Changes in nerve function and nerve fibre structure induced by acute, graded compression.

Rabbit tibial nerves were subjected to direct, acute graded compression by means of an inflatable compression chamber. The acute and long term effects of 50, 200 and 400 mmHg applied for two hours on nerve function and nerve fibre structure were investigated. A pressure of 50 mmHg applied for two hours induced only minimal or no acute deterioration of maximal conduction velocity and nerve fibre structure. Conduction velocity was gradually reduced during compression at 200-400 mmHg pressure for two hours and in those cases the recovery of nerve conduction after pressure release was incomplete. Ultrastructural analysis revealed pronounced, early nerve fibre damage in these nerves. Three weeks after compression, nerves compressed at 50 mmHg for two hours had normal afferent and motor conduction velocity, although there were morphological signs of slight nerve fibre damage. Nerves compressed at 200 mmHg for two hours exhibited reduction of conduction velocity only at the level of compression, in contrast to the nerves compressed at 400 mmHg for two hours in which conduction velocity was reduced both at the level of compression and distal to the compressed segment. Morphologically, the nerves compressed at 200-400 mmHg for two hours showed varying degrees of demyelination and axonal degeneration three weeks after compression.