Fig 1.
The Extended Oxygen Window concept.
Standard oxygen window is about 60 torr in venous blood, and about 85 torr in tissues. When extended by part of partial pressure of carbon dioxide and water vapor, this value can be roughly equalized to partial pressure of oxygen in inspired breathing mixture.
Table 1.
Theoretical body compartments [3].
Table 2.
Decompression rates during Phase 1 of saturation decompression.
Fig 2.
Nitrogen elimination rates calculated for different compartments during Phase 1 of nitrox decompression (PiO2 = 0.5 ata).
Table 3.
Calculation of supersaturation exceeding the extended oxygen window.
Fig 3.
Example profiles of saturation decompressions created with the EOW concept.
A typical shape is clearly visible for both compressed air (FiO2 = 0.21) from a depth of 18 m and nitrox (PiO2 = 0.4 ata) from a depth of 45 meters. The first phase of decreasing ambient pressure from plateau pressure through the EOW is relatively fast. Then the rate of decompression depends on PiO2, so for nitrox, this phase is linear with a constant rate; and for air, when oxygen partial pressure changes due to constant fraction of approximately 21%, the decompression rate decreases. In case of using nitrox, from about 11 meters of depth, the decompression rate also decreases, as a fractional amount of oxygen cannot exceed 24%. The very last phase of decompression (from about 1.5 meter to surface) is a fast decrease of ambient pressure in order to induce slight supersaturation (for details, see explanation in the text).
Table 4.
List of saturation exposures.
Fig 4.
Profiles of decompressions planned and conducted using the EOW concept.
Table 5.
ΔP for air saturations.
Table 6.
Maximum elimination half-time for nitrogen.
Fig 5.
Dose-reaction between supersaturation exceeding the EOW for air and nitrox saturation decompressions published in literature (bars represent the 95% confidence interval).
Fig 6.
Comparison of different saturation decompression profiles.
PL1 is the real conducted air saturation using the EOW concept; PL2 is a hypothetical decompression profile after air saturation without fast Phase 1. Thalmann and US Navy T7 show air saturation decompression proposed in the US Navy [4, 7].
Fig 7.
Comparison of nitrogen elimination rates in different saturation systems.
The left graph shows fast initial phase of saturation decompression indicated by the EOW, and the right graph shows saturation decompression during which the decompression rate is constantly slow from the beginning (US Navy).