Redistribution of Decompression Stop Time from Shallow to Deep Stops Increases Incidence of Decompression Sickness in Air Decompression Dives

Abstract

Classical decompression algorithms limit hypothetical tissue gas contents and prescribe decompression schedules with most of the total stop time (TST) allocated to shallow decompression stops. More recent bubble-model-based algorithms limit hypothetical bubble profusion and size and prescribe decompressions with TST skewed toward deeper stops. A large man-trial compared the efficiency of these approaches. Divers wearing swimsuits and tshirts breathing surface-supplied air via MK 20 UBA, and immersed in 86 ?F water were compressed at 57 fsw/min to 170 fsw for a 30 minute bottom time during which they performed 130 watt cycle ergometer work. They were then decompressed at 30 fsw/min with stops prescribed by one of two schedules. The shallow stops schedule, with a first stop at 40 fsw and 174 minutes TST, was prescribed by the, deterministic, gas content, VVAL18 Thalmann Algorithm. The deep stops schedule, with a first stop at 70 fsw, was the optimum distribution of 174 minutes TST according to the probabilistic BVM(3) bubble model. Decompression sickness (DCS) incidence following these schedules was compared. The trial was terminated after the midpoint interim analysis, when the DCS incidence of the deep stops dive profile (11 DCS/198 dives) was significantly higher than that of the shallow stops dive profile (3/192, p=0.030, one-sided Fisher Exact). On review, one deep stops DCS was excluded, but the result remained significant (p=0.047). Most DCS was mild, late onset, Type I, but two cases involved rapidly progressing CNS manifestations. Results indicate that slower tissue gas washout or continued gas uptake offsets the benefits of reduced bubble growth at deep stops.

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Document Details

Document Type
Technical Report
Publication Date
Jul 22, 2011
Accession Number
ADA561618

Entities

People

  • David Doolette
  • Keith Gault
  • Wayne Gerth

Organizations

  • United States Navy Experimental Diving Unit

Tags

DTIC Thesaurus Topics

  • Active Duty
  • Algorithms
  • Cardiovascular Physiological Phenomena
  • Data Acquisition
  • Data Sets
  • Decompression
  • Decompression Sickness
  • Ear
  • Ergometers
  • Gases
  • Joints (Anatomy)
  • Military Research
  • Pain
  • Partial Pressure
  • Pressure Gradients
  • Respiration
  • Wet Suits

Readers

  • Underwater engineering and Marine Technology.