抄録
Clinical application of electromyography for human recurrent laryngeal nerve paralysis has brought a lot of knowledge about pathophysiology of the disease. There are many cases with a immobile vocal cord which present voluntary activation of some motor units of the paretic muscles.
The main purpose of the present investigation was to relate electromyographical findings to morphological variations. Unilateral recurrent laryngeal nerve of dogs was dissected. In one group, the nerve was partially removed so that the peripheral stump was not regenerated, whereas the cut ends were sutured in order to facilitate regeneration in the other. In the latter, the distance from the larynx to the dissected point was different among the subgroups. The follow-up studies involved observation of the position and mobility of the vocal cord, electromyography of the laryngeal muscles, measurement of the weight of the muscles, and histological examination of the laryngeal structure.
When the nerve was not regenerated, the weight of muscles was decreased rapidly, becoming about a half of that of the un-affected side in three months. The muscle fibers kept being atrophied and finally they were replaced with connective tissue. Fibrillation potentials had lasted until the muscle fibers almost disappeared. There was no change in the position of the vocal cord while atrophy of the muscles was proceeding except for that, in some cases, the paretic cord looked as if it was slightly lateralized because of atrophy the vocalis muscle.
Regeneration of the nerve took place when the dissected nerve ends were connected. It depended on the length of degeneration when recovery of the muscles was completed. Complete morphological recovery was found even in muscles whose weight had been decreased down to 60% of the normal. The mobility of the vocal cord, however, remained disturbed in the majority of the cases. This could be attributed to misdirection of the regenerated axons.
The weight of muscles which presented dominant fibrillation potentials with a small amount of voluntary action potentials was from 61 to 89% of that of the normal. When voluntary potentials were dominant, the weight of the muscles ranged from 67 to 120% of that of the normal side. In the majority, however, it was less than 100 %. The weight of muscles which gave voluntary action potentials without fibrillation potentials ranged from 71 to 110%. It reached 100% in most cases.
