Brainstem auditory evoked response

few slides on basics of auditory evoked responses.
will be helpful for neurology and audiology students and healthcare professionals

1. BRAINSTEM AUDITORY EVOKED RESPONSE MEENAKSHY SUDEEP BSc NEUROTECHNOLOGY

2. HISTORY 1967, Sohmer and Feinmesser were the first to publish ABRs recorded with surface electrodes in humans which showed that cochlear potentials could be obtained non-invasively 1971, Jewett and Williston gave a clear description of the human ABR and correctly interpreted the later waves as arriving from the brainstem 1977 , Selters and Brackman published landmark findings on prolonged interpeak latencies in tumor cases

3. 1974 , Hecox and Galambos showed that ABR could be used for threshold estimation in adults and infants 1975, Starr and Anchor were the first to report effect on ABR of CNS pathology in the brain stem

4. BAEP Brainstem Auditory Evoked Potentials are electric field potentials generated with repetitive auditory stimulation of auditory pathways

5. BAEP Brainstem auditory evoked potentials (BAEPs) reflect neuronal activity in the auditory nerve, cochlear nucleus, superior olive, and inferior colliculus of the brainstem These potentials are recorded from ear and vertex in response to brief auditory stimulation BAEP comprise five or more waves within 10ms stimulus

6. BAEP Short Latency Response < 10mS Middle Latency Response 10 – 100mS Long Latency Response > 100ms

7. BAEP: ELECTRODE PLACEMENT RECORDING ELECTRODE: Cz placed at vertex REFERENCE ELECTRODE: A1 placed at ipsilateral ear lobule or mastoid process GROUND ELECTRODE: A2 p0laced at contralateral ear lobule

8. METHOD OF RECORDING To elicit and record BAEPs an auditory stimulus is delivered to the patient via headphones Auditory stimulus is a s quare wave pulse of 0.1 ms duration The pulse can move earphone diaphragm either towards or away from the ear The earphone movement towards the ear is called condensation phase stimulus The stimulus away from patients ear is called rarefaction stimulus

9. Intensity of stimulation in stimulating ear rangs from 70 to 100 dB As one ear is stimulated with clicks, the other is masked with white noise, typically 30 to 50 dB This method helps to prevent the undesired coactivation of the contralateral ear caused by bony conduction from the ipsilateral stimulated ear Atleast 2000 trials are averaged to get a good quality recording. 2 to 3 repetitions are done and superimposed to check for reproducibility

10. BAEP waveform

11. INTERPRETATION OF RESULT When interpreting the ABR, we look at AMPLITUDE (the number of neurons firing) LATENCY (the speed of transmission) INTERPEAK LATENCY (the time between peaks) INTERAURAL LATENCY (the difference in wave V latency between ears

12. Wave I should be observed but will only be present ipsilaterally Wave III and V should be detactable in all healthy individuals Wave VI and VII appear variably after wave v

13. MEASUREMENT AND NORMAL VALUES OF BAEP The following parameters are measured foe the analysis of BAEP absolute latency and amplitude Interpeak latencies Amplitude ratio of wave v to I or waves IV-V complex and I Inter ear interpeak difference

14. NORMAL VALUES

15. ABNORMAL BAEP BAEP abormalities may include one or more of the following Absence of waveform Abnormal absolute or interpeak latencies Amplitude ratio abnormality Right to left assymetry

16. CLINICAL NEUROPHYSIOLOGICAL CORRELATIONS BAEP has been studied in numerous neurological disorders The most important clinical applications are CEREBELLOPONTINE ANGLE TUMOR INTRINSIC BRAIN TUMOR MULTIPLE SCLEROSIS COMA STROKE

17. PATIENT RELATED VARIABLES AFFECTING BAEP Age Gender Level of arousal Body postion Temperature Pre existing hearing loss

18. References Text book of clinical neurophysiology by UK Mishra and J kalitha Google images

19. THANK YOU…..