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Toxic and Asphyxiating Hazards in Confined Spaces
Published in Neil McManus, Safety and Health in Confined Spaces, 2018
Hyperoxia is the condition resulting when the partial pressure of oxygen exceeds that found at sea level (20.9% or 159 mmHg in dry air). Hyperoxia can occur at normal pressures from contact with enriched mixtures or pure oxygen and through pressurization of atmospheres having normal composition. Breathed continuously, oxygen contained in a hyperbaric or enriched atmosphere acts as a toxic agent (Behnke 1978). Despite this, enrichment has been utilized successfully in surgical procedures and hyperbaric oxygen therapy. Two applications of the latter include transport of inert gases from tissues during decompression and use as a therapeutic agent during decompression sickness (Davis 1979).
Detoxifying effects of optimal hyperoxia (40% oxygenation) exposure on benzo[a]pyrene-induced toxicity in human keratinocytes
Published in Journal of Toxicology and Environmental Health, Part A, 2020
Yong Chan Kwon, Hyung Sik Kim, Byung-Mu Lee
Hyperoxia is a state in which there is an excessive supply of oxygen to organs and tissues (Mach et al. 2011). Hyperoxia has many beneficial effects including (1) an increase in efficiency of mitochondrial respiration, (2) reduction in inflammatory reactions and (3) lowering levels of nitrous oxide (NO) and carbon monoxide (CO) (Hafner et al. 2005; Leverve 2007; Tetzlaff, Shank, and Muth 2003). Hyperoxia may also enhance host defense mechanisms and venous PO2 levels as well as blocking release of NO (Knighton, Halliday, and Hunt 1984; Muth, Shank, and Larsen 2000). However, excess oxygen may also produce reactive oxygen species (ROS), resulting in oxidative stress and tissue damage (Raffaeli et al. 2018; Weaver and Liu 2015). Therefore, application of optimal oxygenation conditions may be critically important to avoid toxicities and to maximize beneficial effects of oxygenation.
Integrating physiological monitoring systems in military aviation: a brief narrative review of its importance, opportunities, and risks
Published in Ergonomics, 2023
David M. Shaw, John W. Harrell
Hyperoxia is a state of excess oxygen supply to tissues and organs.Breathing a higher PO2 (at a barometric pressure of approximately sea-level) can improve cognition, particularly at inspired oxygen concentrations of ∼30–45% (Hayes, Temme, and Onge 2020). Hyperoxia saturates haemoglobin with oxygen (i.e. SpO2 > 98%) and increases dissolved oxygen within the blood (Cheng 2012). Pre-breathing 100% oxygen to denitrogenate the body prior to high-altitude exposure also reduces the risk of decompression sickness (Vann et al. 2011). Although hyperoxic breathing is required to maintain alveolar PO2 and SpO2 at high altitudes (i.e. hypobaria), it can exert adverse physiological effects at low altitudes, despite concomitantly improving cognition (Damato et al. 2020). Hyperoxic breathing inflight also increases the risk of absorption and acceleration atelectasis (Dussault et al. 2016; Pollock, Gates, et al. 2021), producing cough, chest pain, and breathing difficulties. Cerebral blood flow subsequently declines to prevent over-oxygenating the brain (Lambertsen et al. 1953; Mattos et al. 2019). Ventilation initially decreases (Marczak and Pokorski 2004), then increases (Becker et al. 1996; Marczak and Pokorski 2004), which may lead to hypocapnia due to increased carbon-dioxide off-loading. Heart rate decreases and HRV increases (Bak et al. 2007; Gole et al. 2011; Lund et al. 1999), and EEG power amplitudes are altered (Damato et al. 2020; Kizuk et al. 2019). The functional and physiological effects of rapidly oscillating hyperoxic breathing remains uncertain, but to our knowledge are currently under investigation.
Hyperoxia for performance and training
Published in Journal of Sports Sciences, 2018
Oxygen transport from the atmosphere to muscle mitochondria involves multiple steps (Weibel, 1987). It is not the intent to this review to discuss the oxygen cascade in details and we refer to others for further reading on this topic (Cano et al., 2013; Cano, Roca, & Wagner, 2015; Wagner, 2011). Briefly, during inspiration air fills the lungs (ventilation process), O2 diffuses from alveolar to pulmonary capillaries (alveolar-capillary diffusion), where it binds to hemoglobin (Hb). A small fraction of oxygen (O2: ~2%) is freely dissolved in the blood. The cardiovascular system pumps the blood (circulation) to different organs and working muscles. Depending on the level of pressure gradients O2 diffuses into muscle cells (muscle diffusion), where mitochondria produce energy (mitochondrial respiration). Each of the above mentioned steps is important for reiteration of muscle contraction as well as regulating cell metabolism and could represent a limiting factor during exercise in humans and, thus, can be affected by changes in inspired oxygen. One way to increase the blood O2 carrying capacity is by breathing increased oxygen air – normobaric hyperoxia (Bannister & Cunningham, 1954; Ekblom, Huot, Stein, & Thorstensson, 1975; Hill, Long, & Lupton, 1924; M. Nielsen & Hansen, 1937; Welch, 1982; Welch, Bonde-Petersen, Graham, Klausen, & Secher, 1977). Hyperoxia is defined as an increased inspired O2 fraction (FIO2) or content above the normoxic condition (FIO2 = 0.21). Breathing hyperoxia increases arterial oxygen pressure (PaO2), arterial O2 saturation (SaO2) and O2 dissolved in the blood; therefore breathing hyperoxia increases arterial O2 content (CaO2) and O2 delivery independently of blood flow (Ekblom et al., 1975). Another way of increasing blood O2 carrying capacity is different types of blood infusions from normal levels of Hb concentration. Such a manipulation increases Hb mass and O2 carrying capacity with an unchanged PaO2 and consequently enhances maximal oxygen consumption (V̇O2max) (Ekblom, Goldbarg, & Gullbring, 1972). Similarly, administration of recombinant erythropoietin (EPO) increases the production of erythrocytes above normal values and therefore significantly elevates Hb and O2 delivery but not PaO2 during maximal exercise with a corresponding increase in V̇O2max (Ekblom & Berglund, 1991). Training adaptations following an increased O2 delivery to the muscle caused by EPO elevates V̇O2max and submaximal endurance performance (Thomsen et al., 2007). While both blood infusions and EPO treatment are banned by the World Anti-Doping Agency, breathing hyperoxia during exercise training is at the moment allowed.