Evaluation of altitude decompression procedures and development of new decompression strategies

Abstract

Diving at altitude requires different tables than at sea level due to the reduction in surface level ambient pressure. In this work, the rationale for the algorithms extrapolating the sea level diving data are reviewed. When applied to different sets of maximum permissible tissue tensions (M value), the conservatism of an algorithm becomes a function of bottom time, depth and altitude. Aviation altitude exposure decompression sickness (DCS) data is also addressed. Animal experiments performed within the scope of this thesis proved that precordial bubbles can form during the ascent from sea level to 2000-m. supporting a far lower threshold for altitude DCS then the model outputs.Following three pioneering altitude diving expeditions to 2200, 3412 and 3980-m, a set of no-decompression stop (no-d) limits for 3500 m was calculated using linear extrapolation of US Navy M values decreased by 4 feet of sea water. This is a new method of altitude adaptation (NLHE, Nonlinear Hypobaric Extrapolation). These limits were tested at 3412-m. by 10 man/dive per profile without any case of DCS. 212 dives were achieved with a total bottom time of 4110 min. The mean DCS risk estimated according to precordial bubble scores (Spencer's Scale) ranges from 0.3% to 2.8% per profile. The last part of the thesis is devoted to the computation of decompression tables for 3500-m altitudes. This work suggests the use of a continuous variable for the compartment time constants, allowing the simulation of infinite number of compartments and reducing the discrepancy between different algorithms to a single M value expression.