Assr

auditory steady state response
Al Basra General Hospital

1. Auditory Steady-State Response By Dr. Sayf Moniem D. M.B.Ch.B SHO ORL-HNS

2. Reference Cummings Otolaryngology Head & Neck Surgery FIFTH EDITION Carolyn J. Brown, Ph.D. Professor Department of Communication Sciences and Disorders Department of Otolaryngology–Head and Neck Surgery University of Iowa Carver College of Medicine Iowa City, Iowa Essential otolaryngology 9 th edition Derald E. Brackmann MD , FACS Clinical professor of ORL-HNS Clinical professor of neurosurgery University of California school of medicine President House clinic Board of Director , House Ear Institute LA , California Web site search using the key word “ Auditory steady state response “

3. Auditory Steady-State Response : is an auditory evoked potential, elicited with modulated tones that can be used to predict hearing sensitivity in patients of all ages & to predict hearing thresholds for normal hearing individuals and those with hearing loss . The ASSR uses statistical measures to determine if and when a threshold is present . the ASSR can be successfully recorded even from sleeping children . ASSR measures assumed a prominent role either in place of or in addition to ABR—as a means of estimating audiometric thresholds in pediatric populations. Additionally , the ASSR could be recorded from individuals with no measurable ABR

4. It defer from ABR in that the amplitude &/or frequency of the continuous tone is not constant but modulated at rate between 3-200 Hz , so the evoked response follow the rate of modulation rather than the frequency of the tone. ASSR that originate in the brain stem can be obtained by using modulation rate of 70 Hz or greater Lower modulation rate can result in ASSR that represent the brain stem & the cortical area.

5. Differences: ASSR looks at amplitude and phases in the spectral (frequency) domain rather than at amplitude and latency. ASSR depends on peak detection across a spectrum rather than across a time vs. amplitude waveform. ASSR is evoked using repeated sound stimuli presented at a high rep rate rather than an abrupt sound at a relatively low rep rate. ABR typically uses click or tone-burst stimuli in one ear at a time, but ASSR can be used binaurally while evaluating broad bands or four frequencies (500, 1k, 2k, & 4k) simultaneously. ABR estimates thresholds basically from 1-4k in typical mild-moderate-severe hearing losses. ASSR can also estimate thresholds in the same range, but offers more frequency specific info more quickly and can estimate hearing in the severe-to-profound hearing loss ranges. ABR depends highly upon a subjective analysis of the amplitude/latency function. The ASSR uses a statistical analysis of the probability of a response (usually at a 95% confidence interval ). ABR is measured in microvolts (millionths of a volt) and the ASSR is measured in nanovolts (billionths of a volt).

6. Methodology The same to traditional recording montages used for ABR recordings. Two active electrodes are placed at or near vertex and at ipsilateral earlobe/mastoid with ground at low forehead. If collecting from both ears simultaneously, a two-channel pre-amplifier is used . When single channel recording system is used to detect activity from a binaural presentation, a common reference electrode may be located at the nape of the neck. Transducers can be insert earphones, headphones, a bone oscillator, or sound field and it is preferable if patient is asleep. Unlike ABR settings, the high pass filter might be approximately 40 to 90 Hz and low pass filter might be between 320 and 720 Hz with typical filter slopes of 6 dB per octave. Gain settings of 10,000 are common, artifact reject is left “on”, and it is thought to be advantageous to have manual “override” to allow the clinician to make decisions during test and apply course corrections as needed. Most equipment provides correction tables for converting ASSR thresholds to estimated HL

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