[abstract] THE EFFECT OF IN-WATER DECOMPRESSION PROFILE ON BUBBLE FORMATION FOLLOWING SURFACE DECOMPRESSION WITH OXYGEN

Abstract

BACKGROUND: Surface decompression using oxygen is a much used technique in commercial diving and is generally considered as safe as other methods of decompressing from a dive. However, the tables used are not considered satisfactory for deeper air dives, something that has led the HSE in UK to reduce allowable bottom time at deeper depths. At more severe exposures, some decompression in the water is performed in order to reduce the gasload at the surface. MATERIAL AND METHODS: Pigs were dived to 490.6 kPa for 90 minutes on air and divided into three groups. Group 1 (n=7) decompressed using a USN schedule, which goes from 130'-40' at a rate of 180 kPa/minute, with a halt at 220 kPa for 10 minutes and 12 minutes at 190 kPa before reaching surface. After three minutes, the animals were recompressed to 220 kPa breathing oxygen for 78 minutes before final surfacing. Group 2 decompressed to 390 kPa at a rate of 50 kPa/ minute and continued decompressing linearly at a rate of 10 kPa / minute until reaching 190 kPa, thus making the decompression time exactly the same as that of the first group. Group 3 decompressed using the same profile as Group 2, but at exactly the double rate (100 kPa / min to 290 kPa, then 20 kPa/minute. Both groups had the same surface oxygen procedure. Gas bubbles were monitored in the Pulmonary artery in all animals, in Group 2 and 3, bubbles were also counted in the jugular vein. RESULTS: The animals in Group 2 had significantly less bubbles after the dive than the animals in group 1 and the animals in Group 3 had significantly less bubbles both in the pulmonary artery and the jugular vein than the animals in Group 2. CONCLUSION: Modifying the ascent profile had a significant effect on bubble production. The fastest profile led to approximately 100 times less bubbles than the USN profile tested. We believe that our findings support a phase model of decompression.