Safety of accepted decompression table

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Safety of accepted decompression table

• Brubakk AO et al
• Trondheim / Split /UWATEC AG
• Bergen Nov. 2007

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Effect of Nitroglycerin on bubble formation in
manValade et al 2006.
Bubbles/cm2


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Dry / In-water dives54msw/20min 24msw/70min
Bub/cm2 P(DCS)
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Total decompression timeAir dives
Minutes
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HSE 1997

• The outcome of a particular dive is determined by
  many different physical and physiological factors
  normally not accounted for in present
  decompression tables.
• All present tables seem to be unsatisfactory for
  very high gas loads.

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Health Safety Executive 1997

• The amount of separated gas in the pulmonary
  artery can be used as an indicator of
  decompression risk.
• Present procedures probably produce an
  unacceptable large amount of separated gas in the
  pulmonary artery in a significant number of
  divers.

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The effect of prT on DCS incidence (HSE 1996)
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Dive Computer Tests60 fsw Multi-Level Dive
1(24 min. _at_ 40 fsw)
Required Decompression Time
No-Decompression Time
Neuman T., Pers. Comm.
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Behnke 1951/1969

• From the point of view of decompression
  procedures the problem is straightforward
• regulate decompression so as to prevent bubble
  evolution
• if bubbles form, control their number and size so
  that symptoms do not supervene.
• Bubbles form as soon as a state of
  supersaturation is initiated and tolerance to
  decompression is in reality an index of the
  degree of gas embolism tolerated
• There is a sharp demarcation limit of perhaps 5
  feet in diving depth separating injury from a
  state of well-beeing

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Air dives SurDO2 SNSC 1992
DCS incidence 17
DCS incidence 0
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Risk of DCS

• 60 feet / 80 minutes
• Decompression
• 8 min - pDCS 2.8
• 80 min - pDCS 2
• Wheathersby et al 1984

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318 msw. 9 different gas mixes, 11 hours
decompression
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Copernicus
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Copernicus

• Copernicus consists of
• The model itself. A descriptive model of the
  mechanisms behind the occurence of serious (CNS)
  DCS (evolution of vascular bubbles)
• A control algorithm. It calculates a procedure
  that control the model according to our request
  (Dynamic optimization algorithm)
• Validation strategy through bubble measurement
  rather than DCS/NO-DCS endpoint
• The model will have two distinct applications
• Use the model as a simulator to compare and
  evaluate procedures and logged dives
• Use accepted risk/bubble scores as threshold for
  calculating optimal decompression schedules

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Physiological model

• Individually adaptive
• Input
• Weight
• Height
• Fitness (fat percentage)
• Gender
• Cardio-pulmonary performance
• Workload

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Total decompression timeAir dives
Minutes
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Air-dive 24msw/70min
Min
Total deco 72 min
Total deco 69 min.
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Buhlman / Copernicus24msw/70 min
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Possible, tentative and surprising conclusion

• Dives with long, lt 30 minutes, bottom time may
  benefit from deep stops
• Dives with short. gt 30 minutes, bottom time will
  not benefit from deep stops.

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• People who think they know it all really annoys
  those of us who really do.