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Elementary Numerical Integration
Published in Harold Klee, Randal Allen, Simulation of Dynamic Systems with MATLAB® and Simulink®, 2018
The air is a mixture of approximately 20 percent oxygen and 80 percent inert nitrogen. The oxygen component of the air is used by the body, and waste carbon dioxide is exhaled. Under normal atmospheric conditions, the nitrogen component of the mixture has no effect. But under pressure, it dissolves in the blood stream and in tissues and remains there after the diver begins to ascend. If the diver ascends too quickly, the nitrogen expands and equalizes with the decreasing ambient pressure. Nitrogen bubbles form in the blood stream and the tissues leading to an extremely painful condition known as Decompression Sickness (DCS), more commonly known as the “bends” which can cause paralysis and even death.
Man Undersea
Published in Robert A. Ragotzkie, J. Robert Moore, Man and the Marine Environment, 2018
As already discussed in connection with breath-hold diving, nitrogen is taken up by blood and tissues in an amount proportional to its partial pressure (Henry’s Law). Increased amounts of oxygen are also taken up at depth, but the tissues are always utilizing O2, while N2 must come and go unchanged via the circulation and the lungs. If a diver has taken up a consequential amount of nitrogen at depth and then is returned to surface abruptly, bubble formation in the blood and/or tissues becomes likely. Some degrees of bubble formation are tolerated by the body, but beyond a certain point, or with bubbles forming in crucial locations, signs and symptoms will result. This form of bubble trouble is called “bends,” decompression sickness, or caisson disease. Most frequently, it is signaled by pain in or near a major joint. Less often but more seriously, the spinal cord or brain will be affected. Rarely, bubbles will obstruct circulation in the lung producing “chokes” and leading to circulatory collapse. The only effective treatment in most cases of decompression sickness is prompt recompression: placing the victim in a recompression chamber and increasing the pressure in the hope of compressing the bubbles to nonsymptomatic size and inducing the gas in them to return to the dissolved state. Recompression is also the only accepted treatment for gas embolism, but the bubbles in that condition (see above) have quite a different origin.
Basic Physiology and the Effects of Flight
Published in Roger G Green, Helen Muir, Melanie James, David Gradwell, Roger L Green, Human Factors for Pilots, 2017
Roger G Green, Helen Muir, Melanie James, David Gradwell, Roger L Green
Decompression sickness occurs in association with exposure to reduced atmospheric pressure and is characterized by the evolution of bubbles of nitrogen coming out of solution in body tissues. Although nitrogen is only poorly soluble there is enough present to give rise to problems under very particular circumstances. Ascents to altitude above 18 000ft and especially over 25 000ft are associated with a small incidence of decompression sickness unless certain steps are taken to avoid it.
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
Cockpit barometric pressure can range from sea-level to ∼35,000 ft equivalent depending on the aircraft and flight profile. The primary concerns with hypobaria are pathologies of silent bubble formation, decompression sickness, and hypoxaemia above ∼20,000 ft (Webb and Pilmanis 2011). In contrast to arterial PO2 and PCO2, which can be detected by chemoreceptors in the body, there is no physiological baroreceptor of the external environment. Compared with normobaria, hypobaria is suggested to increase the ventilatory dead space (Ogawa et al. 2019; Savourey et al. 2003), which could increase the gradient between the end-tidal and arterial PCO2 to increase ventilation and further reduce arterial PCO2 in hypoxic conditions (Coppel et al. 2015). Hypobaria may also interact with carbon dioxide and hypoxia to blunt CBF and ventilation, which could impair cerebral oxygen delivery (Aebi, Bourdillon, Kunz, et al. 2020). Further, hypobaria appears to increase HR and marginally reduce HRV (Aebi, Bourdillon, Bron, et al. 2020); however, it does not appear to affect EEG power amplitudes (Kraaier, Van Huffelen, and Wieneke 1988). Repetitive changes in barometric pressure could also influence physiological responses; for example, venous gas emboli may increase or be more persistent when shifting between high and low altitudes (Ånell et al. 2020), although this is mitigated when breathing 100% oxygen (Ånell et al. 2021).
Does oxygen-enriched air better than normal air improve sympathovagal balance in recreational divers?An open-water study
Published in Research in Sports Medicine, 2020
André Zenske, Wataru Kähler, Andreas Koch, Kerstin Oellrich, Clark Pepper, Thomas Muth, Jochen D Schipke
Four major differences between dives in pressure chambers and open-water dives could modify the results from the above studies. These differences, listed below, underline the need for open-water studies. (i) During immersion and submersion blood is centralized (Dahlback, Jonsson, & Liner, 1978), thereby increasing cardiac preload (Sheldahl et al., 1987). (ii) By using very dry breathing gases as are air or nitrox, body fluid is lost. In this study 1.2 l per dive was lost on average, which might become important if one considers elevated blood viscosity and its consequences on decompression sickness (Park, Claybaugh, Shiraki, & Mohri, 1998). (iii) While participants of simulated dives likely do not exercise during the dive, open-water divers perform certain physical activities that augment perfusion in the skeletal muscle approximately corresponding to moderate cycling (Mitchell & Bove, 2011). (iiii) Open-water dives will in addition, exert thermal effects, as the high thermo-conductivity of water will lead to loss of heat, thus decreasing the diver’s body temperature (Uhlig et al., 2014).
Weibull Step-Stress Model with a Lagged Effect
Published in American Journal of Mathematical and Management Sciences, 2018
The experiment that motivated this particular research relates to altitude decompression sickness (DCS), a condition frequently observed in pilots flying at high altitudes, mountaineers, and astronauts performing extravehicular activities in space. To assess the effects of different risk factors on DCS, researchers at Brooks Air Force Base performed experiments involving human subjects in a hypobaric chamber. The study over a 20 year period involved exposures to different altitudes, varying preoxygenation routines, and different levels of exercise while at altitude (Kannan et al., 1998). While physiologists agreed that rates of DCS increased with increasing altitude, they were interested in determining whether a staged ascent, wherein subjects were exposed to a lower altitude for a specified period of time prior to exposure to the higher altitude, would reduce the incidence when compared to subjects directly exposed to the higher altitude. In the staged ascent experiments, researchers changed the levels of the risk factor (altitude) at pre-specified times during the exposure.