Auditory brainstem response

Early auditory evoked potentials ( ABR ) are a subset of auditory evoked potentials. They have their electrical source in the auditory pathway between the cochlea, the auditory nerve to the various core areas in the brain stem (upper olivary nucleus ( superior olivary nucleus ) ), Lateral loop ( lateral lemniscus ), Low four hills core ( inferior colliculus ) ). The ABR signal composed of 5 waves, which are numbered according to the Erstbeschreibern Jewett and Williston ( 1971) with JI to JV. Clinically assigns to the origin of each wave a core area in the brain stem, although intraoperative measurements do not support this interpretation.

The ABRs or their measurement are as BERA ( brainstem evoked response audiometry; German: auditory brainstem response ), ABR ( auditory brainstem response) or BAEP ( brainstem auditory evoked potentials) respectively.

Areas of application

FAEPe have two basic applications:

The medical use areas will thus overlap between the fields especially the ENT, Phoniatrics - Pedaudiology one hand and neurology on the other.

• Topodiagnosis: throughput time compared with standard tables or by intra-individual comparison page to disease of the auditory nerve can be investigated. After sudden hearing loss, dizziness, tinnitus ABRs are routinely performed to exclude an acoustic neuroma, but is increasingly being replaced by imaging methods (MRI). Also lead degenerative or inflammatory diseases such as multiple sclerosis as an early sign of a Hörnervenbeteiligung to changes in the maturity and potential.
• Hearing threshold: Especially in pediatric audiology, but generally in uncooperative patients, ABRs are used to determine the threshold of hearing, as they are found especially in sedation or general anesthesia. The stimulus level at which the potential JV is no longer detectable, corresponds to the threshold of hearing. By stimulus filtering process (eg notched noise) and frequency-specific measurements can be made.
• Newborn: Automated Derivation of ABR (so-called measurement AABR ) is provided by an evaluation algorithm of the devices. In recognition of the correct potentials defined stimulus level is a "pass " is displayed as a result, otherwise in case of failure or lack of potential for a " refer ". With combination devices can be changed after the AABR immediately into the diagnostic mode.
• Neuromonitoring: mainly used in neurosurgery.

Stimulation

By default, worked on headphones with capsule with a click stimulus ( also tone -burst ). Including Insert hose or speakers are rarely used because of the longer duration of the stimulus to the eardrum synchronization in the auditory nerve becomes worse.

Derivation / electrode position

The active area of ​​the brain, the "source" should, if possible between the discharge electrodes (1) and (2) are: (1) cowlick on the head ( Cz in the 10-20 system; " vertex "); ( 2) behind the ear ( " mastoid "). A third electrode ( 3) is used as a reference ( "ground" ), usually the forehead or neck.

Evaluation

The auditory pathway generates the following responses:

• Wave I - the peripheral portion of cranial nerve VIII
• Wave II - the central portion of the vestibulocochlear nerve
• Wave III - cochlear nucleus
• Wave IV - the core complex of the superior olivary nucleus respectively. of the lateral lemniscus
• Wave V - lateral lemniscus or. inferior colliculus

The form of the five ABR waves (JI to JV ) depends on the volume of the stimulus from ( stimulus level). Latency is defined as the time between stimulus beginning ( " onset" ) and wave maximum amplitude as the difference between maximum and subsequent minimum.

For the audiological ABR absolute latencies are measured ( stimulus to wave maximum, denoted by LV, LIII or LI), and plotted against the stimulation level ( level latency diagram PLD). From the comparison of the individual PLD with standard curves can be seen on the threshold of hearing - and in the case of hearing loss - close to the place of hearing.

For the neurological ABR compared at a fixed level, the measurement curves of the right and left ear. If this side differences or changes in shape of the waves notice you measure relative latencies (eg LV LI, so-called " brain stem Term").

Only if the measurement parameters are identical, measurement results from different laboratories can be compared.

Technical details of the measuring apparatus

The differences between the various technical parameters of the measuring equipment for the two areas of application, the table shows:

ASSR

ASSR stands for Auditory steady-state responses (translated: Duration responses to auditory stimuli ).

Auditory evoked brainstem potentials are usually transient ( " volatile " ) potentials of a brain stem response to a tone or click stimulus with a latency of 1-20 ms after the stimulus. ASSR are clicks, but preferably by amplitude ( AM) and frequency modulated (FM) stimuli ( usually chirps ) triggered offered at such a high repetition rate, so that overlap the transient responses in the brain stem and thus an apparent duration of response is produced. Through statistical measurements, the ASSR from the signal -to-noise ratio ( SNR, signal - to-noise ratio ) can be calculated. Typically, the amplitude of the stimulus response is compared with the background noise of the EEGs, or its phase variability. One way to "measure" ASSR to it, to submit a number of responses or an averaged response of an FFT in order to investigate amplitude and phase can be. When the amplitude of the ASSR has a significant SNR, the reply is evaluated as "present". In contrast to the classical FAEP no visual, subjective curve assessment by the examiner is required in assessing the ASSR. For stimulus presentation of different frequency chirps with low varying the repetition time can simultaneously both ears with multiple frequencies are measured simultaneously, which over the conventional frequency-specific ABR derivation represents a significant time advantage. By means of device-specific standard value curves can be " calculated " from a frequency- specific ASSR audiogram.