[Studies of the evaluation of cochlea function with distortion product otoacoustic emission]

Distortion product otoacoustic emission (DPOAE) is one of the acoustic responses derived from the inner ears and it has very sharp frequency specificities. The purpose of this study is to investigate the utility of DPOAE as a method for evaluating human cochlea functions. The whole subjects of this study were 414 ears with inner ear hearing loss, 278 ears with normal hearing, 113 ears of neonates, 62 ears of the patients who were administered cisplatin, and 15 ears with functional hearing loss. At first, 5 studies described below were performed to examine the characters and reliability of DPOAE as a clinical test: 1) The average DPOAE-gram of normal hearing ears. 2) The comparison between DPOAE levels and hearing levels. 3) The reproducibility of DPOAE on the different examinations in the same subjects. 4) The influences of respiratory noises on DPOAE levels. 5) The detection of fine cochlea damages using DPOAE which can not be detected by pure tone audiometry. Then the following 2 clinical studies were performed: 6) The utility of DPOAE in neonates and children. 7) The utility of DPOAE in functional deafness cases. From these studies, the following characters of DPOAE were confirmed. Since DPOAE levels have correlations with hearing levels at the same frequencies, normal hearing could be determined by the DPOAE level. DPOAE is useful for following chronological changes in hearing because of its reproducibility in a same subject at different times. The early and fine damages on the cochlea that could not be detected by conventional pure tone audiometry might be detected by DPOAE in some cases. Considering these results, it was concluded that DPOAE could be a new objective hearing test which would help the conventional examinations. Especially in infants who can't be examined with pure tone audiometry, DPOAE is thought to be a very useful examination.