lotnictwo: Hypoxia (medicine)

Evidence: 100 • authority: 72

Hypoxia is a condition in which the body or a region of the body is deprived of an adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise. Hypoxia differs from hypoxemia and anoxemia, in that hypoxia refers to a state in which oxygen present in a tissue or the whole body is insufficient, whereas hypoxemia and anoxemia refer specifically to states that have low or no oxygen in the blood. Hypoxia in which the…

Evidence: 54 • authority: 88

Altitude, Hypoxia and Exercise. Maximal aerobic performance progressively decreases with increasing levels of hypoxia, because of a reduction in arterial oxygen content (CaO2) due to both hypoxia and exercise. Hypoxia limits the oxygen transfer between the lung alveoli and the capillary which results in a drop in CaO2. The successive steps of oxygen transport from the ambient air to the tissues are greatly affected by this drop. Endurance trained athletes are known to undergo a more drastic decrease in maximal oxygen consumption compared with sedentary subjects in hypoxic conditions. Although the facts have been extensively reported, it remains paradoxical and no clear explanation is availa…

Evidence: 48 • authority: 88

Heat to hypoxia cross‐adaptation: Effects of 6‐week post‐exercise hot‐water immersion on exercise performance in acute hypoxia. Abstract Cross‐adaptation occurs when exposure to one environmental stressor (e.g., heat) induces protective responses to another (e.g., hypoxia). Although post‐exercise hot‐water immersion (HWI) induces heat acclimation, its potential to elicit cross‐adaptation remains unclear. This study evaluated the effectiveness of a 6‐week post‐exercise HWI intervention on exercise performance in hypoxia (O 2 = 13%). Twenty healthy volunteers (28 ± 5 years; 47.4 ± 8.9 mL kg −1 min −1 ; 12 males, 8 females) completed interval cycling (4×4 min at 90 ± 5% maximal heart rate, 3×/…

Evidence: 42 • authority: 92

Cardiovascular Exercise Physiology Under Hypoxia, Microgravity, and Heat Stress: A Review with Public Health Implications.. Aerobic exercise capacity, best quantified by maximal oxygen uptake (VO 2max ), varies between individuals and is dependent on cardiac output (CO) and oxygen uptake in the periphery (a-vO 2 diff). Environmental stressors like hypoxia, microgravity, and heat negatively impact these parameters, thereby reducing aerobic exercise capacity. However, in response to acute and chronic exposures to these environments, compensatory processes serve to counteract reductions in VO 2max . In hypoxic environments, reduced oxygen partial pressure (PO 2 ) leads to hypoxic pulmonary vas…

Evidence: 42 • authority: 72

Cerebral hypoxia is a form of hypoxia (reduced supply of oxygen), specifically involving the brain; when the brain is completely deprived of oxygen, it is called cerebral anoxia. There are four categories of cerebral hypoxia; they are, in order of increasing severity: diffuse cerebral hypoxia (DCH), focal cerebral ischemia, cerebral infarction, and global cerebral ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis, resulting in a hypoxic brain injury. Cases of total oxygen deprivation are termed "anoxia", which can be hypoxic in origin (reduced oxygen availability) or ischemic in origin (oxygen deprivation due to a disruption in blood flow). Brain injury as a result of ox…

Evidence: 42 • authority: 92

Lifelong hypoxia produces multigenerational developmental lung disease and pulmonary hypertension in mice.. Chronic hypoxia during development can impair lung and pulmonary vascular growth, but most mouse models of hypoxia-induced pulmonary hypertension expose adult animals for limited periods and do not capture lifelong or multigenerational hypoxic exposure. We developed a multigenerational model of lifelong moderate hypoxia by maintaining wild-type C57BL/6J mice at 13% inspired oxygen fraction ([Formula: see text]), beginning before fertilization and continuing through gestation, postnatal development, and adulthood. This exposure permitted breeding over two generations. Pregnancy and del…

Evidence: 42 • authority: 92

Cerebral blood flow and metabolism under conditions of simulated avalanche burial in humans: The triple H syndrome.. Avalanche burial exposes individuals to a combination of hypothermia, hypercapnia and hypoxia. We investigated the impact of mild hypothermia on cerebrovascular function during room-air breathing and progressive hypercapnic hypoxia. In 14 participants (6 females) the radial artery and internal jugular vein were catheterized to measure blood gases, intravascular pressure, biomarkers of neurovascular damage (tau, neurofilament light (Nf-L) and glial fibrillary acidic protein (GFAP), whereas duplex ultrasound was used to quantify global cerebral blood flow (CBF), cerebral oxygen…

Evidence: 38 • authority: 72

Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,400 metres (8,000 ft) above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations. At intermediate altitudes, the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced. Depending on the protocols used, the body may acclimate to the relative lack of oxygen in one or more ways such as increasing the mass of red blood cells and hemoglobin, or altering muscle metabolism. Proponents claim that when such athletes travel to competitions at low…

Evidence: 36 • authority: 80

Upper airway function of normal horses during exercise

Evidence: 36 • authority: 88

Physiological Adaptions to Acute Hypoxia. When tissues are insufficiently supplied with oxygen, the environment is said to be hypoxic. Acute (exposures to) hypoxia can occur occupationally, within the scope of training and competitions or under pathological conditions. The increasing interest in acute exposure to altitude for training and research purposes makes it more important than ever to understand the physiological processes that occur under hypoxic conditions. Therefore, the scope of this chapter is to describe the main types of hypoxia on the oxygen cascade, to summarize the physiological consequences of acute hypoxia on the three main areas and to highlight the clinical consequence…

Evidence: 36 • authority: 72

Exercise physiology is the physiology of physical exercise. It is one of the allied health professions, and involves the study of the acute responses and chronic adaptations to exercise. Exercise physiologists are the highest qualified exercise professionals and utilise education, lifestyle intervention and specific forms of exercise to rehabilitate and manage acute and chronic injuries and conditions. Understanding the effect of exercise involves studying specific changes in muscular, cardiovascular, and neurohormonal systems that lead to changes in functional capacity and strength due to endurance training or strength training. The effect of training on the body has been defined as the re…

Evidence: 36 • authority: 92

Respiratory modulation of sympathetic activity during hypoxia in adults with overweight and obesity.. We examined the relationship between ventilation and muscle sympathetic nerve activity (MSNA) in adults with overweight/obesity under normoxic and hypoxic conditions. We hypothesized hypoxia would augment respiratory modulation of MSNA, with greater effects in adults with overweight/obesity versus normal weight controls. MSNA and minute ventilation were evaluated in adults with normal weight (8 F/12 M, 23 ± 2 kg·m -2 ) and overweight/obesity (6 F/2 M, 35 ± 5 kg·m -2 ) during normoxia (10 min, 97 ± 1% [Formula: see text]) and steady-state hypoxia (5 min, 82 ± 2% [Formula: see text]). Respira…