Oxygen window in diving decompression
The term "oxygen window" was first used by Albert R. Behnke in 1967. Behnke refers to early work by Momsen on "partial pressure vacancy" (PPV) where he used partial pressures of oxygen and helium as high as 2–3 ATA to create a maximal PPV. Behnke then goes on to describe "isobaric inert gas transport" or "inherent unsaturation" as termed by LeMessurier and Hills and separately by Hills. who made their independent observations at the same time. Van Liew et al. also made a similar observation that they did not name at the time. The clinical significance of their work was later shown by Sass.
|This passage is quoted from Van Liew's technical note:
Van Liew et al. describe the measurements important to evaluating the oxygen window as well as simplify the "assumptions available for the existing complex anatomical and physiological situation to provide calculations, over a wide range of exposures, of the oxygen window".
Oxygen is used to decrease the time needed for safe decompression in diving, but the practical consequences and benefits need further research. Decompression is still far from being an exact science, and divers when diving deep must make many decisions based on personal experience rather than scientific knowledge.
In technical diving, applying the oxygen window effect by using decompression gases with high ppO2 increases decompression efficiency and allows shorter decompression stops. Reducing decompression time can be important to reduce time spent at shallow depths in open water (avoiding dangers such as water currents and boat traffic), and to reduce the physical stress imposed on the diver.
Use of 100% oxygen is limited by oxygen toxicity at deeper depths. Convulsions are more likely when the pO2 exceeds 1.6 bar (160 kPa). Technical divers use gas mixes with high ppO2 in some sectors of the decompression schedule. As an example, a popular decompression gas is 50% nitrox on decompression stops starting at 21 metres (69 ft).
Where to add the high ppO2 gas in the schedule depends on what limits of ppO2 are accepted as safe, and on the diver's opinion on the level of added efficiency. Many technical divers have chosen to lengthen the decompression stops where ppO2 is high and to push gradient[clarification needed] at the shallower decompression stops.
Nevertheless, much is still unknown about how long this extension should be and the level of decompression efficiency gained. At least four variables of decompression are relevant in discussing how long high ppO2 decompression stops should be:
- Time needed for circulation and elimination of gas through the lungs;
- The vasoconstrictor effect (reduction of the size of blood vessels) of oxygen, reducing decompression efficiency when blood vessels start contracting;
- The threshold depth where the critical tissue compartments start off-gassing rather than in-gassing.
- Cumulative effect of acute oxygen toxicity.
- Tikuisis, Peter; Gerth, Wayne A (2003). "Decompression Theory". In Brubakk, Alf O; Neuman, Tom S. Bennett and Elliott's Physiology and Medicine of Diving (5th ed.). Philadelphia, USA: Saunders. pp. 425–7. ISBN 0-7020-2571-2.
- Behnke, Albert R (1967). "The isobaric (oxygen window) principle of decompression". Trans. Third Marine Technology Society Conference, San Diego. The New Thrust Seaward. Washington DC: Marine Technology Society. Retrieved 19 June 2010.
- Momsen, Charles (1942). "Report on Use of Helium Oxygen Mixtures for Diving". United States Navy Experimental Diving Unit Technical Report (42–02). Retrieved 19 June 2010.
- Behnke, Albert R (1969). "Early Decompression Studies". In Bennett, Peter B; Elliott, David H. The Physiology and Medicine of Diving. Baltimore, USA: The Williams & Wilkins Company. p. 234. ISBN 0-7020-0274-7.
- LeMessurier, DH; Hills, Brian A (1965). "Decompression Sickness. A thermodynamic approach arising from a study on Torres Strait diving techniques". Hvalradets Skrifter 48: 54–84.
- Hills, Brian A (1966). "A thermodynamic and kinetic approach to decompression sickness". PhD Thesis (Adelaide, Australia: Libraries Board of South Australia).
- Hills, Brian A (1977). Decompression Sickness: The biophysical basis of prevention and treatment 1. New York, USA: John Wiley & Sons. ISBN 0-471-99457-X.
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- Sass, DJ (1976). "Minimum <delta>P for bubble formation in pulmonary vasculature". Undersea Biomedical Research 3 (Supplement). ISSN 0093-5387. OCLC 2068005. Retrieved 19 June 2010.
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- Vann, Richard D (1982). "Decompression theory and applications". In Bennett, Peter B; Elliott, David H. The Physiology and Medicine of Diving (3rd ed.). London: Bailliere Tindall. pp. 52–82. ISBN 0-941332-02-0.
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- Blatteau, Jean-Eric; Souraud, Jean-Baptiste; Gempp, Emmanuel; Boussuges, Alain (2006). "Gas nuclei, their origin, and their role in bubble formation". Aviation, Space, and Environmental Medicine 77 (10): 1068–76. ISSN 0095-6562. PMID 17042253. Retrieved 2008-04-23.
- "The Divers Alert Network (DAN)". Retrieved 2007-06-15.
- Brian, Eddie. "Oxygen Window". Global Underwater Explorers. Archived from the original on 2007-11-30. Retrieved 2008-12-17. good in-depth article
- The Rubicon Research Repository