Īuditory neuropathy spectrum disorder (ANSD) is a unique type of hearing disorder characterized by normal OHCs function as indicated by the presence of cochlear microphonics (CMs) and/or otoacoustic emissions (OAEs) and absent or severely abnormal auditory brainstem responses (ABRs), absent middle ear muscle reflexes (MEMRs) and abnormal olivocochlear bundle function. Damage of the OHCs causes elevation of the lowest stimulus level required for detection of the basilar membrane motion, compression reduction, and more steepened slope of the I/O function. Normal DPOAE-I/O function show a linear growth in response to low stimulus levels when the basilar membrane is driven at its characteristic frequencies (CF) followed by nonlinear growth (compression) at moderate levels, and a linear response to stimuli presented at high levels. DPOAEs also give information about the rate of growth of cochlear response as a function of increasing stimulus level and this is called DPOAE input/output (DPOAE-I/O) functions. DPOAE amplitudes and signal-to-noise ratio (SNR) are measured, that are judged whether they are normal or not. In such a condition, a distortion product-gram (DP-gram) is recorded in response to single intensity moderate sounds along with a wide range of different frequencies (e.g., 500–8000 Hz). ĭPOAEs are used for identifying normal or impaired OHCs function. ![]() This nonlinearity is essential for normal auditory function including auditory sensitivity, sharp frequency resolution, and wide dynamic range of sounds received by the ear. ![]() This finding suggested different OHC pattern of activity in ANSD patients.ĭistortion-product otoacoustic emissions (DPOAEs) are byproducts of the outer hair cells (OHCs) nonlinearity when two tones interact within the cochlea. Conclusionsĭespite normal DPOAEs recordings in ANSD patients, their amplitudes and DP I/O function are different from that of normal hearing subjects. The pattern of DPOAEs I/O function was different in ANSD and it was dependent on the frequency and intensity of the stimulus. ResultsĭPOAEs amplitudes were significantly higher in ANSD group when compared with control. All cases were subjected to basic audiological evaluation, DPOAEs I/O function recorded at four frequencies of 2f1-f2 and 5 intensity levels of L1 and L2. ![]() This work included 2 groups: control group (GI) composed of 20 normal hearing subjects and study group (GII) consisted of 20 patients with ANSD. This study is designed to address whether the input/output function of distortion product OAEs (DPOAEs I/O) in ANSD patients is similar or different from normal hearing subjects. Auditory neuropathy spectrum disorder (ANSD) is characterized by normal OHCs function as shown by intact cochlear microphonics (CMs) and/or otoacoustic emissions (OAEs) absent or grossly abnormal auditory brainstem responses (ABRs) and absent middle ear muscle reflexes.
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