インピーダンス・オージオメトリーの原理

チンパノグラムとは何か, インピーダンスとは何か. その応用 その1

抄録

This paper explains in detail that an impedance meter is designed so as to measure on a scale of equivalent air volume the change of sound pressure in the external auditory canal (EAC) when the vibration of the tympanic membrane (TM) is fixed and then released by increased and decreased air pressures from the tube of an air pump. Then, the equivalent air volume (EV) is explained by three dynamically different mechanisms in order to understand what tympanogram (TG) is. Subsequently, TG is regarded as a recorded graph showing change of EV for change of TM volume displacements caused by positive and negative air pressures in EAC. This mechanism is calculated by a dynamical equation showing the relation of volume displacements between TM and the diaphragm of the receiver equipped in the probe of a meter.
Common questions askeed by our specialists are that a TG of above 1cc seems to be unreasonable in comparison with the actual dimension of EAC. A TG of 1cc is a sound pressure rate for volume displacement of TM. It is found by calculating a TG of 1cc corresponding with TM volume displacement of 1×10^-6cc. Therefore, it is not unreasonable even if TGs of above 1cc are measured.
Impedance at TM is calculated by the equation to understand what impedance is and how to measure it. Finally, the difference between impedance at TM and TG is explained from the measured data in 4 cases of the ears with the same TG and different volume of EAC.
The mechanism of detection of acoustic reflex is the same as that of TG. Only difference between them is in that higher amplification is used in the former than in the latter. Clinical applications of tympanogram, impedance and acoustic reflex are mentioned.