Abstract
The previously reported method measuring the change of the retraction grade of the ear drum to acoustic stimulation by S. Kawata, Y. Ochiai, M. Esaki and M. Tsuji gave a clue of the observation of the acoustic movement of the ear drum in audiology. It is the purpose of present paper to report the observations and experiments done on ear specimens obtained from fresh human cadavers, and that the movements of the ear drum which acoustic middle ear muscle reflexes caused were recorded objectively through the change of air pressure in the closed auditory canal.
1. The arising portions of the tensor tympani and stapedius muscles were exposed under surgical microscope, and the effects of the contractions of both muscles upon the ear drum and ossicular chain were studied by artificial pull on these muscles along their bone canals. As the result of the experiment, it was ascertained that the contractions of these muscles undoubtedly showed mechanical influer ce on the ear drum and ossicular chain, and the procedure was filmed using 16 mm movie camera.
2. To represent quantitatively the movements of the ear drum of human cadavers the fine changes of air pressure in the closed auditory canal were recorded with an apparatus utilized strain gauge. The reaction modus was different when the tensor tympani or the stapedius muscle was pulled. The former showed the movement correspond to the retraction of the ear drum and the latter the bulge of it. About the mechanism causing the bulge of the ear drum by artificial pull on the stapedius muscle, some consideration was attempted partly on the observations and partly on presumption.
3. Using the same apparatus for measut ing pressure the changes of air pressure of the closed canal to acoustic stimulation were examined in twenty healthy individuals. It was revealed that responses to acoustic stimulation were objectively recorded definitely and there were two different modi of the responses meaning the retraction and the bulge of the ear drums similiar to the reactions obtained by artificial pull on the middle ear muscles of human corpse.
Difference between hearing and reflex threshold was 86.0, 91.4, 89.5, 84.1, 92.7, 106.6 db in each 250-, 500-, 1000-, 2000-, 4000-, 8000cps.
Magnitude of the response usually became larger when acoustic stimulation was increased above refrex threshold. Though the change of retraction grade of the ear drum to acoustic stimulation has been routinely measured on pars tensa of the ear drum, it is a very interesting fact that there was a new type of response coriespond to the bulge of the ear drum other than retraction of it. Considering the result of the observations of the ear specimen, the bulge of the ear drum appears to be mainly due to the movement of pars flaccida. Further studies, however, are required to elucidate the reason of the different response modi in each individual and sometimes in each ear of the same person.
