Brain‐stem Auditory‐evoked Response Peak Research Articles

Effect of gentamicin on the auditory analyzer in sexually immature animals.

Auditory function of immature rabbits was evaluated using two electrophysiological methods, brainstem auditory evoked response (BAER) and distortion product otoacoustic emission (DPOAE), in chronic experiments following administration of therapeutic doses of gentamicin. Impairment of auditory function manifested in increased thresholds and decreased amplitude of the 1st BAER peak was established. DPOAE parameters were not significantly changed. It was suggested that gentamicin decreased activity of spiral ganglion neurocytes in animals with immature auditory analyzer.

Changes in brainstem auditory evoked response latency predict survival after CPR in a rat model of cardiac arrest and resuscitation

Brainstem auditory evoked responses (BAER) are routinely used to monitor brainstem function in hospitalized comatose patients. We used a rat model of cardiac arrest and resuscitation to explore the possibility that the BAER, monitored during and immediately after cardiopulmonary resuscitation (CPR), could be used to determine whether the CPR was effective in restoring brainstem blood flow. Long–Evans rats were subjected to 7 min of cardiac arrest, induced by chest compression under Ketamine anesthesia sufficient to mechanically prevent the heart from pumping blood and were then resuscitated using a standard CPR protocol. During CPR, click stimuli were applied to one ear at 11/s and BAER averages recorded every 15 s. In three rats the BAER did not return after CPR; none of these rats respired spontaneously and all died. In 33 rats the BAER did return; within 15 min after the start of CPR BAER peak latencies decreased rapidly, increased again and then decreased. If the increase in the latency of the N2 peak was less than 0.3 ms, then the rat survived. If it was greater than 0.35 ms the rat died. This signal was used as a cue for intervention in three rats; two survived. Thus, in this preparation, the BAER provided a useful measure of CPR effectiveness, in time to permit successful intervention.

Gerbil brain-stem auditory-evoked responses to maximum length sequences

This study evaluated the feasibility of obtaining brain-stem auditory-evoked responses (BAERs) to trains of clicks with average rates of up to 500 clicks per second in the gerbil, in order to evaluate BAER behavior at rates higher than those possible in conventional averaging, and to evaluate whether these higher rates allow obtaining BAERs more efficiently. Gerbils were anesthetized with Nembutal, and normothermia was maintained with a homeothermic blanket system. Pseudorandom pulse trains, called maximum length sequences (MLSs), were generated by an Ariel DSP-16 board housed in an IBM-AT. Electrical activity was recorded with Grass needle electrodes placed subdermally. This activity was amplified and filtered by a Nicolet Compact Four, and digitized by the A/D of the Ariel DSP-16. Clicks were presented at levels of 50, 60, 70, 80, and 90 dB pSPL. Conventional BAERs were obtained at a rate of 30 Hz. MLS BAERs were obtained by presenting MLS pulse trains which were comprised of 64 pulses. Following collection of the response to MLS pulse trains, the MLS BAER was obtained by cross correlating the response with a recovery sequence. The minimum time between pulses is called the minimum pulse interval (MPI). MLS BAERs were obtained for MPIs of 6, 4, 2, and 1 ms. BAERs were obtained in ten young adult gerbils for all rate by click-level conditions. BAERs were observed in all animals for all click levels and rates. Generally, with increasing click level there were decreases in peak latencies and increases in peak amplitudes. With increasing rate (decreasing MPI), there were increases in peak latencies, increases in the i-iv interval, and decreases in peak amplitudes. Computations suggested the the most efficient rate (i.e., the rate producing a constant signal-to-noise ratio response in the least amount of time) is not necessarily the fastest rate, but depends on the BAER peak and click level.

Differential impact of hypothermia and pentobarbital on brain-stem auditory evoked responses

Two experiments were conducted to determine the effects of hypothermia and pentobarbital anesthesia, alone and in combination, on the brain-stem auditory evoked responses (BAERs) of rats. In experiment I, unanesthetized rats were cooled to colonic temperatures 0.5 and 1.0°C below normal. In experiment II, 2 groups of rats were cooled and tested at 37.5, 36.0, 34.5 and 31.5°C. One group was anesthetized during testing and the other group was awake. The rat BAER was sensitive to cooling of 1°C or less. Peak latencies were prolonged and peak-to-peak amplitudes were increased by hypothermia alone. The effect on amplitude may be related to the time course of temperature change or to stimulus level. Pentobarbital significantly affected both latencies and amplitudes over and above the effects of cooling. The specific effects of pentobarbital differed by BAER peak and by temperature. The findings point up the importance of the potential confound of anesthetic drugs in most of the evoked potential literature on hypothermia and, for the first time, quantify the complex interactions between pentobarbital and temperature which affect the BAER wave form.

