The auditory steady state response: Far-field recordings from the chinchilla

External and middle ear influence on envelope following responses

Considerable between-subject variability in envelope following response (EFR) amplitude limits its clinical translation. Based on a pattern of lower amplitude and larger variability in the low (<1.2 kHz) and high (>8 kHz), relative to mid (1-3 kHz) frequency carriers, we hypothesized that the between-subject variability in external and middle ear (EM) contribute to between-subject variability in EFR amplitude. It is predicted that equalizing the stimulus reaching the cochlea by accounting for EM differences using forward pressure level (FPL) calibration would at least partially improve response amplitude and reduce between-subject variability. In 21 young normal hearing adults, EFRs of four modulation rates (91, 96, 101, and 106 Hz) were measured concurrently from four frequency bands [low (0.091-1.2 kHz), mid (1-3 kHz), high (4-5.4 kHz), and very high (vHigh; 8-9.4 kHz)], respectively, with 12 harmonics each. The results indicate that FPL calibration in-ear and in a coupler leads to larger EFR amplitudes in the low and vHigh frequency bands relative to conventional coupler root-mean-square calibration. However, improvement in variability was modest with FPL calibration. This lack of a statistically significant improvement in variability suggests that the dominant source of variability in EFR amplitude may arise from cochlear and/or neural processing.

Characterization of interstimulus interaction in the multiple auditory steady-state responses at high sound levels

Multiple auditory steady-state response (MASSR) is recommended to estimate hearing thresholds in difficult-to-test individuals. The multiple stimuli that evoke MASSR may present an interstimulus interaction (ISI) that is able to distort the generation of responses. No consensus exists on the effects of the ISI in MASSR when dealing with high sound level stimuli or cases of sensorineural hearing loss. This study investigated the effects of ISI on the amplitude and detectability of auditory steady-state responses, with a focus at and above 65 dB sound pressure level (SPL). Normal hearing (NH) and sensorineural hearing impaired (SNHI) adults were tested with different stimulus types [amplitude modulation (AM) One octave chirp (OC), and a weighted OC (WOC)], stimulus levels, and modalities (single or multiple stimuli). ISI typically attenuated response amplitude of a control stimulus caused by an interference stimulus one octave above the control stimulus. At and above 80 dB SPL, attenuations of around 50% decreased the number of detectable responses near SNHI thresholds, especially for OC and WOC. AM stimuli obtained a higher detection rate than OC and WOC when presented 10 dB above the behavioral hearing threshold of SNHI participants. Using OC in MASSR when assessing elevated thresholds might diminish accuracy on threshold estimation, and extend test duration.

Viability of intraoperative auditory steady state responses during intracranial surgery

BACKGROUND

For intraoperative monitoring of auditory nerve function, the auditory steady-state response (ASSR) analysis may be an alternative to brain stem auditory evoked potentials, offering frequency specificity and short detection times. Clinical studies investigating the viability of ASSR under total intravenous anesthesia have not been performed.

METHODS

During craniotomy under total intravenous anesthesia with propofol and remifentanil in 20 patients, ASSR were recorded. An additional control patient undergoing cerebellopontine angle surgery was included, in whom the auditory nerve could not be preserved. One-minute sinus tones (500, 1,000, 2,000 Hz) were applied with 60-, 70-, and 80-decibel hearing level. Stimuli were amplitude modulated with 40, 90, or 110 Hz and applied monaurally to the left and right ears. Time to detect a significant response and response amplitudes at 40, 90, or 110 Hz in the evoked EEG spectra was evaluated.

RESULTS

Overall, 90-Hz ASSR were successfully detected in all 20 patients, 110 Hz in 18 patients, and 40 Hz in 14 patients after a median of 10 seconds. No ASSR could be detected in the control patient at the end of the surgical procedure. Time-to-significance and ASSR amplitudes were influenced by stimulus intensity, carrier, and modulation frequency (Scheirer-Ray-Hare test, P < 0.005). Ipsilateral responses were higher than contralateral (P < 0.0001).

CONCLUSIONS

In conclusion, 90- and 110-Hz ASSR can be reliably detected under total intravenous anesthesia. Our results are in line with those from previous studies in awake patients. Auditory steady-state response during anesthesia may enable intraoperative frequency-specific audiometry and monitoring of the auditory nerve.

ABR obtained from time-efficient train stimuli for cisplatin ototoxicity monitoring

BACKGROUND

Nonbehavioral methods for identifying cisplatin ototoxicity are important for testing patients with cancer who become too tired or sick to provide a reliable response. The auditory brainstem response (ABR) is a nonbehavioral test that is sensitive to ototoxicity but can be time consuming to implement over a range of frequencies and/or levels. To address this issue, trains of stimuli were developed that offer reliable ABR testing over a range of tone-burst frequencies and levels at a time savings of 77% relative to tone-burst stimuli presented individually. The clinical accuracy of this new method has yet to be determined on a clinical population.

PURPOSE

This project was designed to determine the test performance of a time-effective ABR methodology aimed at identifying hearing shifts from cisplatin among veterans. A secondary goal was to determine whether improved test performance could be achieved by including our previously developed ototoxicity risk assessment model in the ABR prediction algorithm.

RESEARCH DESIGN

A set of discriminant functions were derived using logistic regression to model the risk for cisplatin-induced hearing change. Independent variables were one of several ABR metrics alone and combined with an ototoxicity risk assessment model that includes pre-exposure hearing and cisplatin dose. Receiver operating characteristic curve analysis was used to evaluate the test performance of these discriminant functions.

STUDY SAMPLE

Twenty-two male veterans treated with cisplatin for various cancers provided data from a total of 71 monitoring appointments.

DATA COLLECTION AND ANALYSIS

Data were collected prospectively from one ear of each participant as designated below. Hearing shift was determined for frequencies within an octave of each patient's high-frequency hearing limit, tested in 1/6th-octave steps. ABRs were monitored using a set of two intensity trains from the highest two multiple frequency tone-burst center frequencies (up to 11.3 kHz) that yielded a robust response at baseline. Each intensity train was presented at 65-105 dB peSPL in 10 dB steps. Scorable ABRs were generally limited to the highest two intensities; therefore, analyses concern those levels.

RESULTS

The ABR measurement failure was high, up to 52% for some frequencies and levels. Furthermore, the ABR was not frequently obtained at levels below 85 dB peSPL, consistent with previous studies that suggest a stimulus level of greater than 80 dB peSPL is required to obtain a reliable response to trained stimuli. Using multivariate metrics that included the dose-ototoxicity model, the most accurate scoring function was change in amplitude at lowest half-octave frequency obtained at 105 dB (change in wave V amplitude at frequency 2/105). However, absence of wave V at a monitor patient visit of the ABR response at levels 105 or 95 dB peSPL was deemed the preferred scoring function, because it had lower measurement failure and was within one standard error of the most accurate function.

CONCLUSIONS

Because of the large number of responses that could not be measured at baseline, this technique as implemented holds limited value as an ototoxicity-monitoring method.