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At 6:23 PM 3/28/95, Ake Larsson wrote: >Hi! > >A few months ago there was a thread discussing ascent rates which turned into >a discussion on computerized decompression models. > >Unfortunately I have lost the first letter but as far as I can remember >someone claimed that rapid compression could cause bone necrosis "due to the >high pressure gradients in the tissues" and the same person refered to a >chapter in Edmonds, Lowry, and Pennefather's "Diving and subaquatic >medicine". >I neither can understand how these pressure gradient can occur nor can I find >anything mentioned about it in my edition of "Diving and ...". > >I am presently involved in a project studying the problems with deep single >escapes from disabled submarines. As a part of the project we do rapid >compressions to 50 m / 165feet followed by a normal decompression after 5 min >at pressure. In this case rapid is a doubling of pressure every 4 seconds >which results in a 50m compression taking about 10 seconds. The subjects >usually do only one or two dives each but we who assist the subjects we do >one dive a day for 7 or 8 days a little now and then... >The decompressions are usually not problematic but if the compression per se >can cause dybaric bone necrosis I am very very interested in learning more >about it. Lars - From: McCallum, R.I. and Harrison, J.A.B, 'Dysbaric Osteonecrosis: Asceptic Necrosis of Bone', The Physiology and Medicine of Diving, Peter Bennet and David Elliot Ed., 4th Edition, 1993, W.B. Saunders & Co. Ltd, London The authors note that 'Bone necrosis from a single exposure to pressure was shown dramatically following the escape of five men from a submarine sunk in 120 ft (36.5 m) of water in the China sea in 1931. These men spent 2.5 to 3 hours in gradually increasing air pressure before escaping, and all of them suffered from the bends.' This was the only reference I could find to dysbaric necrosis in a submarine, and it notes that rapid compression was not observed. In the same paper, the authors note that 'The actual manner in which bone necrosis of compressed air workers and divers is caused is not clearly indicated by its pathology and has proved extraordinarily elusive, despite much speculation and numerous animal experiments.' Experiments with mice have produced necrosis by repeated exposure to compressed air (Antopol & Chryssanthou, 1972), but no mention is made of the compression rate. They also noted that necrosis was observed in obese mice that had not been exposed to compressed air. I suggest you read McCallum & Harrison yourself if you're concerned about dysbaric necrosis. Regards, Scott.
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