Nerve conduction studies in experimental non-freezing cold injury: I. Local nerve cooling.

In rabbits, the tibial nerve was exposed in the lower thigh under general anesthesia and cooled in a metal trough at 1 to 2 degrees C or 5 degrees C for 2, 3, or 4 hours. Nerve conduction studies showed local failure of conduction at the site of cooling which persisted after rewarming, and which was followed by distal degeneration of affected fibers. No persistent conduction block was seen. Changes in maximal velocity indicated that the fastest-conducting motor and afferent axons had been preferentially affected. Histological findings in nerves examined at different intervals after cooling confirmed the physiological evidence of primary axonal damage, affecting particularly large diameter fibers. Paranodal demyelination was inconspicuous and restricted to regions just proximal to sites of axonal degeneration. No segmental demyelination was seen. These results clarify previous uncertainties as to the time-course and distribution of nerve damage after local cooling at temperatures just above freezing point.