Resposta auditiva em regime permanente evocada por ruído modulado: uma proposta de protocolo para identificação de perdas auditivas

Abstract

Aim: To propose a hearing loss identification protocol using steady-state auditory responses (ASSR) evoked by amplitude-modulated noise. Materials and Methods: The study consisted in two stages: the stage I of exploratory character and the stage II of investigation of the diagnostic accuracy of the stimuli. In stage I, twenty individuals (12 women) without any history of neurological or audiological diseases, aged from 18 to 59 years participated in stage I. The Audiostim system was used for stimuli generation and ASSR recording, in Fpz (ground electrode), Cz (active electrode) and (A1+A2)/2 (reference electrode) derivations. The tested stimuli were amplitude-modulated Wide-band noise (WBN), Low-band noise (LBN), High-band noise (HBN), Two-band noise (TBN) between 77 and 110 Hz, applied in intensity levels of 55, 45, and 25 dB sound pressure level (NPS). For detection, Magnitude-Squared Coherence (MSC) and Spectral F Test (SFT) were applied with a significance level of 5%. Detection times and rates were compared using the Friedman test and Tukey-Kramer as post hoc analysis. Besides, the true negatives (TN) were calculated in 16 different pass/fail protocols based on the stimulation parameters (stimuli types and intensity levels) and detection techniques (MSC or SFT). In stage II, thirty one individuals attended at Hearing Health Service of Hospital São Geraldo- HC / UFMG, aged between 16 and 70 years were included. Fifty two ears were considered, 32 with hearing loss of different degrees and 20 with normal hearing. The electrophysiological thresholds of WBN and TBN were estimated. The detection of responses was performed by MSC (α=0,05). The ROC curves were plotted considering the intensity range from 90 to 30 dB NPS for WBN and TBN. The areas under the curve were calculated and compared using the Mann-Whitiney test (α=0,05). The sensitivity and specificity of the WBN and TBN for each intensity (90 dB to 30 dB NPS) were obtained. Results: In stage I, the detection rates ranged from 100% to 55.6% in 55 dB NPS, 97.2% to 38.9% in 45 dB NPS and 66.7% to 8.3% in 25 dB NPS .The median detection times ranged from 68 to 157s for 55 dB NPS, 68-99s for 45 dB NPS, and 84-118s for 25 dB NPS. No statistical difference was found between MSC and STF considering the median detection times (p>0.05). TN above 90% were found for Protocols that employed WBN or HBN, at 55 dB NPS or that used WBN or HBN, at 45 dB NPS. For Protocols employing TBN, at 55 dB NPS or 45 dB NPS TN below 60% were found due to the low detection rates of stimuli that included low-band frequencies. In stage II, the ears with normal hearing had thresholds around 40 dB NPS in the evaluated bands. In mild losses the average thresholds ranged between 50 and 65 dB NPS. From moderate losses thresholds varied between 70 dB NPS and 80 dB NPS. The areas under the curve were 0.92 and 0.93 for the WBN of the TBN and did not differ statistically (p <0.05). Sensitivity was found above 95% for intensities below 50 dB NPS for the WBN and the TBN and in these intensities, specificity did not exceed 65%. In the intensities above 60 dB NPS sensitivity varied between 65% and 20% and specificity between 95% and 100% for both stimuli. The intensities of 50 and 60 dB NPS, the WBN had a sensitivity of 77% and specificity of 100% and 90% respectively. The TBN had a sensitivity of 97% at 50 dB NPS and 93% at 60 dB NPS and specificity of 80% at 50 dB NPS and 90% at 60 dB NPS. Conclusions: The application of RDB to 60 dB NPS showed sensitivity rates of 93% and specificity of 90%. These rates are consistent with those obtained by the OAE and the ABR (recommended tests to identify the stage of hearing screening programs).