[Relationship between distortion product otoacoustic emissions and pure tone thresholds in normal and hearing-impaired ears]

Clinical investigation on spontaneous otoacoustic emission (SOAE) in 447 ears

OBJECTIVES

It is known that spontaneous otoacoustic emission (SOAE) is often observed in normal hearing ears, but concrete clinical application of SOAE test has been rarely reported, compared with transiently evoked otoacoustic emission (TEOAE) and distortion product otoacoustic emission (DPOAE) tests. In addition, there have been a variety of opinions concerning laterality of SOAE, and influence of gender and hearing on SOAE. The reason for this may be that each report has the small number of subjects and lacks in statistical power. Therefore, in the present study, SOAE, TEOAE and DPOAE were measured in 447 ears of subjects at various ages with different hearing level, and statistical analysis was performed to investigate the clinical significance of SOAE.

MATERIALS AND METHODS

The subjects were 447 ears in 268 patients (268 ears in females, and 179 ears in males). The age of subjects ranged from 0 to 75 years (mean: 30.8 years), and there were 222 left and 225 right ears. The subjects of schoolchildren or older (414 ears) received pure-tone audiometry, and infants (33 ears) received auditory brain-stem response (ABR). SOAE and TEOAE were measured using ILO88 (Otodynamics, Version 4.20). DPOAE was measured using ILO92 (Otodynamics, Version 1.32).

RESULTS

Incidence of SOAE and the number of SOAE per ear were high in the subjects at age of 50 years or younger, in those with hearing level of not more than 30 dB, in the right ear, and in females. Incidence of SOAE in the whole of normal hearing ears was approximately 38%, but the ears with SOAE had almost normal hearing of not more than 30 dB.

CONCLUSIONS

SOAE is useful for objective hearing assessment. Moreover, SOAE sometimes appeared in the ears in which TEOAE or DPOAE could not be confirmed, and it might be useful for definite diagnosis of disease state to measure SOAE in addition to TEOAE or DPOAE.

Optimal stimulus level conditions for measurements of distortion product otoacoustic emissions

OBJECTIVE

Distortion product otoacoustic emission (DPOAE) is a tool for an objective examination of the cochlea function. While the clinical application of DPOEA test is in progress, the measurements vary depending on the stimulus conditions. We aimed to determine the most appropriate stimulus level in the clinical application of DPOAE test.

METHODS

Ninety-seven normal hearing ears and 80 hearing-impaired ears (total 177) were subjected to this study. Two levels of stimulations (L1 and L2) were applied as follows: L1 = L2 = 70 dB; L1 = L2 = 60 dB and L1 = 60/L2 = 50 dB, and DP level was measured at each stimulation, and compared with hearing level.

RESULTS

DP level was highest at L1 = L2 = 70 dB. Normal hearing ears and hearing-impaired ears were well differentiated at L1 = L2 = 60 dB.

CONCLUSION

In clinical application of DPOAE test, DP levels should be measured at the stimulus level most appropriate for the purposes.