SUMMARY Silk ligatures were tied round the sciatic nerve in guinea-pigs and left in place in order to produce persistent nerve constriction. Serial nerve conduction studies over the following 9 weeks showed a reduction in motor conduction velocity distal to the ligature. The presence of axonal atrophy in tibial nerve fibres in the leg was subsequently confirmed by histological studies. These changes were not seen in a second group of animals in which similar ligatures were tied but removed after 6 hours. When the ligatures were left in place, the animals developed local plantar nerve lesions in the sole of the foot on the affected side, which were thought to be due to pressure from the floor of the cage. Local pressure changes of varying severity were seen in the foot in all the constricted nerves, but were only occasionally found in control nerves from the opposite foot, or in nerves which had been constricted for a few hours by ligatures which were then removed. These results suggest that atrophic nerve fibres distal to a persistent constriction may be particularly sensitive to local pressure.Earlier experiments on guinea-pigs have shown that constriction of the sciatic nerve by a silk ligature in the thigh may be followed by distal axonal atrophy.' For this to occur, it was necessary to tie the ligature tightly enough to cause Wallerian degeneration of most of the large myelinated fibres. When this was done, surviving fibres in the tibial nerve distal to the ligature were found to have a reduced external diameter in relation to internodal length, and a reduced axon/external diameter (g) ratio. Maximal conduction velocity in motor fibres to the plantar muscles was reduced in the leg distal to the ligature, but it was not possible to decide how much of this reduction was due to the degeneration of large fastconducting fibres, caused by tying the ligature, and how much to the atrophic change in surviving fibres.In the present study a constricting ligature round the sciatic nerve in the thigh has again been used to produce distal axonal atrophy in the guinea-pig. In a separate group of animals a similar ligature was tied but removed after 6 hours, so that the effects of tying the ligature could be distinguished from those of pro- longed constriction. When studying conduction in motor fibres to the plantar muscles, particular attention was paid to conduction in the foot itself, which revealed changes that had not been noted in previous experiments. MethodsExperiments were carried out on guinea-pigs aged 3-5 months. The animals were kept in individual cages with solid floors covered by a layer of sawdust 1-2cm in depth.Motor conduction studies were carried out under general anaesthesia before and at 1 or 2-week intervals after tying a ligature round the sciatic nerve in the upper thigh. Stainless steel needles placed close to the tibial nerve in the thigh and at the ankle served as stimulating cathodes. The upper cathode was 15-2 cm distal to the site of ligature; conduction distance between the two sites of stimul...
SUMMARY Asterixis was studied in nine patients, using a new electrophysiological technique: silent period locked averaging (SPLA). There were two types of electromyographic (EMG) silence in the movements clinically judged as asterixis. Thejerky movement in one ofthe two types might be caused by the silent period after the subclinical cortical myoclonus. SPLA would be useful for studying asterixis as well as other EMG silences.Since asterixis was first described by Adams and Foley in patients with hepatic encephalopathy,' it has been reported to be commonly found in a wide variety of disorders.2"5 There has not, however, been any procedure for studying the physiological mechanisms underlying asterixis, other than the electroencephalogram (EEG) electromyogram (EMG) polygraph. 56 We have described a new technique for the physiological analysis of asterixis: silent period locked averaging (SPLA). SubjectsNine subjects with asterixis were studied, four patients with liver cirrhosis, two with renal failure, two with anticonvulsant intoxication and one with metrizamide intoxication. Methods pairs of saddle type surface electrodes. Filters were set 3db down at 8 Hz (high pass) and 3000 Hz (low pass). EEGs and EMGs were recorded simultaneously, with patients extending their wrists or dorsiflexing their ankles. Accelerometric records of hand or foot also were made in some cases. Silent period locked averaging (SPLA)We constructed a special device (Nihon-Kohden Co. Ltd.) that generates a trigger pulse when the amplitude of the rectified EMG remains lower than a preset level for a preset duration (fig 1). Whenever this device produced a trigger Raw EMG Both the electroencephalogram (EEG)-electromyogram (EMG) polygraph and silent period locked averaging (SPLA) methods were used. EEG-EMG polygraphEEGs were recorded with silver-silver chloride cap electrodes positioned in accordance with the international 10-20 system. The ifiter setting of the amplifier was 0-5 to 3000 Hz (-3db).The EMGs of several muscles were also recorded, including those afflicted by asterixis. Recordings were made with
The central motor pathways were studied with the technique of percutaneous electrical stimulation of the central nervous system in 40 normal volunteers. There were no significant differences between the right and left sides, or between males and females. A linear correlation between the cortical latency (Lcor) or the spinal latency (Lsp) and body height was observed, however, there was no correlation between the central conduction time (CCT) (Lcor-Lsp) and body height. Consequently, the CCT appears to provide a reliable estimate of the function of central motor pathways. We have established normal values for eight muscles at rest that would be required for localizing a very small intraspinal lesion.
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