Brainstem Auditory-Evoked Response in the Rat Normative Studies, with Observations Concerning the Effects of Ossicular Disruption

Six young adult Sprague-Dawley rats were unilaterally cochleotomized, Brain-stem auditory-evoked responses (BAERs) to clicks and to 1-, 2-, 4-, 8- and 16-kHz tone bursts were obtained. In addition, response thresholds were estimated before and after ossicular disruption in the noncochleotomized ear of 4 animals. With increasing tone burst frequency, there was a decrease in BAER peak latencies as well as a decrease in threshold. With increasing click and tone burst intensity, there was a decrease in peak latencies and an increase in peak amplitudes. BAER peak latency/intensity functions to click stimuli ranged from -.013 to -.018 ms/dB. With increasing tone burst frequency there was a decrease in the slope of the latency/intensity function. Following ossicular disruption, BAER thresholds to clicks were elevated by an average of 49 dB. Threshold shifts to tone burst stimuli were smallest for 1- and 2-kHz tone bursts (35-36 dB) and increased with increasing frequency up to a maximum of 65 dB for 16-kHz tone bursts.

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). I: Effects of click level, rate, and polarity.

Three experiments evaluating the effects of various stimulus manipulations on the click-evoked gerbil brain-stem auditory-evoked response (BAER) are reported. In experiment 1, click polarity and level were covaried. With increasing click level, there is a parallel decrease in the latency of the first five BAER peaks (i-v) and an increase in BAER peak amplitudes. Mean wave i amplitude was greater for rarefaction than condensation clicks at high click levels; mean wave v amplitude was greater for condensation clicks at higher click levels. Experiment 2 covaried click rate and polarity. The latency of the BAER peaks increased with increasing click repetition rate. This rate-dependent latency increase was greater for the later BAER peaks, resulting in an increase in the i-v interval with increasing click rate. As rate increased, the amplitudes of waves i and v decreased monotonically, whereas the amplitudes of waves ii-iv were largely uninfluenced by click rate. As in experiment 1, mean wave i amplitude was greater for rarefaction clicks, whereas mean wave v amplitude was greater for condensation clicks. The magnitude of these polarity dependencies on waves i and v amplitude decreased with increasing click rate. Experiment 3 evaluated the effects of click polarity on BAERs to high-intensity (100 dB pSPL) clicks presented at a rate of 10 Hz. In eight of ten gerbils evaluated, wave i amplitude was greater to rarefaction clicks, and, in all ten animals, wave v amplitude was greater to condensation clicks. The effects of click level and rate on BAER peak amplitudes, latencies, and interwave intervals are reminiscent of stimulus dependencies reported for the human BAER. The effects of click polarity on the amplitudes of waves i and v of the gerbil BAER have also been reported for the human BAER.

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). II: Effects of broadband noise level and high-pass masker cutoff frequency across click polarity.

Two experiments concerning the effects of masking noise on the gerbil brain-stem auditory-evoked response (BAER) are reported. Experiment 1 evaluated the effects of broadband masking noise on the BAER obtained to condensation and rarefaction clicks. With increasing noise level, there was an increase in BAER peak latencies, an increase in the i-v interval, and a decrease in peak amplitudes. Experiment 2 evaluated the effects of high-pass masking noise on the BAER obtained to condensation and rarefaction clicks. Both high-pass responses and derived-band responses were evaluated. For high-pass responses, with decreasing masker cutoff frequency, there was an increase in BAER peak latencies, a decrease in the i-v interval, and a decrease in peak amplitudes. For derived-band responses, with decreasing derived-band frequency, there was an increase in peak latencies and a decrease in the i-v interval. A comparison of wave i and wave v amplitudes across derived-band frequency demonstrates a greater contribution of high-frequency cochlear regions to wave i than wave v. Small, insignificant, effects of click polarity on BAER peak amplitudes were observed. These trends were in the direction seen in a companion paper [R. Burkard and H. F. Voigt, J. Acoust. Soc. Am. 85, 2514-2525 (1989)] and were, in general, reduced by the presence of broadband or high-pass maskers.