ABSTRACT
This study aims at characterizing and comparing the findings of auditory brainstem response (ABR) using narrow-band chirp (NB-chirp) and tone burst (TB) for both latency and amplitude parameters among those exposed to occupational noise and to determine which among the two serves as a better indicator of noise-induced cochlear neuropathy. Forty adult males in the age range of 20-35 years were considered, wherein 20 of them were exposed to noise > 80 dB (A) for 8 hours per day constituting Noise-exposed group; and Control group consisted of 20 individuals without occupational noise exposure. ABR was recorded using NB-chirp and TB for four frequencies at 80 dB nHL through Etymotic Research - 3A (ER-3A) Insert phones using Interacoustics Eclipse EP-25 in individuals with and without noise exposure. MANOVA was performed to compare between TB ABR and NB-chirp ABR between the two groups. Statistical analysis revealed a notable difference for NB-chirp comparisons between the two groups at three frequencies: 500 Hz, F(1, 38) = 10.6; 1000 Hz, F(1, 38) = 7.91; and 2000 Hz, F(1, 38) = 6.64. Whereas, the difference was evident at only 500 Hz: F(1, 38) = 4.98 in case of TB ABR. However, there was no significant difference seen at any of the frequencies for amplitude parameters in both TB and NB-chirp ABR. Latency of wave V using NB-chirp was considered to be a better indicator compared to TB, acting as a better clinical tool in early identification, diagnosis, and monitoring of noise induced hearing loss (NIHL).
ABSTRACT
INTRODUCTION: Encoding of CE-chirp and click stimuli in auditory system was studied using auditory brainstem responses (ABRs) among individuals with and without noise exposure. MATERIALS AND METHODS: The study consisted of two groups. Group 1 (experimental group) consisted of 20 (40 ears) individuals exposed to occupational noise with hearing thresholds within 25 dB HL. They were further divided into three subgroups based on duration of noise exposure (0-5 years of exposure-T1, 5-10 years of exposure-T2, and >10 years of exposure-T3). Group 2 (control group) consisted of 20 individuals (40 ears). Absolute latency and amplitude of waves I, III, and V were compared between the two groups for both click and CE-chirp stimuli. T1, T2, and T3 groups were compared for the same parameters to see the effect of noise exposure duration on CE-chirp and click ABR. RESULT: In Click ABR, while both the parameters for wave III were significantly poorer for the experimental group, wave V showed a significant decline in terms of amplitude only. There was no significant difference obtained for any of the parameters for wave I. In CE-Chirp ABR, the latencies for all three waves were significantly prolonged in the experimental group. However, there was a significant decrease in terms of amplitude in only wave V for the same group. DISCUSSION: Compared to click evoked ABR, CE-Chirp ABR was found to be more sensitive in comparison of latency parameters in individuals with occupational noise exposure. Monitoring of early pathological changes at the brainstem level can be studied effectively by using CE-Chirp stimulus in comparison to click stimulus. CONCLUSION: This study indicates that ABR's obtained with CE-chirp stimuli serves as an effective tool to identify the early pathological changes due to occupational noise exposure when compared to click evoked ABR.
