![]() Argox – Gas mixture occasionally used by scuba divers for dry-suit inflation.In 2015, the United States Navy Experimental Diving Unit showed that decompression from bounce dives using trimix is not more efficient than dives on heliox. Trimix is often used in technical diving, and is also sometimes used in professional diving. Trimix is a less expensive alternative to heliox for deep diving, which uses only enough helium to limit narcosis and gas density to tolerable levels for the planned depth. Surface personnel often employ a piece of communications equipment called a "helium de-scrambler", which electronically lowers the pitch of the diver's voice as it is relayed through the communications gear, making it easier to understand. Each mix is custom made using gas blending techniques, which often involve the use of booster pumps to achieve typical diving cylinder pressures of 200 to 300 bar (2,900 to 4,400 psi) from lower pressure banks of oxygen and helium cylinders.īecause sound travels faster in heliox than in air, voice formants are raised, making divers' speech very high-pitched and hard to understand to people not used to it. The proportion of oxygen in a diving mix depends on the maximum depth of the dive plan, but it is often hypoxic and may be less than 10%. It is also sometimes used by technical divers, particularly those using rebreathers, which conserve the breathing gas at depth much better than open circuit scuba. Owing to the expense of helium, heliox is most likely to be used in deep saturation diving. Helium diluted breathing gases are used to eliminate or reduce the effects of inert gas narcosis, and to reduce work of breathing due to incresed gas density at depth. Problems playing this file? See media help. Currently, heliox is mainly used in conditions of large airway narrowing (upper airway obstruction from tumors or foreign bodies and vocal cord dysfunction). It was the mainstay of treatment in acute asthma before the advent of bronchodilators. Heliox has been used medically since the early 1930s. Research has also indicated advantages in using helium–oxygen mixtures in delivery of anaesthesia. Heliox has also found utility in the weaning of patients off mechanical ventilation, and in the nebulization of inhalable drugs, particularly for the elderly. Heliox may reduce all these effects, making it easier for the patient to breathe. ![]() Patients with these conditions may develop a range of symptoms including dyspnea (breathlessness), hypoxemia (below-normal oxygen content in the arterial blood) and eventually a weakening of the respiratory muscles due to exhaustion, which can lead to respiratory failure and require intubation and mechanical ventilation. A recent trial has suggested that lower fractions of helium (below 40%) – thus allowing a higher fraction of oxygen – might also have the same beneficial effect on upper airway obstruction. There is also some use of heliox in conditions of the medium airways ( croup, asthma and chronic obstructive pulmonary disease). In the large airways where flow is turbulent, resistance is proportional to density, so heliox has a significant effect. The Hagen–Poiseuille equation describes laminar resistance. In the small airways where flow is laminar, resistance is proportional to gas viscosity and is not related to density and so heliox has little effect. Laminar flow tends to generate less resistance than turbulent flow. Heliox's low density produces a lower Reynolds number and hence higher probability of laminar flow for any given airway. The tendency for each type of flow is described by the Reynolds number. Flow of gas through the airway comprises laminar flow, transitional flow and turbulent flow. Heliox has a similar viscosity to air but a significantly lower density (0.5 g/L versus 1.25 g/L at STP). Heliuox 20/80 diffuses 1.8 times faster than oxygen, and the flow of heliox20/80 from an oxygen flowmeter is 1.8 times the normal flow for oxygen. reduced resistance in turbulent flow due to lower density." Work of Breathing" (WOB) is reduced by two mechanisms: Heliox generates less airway resistance than air and thereby requires less mechanical energy to ventilate the lungs. In medicine heliox may refer to a mixture of 21% O 2 (the same as air) and 79% He, although other combinations are available (70/30 and 60/40).
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