The Influence On The Hearing Tests In Infants By Changing The Frequency Modulation Depth Of Auditory Steady-state Responses

ObjectiveThe purpose of the study was to find the optimal modulation methods of auditory steady-state responses (ASSR) that were most compatible to the behavior auditory thresholds by comparing the ASSR thresholds in different stimulation parameters obtained from infants with normal hearing and sensorineural hearing loss, and to provide the reliable evaluation to infants with hearing loss for diagnosis and treatment.MethodsSeventy-five infants with normal hearing and sixty infants with sensorineural hearing impairment were randomly selected at our center from January,2009 to August,2009. Their ages ranged between 6 and 36 months.All the normal hearing infants received VRA(visual reinforcement audiometry) and ASSR in one of three stimulation parameters which were amplitude modulation (100%AM, ModulationⅠ), ModulationⅡ(100%AM+10%FM) and ModulationⅢ(100%AM+15%FM). The subjects were tested in one of these modulations according to the randomized, controlled, double-blind principle and divided into three groups accordingly. There were fifteen infants (twenty-five ears) in GroupⅠ, thirty infants (fifty-two ears) in GroupⅡ, and other thirty infants (fifty ears) in GroupⅢ. Multiple comparisons among three groups were made from the thresholds of ASSR and VRA responses to demonstrate the ideal modulation parameter of ASSR which was compatible to the behavior auditory thresholds of normal hearing infants.Auditory brainstem response (ABR), ASSR with Modulation II and ModulationⅢwere administered to the infants with sensorineural hearing loss. These pediatric patients were divided into three groups based on the ABR thresholds:group of mild hearing loss (twelve cases, twenty ears); group of moderate-severe hearing loss (eighteen cases, thirty ears); group of severe-profound (thirty cases, fifty-six ears). Comparisons were carried out from the ASSR thresholds of ModulationⅡand ModulationⅢto demonstrate the proper modulation parameters to the infants with sensorineural hearing loss. Results1. Results for VRA thresholds among three groups in normal hearing infants were not significantly different. There was significant difference between ASSR and VRA thresholds, however the distinction between ASSR with MM (ModulationⅡ, Modulation III) and VRA was lower than that between ASSR with AM (ModulationⅠ) and VRA.2. The thresholds of all the three groups in 250 to 4000Hz were significant different (F=10.56,16.26,18.99,11.64,9.41, P<0.05).3. For the three groups, the ASSR thresholds at 250 to 4000Hz and the VRA thresholds were correlated significantly (P<0.05).4. The difference of thresholds between ASSR (ModulationⅠ) and VRA showed significantly higher than difference of ModulationⅡversus VRA and ModulationⅢversus VRA (P＜0.05) through multiple comparisons among three groups in the infants of normal hearing. The thresholds of ModulationⅡand ModulationⅢwere significant different in the 250,500 and 1000Hz carrier frequency (P＜0.05), however not in the 2000, 4000 Hz carrier frequency (p=0.215,0.058).5. By comparing the thresholds of ASSR with ModulationⅡand ModulationⅢfor the infants with mild or moderate-severe sensorineural hearing loss, there was significant difference in the 250,500, 1000Hz carrier frequency affected by the FM depth (P=0.000), but little difference in the 2000 and 4000Hz carrier frequency (p=0.056, 0.090,0.297,0.339, respectively). The comparison also demonstrated the thresholds in ModulationⅢ(100%AM±15%FM) were inferior to those in ModulationⅡ(100%AM +10%FM) respectively.6. The thresholds of ASSR in the 250,500,1000,2000 and 4000Hz carrier frequency weren't affected by the change of the FM depth for the severe-profound hearing impairment group (P=0.422,0.501,0.749,0.888,0.496, respectively)Conclusions1. Among the infants with normal hearing, the mixed modulation (MM) produced smaller thresholds than AM stimuli. The hearing thresholds decreased with the moderate augmentation of the FM depth in MM, especially in the low carrier frequencies (250,500, 1000Hz).2. For the infants with mild or moderate-severe hearing loss, the ASSR thresholds decreased apparently with the moderate augmentation of the FM depth in MM and more similar to the behavior auditory thresholds, especially in the low carrier frequencies.3. The ASSR thresholds weren't influenced by the change of the FM depth in MM for the severe-profound group.