RESUMO
BACKGROUND: Auditory steady-state responses (ASSR) is an objective method of hearing examination in clinic in recent years. ASSR has the frequency specificity as compared with previous auditory brainstem responses (ABR).OBJECTIVE: To investigate the accuracy of ASSR in objective hearing assessment.DESIGN: A case-control observation.SETTING: Department of Otorhinolaryngology, the First Affiliated Hospital of Sun Yat-sen University.PARTICIPANTS: The subjects in the normal hearing group were the 21 undergraduates (42 ears) were enrolled, they all had not any symptoms of ear disease, without history of noise exposure and disease of vestibule system, and they were normal in otoscopy. The outpatients and inpatients with neurosensory deafness were selected from the Department of Otorhinolaryngology, the First Affiliated Hospital of Sun Yat-sen University. All the children cases worn hearing aids, and had the speech ability, and cooperated in the examination. The main types included 6 ears of sudden deafness,8 ears of presbycusis, and 20 ears of neurosensory deafness due to other unknown causes. Central lesions were excluded by MR examination, and all the patients agreed with the enrollment. The results of pure-tone audiometry were all flat or descending audiogram. According to the severity of hearing damage, the patients were divided into mild deafness group (13ears), moderate deafness group (9 ears) and moderate-to-severe deafness group (12 ears).METHODS: ① The pure-tone audiometry was performed at the frequencies of 0.125-8 000 Hz in a sound insulation room. The auditory threshold grades of the subjects with normal hearing all accorded with the standards of GB-7583-87 expected value distribution. The average value of air-conduction auditory thresholds of pure-tone audiometry at the frequencies of 0.5, 1, 2 and 4 kHz was calculated. ② ASSR measurement was performed with the synchronous stimulation pattern in a sound and electromagnetic shielding room, including 8 points for both ears of the same stimulation intensity and the carrier frequency tones of 0.5, 1, 2 and 4 kHz respectively.③ ABR examination was performed by click sounds with sparse waves in a sound and electromagnetic shielding room, and insert earphones were used.The threshold results were judged according to the minimal stimulation sound intensity of the distinguishable Ⅴ wave. ③ The results of pure-tone audiometry were compared with those of ABR examination, and the results of ASSR measurement in different hearing groups were processed with analysis of variance, multi-classification discrimination based Bayes standard and q test.MAIN OUTCOME MEASURES: The thresholds of pure-tone audiometry, ASSR measurement and ABR examination, and the correct rate analyzed by the multi-classification discrimination based Bayes standard were mainly observed.RESULTS: The indexes of the 42 ears in the normal hearing group, 13, 9 and 12 ears in the mild, moderate and moderate-to-severe deafness groups were all involved in the analysis of results. ① The ABR values were accorded with the actual hearing levels, and the closest to the ASSR thresholds at 1-2 kHz; ASSR reflected induction rates at different frequencies were gradually decreased with the aggravation of hearing damage, and that at each frequency varied with the changes of hearing level, the induction rates of ASSR responses were all 100% for the subjects with normal hearing and patients with mild deafness, but those for the patients with moderate and moderate-to-severe deafness were decreased (0.5 kHz: 77.8%,92.8%; 4 kHz: 88.9%, 85.7%). At different frequencies, the ASSR thresholds in the moderate-to-severe deafness group were significantly higher than those in the normal hearing group (P ＜ 0.05). The ASSR thresholds at 0.5 and 4 kHz in the moderate-to-severe deafness group were significantly higher than those in the mild deafness group (P ＜ 0.05). The ASSR threshold at 2 kHz in the mild deafness group was significantly higher than that in the normal hearing group (P ＜ 0.05). The ASSR thresholds at 4 kHz in the everedeafness group were significantly higher than those in the normal hearing group and mild deafness group. ② The incorrect discriminations of actual pure-tone audiometry were analyzed with the interactive clustering discriminant analysis of ASSR measurement and actual pure-tone audiometry, and the results showed that the correct rate of discrimination was 100% in the normal hearing group; Only 1 of the 12 cases in the mild deafness group was incorrectly judged, and the correct rate was 92%; Only 1 of the 19 cases in the moderate deafness group was incorrectly judged, and the correct rate was 89%; the correct rate in the moderateto-severe deafness group was 83%.CONCLUSION: The results of ASSR measurement can detect the incorrect discrimination of objective hearing condition by taking the results of pure-tone audiometry as the standards. ASSR has an acceptable accuracy for deafness higher than mild level in estimating objective hearing, and it has a better prospect of application in practice.