Abstract:

Objective The aims of this study were to investigate the long-term variations in amplitude and frequency of spontaneous otoacoustic emissions(SOAE).
Methods SOAE were measured in a 26 years old woman with normal hearing. Eighteen repeated measurements were recorded over time periods of eighteen weeks. Interval between two tests was one week. Variations in amplitude and frequency of SOAE were assessed.
Results ① Totally 256 SOAE signals were recorded in both ears during the eighteen measurements, 160 SOAE in right ear and 96 SOAE in left ear. Basing on the probability of repetitive appearance of SOAE in eighteen repeated measurement, SOAE were classified into three types: stable SOAE, less stable SOAE and unstable SOAE. The probability of SOAE appearance in total measurements were higher than 75% were defined as stable SOAE. The probability of SOAE appearance between 25% and 75% were defined as less stable SOAE; The probability of SOAE appearance less than 25% were unstable SOAE. Eightyfive point two percent SOAE(84.7% in right ear, 85.9% in left ear) were stable signal in total 256 SOAE signals, less stable SOAE was only recorded in right ears, accounting for 7.5% in right ear, 10.1% SOAE (9.4% in right ear, 11.5% in left ear) were unstable SOAE. ② The probability of repetitive appearance of stable SOAE were 93.2%(92.4%% in right ear, 94.4% in left ear). Only to have 22% of the stable SOAE signal appeared the frequency variation, those frequency variations were still within the original signal. Eighty-nine point six percent of it was only appeared that the peak frequency of SOAE signal declined or raised one minimum scaleofILO 96(12.3Hz). ③ Amplitude of the stable SOAE shows wide fluctuations. Coefficient of variability of the stable SOAE amplitude
fluctuated between 10.5% and 25.6% in right ear, and between 17.0% and 41.2% in left ear. The range of maximum fluctuation of SOAE level was 15.3 dB in right ear and 16.2 dB in left ear over a time interval of one week. ④ The maximum probability of repetitive appearance of unstable SOAE was only 22%. Sixtynine point two percent (18/26) of unstable SOAE occurred in lower than 2 kHz, only 30.8%(8/26) of unstable SOAE occurred in higher than 2 kHz. The mean of unstable SOAE level was(-20.30±7.13) dB. The mean level for unstable SOAE occurred in lower than 1 kHz was(-12.48±2.60) dB, which was significantly higher than the mean level for unstable SOAE occurred in higher than 1 kHz(-26.03±1.69dB)(t=15.10, P＜0.05).
Conclusion SOAE shows a high probability of repetitive appearance and high stability in frequency. However, amplitude of the SOAE shows wide fluctuations.

Key words: spontaneous otoacoustic emissions, frequency, level, stability, out hair cell