Assessment of the medial olivocochlear efferent system in children. Pure tone 1.0 kHz and 2.0 kHz suppressive effects on transient evoked otoacoustic emission

The role of medial efferent system in regulating outer hair cell function has been studied by many investigators. Usually narrow band noise or white noise as contralateral stimulation (CS) suppressors have been used and changes in OAE amplitudes estimated. Thirty children aged 6-15 years (mean 12.5 ± 4.7), without any changes in tonal and impedance audiometry and with negative history regarding otiatric diseases were examined. Transient evoked otoacoustic emissions (TEOAE) were recorded using ILO 92 Otodynamics Analyser. CS was performed using 1.0 kHz and 2.0 kHz continuous pure tones of 30 dB SL or 50 dB SL. Effects of CS on TEOAE evoked by click of 80, 70 and 60 dB SPL were investigated. TEOAE analysis included assessment of TEOAE amplitude of half octave frequency bandwidth (HOFBW-1.0; HOFBW-1.5; HOFBW-2.0; HOFBW-3.0 and HOFBW-4.0 kHz) and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes centred at 1.0; 2.0; 3.0; 4.0 and 5.0 kHz. TEOAE amplitude recorded for stimuli 80, 70 and 60 dB SPL without CS decreased: mean values respectively 6.1 ± 4.2; 5.4 ± 4.5 and 3.3 dB SPL ± 4.3. CS effect on TEOAE was observed for all CS options, however, larger suppressive effect was recorded on TEOAE elicited by 70 dB SPL stimulus using 1 kHz/50 dB SL tone as a suppressor and on TEOAE elicited by 60 dB SPL stimulus using 2 kHz/50 dB SL tone as a suppressor. HOFBW and 0.8-FBW analyses showed the association between the frequency/intensity of the suppressors and decreasing of amplitudes of adequate frequency bands. It is concluded that the described method of investigating of the medial olivocochlear efferent system seems to be sensitive and confirms frequency-dependent suppressive effect on OAE.