Abstract #774, Date Wednesday, Jan 30 2002 1:00PM - 12:00PM Session V1 DPOAE
Audiometric Threshold Estimation in Cochlear Hearing Loss Ears by Means of Weighted Extrapolated DPOAE I/O-Functions
Johann Andreas Oswald, Jörg Müller, Thomas Janssen
DPOAE threshold and audiometric threshold have been shown to be closely related when estimating DPOAE threshold by simply extrapolating DPOAE I/O-functions using linear regression analysis (Boege and Janssen 2001). The purpose of this study was to improve and to evaluate this new method for clinical application. DPOAE I/O-functions were recorded in 826 sensorineural hearing loss ears at up to 50 frequencies between 500 Hz and 8 kHz in a wide level range from L2=20 to L2=65 dB SPL at up to 10 levels (L1=0.4 L2+39). DPOAEs were accepted as valid for signal-to-noise ratios (SNR) exceeding 6 dB. For estimating DPOAE threshold an extrapolation of the DPOAE pressure I/O-function was performed by determining the point of intersection of the extrapolated regression line with the L2 coordinate. In the linear fit pDP(L2)=a+bL2, a and b give the threshold and the slope of the DPOAE growth, respectively, representing estimates of sensitivity and compression of the cochlear amplifier. According to Boege and Janssen, in 54% of the DPOAE I/O-functions a linear dependency of the DPOAE sound pressure pDP on the primary tone level L2 was found. However, when adapting the proposed acceptance criterions and using weighted LMSE regression with two independent weighting factors Min&[sum] w1 w2(pDP (L2)-p(L2))2 with w1=70-L2 and w2=SNR(L2)/6dB, 74% of the I/O-functions (n=12165) can be used for the linear fit. High correlation and small differences between DPOAE-threshold and pure-tone threshold (r=0.52, Mean 3.8 dB, SD 12.7 dB) were found, which proves weighted extrapolated DPOAE I/O-functions to be a valuable clinical tool for estimating quantitatively cochlear hearing loss.