organisms for investigating biological processes such as photosynthesis, respiration, circadian rhythm, photoregulation of gene expression, developmental gene rearrangements, and specialized cell differentiation. They are nearly ubiquitous in distribution, have colonized a wide range of ecosystems including soil, air, dry rock, and aquatic systems, and even occupy extreme niches that are inaccessible to other organisms. Such wide ecological distribution reflects their capacity to acclimate to extreme environments. They show great adaptive abilities and have survived various adverse physiological growth conditions like desiccation, high temperatures, extreme pH, cold, osmosis, salt, light, nitrogen, and high salinity. Their ancient origin and surviving through numerous stresses during evolution indicates their remarkable capabilities to survive and prevail under different environmental and man-made stresses. It has been hypothesized that similar and overlap stress response mechanisms help them to survive different stresses. It has been stated that responses against stresses like radiation has been accidental-exhibited because of similar response against desiccation stress, which has prevailed more during evolution. These overlaps and similarities in stress responses have been instrumental in making these organisms a large class of biological entities today. Present review discuss about stress tolerance in cyanobacteria against two extreme stresses - desiccation and gamma radiation. It also discuss the commonality and underlying molecular mechanisms in these two stress responses.
Topics: Acclimatization; Cyanobacteria; Desiccation; Ecosystem; Gamma Rays; Nitrogen Fixation; Oxidative Stress; Photosynthesis; Radiation Tolerance
PubMed: 30080267
DOI: 10.1002/jobm.201800216 -
The Clinical Respiratory Journal Mar 2021The aim of this work is to present a review on the impact of genetics and altitude on lung function from classic and recent studies. (Review)
Review
OBJECTIVES
The aim of this work is to present a review on the impact of genetics and altitude on lung function from classic and recent studies.
DATA SOURCE
A systematic search has been carried out in different databases of scientific studies, using keywords related to lung volumes, spirometry, altitude and genetics.
RESULTS
The results of this work have been structured into three parts. First, the relationship between genes and lung function. Next, a review of the genetic predispositions related to respiratory adaptation of people who inhabit high-altitude regions for millennia. Finally, temporary effects and long-term acclimatisation on respiratory physiology at high altitude are presented.
CONCLUSIONS
The works focused on the influence of genetics and altitude on lung function are currently of interest in terms of studying the interactions between genetic, epigenetic and environmental factors in the configuration of the pathophysiological adaptation patterns.
Topics: Acclimatization; Adaptation, Physiological; Altitude; Humans; Lung; Respiratory Physiological Phenomena
PubMed: 33112470
DOI: 10.1111/crj.13300 -
Scandinavian Journal of Medicine &... Jun 2015Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus...
Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise-heat exposures over 1-2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vest), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat.
Topics: Acclimatization; Athletic Performance; Body Temperature Regulation; Dehydration; Drinking Behavior; Exercise; Fluid Therapy; Heat Stress Disorders; Hot Temperature; Humans; Sports
PubMed: 25943653
DOI: 10.1111/sms.12467 -
Molecular Biology Reports Aug 2023Environmental variation is the most crucial problem as it is causing food insecurity and negatively impacts food availability, utilization, assessment, and stability.... (Review)
Review
Environmental variation is the most crucial problem as it is causing food insecurity and negatively impacts food availability, utilization, assessment, and stability. Wheat is the largest and extensively cultivated staple food crop for fulfilling global food requirements. Abiotic stresses including salinity, heavy metal toxicity, drought, extreme temperatures, and oxidative stresses being the primary cause of productivity loss are a serious threat to agronomy. Cold stress is a foremost ecological constraint that is extremely influencing plant development, and yield. It is extremely hampering the propagative development of plant life. The structure and function of plant cells depend on the cell's immune system. The stresses due to cold, affect fluid in the plasma membrane and change it into crystals or a solid gel phase. Plants being sessile in nature have evolved progressive systems that permit them to acclimatize the cold stress at the physiological as well as molecular levels. The phenomenon of acclimatisation of plants to cold stress has been investigated for the last 10 years. Studying cold tolerance is critical for extending the adaptability zones of perennial grasses. In the present review, we have elaborated the current improvement of cold tolerance in plants from molecular and physiological viewpoints, such as hormones, the role of the posttranscriptional gene, micro RNAs, ICE-CBF-COR signaling route in cold acclimatization and how they are stimulating the expression of underlying genes encoding osmoregulatory elements and strategies to improve cold tolerance in wheat.
Topics: Triticum; Cold Temperature; Oxidative Stress; Plants; Cold-Shock Response; Gene Expression Regulation, Plant; Acclimatization; Plant Proteins
PubMed: 37378744
DOI: 10.1007/s11033-023-08584-1