An in vivo study of peripheral nerves in continuity: biomechanical and physiological responses to elongation.

Using an animal model, the in vivo visco-elastic properties of peripheral nerve in continuity were examined. The nerves were stretched by either 1 cm - Group A (8.8% strain) or 2 cm - Group B (16.1% strain). At constant strain, the stress-relaxation curves were plotted. Maximal relaxation was observed in the first 20 min. After 1 h, the decrease in tensions in Groups A and B were 36.8% and 41.8%, respectively. Throughout this hour and for 30 min after the release of tension, regular recordings of nerve blood flow using laser doppler flowmetry and peak nerve conduction velocity were taken. Nerve blood flow was reduced by similar amounts (Group A, 70%; Group B, 78%) by application of traction. On release, however, Group A displayed a reactive hyperaemia (blood flow 151% starting value) while Group B failed to recover (50% starting value at 30 min). Peak nerve conduction velocity was not significantly altered in Group A in response to traction, whereas in Group B the result was a gradual, but significant reduction in peak velocity to 66% starting value. The lack of correlation between blood flow and peak nerve conduction velocity in these studies suggests that ischaemia is not solely responsible for the increased latency.