Effects of spontaneous otoacoustic emissions on distortion product otoacoustic emission

Objective: It has been reported that spontaneous otoacoustic emission (SOAE ) can prolong the responses or increase the echo power of transiently evoke d otoacoustic emission (TEOAE), yet the effects of SOAE on distortion produ ct otoacoustic emission (DPOAE) have been studied less thoroughly. As most of the previous studies have not paid attention to the patient's age, sex a nd hearing level, they have not reflected possible effects of those factors . We studied the effects of SOAE specifically on DPOAE in the following sub jects. Subjects and methods: The subjects were all females ranging in age f rom 19 to 24 (average: 21.4) and the 78 ears had a hearing threshold under 15 dB for 1, 2, and 4 kHz on pure-tone hearing test. IL088 (Otodynamics) wa s used for measurement of SOAE and IL092 (Otodynamics) for DPOAE. SOAEs wer e measured by time-averaging over 100 of the responses, of which those show ing a clear peak 3 dB above the noise floor and being reproducible were con sidered as SOAE-positive. In all the ears, DPOAE responses were measured at L-1 = L-2 = 70 dB, and in 42 ears also at L-1 = L-2 = 60 dB and L-1/L-2 = 60/50 dB. The subjected ears were grouped into two by the presence or the a bsence of SOAE, and DPOAE amplitudes of 1, 2, and 4 kHz were compared, resp ectively. Results: Of the total, 39 ears were SOAE-positive and 39 SOAE-neg ative. Statistically no significant difference was observed in the average hearing level between the SOAE-positive and SOAE-negative groups. The heari ng levels did not significantly differ in the frequencies of i, 2, and 4 kH z, respectively, indicating that influence of the hearing level on DPOAE co uld be excludable. DPOAE amplitudes at L-1 = L-2 = 70 dB in the frequencies of 1, 2, and 4 kHz were higher in the SOAE-positive group than in the SOAE -negative group. And DPOAE amplitudes were also higher in SOAE-positive gro up at L-1 = L-2 = 60 dB and L-1/L-2 = 60/50 dB in the frequency of 1, 2, an d 4 kHz, but significant differences were observed only in the frequencies of 4 kHz. By grouping the ears by the number of SOAE, we revealed the tende ncy that the larger the number of SOAE, the higher the DPOAE amplitudes. Co nclusions: We evidenced that SOAE has significant effects on DPOAE response s. In clinical application of DPOAE measurement, therefore, the effects sho uld be seriously taken into account. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.