[abstract] THE OCCURRENCE OF DECOMPRESSION ILLNESS IN GOATS, FOLLOWING SIMULATED SUBMARINE ESCAPE

Abstract

BACKGROUND: Should a submarine be unable to surface, men can evacuate the stricken boat by means of tower escape. Compression approximates doubling of pressure in four seconds. It takes four seconds to leave the escape tower and ascent is made at an average rate of 0.275 bar.s-1, thus minimizing the time exposed to pressure. The method has a low incidence of DCI in man from depths down to 180 metres of seawater (m). This study aims to define the limits to escape. METHODS: Adult female or castrated male goats in the weight range of 35 - 75 kg were used. The pressure profiles were conducted in a purpose built, computer controlled, hyperbaric facility, which can control the pressure profile accurately. Groups of ten to twenty-four animals were exposed to simulated escapes (dry) from 150 m to 290 m following exposure to normobaric conditions or pressures of 1.5 to 1.9 bar for 24 hours immediately prior to the simulated escape. The animals were observed for signs of DCI. DCI was always treated with recompression and hyperbaric oxygen. RESULTS: The incidence of DCI is given in the table as no. of cases/no. exposed. 0.5 indicates a symptom of resolved within 20 minutes of onset, without further treatment. The numbers in brackets indicates the number of suspect cerebral arterial gas embolism (CAGE) cases. :0m: 150m: 200m: 220m: 240m: 250m: 260m: 270m: 280m: 290m 1.0 bar: 0/20:1/20 (1):2/18 (1):2.5/20 (2):1/19:0/18:2/10 (2):3/14 (3) 1.5 bar:0/20::::1/20:2/5/20 (2):2/20::: 1.7 bar:0/20:::1/20:0/20::1/20::: 1.8 bar:0/24:2/10:2/20::5/20 (1):: 1.9 bar:7/24:: CONCLUSION: As the pre-escape pressure or the depth of escape increases the risk of DCI increases. Safe escapes can be made by goats from depths down to 290 msw, indicating that the current limit for man may be pessimistic. However, there is a risk of CAGE, the cause of which is not yet clear.