[in Japanese]

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Recovery from adaptation was studied as changes in compound action potential (CAP) in response to clicks after broadband noise masking in volunteers with normal hearing. CAP was transtympanically elicited from the promontory using a needle electrode. Preceding masking noise and subsequent click stimuli were delivered separately from 2 loud speakers 80cm from the tested ear. We evaluated the effect of masking noise duration and intensity on CAP recovery from adaptation as a function of Δt, defined as the interval between masking noise offset and click stimulus onset.
Results were as follows: At Δt shorter than 200 ms or less, recovery from latency prolongation and amplitude decrease slowed with increasing masking noise duration and intensity. At Δt longer than 200ms, no significant difference was seen in CAP recovery based on changes in masking noise duration or intensity.
Recovery from adaptation, which depended on click intensity, took about 700ms at a 40 dBnHL click and about 300ms at a 60 dBnHL click.
The influence of the middle ear muscle reflex on CAP recovery patterns is neglected when considering the intensity both masking noise and click stimulus.
In CAP recovery, accumulated effects of the relative auditory-nerve refractory period may adversely affect recovery at very short Δt, while recovery from short-term adaptation, assumed involved in cochlear-hair cell synapse function, may be an important factor at Δt longer than 30-40ms.
Based on animal experiments showing different recovery times dependent on different auditory nerve spontaneous rates (SR), we concluded that at Δt of 200ms or less, CAP recovery reflects high SR neuron activity, while at Δt longer than 200ms, it mainly reflects that of low SR neurons.

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Objectives: We studied the postoperative stability of canal wall down tympanoplasty with canal reconstruction for middle ear cholesteatoma with preoperative otorrhea. Subjects and Methods: 155 ears with middle ear cholesteatoma treated with canal wall down tympanoplasty with canal reconstruction were evaluated retrospectively. A comparison was made between the group of 80 ears which showed otorrhea, preoperatively, and the group of 75 without preoperative otorrhea. Problems observed in the tympanic membrane or reconstructed external auditory canal were evaluated both at the postoperative initial stage and more than 1 year after surgery. Postoperative hearing prognosis was also studied. Results: 1) In the postoperative initial stage, local infection and necrosis of materials for canal reconstruction were significantly more likely to be observed in ears with preoperative otorrhea. 2) In ears with postoperative local infection, necrosis of materials for canal reconstruction occurred more frequently, and the period until drying of the reconstructed external auditory canal was significantly extended. 3) No significant difference was seen in postoperative status of the tympanic membrane and reconstructed ear canal at least 1 year after surgery. 4) The presence of preoperative otorrhea had no influence on hearing prognosis. Conclusions: When canal wall down tympanoplasty with canal reconstruction is used for ears with preoperative otorrhea, careful attention should be paid to local treatment at the postoperative initial stage. However, no significant problem occurred in the outcome of preoperative ear draining at least 1 year after surgery.

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The influence of septal perforation on results of acoustic rhinometry was studied using cases of septal perforation and a human-nose model.
Acoustic rhinometry was conducted before and after closing the perforation (average 16mm in diameter, 23mm from the nostril) by thin cotton patches in 33 cases (19 men and 14 women). The decrease in cross-sectional area and volume after closure was statistically significant.
A human-nose model with septal holes ranging from 5, 10, 15, to 20mm and locations ranging from 20, 40, to 50mm from the nostril was studied by acoustic rhinometry. Our results suggest that the effect of perforations on the measurement is much greater in anterior perforations than in posterior perforations.

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To evaluate qualitative diagnosis of stapes lesions by 3-dimensional computed tomography (3D-CT) combined with superselective image processing (3D-SS) of stapes, we studied helical 3D-CT on a phantom model of the temporal bone. Two stapes models were used-1 made from the bone filler, Celatite, consistent in bone density but changing in cross sectional area, and the other made from an apacerum rod used in quantitative computed tomography (QCT), consistent in cross sectional area but changing in bone density. These stapes models were put into a skull phantom and analyzed by helical 3D-CT. The influence of the tympanic cavity conditions on CT images of stapes was evaluated by filling the phantom model with Vaseline following 3D selective reconstruction. In all stapes models, lowering the lower CT window width threshold resulted in an enlarged cross-sectional area of the model. The higher the bone density, the lower the increase in cross-sectional area in the image. The stapes model with lower density had greater influence on the imaging by tympanic cavity conditions and was likely to be misdiagnosed as showing higher bone density.
Based on the experimental study, 3D-SS by helical 3D-CT appears to be a useful measure for qualitatively diagnosing stapes lesions.

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