[A study on the contralateral suppressive effects of distortion product otoacoustic emissions].

To investigate the physiological properties of contralateral suppressive effects of otoacoustic emissions, the effects of contralateral norrow band noise (NBN) on distortion product otoacoustic emissions (DPOAE) in 23 young subjects (46 ears) with normal hearing were studied using ILO92 otodynamic system. The results showed: 1. The amplitude of DPOAE (2f1-f2) was significantly reduced as the intensity of contralateral NBN increased. They were in significant minus correlation (F2 from 1 to 6 kHz, coefficients were -0.49(-)-0.24, all P < 0.05, the slope 0.26-0.08 dB/10 dB); 2. The suppressive effect was the biggest when the primary F2 was 1 kHz or 2 kHz and between 45 dB SPL and 65 dB SPL of intensity level, and damped as primary frequency increased. The most significant reduction of DPOAE amplitude was 3.85 dB SPL; 3. When contralateral NBN was below 50 dB HL, the suppression was frequency-selective; and the most suppressive effect happened when NBN intensities were between 20 dB HL and 50 dB HL. 4. The noise floor in ipsilateral car canal has not been altered by contralateral noise (20-50 dB HL). The underlying mechanism was discussed in this study. It appears that contralateral suppressive effects of DPOAE can be used as a tool in exploring the function of medial olivocochlear system.