AbstractsBiology & Animal Science

This study investigates how well the air- (AC) and bone-conduction (BC) auditory steady-state response (ASSR) detects conductive hearing loss compared to the gold standard method, the auditory brainstem response (ABR). Similar studies using infants with sensorineural hearing loss have suggested that the ASSR is an effective method for assessing hearing thresholds and detecting hearing loss in infants. This study compares AC and BC ASSR and ABR thresholds in infants with normal hearing and conductive loss. Twenty-three normal hearing infants and 15 infants with conductive hearing loss (0-6 months) were assessed using the ABR and 80-Hz ASSR elicited to AC and BC stimuli (AM²). Mean thresholds for normal hearing infants were : 500 Hz (i) AC ABR : 25 dB nHL, (ii) BC ABR : 10 dB nHL, (iii) AC ASSR : 30 dB HL , (iv) BC ASSR : 17 dB HL and 2000 Hz (i) AC ABR : 18 dB nHL, (ii) BC ABR : 15 dB nHL, (iii) AC ASSR : 20 dB HL, (iv) BC ASSR : 26 dB HL. For infants with confirmed conductive hearing loss, 500 Hz thresholds air-conduction ABR thresholds increased to approximately 48 dB nHL, while bone-conduction ABR thresholds were approximately 12 dB nHL. Air-conduction ASSR thresholds for infants with conductive hearing loss increased to approximately 37 dB HL and bone-conduction thresholds were approximately 15 dB HL. Overall, mean bone-conduction thresholds were similar between groups, while there was a trend for mean air-conduction thresholds to be higher for infants with conductive hearing loss than infants with normal-hearing for both ABR and ASSR testing methods. Previously suggested “normal levels” in the literature appear to be too high to detect mild conductive hearing loss at 500 Hz. Normal levels of 40 and 30 dB HL is suggested for air- and bone conduction 500 Hz ASSR, respectively, to be more accurate in detecting mild hearing losses. Even with an adjusted “normal level”, it appears to be difficult to use the ASSR to differentiate between normal hearing and mild conductive hearing loss. More research is needed using infants with varying degrees of hearing loss at multiple frequencies.