振動ゾンデ法の検討

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タイトル別名
  • A STUDY OF AN ACOUSTIC PROBE APPLIED IN TYMPANOPLASTY
  • シンドウ ゾンデホウ ノ ケントウ

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The aim of the present study is to evaluate the feasibility of an acoustic probe as a measure estimating the prognosis of postoperative hearing before tympanoplasty.<br>The probe used is a simple device made of piano wire. It has a small ball-or a spiral spring shaped tip, and the other end is attached to a bone conductor.<br>First, acoustic characteristics of the probe were examined by means of a piezoelectric pick-up and a capacitative probe. The results were satisfactory enough to bear further experimental and clinical use. The reference level of the ossicle hearing loss was obtained by the acoustic probe applied to the malleus handle of normal ear.<br>Next, clinical investigations were carried out. Subjects were 120 cases who were tested with an acoustic probe before surgery.<br>1) The ossicle curve was measured to estimate ossicular disruption. The results showed that there was less chance of mistaking cases with intact ossicular chain for those with ossicular disconnection than the reverse situation. In other words, when clinically used there was less danger of the method to mistake the disconnected for the intact than reversed case.<br>2) Ossicle hearing loss obtained before surgery was compared with postoperative air conduction hearing. In the group with disrupted ossicles and after surgery of Wullstein's type III or IV, the following relationship was observed, that is, the larger the degree of ossicle hearing loss, the poorer was it prognosis of postoperative hearing. On the other hand, there could be seen comparatively less. relationship between the two values in the group with intact ossicular chain and after surgery of Wullstein's type I or II.<br>3) After closure of central perforation of the drum by a prosthesis, air conduction loss was reexamined and compared with the ossicle curve. The mean value of the ossicle hearing loss showed no manifest variation up to 30db air conduction loss, but beyond the former level, gradual tendency increasing in proportion to hearing loss was exhibited.<br>An interpretation was made on the above observations. The ossicles seemed to act as a step-down transformer. Furthermore, it was considered that in cases of larger ossicle hearing loss, the sound conductive system might be involved by some pathological changes other than disruption of ossicles.<br>As a conclusion, the acoustic probe could be a useful measure for estimation of postoperative hearing in tympanoplasty. And, for a better probe, it seemed to be more advisable to use material with lower mechanical impedance.

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