Reduction of decompression illness risk in pigs by use of non-linear ascent profiles

An established swine model of neurologic decompression illness (DCI) was adapted to investigate the influence of no-stop ascent profile shape on DCI risk after deep air and heliox dives. Pigs underwent a simulated air dive in a dry chamber to 200 fsw (613 kPa) for 24 min bottom time. They were then decompressed at either a linear rate of 20 fsw/min (61 kPa/min) or on a non-linear, fast-deep/slow-shallow profile. Both decompressions lasted 10 min. In the linear group, there were 11/20 cases of neurologic DCI, including 1 death and 8 severe cases, compared to 5/20 cases (1 severe) in the fast/slow group. Thirteen out of 20 from the linear group, vs. 6/20 of the non-linear group, had moderate or severe skin DCI affecting > 20% skin surface area. A similar study, but of paired, randomized, investigator-blind, and sequential design was performed with pigs breathing 80/20% heliox: Pigs were compressed to 250 fsw (766 kPa) for 8 min 50 s, then decompressed at either a linear 30 fsw/min (92 kPa/min), or on a fast/slow profile. Neurologic DCI occurred more frequently (P = 0.024) in the linear group (16/20; 1 death and 11 severe) than in the fast/slow group (8/20; 3 severe). Moderate or severe skin DCI affected 16/20 of the linear group compared to 3/20 of the fast/slow group (P = 0.0002). The study findings suggest that substantial reductions in DCI risk may be obtainable by manipulating the ascent profile after deep no-stop diving. This finding has potential application in both military and civil diving operations.