Experimental studies on the nerve interception and atrophy of the intrinsic muscles of the larynx

Abstract

The author used 48 mature dogs in doing the above mentioned experiment. One side of the vagus, the recurrent laryngeal nerve and the superior laryngeal nerve were excised. Also the sympthetic superior cervical ganglion and the stellate ganglion were removed. The purpose of this experiment is to observe the influences of nerve interception and the histological changes of the intrinsic muscles of the laynx.The results were as folios :1. In case of dogs, in which one side of the recurrent laryngeal nerve was excised, atrophy of the thyreoarytaenosd muscle (the vocal cord muscle) on the same side appeared most pronounced among intrinsic muscles. Atrophy of the posterior cricoarytaenoid muscle and lateral cricoarytaenoid muscle were then evident in order.2. In case of excision of the vagus on one side, the effects were quits equal in above mentioned cases, but the histological changes were not so pronounced.3. When the superior laryngeal nerve was cut off on one side, the atrophy of the cricothyreoid muscle on that side was most pronounced. Moreover, a slight atrophy of the vocal cord on the same side was seen histologically.4. When the superior cervical ganglion was removed, fibers of the cricothyreoid muscle slightly increased in size on the same side. These histological signs were considered as muscle dystrophy.5. When the stellate ganglion was removed, there appeared various wide muscle fibers in the vocal cord muscle in the transversal arytaenoid muscle and in the lateral cricoarytaenoid muscle on the same side, by turns. These histological changes were recognized as degenerative dystrophy of muscles.6. By excision of the recurrent laryngeal nerve on one side, nuclear numbers of the perim. ysium of the posterior cricoarytaenoid muscle and vocal cord muscle increased remarkably on the same side. These muscles seem to have the most important function of opening and closing of the glottis than the other intrinsic muscles. Consequently, these muscles react very strongly to nerve interception and have shown within themselves restorative powers.II) In the following experiment 17 mature dogs were used. By pulling up the exposed recurrent laryngeal nerve with a small piece of ivory on one side, the following results were obtained by repeated observations of the larynx.1. After three days of pulling up, the nerve fiber degeneration and the atrophy of the vocal cord muscle had partially set in.2. After one month, the muscle fibers were separated, cut, and collapsed and necrosis had noticeably set in. In this times, the changes are quite irreversible, function of the vocal cord muscle also.3. The drawing of the nerve fibers was conti-nued for three weeks and then released. Then it was found that within six months the paralyzed began to move normally.4. In the above mentioned experiment, two out of four cases showed the paralyzed vocal cord in paramedian position. In the other two cases the paralyzed vocal cord took the median position.Thus it was considered that the position of the vocal cord is changeable according to the direction or strength of the affecting power on the nerve fiber.In other words, when pressure or traction exerted upon the nerve fiber is slight, there may occur only incomplete paralysis of the vocal cord, and the vocal cord will take radian position. When affection is stronger, then the vocal cord will take paramedian position, as in the case of nerve interception, and this is a condition of complete