COLD AND POSTTRAUMATIC PAIN - MODELING OF THE PERIPHERAL-NERVE MESSAGE

Hypersensitivity to cold is a relatively frequent sequel of peripheral nerve injuries but its mechanism is not well understood. We suggested that incomplete recovery of diameter of regenerated fibers is one of the factors involved in cold intolerance after nerve damage. Conductio n velocity is correlated to fiber diameter, and is slowed down by cold . In normal subjects, cold does not desynchronize the volleys of senso ry impulses sufficiently to change the intelligibility:of the peripher al 'messages'. Sensory perceptions remain accurate although they acqui re a characteristic numbness. On the other hand, post-traumatic reduct ion in fiber diameters causes a permanent distortion of the messages. We considered that when the distortion is severe, the resulting messag es may be perceived by the centers as containing nociceptive component s. We further hypothesized that, even in cases of moderate permanent d istortion, cold acts by increasing the post-traumatic abnormalities of impulse synchronization. In winter, decompensation is observed when a threshold of desynchronization is reached. We constructed a model of peripheral nerve messages in an attempt to represent and quantitate th e desynchronizations produced by cold and crush damage lesions in peri pheral nerve messages. A number of parameters concerning fiber anatomy , exposure to cold, and type of nerve damage were taken into considera tion. Four elementary types of desynchronization could be recognized b y considering the times of arrival of pairs of impulses at the nervous centers. The difference between a normal and a distorted message coul d be expressed by eight variables. Thus, although our model was quite simple, a large amount of data was obtained and a preliminary statisti cal study was necessary in order to orient the final analysis. Then, w e used factor analysis in an attempt to obtain a satisfactory interpre tation of the data.The results indicated that peripheral desynchroniza tion might explain, at least in part, the painful sensations experienc ed in winter by many patients after peripheral nerve injury. (C) 1997 Elsevier Science Ireland Ltd.