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Wilmshurst 1998 BMJ

From Bioblast
Publications in the MiPMap
Wilmshurst P (1998) ABC of oxygen. Diving and oxygen. https://doi.org/10.1136/bmj.317.7164.996

Β» BMJ 317:996-9. PMID: 9765173 Open Access

Wilmshurst P (1998) BMJ

Abstract: All organisms require oxygen for metabolism, but the oxygen in water is unavailable to mammals. Divers (and diving mammals such as whales and seals) are entirely dependent on the oxygen carried in the air in their lungs or their gas supply. Divers also have a paradoxical problem with oxygen. At higher partial pressures oxygen causes acute toxicity leading to convulsions. To understand the diver's narrow knife edge between fatal hypoxia and fatal hyperoxia we need to recall some of the physical properties of gases. At sea level atmospheric pressure is 1 bar absolute (1 standard atmosphere =101 kPa=1.013 bars). The weight of the atmosphere exerts a pressure which will support a column of water 10 m high; 10 m under water the pressure on a diver is 200 kPa. The volume of gas in an early diving bell full of air at sea level is halved at 10 m according to Boyle's law; at 20 m pressure is 300 kPa absolute and the gas is compressed into one third the volume. Dry air is composed of roughly 21 % oxygen, 78 % nitrogen, and 1 % other gases. According to Dalton's law the partial pressure of oxygen at any depth will be 21 % of the total pressure exerted by the air and the partial pressure of nitrogen will be 78 % of total pressure. Gases dissolve in the liquid with which they are in contact. Nitrogen is fat soluble and at sea level we have several litres dissolved in our bodies. If the partial pressure of nitrogen is doubled (by breathing air at 10  m depth) for long enough for equilibration to take place we will contain twice as many dissolved nitrogen molecules as at sea level. Gases dissolve in the liquid with which they are in contact. Nitrogen is fat soluble and at sea level we have several litres dissolved in our bodies. If the partial pressure of nitrogen is doubled (by breathing air at 10  m depth) for long enough for equilibration to take place we will contain twice as many dissolved nitrogen molecules as at sea level. The effect of the increased partial pressures of oxygen is more complex. Doubling our inspired partial pressure of oxygen doubles the amount of oxygen in solution but does not double the amount of oxygen in the body since a large part of our oxygen content is bound to oxygen carrying pigments. The haemoglobin in arterial blood is virtually saturated at an inspired partial pressure of oxygen (Fio2) of 21 kPa, and increasing the partial pressure of oxygen has little effect on the amount of oxygen bound to haemoglobin.

β€’ Bioblast editor: Gnaiger E


Labels: MiParea: Respiration, Exercise physiology;nutrition;life style 

Stress:Hypoxia  Organism: Human 





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