Respiratory Heat Transfer in Cold Water and During Rewarming

Hayes, Peter; Padbury, E. H.; Florio, J. T.; Fyfield, T. P.

doi:10.1115/1.3138302

Cited by 5 publications

(1 citation statement)

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“…In order to minimise heat loss from the breathing system, either the umbilical-supplied gas must be heated or careful consideration must be given to breathing system configuration of the self-contained diver. 56…”

Section: Diving Systemsmentioning

confidence: 99%

Circle (CO₂ reabsorbing) breathing systems: Human applications

Magee¹

2017

Proc Inst Mech Eng H

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Artificial breathing systems to help humans survive extreme environments are used over a range of ambient pressures, using various gases of different volumetric concentrations. These activities include anaesthesia and intensive care activity, high-altitude mountaineering, firefighting, aerospace extravehicular space activity and underwater diving operations. A circle breathing system is one in which the exhaled carbon dioxide is absorbed by an alkali substance and the remaining unused gases are recirculated, usually for the sake of economy and environment. This allows the flow of the fresh gas to be considerably reduced, thereby saving on fresh-gas supply. Circle systems are often used in the circumstances cited above, although not always at low fresh-gas flows. The circle system used in anaesthesia and intensive care has the least engineering demands made on it, although it is used on patients who are highly vulnerable; it usually provides a mixture of air and oxygen, and perhaps a breathable anaesthetic gas, all at sea-level pressure. Mountaineering and firefighting applications involve an extreme earthbound environment, with the user undergoing extreme physical work. The astronaut's spacesuit and life support system contains a high-flow circle system, the breathing gases themselves pressurising the suit as well as providing respiratory life support and thermal comfort; the gas provided is pure oxygen at about a third of sea-level atmosphere. There are numerous varieties of breathing systems for diving, including a circle system, often for clandestine naval activity; the gases used are a combination of oxygen, nitrogen and helium, to minimise the possibility of decompression sickness, nitrogen narcosis and oxygen toxicity and must be provided at a varying pressure and concentration appropriate to depth.

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Section: Diving Systemsmentioning

confidence: 99%

Circle (CO₂ reabsorbing) breathing systems: Human applications

Magee¹

2017

Proc Inst Mech Eng H

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Cold Stress and Strain

Mahar¹

2001

Patty's Toxicology

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The human body has the thermoregulatory capacity to maintain its body temperature within about 1°C of normal (i.e., 37°C) under a variety of external environmental temperatures. When the body's heat loss to the environment is greater than its ability to maintain its internal homeostatic temperature, the body undergoes cold strain in response to the external cold temperature stress. Prolonged exposure to any temperature less than normal body temperature to which the body's thermoregulatory capacity cannot accommodate may result in cold‐related injuries to tissues or cause other systemic changes, including hypothermia and death. Those injuries may involve local tissue damage that results when the tissue actually freezes (e.g., frostbite) or that can result from nonfreezing conditions in tissue sufficient to cause temporary or permanent vascular damage (e.g., chilblain, immersion foot). Heat loss sufficient to overcome the body's thermoregulatory mechanisms can produce a critical drop in the body's deep‐core temperature and eventually hypothermia and death. Exposure to cold stress may also produce physiological or metabolic changes or shifts in endocrine systems, affect judgment or behavior, or exacerbate existing medical conditions (e.g., cardiovascular disease). For acute exposures, the body's response to cold stress is a function of the rate of heat loss, the temperature to which the individual is exposed, and the duration of exposure. For chronic exposures which produce subtle endocrine and metabolic shifts, the diurnal or seasonal (e.g., circannual) periodicity of that exposure may be more important than the environmental temperature to which the person is exposed. In assessing the impacts of exposures to cold stress, one should differentiate between normal changes that result as the body accommodates to that stress (homeostatic response mechanisms) and actual damage or disruption that result when the body's homeostatic response mechanisms are exceeded.

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