Múltiplas respostas auditivas em regime permanente de 70 Hz a 110 Hz: uma proposta de triagem auditiva

Abstract

Multiple Auditory Steady-State Response (MASSR) has been reported in several studies as a complementary diagnostic method, mainly by its specific frequency audiological profile. Nevertheless, there is no consensus on clinical diagnostic protocols. Moreover, the use of MASSR in auditory screening is rarely reported. Thus, it is necessary to improve the technique to present standardized results, with protocols that can be replicated in clinical populations. The aim of this study is to determine a protocol for hearing screening based on 70 Hz to 110 Hz MASSR using the Audiostim (Center for Research in Engineering Biomedical- NEPEB/UFMG). The sample consisted of 23 individuals, aged between 9 and 12 years and normal hearing detected by pure tone audiometry. The silver/silver chloride electrodes were positioned at Cz (active electrode), below the hairline (reference) and Fpz (ground). Stimulation was binaural, consisting of four AM tones in each ear, whose carriers of 500, 1000, 2000 and 4000 Hz were modulated at 77.15 Hz, 86.91 Hz, 98.63 Hz, 104.49 Hz - right ear - and 81.05 Hz, 94.73 Hz, 100.59 Hz, 106.45 Hz - left ear. The record of MASSR was downward, testing the intensities of 50, 40 and 30 dB SPL. To identify the MASSR was used the Magnitude Squared Coherence (MSC) and the Spectral F Test (SFT). The results showed weak and asymmetric correlation between frequencies and the lowest intensity that evoked a response. On the other hand, as the behavior of the parameters of stimulation, the frequency of 500Hz showed significantly lower percentages of MASSR detection (p<0.05) than does of frequency of 2000Hz, for both techniques MSC and SFT. The intensity of 30 dB SPL showed significantly lower percentages of detection than the others (p<0.005) in both techniques. The MSC presented significantly higher percentages of detection (p<0.02) than the SFT, except for 50 dB SPL in the left ear. The results suggest the use of a stimulation protocol and recording of MASSR in auditory screening, that consisting in assessment the carriers of 1000 Hz, 2000 Hz and 4000 Hz in the 50dB SPL intensity (negative predictive values above 90%) with the MSC. However, it is still necessary to carry out researches in individuals with hearing loss and the analysis of efficiency of other types of stimulation for determining a protocol with adequate levels of sensitivity and specificity.